Behavioral hormoligosis in oviposition preference of Bemisia tabaci on cotton

The study on behavioral hormoligosis in oviposition preference in Bemisia tabaci (Genn.) on cotton was conducted, at Entomological Research Farm, Punjab Agricultural University (PAU), Punjab, India, during 2001 crop season and repeated in the same season. Multiple-choice test was followed for conducting the experiment. Quinalphos (250, 375, and 500), carbaryl (625, 938, and 1250), acephate (750, 1125, and 1500), endosulfan (438, 656, and 875), and fenvalerate (25, 38, and 50 g ai/ha) were repeatedly sprayed on potted plants of American cotton (var. LH-1556). The impact of these insecticides was evaluated in term of oviposition preference by B. tabaci to treated plants. Also, it investigated changes in biochemical components of treated cotton leaves and the correlation with oviposition preference. The results revealed that, fenvalerate treated plants were more preferred by whitefly for oviposition. Maximum number of eggs was observed on fenvalerate treated plants, 38, 50, and 25 g/ha (39.3, 37.3, and 36.1 eggs/leaf, respectively) followed by acephate 1500 g/ha (26.9 eggs/ leaf) compared with untreated control (14.1 eggs/leaf). Almost similar trend of results was observed in the repeated experiment. The results obtained from biochemical studies revealed that all the insecticidal treatments caused reduction in total sugars compared with untreated control except fenvalerate and low dose of quinalphos. All insecticides caused increase in total free amino acids and brought significant changes in total phenols and pH value of treated plants. These results have confirmed the behavioral hormoligosis in oviposition preference that induced by fenvalerate and acephate in B. tabaci, which may be one of the causes behind its resurgence on plants repeatedly treated with these insecticides.     

Pesticide-mediated homeostatic modulation in arthropods

The term hormesis was coined to describe a phenomenon where exposure to high levels of stressors is inhibitory whereas low (mild, sublethal, and subtoxic) doses are stimulatory. The stimulatory effects are believed to be the result of compensatory biochemical processes following a destabilization of normal homeostasis. Exposure of arthropods to mild levels of chemical stressors (i.e., pesticides) may result in enhanced reproduction that has been associated along with other factors with pest outbreaks and resurgences. Hormesis, however, cannot be claimed for cases in which the observed stimulatory effects were due to exposure of non-target pests (i.e., mites) to pesticides (DDT, carbaryl, insecticidal pyrethroids or imidacloprid). Pesticides applied to non-target pests cannot be regarded as stressors since inhibition or mortality at very high doses can hardly be observed and measured. Pesticide-induced homeostatic modulation (PIHM) is suggested as a broader term to include both hormesis and stimulatory effects of pesticides on non-target pests. The specific role played by PIHM in inducing pest outbreaks in agroecosystems is difficult to evaluate as other complex environmental factors are most likely involved. The time factor is significant where applied pesticides undergo physical dissipation as well as biological, chemical, and/or photochemical modifications. A delay in outbreaks may be anticipated as arthropod pests exposed to effective residues and degradation products will be subjected to PIHM resulting in enhanced reproduction. Knowledge about hormesis and PIHM has practical aspects for designing pest control strategies and pest resistance management practices.