Bases para o manejo da mosca-branca Aleurodicus cocois (Curtis, 1846) (Hemiptera: Aleyrodidae) na cultura do cajueiro

Abstract

The cashew whitefly Aleurodicus cocois (Curtis, 1846) (Hemiptera: Aleyrodidae) is one of the main pests of the cashew tree Anacardium occidentale L. in Brazil. In the search for new control strategies for A. cocois, this studie aimed to: 1- Characterize the volatile organic compounds (VOCs) emitted by dwarf cashew tree clones, and evaluate the behavioral response of A. cocois to these compounds in laboratory and in the field; 2- Evaluate the olfactory response of the predator Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae), to dwarf cashew volatiles induced by A. cocois herbivory, as well as the predation potential of this natural enemy on eggs and nymphs of A. cocois; 3- Evaluate the chemical profile and toxicity of the mixture of essential oils of Lippia sidoides Cham (Verbenaceae) and Cymbopogon winterianum Jowitt (Poaceae) on the third and fourth nymph stages of A cocois, as well as its selectivity to the predator C. externa. A four-arm olfactometer was used to investigate the behavioral response of adult females of A. cocois to volatile compounds from leaves of cashew tree clones (CCP 76, EMBRAPA 51 and PRO 143/7). The volatile compounds emitted by the leaves of the three cashew tree clones were analyzed by microextraction in solid phase coupled to GC-MS. In the field trials CCP 76 and EMBRAPA 51 were cashew tree clones most infested by A. cocois. Bioassays revealed that CCP 76 volatiles were attractive to A. cocois, while EMBRAPA 51 and PRO 143/7 volatiles were less attractive to insects when compared to a control (air). According to the analysis of principal components, there is a difference between the chemical profiles of the three cashew tree clones, and in clone CCP 76 the emissions of compounds are at intermediate levels. The functional response of first-instar larvae of C. externa fed on eggs and nymphs of A. cocois, as well as the olfactory response of third-instar larvae of this predator, to the volatiles of two dwarf cashew tree clones (CCP 76 and PRO 143 /7) induced by herbivory of A. cocois were conducted in the laboratory. The volatile compounds emitted by the leaves of the two cashew tree clones, infested and not infested by A. cocois, were analyzed by microextraction in solid phase coupled to GC-MS. Logistic regression indicated that first-instar larvae of C. externa exhibited a type II response when fed A. cocois eggs and nymphs. In the behavioral tests, third instar larvae of C. externa were able to distinguish and select the volatile signals emitted after infestation by A. cocois, regardless of the cashew tree clone evaluated. According to the volatiles of the evaluated cashew tree clones, there is a difference in the chemical profiles of plants infested and not infested by A. cocois. In the laboratory, the chemical profile and toxicity of the mixture of essential oils from L. sidoides and C. winterianum on the third and fourth nymphal stages of A cocois, as well as its selectivity to the predator C externa, were evaluated. The results revealed that the essential oils of both plants are composed of monoterpenes. In the concentration and mortality bioassays, the toxicity of the mixture of essential oils evaluated on the third and fourth nymphal stages of A. cocois was revealed through its LC50, estimated at 0.97 µL/cm2 and 1.48 µL/cm2, respectively. In all evaluated concentrations, the mixture of essential oils caused low mortality of eggs and larvae of C. externa and did not change the development time of the predator. However, the mixture of oils was repellent to the predator.