Inventário de visitantes florais na cultura do morangueiro e efeitos de inseticidas sobre as abelhas nativas Melipona quadrifasciata e Tetragonisca fiebrigi (Hymenoptera: Apidae)

Abstract

Pollination is of great importance in the production of various agricultural crops. In the strawberry, it is facilitated with the aid of insects, such as bees, which play a fundamental role in reducing the rates of deformation of the fruits. The objectives of this study were: a) make an inventory of floral visitors associated with the strawberry of the Albion cultivar grown in the semi-hydroponic system in the Serra Gaúcha region and to identify potential species of native pollinating bees; b) determine the lethal effects (mortality), sublethal (locomotor activity), as well as the detoxification profile of insecticides and acaricides used in strawberry cultivation on native stingless bees Melipona quadrifasciata and Tetragonisca fiebrigi; c) conduct a systematic review followed by meta-analysis addressing the effects of insecticides on bees. In first study, the insects present in the strawberry crop were captured at 9:30 am, 12:30 a.m. and 3:30 p.m., in three commercial crops located in Bento Gonçalves and Farroupilha. In second study, bees were exposed to the commercial formulation of the insecticides novaluron (Rimon Supra®), spinetoram (Delegate®) and thiamethoxam (Actara® 250 WG) and acaricide abamectin (Vertimec® 18 EC), through the oral and topical route, to determine the LC50 and LD50, respectively. The behavioral effect on locomotor activity of bees was evaluated after exposure to sublethal doses (CL10 and CL50). Inhibition of the esterase enzyme was evaluated in T. fiebrigi after application of thiamethoxam. In third study, we investigated the effects of organophosphates, pyrethroids, neonicotinoids, inhibitors of chitin synthesis and spinosyns in bees. The flowers of the strawberry were visited by 47 species of insects being Apis mellifera the most abundant, constant, dominant and frequent. Twelve species of native bees were identified as Tetragonisca fiebrigi, Plebeia emerina and Plebeia remota as those with greater potential for directed pollination of the strawberry in protected cultivation due to abundance and ease of handling. The secondary effect of insecticides varied according to the form of exposure and species of bee. In the oral route, M. quadrifasciata was more sensitive than T. fiebrigi to all insecticides, except for abamectin, whereas in the topical route T. fiebrigi was more susceptible. Thiamethoxam followed by spinetoram and abamectin were the most lethal, for both species and forms of exposure, while novaluron was not harmful. The locomotor activity of bees was altered when exposed to sublethal doses of abamectin, spinetoram and thiamethoxam. Enzyme assays indicated that the esterases may be involved in the detoxification process of thiamethoxam in T. fiebrigi. Under the conditions evaluated, spinetoram and abamectin may be as toxic as thiamethoxam for M. quadrifasciata and T. fiebrigi. These results should be confirmed in field experiments to define the possibility of integrated pest and pollinator management. Neonicotinoids are the most studied group of insecticides in the world and most commonly reported to cause sublethal effects on bees. Many gaps on the impacts of insecticides still remain, especially in relation to native stingless bees and susceptibility under field conditions.