| Rotting fruits offer all of the known resources required for the livelihood of Drosophila melanogaster, including larval growth, development, metamorphosis, and reproduction. Consequently, successful orientation to and correct location on the rotting fruits are very important in the adaptation and competition of the adults, and thus construct major selective pressure. During evolutionary history, D. melanogaster has already obtained a series of detecting mechanisms and behavioral responses, by which the adults can rapidly discover their food source, potential mates and oviposition substrates.During fruit fermentation, carbohydrates are decomposed to produce some volatile alcohols such as methanol, ethanol, n-propanol, isopropanol and n-butanol, whereas proteins and amino acids are decomposed to generate a lot of volatile amines such as ammonia and urea. It has been documented that D. melanogaster adults can detect these chemicals to locate the rotting fruits.On the other hand, those volatile chemicals are toxic to D. melanogaster adults. In the present paper, a preliminary research was carried out to test the influence of these toxic volatiles on chemotaxis and thogmotaxis of D. melanogaster adults. Our results may shed light on the evolution of these taxises and facilitate the development of field management strategy based on behavioral regulation in pests.A. Negative effects of toxic volatiles on survivalMethanol, ethanol and ammonia could kill the larvae and the adults of D. melanogaster. Five chemicals, piperonyl butoxide (PBO),3-amino-1,2,4-triazole (3-AT);4-methylpyrazole (4-MP), diethylmeleate (DEM), and triphenyl phosphate (TPP), the inhibitors of cytochrome P450monooxygenases (CYPs), catalases, alcohol dehydrogenases (ADHs), glutathione S-transferases, and esterases (Ests) respectively, could enhance the toxicities of the three volatiles. These three volatiles were more toxic to D. melanogaster loss-of-function mutants of Adh gene, and formaldehyde dehydrogenase Fdh gene and a knockdown mutant in a-Est7gene.B. Orientation to ammoniaWe compared the olfactory responses and movement of male flies from CS, Adhnl and FdhnNcl/FM6strains varying in mating status and nutritional state to ammonia source using a glass Y-tube olfactometer. When ammonia and artificial diet were put together in the odor arm, ammonia attracted more hungry mated males. The attractiveness increased almost linearly with ammonia concentration from the lowest to the highest. Furthermore, odorant concentration, mating status and nutritional state affected the flies’dispersal. Mated and starved males dispersed at a higher rate than virgin and satiated ones. As for Adhnl and FdhnNCl/FM6strains, mutations in Adh and Fdh genes decreased the attractiveness of ammonia.C. Influence of toxic volatiles on thogmotaxis during motionDuring evolutionary history, D. melanogaster has already obtained thogmotaxis behavior to avoid natural enemies. However, whether this behavior could be affected by toxic volatiles remained to be tested. In this study, we examined the influence of some mutants including Adhnl and Fdh"NCI/FM6strains and loss-of-function mutants in RhoGDI and RhoI genes on thogmotaxis. It was found that all the mutants exhibited stronger thogmotaxis than CS strain in the absence of toxic volatiles. When the strains were exposed to methanol or ethanol, the thogmotaxis behavior was further enhanced. Moreover, the enhancement effect of methanol was more stronger than that of ethanol. It seems that harmful environmental condition and unhealthy physiological state increased thogmotaxis extent.D. Influence of toxic volatiles on thogmotaxis during ovipositionIn this study, we discovered that the thogmotaxis behavior was still exhibited during oviposition. Both CantonS strain and FdhnNCI/FM6mutant showed similar thogmotaxis behavior and deposited their eggs along sides. The presence of H2S, methanol, ethanol and ammonia had little effect on the thogmotaxis behavior during oviposition. |
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