Among Sixty-five species of plant hoppers recorded to be associated with Rice ecosystem, Brown plant hopper, Nilaparvata lugens (Stal) (BPH) is the most economically important insect pest causing damage to rice. These are small insects, the adults measuring about 4-6 mm in length and 3-4 mm in width. BPH damage rice crop by draining out enormous quantities of plant sap and causes hopper-burn. The management strategies so far employed for BPH were evolved just like for other insect pests. However, Morphological and physiological diversity in BPH populations were not given sufficient consideration. The diversity in rice as a species existing before green revolution era also appeared to have some impact on BPH populations. The human management systems can have sufficient effect on BPH management also, along with rice production technologies. A comprehensive understanding of all these are essential for devising better BPH management strategies for future along with the recognition of importance of human population control. Here in this review we will see how the details of all these are useful for future BPH management and sustained rice production.
Existence of Diversity in BPH and its Relevance to Management of the Insect
Several theoretical variations contributing to diversity in BPH populations can exist in a field. Among those, the existence of black colored variants of BPH and increase in their proportion in a given BPH population is the common concern expressed by many rice entomologists in India and also in other countries. The variation in body coloration is very common in many insect species across all orders. So is the case with BPH. The variation may be dependent on the climate and the food quality etc. In case of BPH brown individuals are in high proportion during early stages of crop growth, mostly up to second generation. Later on the proportion of black individuals tends to increase. This again is not uniform in all the fields even within the given area. The exact biochemical reason with regard to BPH is not available in literature. But based on the information available from other insects, development of higher concentration of the pigment “melanin” in the body wall of such individuals in a BPH population could be the most probable cause. Melanin is usually and mainly formed due to polymerization of quinones. These quinones are generally formed by oxidation of phenols involving very complex enzyme systems and many steps. But in general, the initiation of this process is associated with external organisms which release some chemical elicitors like β-1, 3-glucan, peptidoglycan or lipopolysaccharide which bind to their specific pattern recognition proteins. Then the whole system involving a cascade of serine proteases is activated resulting in the cleavage of the pro-form of the pro-phenol- oxidase-activating enzyme (PRO-pro PO-AE) into the active pro PO-AE. This pro PO-AE cleaves pro-PO to generate the active enzyme, phenol oxidase (PO). PO catalyzes the oxidation of phenols to quinones, which then will polymerize non-enzymatically to form melanin (González-Santoyo and Córdoba-Aguilar, 2012). But the main question here is whether such an initiation can occur due to insecticide poisoning or during the course of development of resistance to insecticides in BPH has never been documented so far.
It may be beneficial to study this aspect from biochemical angle apart from the climatic and biotic factors. It is the suspicion of many rice entomologists that black coloration may have some linkage with the development of wide spread neonicotinoid insecticide resistance in BPH in many areas in India. But nothing concrete can be said about the validity of their suspicion unless some genetic linkage studies are conducted.
Another significant morphologically distinct variant within a population of BPH is the existence of some individuals with “conspicuous red eyes”. But the proportion of such individuals is very low i.e. one in a thousand or few thousands. Attempts were made at Directorate of Rice Research (DRR), Hyderabad to culture that morphological variant. Interestingly it could be maintained in that completely morphologically similar state for many generations through isolated breeding. But no studies could be conducted to establish the relationship of that distinct trait with other morphological or physiological characters.
Variation between the Normal BPH and BPH feeding on Leersia hexandra
Another important point to be discussed here is confusion regarding the identification of the BPH population under field conditions. During late nineteen eighties and early nineteen nineties, some reports exist from The International Rice Research Institute (IRRI), that BPH feeding on TN1 variety of rice could not feed on Leersia hexandra, the most common weed present in rice ecosystem and also BPH present on Leersia hexandra could not feed on TN 1 the most susceptible rice variety for BPH.
Here we have to consider the fundamental concept of “what is a species?” “A species is a group of naturally occurring organisms which are potentially interbreeding and reproductively isolated from other similar groups”. (Ernst Mayr, 1969) The first criterion to qualify a group of individuals as a species is that it should exist in nature. Any group of individuals that have been created by man in the laboratory cannot be termed as a species as per rules and the code governing international zoological nomenclature. Thus it is in the common knowledge of many entomologists that a number of groups of individuals from genus Drosophila created in the laboratory experiments never attained species status. The second criterion which is very essential in the context of BPH is “potentially interbreeding”. The real meaning of potential is that it can vary from 90% to 99.999% in mathematical terms. However still that group of organisms can be considered as a species. In the case of BPH normally feeding on TN1 when the insects were confined to the weed Leersia hexandra, it could not feed or multiply. This is very common thing as there are many observations that BPH cannot feed substantially and multiply on any plant other than Oryza sativa. But the insects reportedly observed feeding on Leersia hexandra cannot be Nilaparvata lugens (Stal). Most probably it could be some other species of the genus Nilaparvata or some other species belong to other genus but morphologically similar to Nilaparvata lugens (Stal). In fact quite satisfactory answer to this controversy was given after conducting mating experiments and also analyzing courtship signals of these two morphologically similar populations and was concluded that those should be considered as two distinct biological species (Claridge and Morgan, 1987).
We have already seen that in case of BPH three geographically isolated biotypes exist which are distinct from each other on several aspects like their reaction to host plant resistance, insecticide resistance development, morph form development, viral transmission ability and possibly so many other aspects for which sky is the only limit if one starts listing (Krishnaiah, 2014 a, b, c). All these are not the result of human intervention and these must have been incorporated into BPH genome during a million or so years of its evolution to the present state of existence.
In rice also apart from the two main cultivated species already mentioned, there are several other species of the genus Oryza. Ever since the problem of BPH has aggravated rice breeders all over the rice growing world have started incorporating the genes from related Oryza species. This human made genetic intervention recently possible after wide scale adoption of biotechnological tools created further diversity in the cultivated rice genome. This for the present may pose some barriers in normal biological processes of BPH. But is BPH not capable of overcoming these adversities? How long these genes can really help in the practical management of the insect pest is big question mark yet?
How diversity in BPH can be Utilized for Its Management in Future
First of all let us examine whether there is any evidence to think that sufficient diversity in BPH at practical level exists in vast rice growing countries like India and China which have contiguous stretches of rice growing tracts and at the same time there is possibility of highly migrating BPH for thorough intermixing which can make the insect to reach practical genetic uniformity within few seasons. First of all let us examine the practical means available with us to judge the genetic uniformity in BPH in such situations.
There are four such important aspects which are available and which can be used for our advantage. These are
1. Virulence spectrum of the insect to a set of varieties with known resistance genes
2. Virulence pattern with regard to transmission of virus diseases.
3. Developmental pattern of morpho-forms.
4. Spectrum of insecticide resistance for recommended insecticides against BPH and those which are commonly used in rice ecosystem against other pests.
Let us examine the scope of each of these aspects with regard to South-Asian biotype of BPH prevalent in Indian sub-continent
Virulence spectrum of BPH to a Set of Varieties With known Resistance Genes
Such varieties are usually called differentials. Differences in virulence in different populations present in different states to such differentials will normally be present after release of varieties with one or two genes and large scale adoption of those varieties in a state or states for a minimum of 4-5 years. Then population of BPH present in those areas is likely to develop virulence to overcome the resistance effect of that particular gene or genes. As the matter stands today, there are no varieties with BPH resistance that have been grown over vast areas in any rice growing state or even a tract. So this approach is unlikely to lead us to understand the extent of physiological diversity or homogeneity existing in BPH population either in India or in China.
Virulence pattern with Regard to Transmission of Virus diseases
Grassy stunt and ragged stunt are the two important virus diseases transmitted by BPH. Both in India and China, BPH has never caused serious damage to rice crop as vector of grassy stunt or ragged stunt during the past 40 year history of large scale damage by BPH in these two countries. This fact certainly indicates that this aspect cannot give clues regarding the diversity or homogeneity in BPH population.
Developmental Pattern of Morph-forms
During a long history of BPH migrants to Japan and intensive studies by entomologists there, led to identification of discernible differences in percentage of macropterous and brachypterous forms that develop in the progeny of migrants. This helped them to some extent to identify the source of migrants either from South-East Asian countries like Vietnam or from mainland China along with viral transmission pattern. However, pursuing this aspect is unlikely to lead us to the present desired goal in India.
Spectrum of Insecticide Resistance for Recommended Insecticides Against BPH and Those which are Commonly used in Rice Ecosystem Against other Pests
If we closely follow the pattern of insecticide use in India and China since 1973 against BPH and also against other important insects we get certain clues. During the earlier years up to 1995, major insecticides used in India against BPH were monocrotophos, carbaryl, acephate, BPMC, MIPC and carbosulfan as sprays. However, there were no indications of insecticide resistance development in BPH against any of these insecticides till 1996 (Sarupa et al., 1998). After 1999, neonicotinoids like imidacloprid, thiam- ethoxam, acetamiprid, thiacloprid were introduced into insecticide market and used extensively against BPH in many rice growing states in India. By 2004, discernible level of resistance in BPH has been recorded in Krishna-Godavari tract of A.P. (Krishnaiah et al., 2006) and later studies confirmed these findings (Jhansi et al., 2010). The only worthwhile attempt in India on BPH insecticide resistance studies during later period was by Basanth et al., (2013). They have collected BPH populations from different places in southern region of Karnataka state present in southern part of India. The detection method used was stem dipping technique and the susceptibility levels to different insecticides in field populations were compared with BPH population received from Rice Research Station, Mandya, which was considered as susceptible population. The resistance ratios varied greatly among the populations’ viz., imidacloprid (0.53- to 13.50-fold), thiamethoxam (1.01- to 2.19-fold), clothianidin (1.92- to 4.86-fold), chlorpyriphos (1.13- to 16.82-fold), acephate (1.34- to 5.32-fold), fipronil (1.13- to 4.06-fold), dinotefuran (0.82- to 2.22-fold) and buprofezin (1.06- to 5.43-fold). These results indicate that intermixing of BPH populations is not to the extent we have been thinking. Within a small local rice growing region of the same state of Karnataka the differences in resistance levels to each of the insecticide tested were quite significant. Further the level of resistance observed in each of the areas is very well correlated with insecticide use spectrum on rice crop in those areas. Thus there is no large scale migration of BPH from one area to another area within the southern region of Karnataka state.
Let us now examine whether there is any such evidence available from China. Hu et al., (2014) made a thorough analysis for the major causes of BPH outbreaks in Yangtze River Delta in China, the largest rice growing tract of the country. In particular, the major outbreak mechanisms i.e. immigration or local reproduction was critically studied with field surveys of BPH in Jiangsu and Zhejiang Provinces in 2008 to 2010 and related historical data from 2003 onwards. Their results showed that outbreaks of BPH in the Yangtze River Delta were mostly associated with an extremely high increase in population through high to very high level of BPH reproduction rather than immigration from distant sources as the cause of the infestations. However, mass migration usually occurs late in the season (late August and early September), but the source areas of BPH as indicated by light trap catches are mainly located in nearby rice growing tracts within the Yangtze River Delta itself, including Anhui and northern Jiangxi Provinces. All these results indicate that mass migration in BPH over few thousand kilometers range is rather a rare phenomenon and resorted to when it is absolutely essential as it occurs from China to Japan and Korea and from southern or eastern regions of India to Indo-Gangetic Belt. Thus it is also clear that it is the most favorable ecology in rice crop that is causing outbreaks and migration is only aiding that when it is necessary.
Hence there is sufficient diversity existing in BPH populations when the whole of rice growing countries is taken into consideration. This diversity will certainly be useful to devise different strategies for BPH management through continuous monitoring of relevant parameters described above.
Diversity in Rice as Influenced by its Origin, Evolution and Domestication
Rice as it exists today is the result of domestication of thousands of years involving a lot of human effort. Today there are mainly two species of cultivated rice in the world. The major species Oryza sativa is cultivated in the entire Asian countries while Oryza glaberrima is under cultivation in Africa. O. sativa is considered to have been evolved and domesticated somewhere in Asian region near Himalayan mountains involving the geographic areas presently located in Northeastern parts of India, parts of Myanmar, southern parts of China and the adjoining areas. Within O. sativa there are three subspecies viz., Indica, Japonica and Javanica. Indica has evolved as a result of long domestication in tropical areas mainly in South India, Sri Lanka, southern tip of China and almost All South-East Asian countries. Japonica is the result of continuous cultivation for thousands of years in temperate countries mainly major parts of China Japan and Korea. Javanica was first confined mainly to a small Indonesian island called “Java” and hence the name.
Major Differences Among Subspecies of O. sativa
There are many differences in morphological and genetic traits among the three major subspecies of O. sativa. We need not go into all those details which are beyond the scope of the present article. Only certain important aspects which have great relevance in relation to BPH and its management we will consider.
In general, Indica subspecies represented by thousands of varieties are traditionally tall in stature lodging when grown under high nutrition, weak culm, generally having long or sometimes short panicles and in general puffy in grain quality after cooking. Thus people living in all the countries where Indica varieties are grown are habituated to eating puffy rice varieties for thousands of years.
Contrary, Japonica varieties in general are relatively shorter in stature, with more tillers, better responsiveness to nitrogen application; do not lodge to the extent of traditional tall Indicas. But they also differ substantially in grain quality after cooking. Japonica varieties are generally sticky after cooking. So the people of temperate rice growing countries have habituated to eat sticky rice over thousands of years.
Javanica varieties in general possess lower yielding capability than even traditional tall Indica varieties. So they have been used mainly in breeding programs to improve Indica varieties during and after green revolution era due to their better compatibility than Japonicas.
Green Revolution in Rice and After Math Development
Establishment of IRRI the Origin of Revolution in Tropical rice
The rice revolution started with the establishment of International Rice Research Institute (IRRI) at Los Banos, in Laguan Province of Philippines, which is about 120 kilometers from the capital city of Manila, which is in a typical tropical belt. The earliest attempts to improve the yielding ability of traditional tall Indica rices by different management practices like higher fertilizer application, higher planting density and better water management etc. failed to yield desired results of substantial yield enhancement. Then the International establishment at IRRI decided that genetic improvement in rice is a must. The first high yielding dwarf variety was developed based on the basic principles that have already been established in wheat revolution under the leadership of the well-known personality and the only Nobel Laureate among the entire agricultural scientists of the world, Dr. Norman E. Borlaug. They fixed certain criteria that dwarf-ness, with thick culm, high tillering ability coupled with non-lodging and high fertilizer responsiveness must form the base among the desirable traits of future rice varieties in the entire tropical belt. These traits also existed among the japonicas widely grown in Japan and Korea even by that time also formed the base for the design of future tropical rice varieties. The first fruit of sincere and dedicated efforts of scientists of those days is Taichung Native-1(Dwarf Chow-Wu-Gen x Tsai), in short called TN1. But that was also the variety with very high degree of susceptibility to all insect pests and diseases existing at that time. The very fact that TN1 is still used as a susceptible check for all host plant resistance screening trials in all tropical rice growing countries even today is a testimony of that fundamental fact.
Initiative by Government of India Triggered Rice Revolution in Tropics
During 1965, Government of India also focused its attention on genetic improvement of rice varieties already existing in the country and established All India Coordinated Rice Improvement Project (AICRIP) at Rajedranagar, which is about 30 kilometers away from central part of Hyderabad, presently the capital of Telengana State situated again in the typical tropical belt. By that time the first real dwarf rice variety IR8 was not developed by IRRI and the only dwarf variety available was TN1 with many undesirable traits excluding its ability to serve as a base for future dwarf rice variety development program in the country. Although there was some controversy that importing such a variety with very high degree of susceptibility to all insect pests and diseases existing at that time with the only positive trait of dwarf-ness may boom rang in the long run for aggravation of insect pest and disease problems. However, the Government of India finally saw more into the optimistic future. Because there was very limited scope in yield improvement prospects in already developed traditional tall Indica varieties, and finally permitted to import TN1 and start the process of genetic improvement in rice.
IR8 the first “Miracle Rice” from IRRI
By 1968-69 IRRI developed and released IR8 which was the result of cross between Chinese dwarf variety known as Dee-geo-woo-gen (DGWG) and a tall variety from Indonesia, Peta. At that time IR8 was termed as “wonder rice” and its cultivation was started in Philippines in a big way and thus IRRI served as the most effective catalyst for rice revolution in Philippines by multiplying and distributing the seed of IR8 by the organizational infrastructure which is an indication of its magnanimity. By 1970, AICRIP under the brilliant and dynamic leadership of Dr. S. V. S. Shastry could also develop the first HYV in India named as Jaya (meaning the victory over IR8 as claimed by the organization) by crossing TN1 with a traditional tall variety Type141. Simultaneously Indian Government took a bold decision of permitting large scale cultivation of Jaya and also IR8 not only in traditional rice growing belt of Southern and Eastern parts of India but also the non-traditional Indo-Gangetic belt situated in northern part of the country. This was followed by release of some excellent varieties with high yield and good grain quality like Phalguna and Vikram with resistance to gall midge and Sasyasree and Vikas with moderate level of resistance to stem borer the most important traditional pests and also yield limiting factors at that time. Large scale cultivation of all these varieties together with good support price from government side by very dynamic involvement of Dr. S. V. S. Shastry laid strong foundation for initial phase of rice revolution in India. The most interesting point is even today (after 45 years of release) Jaya is one of the most widely grown varieties not only in India but also in many South-East Asian nations along with their own varieties developed locally. If we critically observe the list of varieties whose breeders seed is requested by different organizations in India and sent to AICRIP (Later renamed as Directorate of Rice Research(DRR) and currently named as Indian Institute of Rice Research (IIRR), it is Jaya which is the number one variety with maximum quantity of requested seed. That is the real power of the variety “Jaya”. All these developments led to a real rice revolution in India by1973 and thus the initial phase of rice revolution has taken a firm footing not just in India but also in many tropical rice growing countries. That was the entry time of BPH, which was not at all heard by any rice farmer but only mentioned in rice entomology academic curriculum that an insect like BPH also exists in rice ecosystem.
It may not be out of place here to mention the personal experience of the author. During 1973 kharif season, when the author was working as a Research Assistant in AICRIP under the Rockefeller foundation support to the organization with Dr. Wayne H. Freeman, Joint Coordinator of AICRIP. The author was temporarily stationed at Agricultural Research Station Maruteru, situated in eastern part of A.P. in the most intensively rice growing coastal belt and already hotspot of all traditional insect pests like stem borer leaf folder and so on. Almost towards the end of October 1973, a big farmers meeting was held at Eluru the capital of West Godavari district where Maruteru is situated. In the meeting Dr. S. V. S. Shastry was not only the chief guest but also the main speaker. When he has completed explaining about the importance of replacing tall varieties with dwarf varieties, towards the end of the meeting some farmers brought to his notice the presence of BPH and its damage. Thus the beginning of rice revolution in India and many tropical rice growing countries is also the initial point of BPH attack to rice crop in tropics. What all the rice varieties that have been developed since that time almost all of them had derived their blood for dwarf-ness mainly from TN1 and IR8. Thus the rice varieties before green revolution era having a broad genetic base evolved over millions of years and domesticated over thousands of years still retained very broad genetic base not just for reaction to BPH and also to so many other biotic and abiotic factors. But the main question is “Can we be able to develop again such broad diversity without sacrificing yield levels?” To our present level of imagination the answer could only be “Just Impossible”
Knowledge Consolidation and Advancement by IRRI- Another Major Factor for Quantum Jump in Tropical Rice Yields
As one can easily understand, rice is much different from all other cultivated plants that it is aquatic in its basic features. So the basic aspects of physiology of rice plant and the chemistry and conditions of the soil in which it is grown are bound to be fundamentally different from all other crop ecologies. So, along with the thrust in developing the dwarf HYVs, IRRI also made tremendous contributions in advancing our knowledge on both these basic aspects. Significant among the scientists are Dr. Shouichi Yoshida and Dr. Felix N. Ponnamperuma who played key roles in the fields of rice physiology and chemistry of flooded soils respectively at IRRI during initial phases. As far as rice entomology is concerned, Dr. Mano Dutta Pathak (M. D. Pathak) the first entomologist at IRRI worked for his Ph.D. program with Reginald. H. Painter widely considered as father of host-plant resistance to insects in crop plants and the origin of the very concept. Dr. Painter is also the author of the first book on this aspect “Insect Resistance in Crop Plants”, which is still referred even after more than 64 years after its publication in 1951. Dr. Pathak always lived up to the expectations of everyone, first as entomologist and later as Director of Research Coordination at IRRI. The young, brilliant and dynamic Dr. Pathak took an excellent initiative within a short stint after joining and arranged an international conference on rice entomology at IRRI in 1963. In that conference the scientists working on different aspects of insect pests of rice crop in different rice growing countries both tropical and temperate regions along with the most prominent entomologists from advanced countries like U.S. were invited. A long and detailed deliberations of the conference resulted in a significant consolidation of the existing knowledge at that time not just on mere entomological aspects but also the related subjects like virus transmission by insects and statistical aspects having relevance to entomology. More importantly on basic aspects like bio-ecology, damage estimation and economic thresholds, field sampling techniques etc. The detailed papers presented and the discussion took place was later published as a book entitled “Major Insect Pests of Rice Plant” by IRRI in 1964. That laid very strong foundation for chalking out several research aspects on rice entomology and also the book is still considered the most authoritative publication on all insect pests existing at that time. Again the wonder and the beauty of the whole thing is there was no consideration for rice brown planthopper “our hero” as a pest of rice in that entire book “Major Insect Pests of Rice Plant”. Damage and importance of BPH in Japan and Korea came to forefront only during 1978 symposium held at IRRI exclusively meant for BPH. Now one can very clearly understand the real origin of BPH problem and the whole of the above narration is only to reveal that most significant point.
Thus we can very clearly visualize how IRRI is striving hard to promote knowledge sharing among different rice growing countries, the importance of which was emphasized by Dr. Norman Borlaug in his Nobel Lecture in 1970 as “I am convinced that the international agricultural research institutes are developing a bond of understanding among nations, based upon the common need for increasing food production. We must all strive to strengthen this bond in the spirit of Alfred Nobel to promote brotherhood among the nations".
Existence of Diversity in Rice before Green Revolution era in the Tropical Rice Belt
Before the onset of rice revolution all over the world there were innumerable varieties that have been cultivated for thousands of years after the domestication of the species Oryza sativa had been initiated. There were rice breeding programs and rice breeding research stations in many countries including India and many South and South-East Asian nations. In India, the first effort towards scientific advancement in rice cultivation had its beginning in 1946 with the establishment of Central Rice Research Institute (CRRI) at Cuttack of Orissa state near the eastern coastal region of the country. At the time of inauguration then Prime Minister Jawaharlal Nehru asserted that “Anything can wait but not agriculture.” But there was not much impact of CRRI on improvement in rice cultivation technology in India until the establishment of AICRIP. That was also the main reason for establishment of AICRIP and also allowing the import of TN1 and its involvement leading to release of Jaya the first HYV which heralded the beginning of rice revolution in the country and giving helping hand to many neighboring countries. However, there were already a number of rice research stations established and managed by different state governments which have at least playing some role in releasing varieties suitable for cultivation in those areas by following traditional breeding methods.
For instance, Paddy Breeding Station (PBS) located in Coimbatore in Tamil Nadu State was established in 1912 developed the first variety GEB 24 with excellent grain quality by Pure Line selection method and released in 1921. This variety really triggered the growth of rice production in the State during those days. Other noteworthy rice varieties released from PBS were CO4, CO25, CO37, CO38, CO40, CO43, CO47, etc. Similarly, a number rice breeding stations also existed in other states of India including Andhra Pradesh. Within A.P. the prominent rice breeding centers were Maruteru, Pulla and Nellore. Similarly other research stations existing within the southern typical tropical belt of India include Paddy Experimental Station in Tirukuppam in Tamil Nadu, Pattambi and Moncompu in Kerala State and Mandya in Karnataka State. In eastern parts of India, the prominent rice research stations were at Chnisurah and Bankura in west Bengal and Jorhat in Assam. Each of these stations had their own contribution to generate diversity in rice varieties available mainly to cater the needs of local rice farmers. Another interesting point here is some of those varieties released by these stations later served as excellent sources of resistance to major insect pests of rice. For instance PTB33 and PTB2 which were once released as varieties by Pattambi Rice Research Station are the foremost sources of resistance to BPH and GLH respectively. Another variety TKM6 which was released from Tirukuppam is the only source of resistance to stem borers in rice. By using TKM6 variety a lot of research was carried out at IRRI to isolate the biochemical responsible for resistance to stem borers and even to commercialize the same if possible. Similar situation also existed in Sri Lanka, Indonesia, Thailand and Vietnam etc.
Diversity in rice before HYV-era and its Possible Influence on BPH
Although many of those varieties prevalent before HYV era might not be having resistance genes contributing directly for adversity to BPH biology, the very fact that the existence of such a high diversity in the genetic makeup of varieties might have certainly contributed to BPH biology. This might have influenced BPH to keep itself as an insect associated with rice plant for thousands of years without ever raising to the level causing significant yield losses throughout the tropical rice growing belt of Asia. After the development of Jaya and IR8 and their extensive propagation in many countries apart from their countries of origin has created a more homogeneous and also favorable varietal genetic base conducive for rapid multiplication of BPH within a growing season. That could add fuel, in finally enabling BPH to establish itself in those countries as a permanent threat through the process of migration. BPH migration as we have seen often extends beyond the frontiers of politically divided barriers of the countries (Krishnaiah, 2014 a, b, c). Another important point is from IR8 and Jaya, a number of other varieties developed later in AICRIP like Phalguna, Vikram with gall midge resistance coupled with high yield or Sasyashree and Vikas with stem borer resistance also gained lot of favor with farmers. All these were prevalent in vast areas in early rice revolution era not just in India but also in several neighboring and distant countries. The most important point we have to note here is all these varieties mentioned above are highly susceptible to BPH. That is the most pathetic part of the whole story that led to making BPH a threat to rice cultivation in Asia that aptly suits to name the first international symposium in 1978 at IRRI as “ Rice Brown Planthopper: A Threat to Rice Production in Asia.” All these what we are talking about is apart from the major factor i.e. the existence of most favorable abiotic environment in dwarf rice varieties mainly in enhanced water vapor pressure and relative humidity (Krishnaiah, 2014 a, b, c).
Influence of Human diversity on Rice production technology & BPH management strategies
China- the Origin and Success of Hybrid rice technology
In China they have taken a major step in developing hybrid rice and lower importance to HYV development. Today we all see China as number one country in the hybrid rice technology and even IRRI is only barrowing few things from China and trying to adopt it to tropical rice growing countries including India. The major breakthrough in hybrid rice technology is pioneered by Yuan Long Ping the most dedicated rice scientist of the world and really deserving the title “The Father of Hybrid Rice”, the pale and fragile personality to look at, yet astonishingly hard working. The cultivation of hybrid rice started in China in 1976 and within 10 years it occupied an area of more than 10 thousand hectares. In 1990, hybrid rice area exceeded 15 million hectares and accounted for about 50% of the total rice-growing area in China. Since then, the percentage of hybrid rice area has increased gradually to about 60% later on (Cheng, 2009). The China National Seed Company established in 1978 to popularize improved seed varieties and similar systems developed by Chinese administration has effectively integrated the seed production system with the cultivation system in hybrid rice. That appears to be the major factor along with the real power of hybrid rice technology and scientific in depth understanding of the whole technology in China which is responsible for phenomenal success in China which was not possible in other tropical and developing rice growing countries including India.
Hybrid rice technology in India:
During the same time when China was very rapidly progressing in hybrid rice technology development and implementation there was talk of hybrid rice technology development in India many a times at DRR and also in AICRIP annual workshop meetings. It was simply brushed aside that hybrid rice technology involving cumbersome seed production process and requirement of seed renewal each time is not suitable for Indian conditions.
Now let us see what happened to hybrid rice technology development and actual cultivation in India till now. In fact the whole of hybrid rice technology process developed by China was just imported into the country through IRRI. Only two cytoplasmic male sterile lines (CMS) were involved in breeding program for a very long time. The whole of seed production process has been taken over by private companies whose main motto is only profit. Thus the seed cost has gone very high. The net result of all these phenomena is even after 27 years (the program has its beginning in 1988) the total area in India under hybrid rice could not cross 1 million hectares i.e. less than 2.5 % of the total area under rice.
Influence of Hybrid rice technology on BPH management strategies in China
After large scale adoption of hybrid rice cultivation in China, there was slow shift in the insect pest spectrum. BPH which was very dominant insect pest has slowly gone to the third position leaving the first and the second positions to WBPH and leaf folder. As the genes conferring resistance to BPH are not at all useful to afford even moderate protection to WBPH they have to shift their hybrid rice technology development to incorporate WBPH resistance. Secondly leaf folder has no worthwhile sources of host plant resistance in the entire rice germplasm. So for the management of both the insects, total dependence on insecticide use is a must to protect the already fragile hybrid rice fields. Thirdly the insecticides which are useful for the management of WBPH cannot check leaf folder and vice-versa. So, heavy dependence on general insecticides like OPs and carbamates becomes an imperative necessity leading to more environmental pollution and other associated problems. The problem of insecticide resistance gets aggravated apart from increased cost of production. Thus a chain of associated problems started arising as rice is the staple food of the most population of China.
Duck rice and fish rice in China- the need driven technological marvel
Duck-Rice and Fish-Rice are two important strategies adopted in China for quite some time. These are in fact a part of the whole strategy of organic rice farming. At the same time it has lot of practical relevance for pest management in rice in general and whole management strategy of BPH in particular. Duck-Rice and Fish-Rice requires certain set of ecological and social pre-conditions for their success. The soil fertility must be generally high and does not need any inorganic fertilizer application. There must be abundant year round supply of irrigation water which is free from any toxic pollutants. The general topography must be suitable for water stagnation. The most important above all these is also the social type of cultivation system existing. When these concepts were being talked about in China and have been taking practical shape, there was lot of propaganda about these in other South and South-East Asian countries also, including India. But these topics till today remained only to platform speeches and never took roots into practical application under farmers’ conditions. In India, fish farming alone has come in a big way in suitable wetlands which were under rice cultivation earlier just by the side of rice fields. Those are continued for fish and prawn culture with many ups and downs even today. But those are also creating many environmental and social problems. But the main point is the concept of combined Duck-Rice or Fish-Rice in the same field has never taken practical shape.
The main reason for this is, in most of the other tropical rice growing countries, except China the individual farmers hold small bits of land and each one is independent to follow and adopt his cultivation practices for rice. Hence Duck-Rice and Fish-Rice is impossible for practical adaptation. Even a slight contamination anywhere in the water stream can create havoc. This is where the diversity in human systems can have profound influence on practical management of rice farming.
Apart from adding additional income to rice farmer, Duck-Rice and Fish-Rice systems can have profound and direct influence on BPH management strategies with which we are mainly concerned. In this connection the detailed, enlightening and the most worthwhile studies conducted by Luo et al., (2009) deserves special consideration. Duck-Rice and Fish-Rice systems are known to reduce BPH infestation considerably without any other management strategies like use of insecticides. In fact insecticide use is prohibited in these systems. They utilized this practical necessity to study the effect of Duck-Rice and Fish-Rice systems on niches and interspecific competitions of wolf spiders and mirid bug Cyrtorhinus lividipennis (GMB) compared with normal rice cultivation systems. The results suggested that ducks might prey upon wolf spiders resting on the base of rice plants, thus the populations of wolf spiders decreases in duck-rice treatment. The impact of ducks on GMB was not significant because it preferred to congregate on the mid-part of rice plants. Further, competition between wolf spiders and GMB was significantly more intense in duck-rice or fish-rice treatment than in natural control treatment at different stages. Probably, ducks and fishes drove wolf spiders away from their original spatial niche, the base to the mid-part in rice plants, enhancing competition between wolf spiders and GMB in duck-rice or fish-rice treatments. Thus the results of their study strongly indicate duck-rice or fish-rice, as effective and prudent BPH management strategies, the practical adaptation of which is greatly influenced by human diversity.
BPH management strategy in technologically advanced Japan
If one critically assesses and analyses the entire BPH management strategy in Japan certain interesting points will emerge. Among all the rice growing countries of Asia Japan is and has been in the forefront of science and technology and moved along with Europe and U.S. during industrial revolution era from almost 18th century. But the staple food for almost entire Japanese population remained only rice. So we have already seen how the varietal development and associated management technologies in terms of water and weed management, as well as plant nutrition management have taken a modern path both in philosophy and practice much earlier than other Asian countries. (for details see the chapter “BPH Out-Breaks in Tropics after HYV Era: A Critical Analysis”)
Almost a similar approach has been adopted by Japanese rice scientists, administrators and farmers. Unlike in other Asian countries, rice farmer in Japan is not just a farmer dependent on tilling the land, sowing and harvesting the produce for home consumption and selling the surplus if any. Rice farming in Japan is only a part time avocation for majority of those involved in the process. They do lot many more jobs like working in nearby industries, engaged in other jobs like teaching, driving, repairing many of the household items etc. So unlike in other Asian countries rice farmer in Japan cannot devote his entire time just for cultivation. If then, we cannot expect Japanese rice farmer to spare too much time for BPH management which certainly will have its impact on the type of BPH management strategy.
Although BPH is one of the most ancient pests of rice in Japan, the scientists there never gave any time for something like host plant resistance. Although it is not very clear from the literature whether Japanese rice scientists ever tested the stability of a rice variety with some degree of resistance to BPH i.e. for how long the resistance factor will be active in that variety and how the virulence in BPH will be able to nullify the resistance factor. Nevertheless they never gave any credence to the concept of rice resistance to BPH. They vigorously pursued only the path of insecticide use. So (as we have already seen) the usage of all insecticide groups and their members had their beginning in Japan. Another important thing is, this approach is probably their strategy to develop and standardize the insecticide development programs by private concerns which are far more financially rewarding in the long run apart from keeping the nation in the forefront in the entire field of pesticide industry. This supposedly hidden approach has really brought Japan to number one position in the world in pesticide industry as a whole along with their favorite avocations of automobiles and electronics.
It may be most appropriate to conclude by saying that in all our endeavors towards long-lasting and sustainable BPH management we have to consider the entire diversity in BPH and rice as integral components of the ecosystem comprising not just that of rice, not just that of the earth but the entire universe. When we add the human dimension to that then it really becomes the “Divine Ecosystem” that we can visualize and beyond. To understand what that “Divine Ecosystem” could be it is appropriate to recall a few words from Dr. Norman Borlaug in his Nobel Lecture in 1970 as “We must recognize the fact that adequate food is only the first requisite for life. For a decent and humane life we must also provide an opportunity for good education, remunerative employment, comfortable housing, good clothing, and effective and compassionate medical care. Unless we can do this, man may degenerate sooner from environmental diseases than from hunger. And yet, I am optimistic for the future of mankind, for in all biological populations there are innate devices to adjust population growth to the carrying capacity of the environment. Undoubtedly, some such device exists in man, presumably Homo sapiens, but so far it has not asserted itself to bring into balance population growth and the carrying capacity of the environment on a worldwide scale. It would be disastrous for the species to continue to increase our human numbers madly until such innate devices take over. It is a test of the validity of sapiens as a species epithet.”
Let us continue with few more words of the Nobel Peace Prize winning noble soul to have better clarity. “Since man is potentially a rational being, however, I am confident that within the next two decades he will recognize the self-destructive course he steers along the road of irresponsible population growth and will adjust the growth rate to levels which will permit a decent standard of living for all mankind. If man is wise enough to make this decision and if all nations abandon their idolatry of Ares, Mars, and Thor, then Mankind itself should be the recipient of a Nobel Peace Prize which is "to be awarded to the person who has done most to promote brotherhood among the nations".
Such a broad approach alone can lead us to the real and truthful BPH management strategy not just long lasting and sustainable strategy, as BPH became a major threat to rice production today as a result of a slight human greed to exploit rice ecosystem to meet the needs of ever growing population. This broad understanding in all our future endeavors in BPH management alone can eventually lead to perfect harmony and human survival for infinite time to come where BPH management is a small but significant aspect.
Summary and Conclusions
Apart from normal brown colored individuals, presence of black colored variants of BPH is the common phenomenon in almost all places. Development of higher concentration of the pigment “melanin” in the body wall of such individuals could be the most probable cause.
Physiological diversity in BPH can exist as virulence to a set of varieties with known resistance genes, virulence pattern with regard to transmission of virus diseases, developmental pattern of morpho-forms and Spectrum of insecticide resistance. All these can be intelligently used for understanding migration patterns and also devising management strategies.
Within the species of cultivated rice in Asia (Oryza sativa), there are three subspecies viz., Indica, Japonica and Javanica.
Indica is represented by thousands of varieties which are traditionally tall in stature, lodging when grown under high nutrition, weak culm and in general puffy in grain quality after cooking.
Japonica varieties are relatively shorter in stature, with more tillers, better responsiveness to nitrogen application, do not lodge to the extent of traditional tall Indicas and rice is sticky after cooking.
The people living in tropical world are generally habituated for eating puffy rice and those in temperate countries for sticky rice that led to perpetuation of varieties with similar grain quality over thousands of years of domestication of rice in Asia.
Javanica varieties in general possess lower yielding capability than even traditional tall Indica varieties. The rice revolution in tropics has started with the establishment of International Rice Research Institute (IRRI) in Philippines and later All India Coordinated Rice Improvement Project (AICRIP) by Government of India at Hyderabad.
IR8 is the starting point for HYVs from IRRI. Later “Jaya” from AICRIP followed by a score of other varieties laid a strong foundation for further advancements in rice cultivation from 1973 onwards in all tropical rice tracts. It is also the starting point of BPH attacks to rice crop.
Knowledge consolidation and advancement by IRRI in rice physiology, chemistry of flooded soils and rice entomology further strengthened the rice revolution in tropics.
Lot of diversity in rice existing in the entire tropical rice belt before green revolution era in the form of thousands of varieties has got eroded by cultivation of few HYVs with their origin from TN1 and IR8.
Diversity in human management systems can have tremendous influence on rice production technology and BPH management strategies as evidenced by the success of hybrid rice in China and not sufficient progress of the same in India. Development and adoption of duck rice and fish rice in China which has direct relevance to BPH management and nonexistence of the same in India is another story of the need driven technological marvel influenced by human management systems and food habits.
BPH management strategy in technologically advanced Japan where human time and effort are used based on their economic value, is almost always different from the tropical world.
Diversity in BPH, rice and humans can have tremendous influence on BPH management either directly or indirectly. Thus understanding the whole of these as a component of human existence and survival and moderating human thinking in population control and lowering the exploitation of nature including rice production can lead to real and truthful BPH management which will certainly be long lasting and sustainable.
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