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Effects of the ecdysteroid agonists RH 5849 an Rh 5992, alone and in combination with a juvenile hormone analogue, pyriproxyfen, on larvae of Spodoptera exigua

Smagghe, G.; Degheele, D.

Entomologia Experimentalis Et Applicata 72(2): 115-123

1994


ISSN/ISBN: 0013-8703
DOI: 10.1111/j.1570-7458.1994.tb01809.x
Accession: 008583792

Biological activity assays with RH 5849 and RH 5992 indicated that both compounds affected growth and development of last-instar larvae of Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) in a dose-dependent manner. Within the first 24 h after treatment by continuously offering leaves dipped in a water solution of gt 50 mg/l RH 5849 and gt 0.5 mg/l RH 5992, symptoms of a prematurely induced larval moult and head capsule apolysis were visible. Intoxicated larvae died shortly afterwards, showing signs of unsuccessful ecdysis. LC-50-values of RH 5849 and RH 5992 for fifth-instar S. exigua larvae were 110 and 2.5 mu/l, respectively. Pyriproxyfen alone affected the larval stage and disturbed normal metamorphosis. One supernumerary larval instar occurred occasionally. LC-50-value for pyriproxyfen was 1.7 mg/l. Larvae simultaneously treated with RH 5849 or RH 5992 and pyriproxyfen, continued to grow until they attained a size and weight about 2-3 times that of the controls. This growth was accompanied by at least one and sometimes two supernumerary moults. Concerning the in vivo imaginal wing disc growth and development, only in larvae treated with 10 and 50 mg/l RH 5849 or 0.5 mg/l RH 5992, tracheole migration was observed earlier than in the controls. When applying 300 mg/l RH 5849 or 3-7 mg/l RH 5992, the discs remained small and no signs of tracheole migration were observed. In larvae simultaneously treated with RH 5849 or RH 5992 and pyriproxyfen, tracheole migration was not prematurely induced and a pupal cuticle was produced in the discs of larvae, undergoing a supernumerary moult. No clear signs of evagination were observed.

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