اثرات زیرکشنده پروپیکونازول و دو جدایه تریکودرما (.Trichoderma spp) روی فیزیولوژی لارو زنبورعسل Apis mellifera (Hymenoptera: Apidae)

The honeybee, Apis mellifera L. (Hymenoptera: Apidae), is considered one of the most beneficial insects either as a pollinator or a producer of economically valuable products such as honey, royal jelly, venom, propolis, and pollen. Honeybees can be exposed to pesticides during their lifespan, which might negatively affect the physiological status of different life stages of this insect, including the larvae. The chemical fungicide propiconazole (PRO) and the biofungicide Trichoderma spp. are widely used in agriculture, and on various crops normally visited by honey bees. In this research, the effects of PRO and two mixtures of wild and mutant strains of Trichoderma spp. (TriW and TriM, respectively) were investigated on the mortality and physiological parameters of honeybee larvae under colony conditions. Concentrations of PRO (4.5-10,000 ng ai/ml) and TriW or TriM (106-108 spore/ml) in 50% sucrose solution were prepared, and 5 µl of each was added to the cells containing 4th instar larvae. Control larvae were treated with 10 µl of sugar syrup. Treated larvae were returned to the colony from which they had been taken. The experiment was conducted using a completely randomized design with three replications of 20 larvae each. Cells were examined for larvae survival 3 days after treatment. Capped brood cells were considered alive, while empty cells or those containing non-active or brown-colored larvae were regarded as dead. Alive larvae were taken out from the capped cells and kept at -80 °C for analysis of physiological parameters, including activities of acetylcholinesterase (AChE), glutathione S-transferase (GST), carboxylesterase (CaE), ascorbate peroxidase (APX), superoxide dismutase (SOD), α-amylase, protease, and concentrations of carbohydrate, glycogen, lipid, and protein. Results showed that PRO, TriW, and TriM did not generally affect the mortality of treated larvae significantly but caused remarkable effects on their physiology. GST and CaE activities were upregulated and downregulated, respectively, compared to the control (p<0.01), while AChE activity did not show any significant variation (p>0.05). The application of PRO, TriW, and TriM resulted in significant inhibition of APX and SOD activities (p<0.01) as main antioxidant enzymes. The activity of α-amylase in honeybee larvae decreased significantly compared to the control (p<0.01), while the protease activity remained constant (p>0.05). Energy reserves contents of A. mellifera larvae decreased significantly in response to PRO, TriW, and TriM exposure (p<0.01). Our results showed that although PRO and Trichoderma spp. might not affect the honeybee larvae in terms of mortality, variations in the physiological status of the larvae caused by these pesticides may negatively affect the growth, development, and fitness of a colony in long-term exposure. Therefore, it is suggested that in addition to lethal toxicity, the physiological indices should be also evaluated as biomarkers for the risk assessment of pesticides on honeybees.