Pharmacology of Contractile Responses in the Alimentary System of Caterpillars: Implications for Insecticide Development and Mode of Action
Authors: Walker, Leslie E.; Bloomquist, Jeffrey R.
Source: Annals of the Entomological Society of America, Volume 92, Number 6, November 1999 , pp. 902-908(7)
Publisher: Entomological Society of America
Key:
- Free Content
- New Content
- Subscribed Content
- Free Trial Content
- Free Content
- New Content
- Subscribed Content
- Free Trial Content
Abstract:
Fifth-instar larvae of the imported cabbageworm, Pieris rapae (L.) (Lepidoptera: Pieridae), reared on artificial diet, were used for pharmacological studies of alimentary muscle. The alimentary system was dissected free, with the posterior end fixed in a perfusion chamber and the foregut ligated and connected to an isotonic force transducer. Stimulus-evoked contractions at the level of the hindgut were used to study the effects of antagonists, and unstimulated preparations were used to assess the effect of compounds that increased gut motility. Screening studies with sodium channel (tetrodotoxin) or glutamate receptor (spermine) antagonists showed that stimulation-evoked contractions were the result of direct depolarization of motor nerve terminals and release of neurotransmitter. Gut motility was significantly stimulated by 5-hydroxytryptamine, glutamate, and μ-agatoxin-4. The pentapeptide proctolin also augmented contractions, but its effects were variable. Evoked contractions were antagonized by glutamate, ibotenic acid, octopamine, and emamectin. The inhibitory effect of emamectin was much less potent on gut preparations from larvae reared on broccoli, suggesting that glutamate H receptors of visceral muscle are somehow altered by diet. Dopamine, GABA, and histamine had little or no effect on motility of imported cabbageworm visceral muscle. The peptide ω-agatoxin-IA was also inactive, suggesting that a toxin insensitive subtype of calcium channel is participating in the evoked contractions of this muscle. The implications of these results for exploiting the visceral musculature as a target for caterpillar control strategies are discussed.Keywords: Pieris rapae; ibotenic acid; avermectin; spider toxin; neurotransmitter
Document Type: Research article
Key:
- Free Content
- New Content
- Subscribed Content
- Free Trial Content
- Free Content
- New Content
- Subscribed Content
- Free Trial Content
Click here for Page Help