Dinâmica da ativação ovariana em Zabrotes subfasciatus (boh.) (Coleoptera: Chrysomelidae, Bruchinae): a necessidade de sementes e machos

Abstract

The beetle Zabrotes subfasciatus is an insect that preys on stored grains, particularly beans (Phaseolus vulgaris). Therefore, understanding the biology of Z. subfasciatus allows the planning and adoption of sustainable grain control strategies. Despite its importance, there is little work developed on the parameters involving the biology of insect reproduction. Electroantenographic assays suggest that contact between Z. subfasciatus females and the host and males stimulates oogenesis and oviposition. However, the morphological and molecular dynamics of the ovarian ontogenesis of these insects in response to these stimuli is unknown. That said, we sought to determine how male and host participate in the reproductive physiology of Z. subfasciatus females. Immature individuals were selected and subjected to controlled humidity and temperature conditions, varying the factors that possibly interfere with oviposition (male and bean seeds, in various combinations). Thus, the number of eggs, daily oviposition behavior for ten days and the emergence of adults after 25 days of the last daily oviposition measurement were verified. Subsequently, experiments were carried out for the morphological and molecular analysis of ovarian activation in females subjected to combinations of variables. For morphological analyses, females were dissected to remove the ovaries that were processed (DAPI - phalloidin) for fluorescence microscopy. For molecular analyses, ovaries and carcasses of females were collected from which total RNA was extracted. These samples were used in qPCR assays to determine the transcription levels of the vitellogenin gene (Vg) and its receptor (VgR), as they are important indicators of reproductive capacity. The results of female fecundity analyses under different conditions suggest that, alone, the variables are not sufficient to induce egg-laying activity. It was also observed that females are ready for reproduction on the first day of adult life and show a concentrated period of oviposition in the first 6 days of life. Morphological analyses indicate that at the beginning of adult life, Vg endocytosis, mediated by the action of VgR, already occurs in ovarioles (which does not happen in pupae) and that ovarian activation decreases over time. Molecular analyses showed that vitellogenesis (expression of Vg in carcass and Vg receptor in ovaries) is promoted by the presence of the host and that the presence of the male stimulates the synthesis of Vg in the ovaries.