EFFECT OF DIFFERENT INSECTICIDES ON THE REPRODUCTION OF THE MIGRATORY LOCUST LOCUSTA-MIGRATORIA

Fifth-stage larvae of the migratory locust Locusta migratoria were treated with three doses of the insecticides Dieldrin, Methomyl, Fenitrothion and Permethrin, corresponding to the lethal doses (LD) 30, 50 and 80. The reproductive ability of the surviving adults were monitored. Compared to untreated controls, a decrease was observed in the number of eggs per ootheca layed, in the hatchability of the eggs and in the survival of the emergent F1 larvae, except for the number of eggs per ootheca at the LD30 with Dieldrin where an increase is observed. These decreases was more significant with increasing doses of the insecticides. No modification in the mean weight of the newly hatched larvae was observed. The effect of the growth regulator Teflubenzuron was also monitored. Variable doses (5-50-mu-g/insect) were applied to 7-10 days old adult insects. A reduction in the number of eggs per ootheca was observed. At 30-mu-g/insect dose of the product, there was a significant decrease in the hatchability of the eggs layed. No significant modification of the weight of the newly hatched F1 larvae was observed except at 10-mu-g/insect. There was a very significant higher mortality of the newly hatched larvae after the first moult. We suggest the use in the field of a mixture of insecticide and a growth regulator.