Effects of several insect growth regulators on the cabbage maggot, Delia radicum Linnaeus (Diptera: Anthomyiidae)

Young, Terry-Lynn (1988) Effects of several insect growth regulators on the cabbage maggot, Delia radicum Linnaeus (Diptera: Anthomyiidae). Masters thesis, Memorial University of Newfoundland.

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Abstract

A procedure was developed for maintaining a stock colony of the cabbage maggot, Delia radicum (Linnaeus), in the greenhouse, A petri dish rearing method producing a high yield of adults was developed for laboratory screening of insect growth regulators against this pest. -- Topical application of the chitin synthesis inhibitor, diflubenzuron (Dimilin ®), at a rate of 1.0 μg per egg significantly reduced hatch of 24-28 hour old eggs and caused 100% mortality of first instar larvae before they could feed on rutabaga slices. Diflubenzuron had no effect on mature larvae or pupae of D. radicum. Methoprene (Alttosid ® 5E), a juvenile hormone analogue, applied at the same dose, did not adversely affect egg hatch but prevented the eclosion of adults from pupae that subsequently developed from treated eggs. Pupal-adult intermediates were, observed inside treated puparia. Treatment of mature, post-feeding larvae and recently formed pupae with methoprene also produced non-eclosing pupal-adult mosaics. A dose of 0.05 μg per larva completely suppressed adult eclosion. However, diflubenzuron applied to third instar larvae or pupae did not affect adult eclosion. Juvenile hormone I and the anti-juvenile compound, precocene II, did not affect D. radicum when applied to the egg, larval or pupal stages. -- Thin-layer chromatography and colorimetric analysis of hemolymph metabolites 36 hours after treatment of post-feeding larvae demonstrated that methoprene caused a significant reduction in trehalose, the predominant carbohydrate in the hemolymph. Methoprene did not disrupt hemolymph amino acid or protein concentrations. -- This study suggests that methoprene and diflubenzuron are potential insecticides against D. radicum and that further studies on their effectiveness in the field and basis of disrupted development in D. radicum and other non-target insects is warranted.

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