Lessando M. Gontijo

Bioinsecticide-Predator Interactions: Azadirachtin Behavioral and Reproductive Impairment of the Coconut Mite Predator Neoseiulus baraki

Synthetic pesticide use has been the dominant form of pest control since the 1940s. However, biopesticides are emerging as sustainable pest control alternatives, with prevailing use in organic agricultural production systems. Foremost among botanical biopesticides is the limonoid azadirachtin, whose perceived environmental safety has come under debate and scrutiny in recent years. Coconut production, particularly organic coconut production, is one of the agricultural systems in which azadirachtin is used as a primary method of pest control for the management of the invasive coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae). The management of this mite species also greatly benefits from predation by Neoseiulus baraki (Athias-Henriot) (Acari: Phytoseiidae). Here, we assessed the potential behavioral impacts of azadirachtin on the coconut mite predator, N. baraki. We explored the effects of this biopesticide on overall predator activity, female searching time, and mating behavior and fecundity. Azadirachtin impairs the overall activity of the predator, reducing it to nearly half; however, female searching was not affected. In contrast, mating behavior was compromised by azadirachtin exposure particularly when male predators were exposed to the biopesticide. Consequently, predator fecundity was also compromised by azadirachtin, furthering doubts about its environmental safety and selectivity towards biological control agents.

Azadirachtin-Induced Hormesis Mediating Shift in Fecundity-Longevity Trade-Off in the Mexican Bean Weevil (Chrysomelidae: Bruchinae)

ABSTRACT Insecticides can have lethal or sublethal effects upon targeted pest species, and sublethal effects may even favor pest outbreaks if insecticide-induced hormesis occurs. Hormesis is a biphasic dose—response of a given chemical compound that is stimulatory at low doses and toxic at high doses. The former response may result from the disruption of animal homeostasis leading to trade-off shifts between basic ecophysiological processes. A growing interest in the use of biorational insecticides, such as azadirachtin to control stored-product pests, raises concerns about potential sublethal effects. In this study, we explored the hypothesis that azadirachtin can negatively impact the reproductive capacity of the Mexican bean weevil, Zabrotes subfasciatus (Boheman) (Chrysomelidae: Bruchinae), a key pest of stored beans. In addition,weinvestigated whether adults of this species could compensate for any sublethal effect that might have affected any of their reproductive parameters by adjusting the allocation of its reproductive efforts. The results showed that females of Z. subfasciatus increased fecundity daily to compensate for azadirachtin-induced decreased longevity. In addition, a stage-structured matrix study revealed that populations of Z. subfasciatus engendered from females exposed to azadirachtin exhibited a higher rate of population increase (r) and a higher net reproductive rate (Ro). Finally, a projection matrix analysis showed notably higher densities along the generations for azadirachtin-exposed Z. subfasciatus populations. Thus, our study provides empirical evidence for the capacity of Z. subfasciatus to adapt to sublethal effects caused by biorational insecticides; consequently, this study highlights the importance of understanding this phenomenon when devising pest management strategies.

Seletividade de inseticidas a Doru luteipes (Scudder, 1876) (Dermaptera: Forficulidae) e Cotesia sp. (Hymenoptera: Braconidae) inimigos naturais de Ascia monuste orseis (Godart, 1818) (Lepdoptera: Pieridae)

This work aimed to study the selectivity of the insecticides carbaryl, deltamethrin, methyl parathion, permethrin and trichlorfon in favor of the predator Doru luteipes (Scudder) (Dermaptera: Forficulidae) and of the parasitoid Cotesia sp. (Hymenoptera; Braconidae) in relation to the control of the kale leafworm Ascia monuste orseis (Godart) (Lepidoptera: Pieridae). LC90 were determined for A. monuste orseis, and these were used as discriminatory doses to evaluate the degree of selectivity of the insecticides. Deltamethrin and permethrin were highly selective in favor of D. luteipes. Deltamethrin was intermediate selectivity in favor of Cotesia sp., while permethrin was not selective in favor of this parasitoid. Trichlorfon was highly selective in favor of fourth instar nymphs and adults of D. luteipes, and it was intermediate selectivity in favor of Cotesia sp. and first instar nymphs of the predator. Carbaryl was intermediate selectivity in favor of Cotesia sp., but it did not show selectivity in favor of D. luteipes. Methyl parathion did not show selectivity in favor of D. luteipes and Cotesia sp. Adults of D. luteipes were less sensitive to deltamethrin, permethrin and trichlorfon than adults of Cotesia sp. and the inverse happened with carbaryl. Both natural enemies presented high sensibility to methyl parathion. Fourth instar nymphs of and adults of D. luteipes were more sensitive to methyl parathion and trichlorfon than first instar nymphs. Both nymphs and adults of D. luteipes presented similar sensibility to the carbaryl, deltamethrin and permethrin.

Identificação e quantificação dos componentes de perdas de produção do tomateiro

Identification and quantification of tomato yield loss components The components of loss in tomato production were identified and quantified, in the summer-autumn period. The critial component and the key factor in the cultivation loss become evident using the methodology of the crop life table. The experiment was conducted at the Universidade Federal de Vicosa, Minas Gerais State, Brazil, from January to June 2001 and consisted of two treatments (cultivars Santa Clara and F1 Debora Plus) in a randomized complete block design with 5 replications. During the tomato cycle, the number of dead plants, the causes of this and the number of flowers and fruits/ plant were evaluated. At harvest, the healthy fruits were counted, weighted and classified; the causes of fruit damage were identified and the loss quantified. Total loss was more influenced by the fluctuation of the component plants (r=0,89) (P<0,01) than by other production components; consequently, plants were considered the critical production components of tomato. TSWV virus was the only factor affecting plant death, being considered the key-factor in the loss of this tomato production.

Female beetles facilitate leaf feeding for males on toxic plants

Milkweed plants produce latex, which works as a defence against some herbivorous insects. The cerambycid beetles Tetraopes femoratus (LeConte) puncture the leaf midrib vein to extravasate the latex, and thus render the leaf edible. Nonetheless, it has not yet been investigated whether there is any further implication beyond food acquisition regarding this behaviour. The present study examined the hypothesis that leaf latex drainage is done mainly by females of T. femoratus, and that the males opportunistically prefer to feed on those ‘disarmed’ leaves. The experiments revealed that puncturing the leaf midrib vein to extravasate latex is done mainly by females of T. femoratus and not only serves their purpose of food acquisition, but also mediates an opportunistic feeding behaviour among males. Males of T. femoratus preferred to feed on milkweed leaves that had previously been fed upon by females. In addition, field observations showed that mating occurred more frequently on recently ‘disarmed’ leaves, suggesting increased copulation opportunities for females during leaf feeding. In sum, the results reveal that the feeding defence strategy of T. femoratusfemales to toxic milkweed foliage has created an opportunity for males to feed on milkweed leaves with a reduced risk of latex exposure and entanglement. Thus, this research provides empirical evidence of plant–insect interactions contributing to the appearance of an opportunistic adaptive feeding behaviour, which has broader implications for eco‐evolutionary systems.

Survival and Locomotory Behavior of Earwigs After Exposure to Reduced-Risk Insecticides

Abstract The conservation of natural enemies is an important tactic to promote biological control of arthropod pests. The earwig Doru luteipes (Sccuder) is the most important predator of the fall armyworm Spodoptera frugiperda (J.E. Smith) in corn fields. One way of conserving these predators in the field is by using only selective insecticides when the pest population reaches the economic threshold. Some recent insecticides such as azadirachtin, chlorantraniliprole, and novaluron have been claimed to pose reduced risk for natural enemies. Nevertheless, there is a dearth of information regarding the selectivity of these insecticides upon earwigs in specific. In this study, we carried out a series of laboratory assays to examine the survivorship and locomotory behavior of D. luteipes after exposure to fresh dry residue of azadirachtin, chlorantraniliprole, and novaluron. Our results show a significant survival reduction for D. luteipes nymphs exposed to fresh residues of chlorantraniliprole and novaluron. In the behavioral studies, adults of D. luteipes stopped more often, spent more time resting (inactive), and moved more slowly immediately after exposure to chlorantraniliprole residue. These results suggest that chlorantraniliprole may mediate an impaired movement and a behavior arrestment of earwigs after contact with this insecticide fresh residue. This could translate into reduced foraging efficiency, and increase exposure and insecticide uptake. Although chlorantraniliprole and novaluron showed a potential to undermine the biological control provided by earwigs, it is yet essential to conduct field trials in order to confirm our laboratory results.