William L. Parrott

Resistance of Plants to Insects

Publisher Summary This chapter discusses the resistance of plants to insects. Resistance is the ability of a certain variety to produce a larger yield of good quality than other varieties at the same initial level of infestation and under similar environmental conditions. Three basic components or mechanisms are involved in plant resistance. First, plants may be nonpreferred for oviposition, shelter, or food, primarily, because of the lack of or presence of chemical or physical factors. Second, resistant plants may affect the biology of the insect adversely that is called antibiosis. Third, resistant plants may be tolerant, surviving under levels of infestation that would kill or severely injure susceptible plants. Several problems may occur at various stages in the development of any host plant resistance program. Some of these problems include: proper finance, entomological problems, and problems in technique development. Resistance is most often found in off types or exotic wild species, and considerable crossing and selection is required to move the resistant genes into a desirable agronomic background. The greatest use of resistant varieties would undoubtedly be as one component part of pest management system.

Elucidating mechanisms of tobacco budworm resistance to allelochemicals by dietary tests with insecticide synergists

Abstract Three major cotton ( Gossypium hirsutum L.) plant allelochemicals—gossypol, a mixture of condensed tannins, and isoquercitrin—were fed to 1-, 3-, and 5-day-old tobacco budworm ( Heliothis virescens Fab.) larvae at the 0.06% level with and without 0.02, 0.06, and 0.60% piperonyl butoxide, an insecticide synergist that inhibits the activity of an insects existing detoxifying enzymes. All three allelochemicals were toxic to the 1- and 3-day-old larvae, but they were not toxic or were only marginally toxic to the 5-day-old insects. Piperonyl butoxide was toxic to the 1-, 3-, and 5-day-old insects, although less so to the 5-day-old insects. With both the allelochemicals and piperonyl butoxide in the diet, further decreases of growth were observed. Seven additional synergists representing several classes of compounds known to inhibit mixed function oxidases (MFOs; polysubstrate macrooxygenases, PSMOs) or esterases in the insect were also added to the diet at the 0.02 and 0.06% levels, with and without allelochemicals at the 0.06% level. However, only piperonyl butoxide decreased the growth rate of 5-day larvae fed the three allelochemicals. Thus, one effect of gossypol and other allelochemicals on insect feeding can be inferred to be toxicity, but gossypol may also act as an antifeedant.