Flower and Pod Source Influence on Pea Weevil ( Bruchus pisorum) Oviposition Capacity and Preference

Push-pull strategies involve the behavioral manipulation of insect pests and their natural enemies via the integration of stimuli that act to make the protected resource unattractive or unsuitable to the pests (push) while luring them toward an attractive source (pull) from where the pests are subsequently removed. The push and pull components are generally nontoxic. Therefore, the strategies are usually integrated with methods for population reduction, preferably biological control. Push-pull strategies maximize efficacy of behavior-manipulating stimuli through the additive and synergistic effects of integrating their use. By orchestrating a predictable distribution of pests, efficiency of population-reducing components can also be increased. The strategy is a useful tool for integrated pest management programs reducing pesticide input. We describe the principles of the strategy, list the potential components, and present case studies reviewing work on the development and use of push-pull strategies in each of the major areas of pest control.

Tannins are the most abundant secondary metabolites made by plants, commonly ranging from 5% to 10% dry weight of tree leaves. Tannins can defend leaves against insect herbivores by deterrence and/or toxicity. Contrary to early theories, tannins have no effect on protein digestion in insect herbivores. By contrast, in vertebrate herbivores tannins can decrease protein digestion. Tannins are especially prone to oxidize in insects with high pH guts, forming semiquinone radicals and quinones, as well as other reactive oxygen species. Tannin toxicity in insects is thought to result from the production of high levels of reactive oxygen species. Tannin structure has an important effect on biochemical activity. Ellagitannins oxidize much more readily than do gallotannins, which are more oxidatively active than most condensed tannins. The ability of insects to tolerate ingested tannins comes from a variety of biochemical and physical defenses in their guts, including surfactants, high pH, antioxidants, and a protective peritrophic envelope that lines the midgut. Most work on the ecological roles of tannins has been correlative, e.g., searching for negative associations between tannins and insect performance. A greater emphasis on manipulative experiments that control tannin levels is required to make further progress on the defensive functions of tannins. Recent advances in the use of molecular methods has permitted the production of tannin-overproducing transgenic plants and a better understanding of tannin biosynthetic pathways. Many research areas remain in need of further work, including the effects of different tannin types on different types of insects (e.g., caterpillars, grasshoppers, sap-sucking insects). Copyright © 2011 Elsevier Ltd. All rights reserved.