An Assessment of the Impact of ChemicalInsecticides Used to Control Desert Locust(Schistocerca gregaria) (Orthoptera, Acrididae) onLacertid Lizard Acanthodactylus spp(Sauria, Lacertidae) in Niger

摘要

Chemical treatments still constitute the main method used to control desert locust during the invasion phases. In addition to their relatively high costs, these pesticides are not target specific in the majority of the cases; they can have negative effects on the biotic and abiotic components of the ecosystem. The goal of our study, conducted under natural conditions, was the assessment of the ecological effect of ethyl chlorpyrifos and fenitrothion, the most widely used organophosphate pesticides in desert locust control in Niger. To assess the impact of pesticides on the relative abundance of lacertid lizard Acanthodactylus boskianus and Acanthodactylus sp before and after treatments, we used the method of pedestrian transect. The analysis of the variance was used to carry out a statistical comparison based on BACI (Before-After-Control-Impact) method. The experiments were carried out in a randomized complete block design with three replications. The experimental plots had an area of 16 ha each, the treatments consisted of ethyl chlorpyrifos at the rate of 225 ga.i./ha; fenitrothion at the rate of 450 ga.i./ha. Unsprayed plots were used as controls. These rates are those recommended by the Food and Agriculture Organisation of the United Nations (FAO) to control desert locust. Chemical treatments were carried out in total cover using a battery driven hand-held spinning disk sprayer (Micro-Ulva~(?)), in accordance with the technical directives of the FAO for ultra-low volume applications. The field trial was carried out in the valley of Tafidet located in the eastern side of A?r Mountains in Niger, from June to December of the years 2004 to 2006. Ineach experimental plot, two lines of 300 m length and 10 m width were used as area of counting. These lines of counting skirted one of the diagonals of each plot. The results demonstrate the noxious effect of ethyl chlorpyrifos and fenitrothion (organophosphate pesticides) on lizard. We recorded the first decrease of population at 9 days after treatment. The first decrease of the lizard populations was noted in the phase I (1-12 DAT). We also recorded the first dead or moribund lizards between 9 and 21 days after chemical treatment. The number of death or moribund lizards ranged from 0, 33±0.57 to 4±1 in the plots treated with chlorpyrifos and fenitrothion respectively. The optimum of the efficacy of the pesticides was noted in phase II (15-30 DAT) it was decreased from 76% to 98% with chlorpyrifos and fenitrothion. It was also observed; the chemicals had a delayed effect on the lizard. In the last phase (45-60 days after the treatment) no death or moribund lizards is noted in all plots (treated and untreated).