UBC Theses and Dissertations
Roles of juvenile hormone in the green peach aphid, myzus persicae sulzer (homoptera: aphididae) Verma, Kulbhushan
The role of juvenile hormone (JH) in alate-apterous polymorphism was investigated in the green peach aphid, Myzus persicae. At higher concentrations (65 ppm), the juvenile hormone analogue (JHA), kinoprene, was immediately toxic to apteriform nymphs. At lower concentrations (10 ppm), the compound was non-toxic and exhibited no apparent morphological activity in apteriform stages. In contrast, 65 ppm kinoprene administered to alatiform nymphs had juvenilizing and apterizing effects. The extent of these effects depended upon when the kinoprene was applied. Fourth instar alatiforms were the least sensitive as kinoprene-treated nymphs developed into normal adults with reduced sclerotization and pigmentation. Kinoprene-treated third instars underwent a supernumerary moult before metamorphosing into adults with malformed wings. Sclerotization and pigmentation were also lacking in these insects. When first and second instar alatiformsiwere treated with kinoprene, they also underwent a supernumerary moult. The adults which emerged exhibited both larval and apterous characteristics. Wing development was almost totally inhibited; the cauda and genital plate were poorly developed. In addition, sclerotization and pigmentation were reduced and ocell lacking. The secondary antennal sensoria were also malformed. These findings clearly (1) demonstrate that kinoprene can be employed as a JH mimic to alter the normal programming of the epidermal cells in alatiform nymphs and (2) indicate that JH plays an important role in aphid morphogenesis and polymorphism. The differential responses of the four alatiform nymphal instars suggest that elevated JH levels during the first and second instars are particularly important in inhibiting wing development. To determine the prenatal effects of JH on wing development and morphogenesis, kinoprene was also administered to newly ecdysed apterous adults. Even though conditions favoured alate production, 75% of the offspring produced by kinoprene-treated virginoparae developed into normal apterae. This suggests that elevated JH titers in maternal haemolymph inhibit wing development and promote development of apterae. Topical application of the anti-allatotropin, precocene-II, had variable effects on apteriform nymphs and adults. In all stages, precocene produced a significant decline in larvi-position. The effects were more pronounced in first and second instar apteriform nymphs and apterous adults than in third and fourth instar nymphs. When kinoprene was applied to these insects, larviposition increased significantly after 2 days. The findings demonstrate that JH stimulates reproduction in viviparous morphs of persicae.
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