Toxicity and cuticle softening effects of a petroleum oil and vegetable oils to the cotton boll weevil Anthonomus grandis Boheman (Coleoptera:Curculionidae).

STADLER, T.; ZERBA, M.I.; BUTELER, M.

Sidney, Australia

Conferencia; Spray Oils Beyond 2000; 1999

University of Western Sidney

To better understand the toxic effects of oils on insects, we tested soybean (Glycine max (L.) Merr. [Fabales: Fabaceae]), cottonseed (Gossypium hirsutum L. [Malvales: Malvaceae]) and an nC23 mineral oil on cotton boll weevil (Anthonomus grandis Boheman [Coleoptera: Curculionidae]) to compare their effect on insect cuticle hardness and to correlate this with oil toxicity. Adult weevils were obtained from USDA-ARS Mississippi, USA. In 2 independent bioassays, groups of insects were treated topically with oils (1 µL or 0.5 µL) to assess changes in cuticle hardness and toxicity. Cuticle hardness was evaluated by measuring the pressure required to crush the cuticle of the weevils with a Gel-Tester. Toxicity was evaluated from mortality. The reduction in cuticle hardness was in the order cottonseed oil (11.8%) < soybean oil (17%) < mineral oil (22.4%). However, cuticles of insects treated with cottonseed oil were not significantly softer than cuticles of untreated insects. We found a relationship between cuticle softening and toxicity: greater softening correlated positively with oil toxicity. Variation in cuticle hardness could represent structural changes at the cuticular level, with lethal consequences for the insects. These results allow speculation on a new target for insecticide oils. This could encourage further research on the influences these products have on the structure and properties of the body surface of insects.