Assessment of sublethal effects on behavior and demographic traits of insecticides employed in tomato crops on mirid predators

Abstract

The control of the South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and the whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) on tomato crops is based mainly using chemical compounds. The biological control of pests represents an alternative environmental safe. However, this method is used few due to the lack of studies concerning the bioecology of natural enemies, as well as the possible effects of insecticides and bioinsecticides upon these organisms. The objective of this study was (i) to evaluate the effects of the bioinsecticide Prev-am® and insecticide lambda-cyhalothrin in the population growth of T. absoluta and B. tabaci pests, as well as the Nesidiocoris tenuis (Hemiptera: Miridae) predator; (ii) to determine the population growth of T. absoluta and B. tabaci after Prev-am® and lambda-cyhalothrin contact, in the presence and absence of N. tenuis; (iii) to evaluate the sublethal effects of these products in the longevity, behavior and predation of N. tenuis; and (iv) to determine the lethal and sublethal effects of insecticides (spinetoram, chlorantraniliprole + abamectin, triflumuron and tebufenozide) in the biological and behavioral characteristics of Macrolophus basicornis (Hemiptera: Miridae). The experiments were carried out laboratory conditions, using the completely randomized design. Aiming to determine the demographic growth of B. tabaci and T. absoluta, the adults were exposed to Prev-am®, lambda-cyhalothrin and distilled water, in the presence and absence of N. tenuis. The number of insects emerged was recorded after 11 days the experiment was set up. The bioassays aiming to evaluate the N. tenuis behaviour were carried out into Petri dishes, after the predators exposition to the maximum concentration of Prev-am® and lambda-cyhalothrin. Bemisia tabaci and T. absoluta were used as prey; regarding the predator behavioral response were assessed predation, resting, cleaning and plant feeding. Aiming to quantify the lethal and sublethal effects of insecticides upon M. basicornis, nymphs were exposed to plants treated, and adults directly treated. In addition, the insecticides effects in the M. basicornis flight response was assessed. The results concerning the T. absoluta bioassays showed a high capacity of N. tenuis to reducing the pest population growth. Lambda-cyhalothrin and Prev-am® reduced the predatory capacity of N. tenuis. One the other hand that was verified to lambda-cyhalothrin, the biopesticide did not alter the predator behavior. In the bioassays performed to M. basicornis, abamectin caused lethal effect on the predator, while the other insecticides (spinetoram, chlorantraniliprole + abamectin, triflumuron, tebufenozide) caused sublethal effects. Regarding the study using B. tabaci, the biopesticide Prev-am® was unable to reducing the population pest, and compromised the population growth of the predator. However, Prev-am® showed smaller toxicity on predator compared to lambda-cyhalothrin. The use of insecticides and bioinsecticide need be employed carefully, and experiments should carried in standard conditions to prove the toxicity of compounds evaluated in this work.