Sublethal effects of two neurotoxicans insecicida on Araneus pratensis

ALDA GONZALEZ

Bélgica

Simposio; 59° International Symposium on crop protection; 2007

Spiders are important predators of various insects pests of soybean crops and they are indicators of ecosystem disturbs. In Argentina the cultivated area of soybean crop has increased from the introduction of transgenic soybean resistant to glyphosate. This expansion produced an increment in the pesticides to control pests. In contrast, the new techniques in pest control according to Integrated Pest Management premises that claim for non-indiscriminate use of pesticides. Accordingly, the essential previous step is to determinate the side effects of pesticides on beneficial organisms to select those more environmental-friendly. Araneus pratensis (Emerton) is a generalist predator and in soybean crops it is one of the most common spiders that belong to the web-building spiders. This specie is voracious, feeding from numerous soybean pests. The objective of this work was to evaluate the side effects of subletal doses of two neuroticans insecticides with a different mode of action, endosulfan (Endosulfan 35 Glex®, 25 and 2,5ppm) and spinosad (Tracer®, 48%, 30 y 3ppm). The first belongs to the conventional organochlorine pesticides and the other one to the biorational pesticides group. The insecticides were applied by ingestion way through the treated prey (Musca domestica). The endpoints were: mortality (lethal effect), behavior (prey consumption, regurgitation, spider web building, mating, ootheca construction and fertility) in the survivors. The experimental unit was one spider and it was replicated 30 times per treatment. The preys were treated with insecticides dilutions plus tensioactive (Tween 20®) and distillated water was employed as dissolvent. The controls were treated with dissolvent ±tensioactive. Data were analyzed with non-parametric Kruskall-Wallis test and medians separations were done with the graphic Box and Wisker Plot method. Endosulfan (50 ppm) was more harmful than spinosad (30 ppm) on the survival rate of adults. Tremors and non-coordinated movements were observed in both treatments. The prey consumptions were significantly reduced by the two insecticides (~40% lower than control). Also, the spider web building was affected by the two insecticides but more significantly by spinosad. Moreover, though the mating was not affected by treatments, abnormal oothecas and dehydrated eggs were observed in treatments. This work report that sublethal concentrations [(that represent ~25 and 2,5% of maximum field recommended concentrations (105 y 120ppm)] showed a high risk to spiders. The consequences in the behavior changes of spiders and its role as a natural mortality factor of pests are discussed.