Effect of Sublethal Doses of Chlorpyriphos-Ethyl on Some Parameters of Mating and Laying in the Locust Schistocerca Gregaria Forskal, 1775 (Orthoptera: Acrididae)

The objective of this study has been to evaluate the impact of sublethal doses of chlorpiryphos-ethyl on the steps of the mating and oviposition behavior in Schistocerca gregaria and its descendants. The sublethal doses of chlorpiryphos-ethyl were tested on locust imago’s five days old (sexually immature). The effects of these treatments on locusts and their descendants were evaluated on the mating (rate of real and false matings) but also on some laying parameters (rate of real and false laying and number of laying / female). The locust imagoes were reared in the insectariums of the Faculty of Biosciences, University Felix Houphouet-Boigny in Côte d'Ivoire between July 2008 and June 2009. Six cages with nesting boxes, each containing 50 locusts (25 males and 25 females) were used. Two cages were used to test the contact effect with 2 ml /cage dose at 0.012 g / l of chlorpiryphos-ethyl sprayed directly on locusts. Two other cages were dedicated to evaluate ingestion effect through providing of leaves of maize (Zea mays L. Poaceae) variety Ferké 79, impregnated with 2 ml of chlorpiryphos-ethyl at 0.15 g / l, to serve as food for locusts. The last two cages were used as controls. It was observed in the offspring of controls population 93% of real matings against 0% in the offspring of treated individuals. 100% of the offspring of treated locusts do not mate until their death. These treatments significantly reduced the number of layings 3.23 ± 0.2 to 1.32 ± 0.06 (59.13%) and 3.23 ± 0.2 to 0.91 ± 0.08 (71.83%) in the treated locusts respectively on contact effect and ingestion effect. Treatment with sublethal doses of chlorpiryphos-ethyl induced decline in fertility among treated locusts and the sterility in their offspring. These results show that the treatment with sublethal doses of chlorpiryphos-ethyl could be a solution to limit the possibilities for locusts to reach the critical density threshold, and thus reduce their damage.