Análise dos efeitos do fipronil e dimetoato em larvas e pupas de Apis mellifera L. (Hymenoptera: Apidae) africanizada criadas em condições laboratoriais

Abstract

Africanized Apis mellifera bees Linnaeus, 1758 (Hymenoptera: Apidae), although not native to Brazil, is very important both for the environment and for the economy. However, with the growth of food production and biofuels, there was an expansion of the areas of monoculture consequently was increased also the use of fertilizers and pesticides. Although some insecticides such a fipronil (used in sugar cane) and dimethoate (standard substance in larval tests standardized by the Organization for Economic Cooperation and Development and used in cotton crops), are toxic to bees. Thus the present study aimed to evaluate the biological and histological effects of toxicity of pesticides in the ontogenetic development of Africanized A. mellifera. For this, worker larvae of 1st instar were collected from healthy colonies of the apiary located in the rural town of Piedade/SP and transferred to sterile polystyrene cells, which contained larval diet. After the transfer, the cells were maintained at a temperature of 34±2° C and RH 85±5%, the larvae fed daily from 1st to 5th day. On day 4, were prepared with three different concentrations (20, 5 and 0.5 ng a.i./&#956;L) fipronil and dimethoate a concentration (200 ng a.i./&#956;L) was added 1 &#956;L of each concentration prepared (isolated) under integument of the larva, called acute treatment. The results showed that there was no larval mortality (72 hours) significantly between groups (p>0.20), exposed to fipronil and control, but the pupae rate anomalous (p<0.03) and emergency (p<0.04) was found significant difference. The most common abnormalities were pigmentation on the upper and lower body, head and malformation in the absence of members; pink eye pupa (Pp) and white eyed pupae (Pw) with malformation of the limbs, having formed the eye and with larval body. It is assumed that the fipronil be a neurotoxic compound, he is acting in the regulation and release of Ecdysteroid hormones that are involved in the passage from larva to adult (metamorphic process). After the bioassay dimethoate, pre-pupae were collected (D9) for morphological and histochemical analysis for both treatment groups and for the control. Pre-pupae were processed routinely. Histological sections were stained with Hematoxylin-Eosin. For immunohistochemical analysis, we used the Bromophenol Blue reactions, Periodic Acid-Schiff and Feulgen. By morphological and histochemical analysis, changes were observed in muscle tissue, intracellular spacing of trophocytes and oenocytes, increase in the amount of proteins and lipids and nuclear branch in trophocytes. Most of these characteristics are described pupae, however individuals were analyzed in the pre-pupae stage, namely, and it is likely that the substance studied on the development of bees exposed to the insecticide. Dimethoate could activate the cellular detoxification system by carboxylesterases enzymes and, in this way, cause the hydrolysis of the Juvenile Hormone and hence the acceleration of the metamorphic layers. The high rate of abnormalities in the pupal stage and decreased emergency rate in individuals exposed to fipronil raises concerns with decreasing productivity in commercial apiaries located in agro-ecosystems. In addition, the advance from the present study calls attention to damage in the colony, as in nature the metamorphosis of the phases have certain duration. This can cause physiological disorder could indirectly damage the chain pollination by bees.