Morphogenetic abnormalities of alatiform mustard aphid, Lipaphis erysimi following topical application of juvenile hormone analogues

Abstract

Two juvenile hormone analogues (JHAs), R-20458(6,7-epoxy-1 (p-ethylphenoxy)-3, 7-dimethyl-2-octene) and ZR-512 (ethyl 3,7,11-trimethyl-2, 4-dodecadienoate) were topically applied to various instars of mustard aphid, Lipaphis erysimi (Kalt), delivering doses ranging from 0.000015 to 1.0 μg in acetone on the dorsum of each test insect with the help of a microsyringe. Deformed individuals were categorized as adultoids (crumpled and twisted wings), nymphal-adult intermediates (sclerotized wing pads) and supernumerary nymphs (one extra moulting) and a scale was devised to asssess the extent of deformities. The process of embryogenesis was observed to be normal and the adultoids and nymphal-adult intermediates (with normal gonopores) reproduced normally. Only in case of supernumerary nymphs where gonopores were absent and those intermedites which had occluded gonopores, parturition could not take place. Antennae, legs and cornicles of the deformed individuals also exhibited some degree of deformation due to the hormone treatment. The third, second, fourth and first instar aphids ranked in descending order in developing abnormalities under exposure to the JHAs; a dose as low as 0.000015 μg/aphid of ZR-512, significantly deranged the morphogenesis of the third instar aphids. The lowest doses imparting significant degrees of abnormality to the aphid were 0.0039 and 0.00006 μg/aphid for R-20458 and ZR-512, respectively; showing the latter as more potent agent of morphogenetic abnormalities.