Corn Earworm Larvae (Helicoverpa zea) Bounded on Warmer Direction (Thermotropism)  

Robert J. Zhu1 , Mariana Krugner2
1. Haide Institute of Tropical Agricultural Resources (HITAR), Hainan, 572025, China
2. SynTech Research Inc. Sanger, CA, 93657, USA
Author    Correspondence author
Biological Evidence, 2014, Vol. 4, No.   doi: 10.5376/be.2014.04.0001
Received: 13 Sep., 2014    Accepted: 30 Oct., 2014    Published: 18 Nov., 2014
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Preferred citation for this article:

Zhu and Krugner, 2014, Corn Earworm Larvae (Helicoverpa zea) Bounded on Warmer Direction (Thermotropism), Biological Evidence, Vol.4, No.1 1-5 (doi: 10.5376/be.2014.04.0001)


Thermotropism of corn earworm neonates was observed during Bt (Bacillus thuringiensis) toxicity bioassay against corn earworm (Helicoverpa zea). Six photos provided in this report convinced us that the corn earworm larvae moved to a warmer area within 24 hours of hatching. Possible reasons for the thermotropism are discussed but are not yet clear.

Corn earworm; Helicoverpa zea; Larva; Thermotropism

The Corn earworm (Helicoverpa Zea) is one of the world's most important polyphagous pests and can significantly harm a number of crops such as cotton, corn and tomato. Insecticide resistance in corn earworm has been reported for almost all classes of chemical insecticides. In addition, with the large-scale planting of Bt cotton and other transgenic Bt crops, the constant expression of Bt toxin has caused a strong selection pressure leading to resistance of corn earworm to Bt toxin. Therefore, our group carried out a series of Bt strain screenings, as well as the identification and cloning of toxic protein genes (Fang and Zhang, 2012; Marco and Porcar, 2012; Zhang et al., 2012; Fang et al., 2013; Alkuddsi et al., 2013). When toxicity bioassays of those Bt strains were performed against corn earworm (Helicoverpa zea), we found that neonate larvae had an obvious thermotropism. Photographed with a Canon Camera (PowerShot G12, Japan), here we presented six photos to record this biological phenomenon.


Photo slide

The phototaxis of corn earworm adult is well known, but to our knowledge thermotropism in corn earworm larvae has not been reported. External parasitic insects (e.g. mosquito, flea and lice) are known to be stimulated by the host’s temperature, leading them to find their host animals. As for corn earworm, it is not known why neonates are oriented by temperature. We propose,  although it is well known that corn earworm larvae are very aggressive, killing and cannibalizing other larvae; increased temperature will speed up their development. Therefore, thermotropic larvae would develop more quickly and have an advantage during cannibalization, which may explain the evolutionary preservation of thermotropism. However, as the larvae start to eat, those eating more will develop more quickly and no longer demonstrate thermotropism.
The authors recorded this thermotropism phenomenon through photos, however, the phenomenon needs to be further explored.
Haide Institute of Tropical Agricultural Resources (HITAR) greatly appreciates SynTech Research for the support of this project. This study was carried out at the SynTech Research Technical Center in Sanger, CA, 93657, USA.
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Fang X., Xi W., Zhang W., and Xie L., 2013, Bt S2096-2, A Bacillus thuringiensis Strain with Highly Larvacidal Toxicity against Hookworm II Rhabditiform Larva (Necator americanus), Bt Research, 4: 21-23
Fang X., and Zhang W., 2012, Bt S2160-1, a High Mosquitocidal Strain of Bacillus thuringiensis, Bt Research, 3: 29-31
Marco G., and Porcar M., 2012, Ecological Mysteries: is Bacillus thuringiensis a Real Insect Pathogen? Bt Research, Vol.3, No.1 1-2
Zhang W., Crickmore N., George Z., Xie L., He Y.Q., Li Y., Tang J.L., Tian L., Wang X., and Fang X.J., 2012, Characterization of a new highly mosquitocidal isolate of Bacillus thuringiensis--an alternative to Bti? J Invertebr Pathol 109 (2):217-222.; PMid:22137876
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