Research On An Eye-color Mutant Of The Cotton Bollworm, Helicoverpa Armigera

The cotton bollworm, Helicoverpa armigera (Hiibner) (Lepidoptera:Noctuidae), is one of the most serious insect pests in China and has a wide range of host plant, including both cultivated crops and wild plants. In China, this species has four or five generations a year in most areas and over-winters as diapause pupae in soil. In this research, we found an eye-color mutant in the laboratory, which shows color differences from egg to adult, and explored its genetic mechanism and its adaptation compared with the wildtype.The eye color mutant is shown the compound eye is yellow, called yellow mutant, while the wildtype is shown green as compound eyes. Fertile eggs from the mutants does not change its color until its hatching and young larvae look like greenish. However, fertile eggs from wildtype are brownish and larvae are brownish, too. By cross the mutants to wildtype, all hybrids are shown as wildtype. Back-cross of hybrids to the mutants get one half mutants and one half wildtype. Self-cross of the hybrids get one-fourth mutants and three-fourth wild type individuals. Through the tradition genetic analysis, the eye color mutant is controlled by recessive gene locating on auto-chromosome.Is the mutant harmful? We systematically compared the growth and development for both the mutant and the wildtype with the back cross generation. The results showed that the development duration did not significantly differ each other. Moreover, the pupal weight did not differ either. Fecundity and fertile eggs were recorded that did not differ each other. The study showed that the mutant is not harmful.Does the mutant bring changes in sex pheromone ratio and mate selection? The sex gland for both the mutants and wildtype females were cut and sex pheromone were extracted and analyzed. The results showed that Z9-16 ald and Z11-16 ald are two main compositions. The ratio of Z11-19 ald:Z9-16 ald is 92:8 and 96:4 for the mutants and wild type, which is not significantly different. The mate selection showed that both males of the mutants and wildtype did not recognize female whether it is the mutant or the wild type. It was some for both females of the mutants and wildtype who did not recognize male of mutants from wildtype.Finally, we carried out the experiments of predation and parasitism by natural enemies because larval color is completely differences between the mutant and the wildtype. First, we evaluate the predation by birds and hens in cages planted tobacco, hot pepper and tomato, respectively, in the field. When plants were ready for experiment, same number of each kind larvae of both the mutants and the wildtype were released on plant and letting feeding on plants a day. Then two birds and two hens were released to predate H. armigera larvae for one day and finally the left larvae on plants were counted and compared the number of the mutant and wildtype larvae. The results showed that larvae from mutants were more successfully escape the predation than did the larvae from the wildtype. However, for the parasitism wasps who use volatiles to locate pests had nearly the same parasitism for both the green larvae and the brown larvae.Through the study, we know the mutants are regulated by the recessive gene locating on auto-chromosome. The phenotype of the mutants is completely different from the wildtype, which shows green larvae. Although the performance of the mutants is not different from the wildtype and the mutation is not harmful, the mutant green larvae shows more ability to escape the predation since its color is similar to host plants, which may indicate increased population dynamics and may guide pest management in future.