Effects of Latex from Pergularia tomentosa and the Aggregation Pheromone, Phenylacetonitrile, on Locusta migratoria Larvae

Despite being a serious risk to human health and environment, chemical insecticides remain the most used for locust control. Searching for alternative control methods, effective and compatible with the environment, has become of increasing interest. Plant latex is an endogenous fluid secreted from highly specialized laticifer cells and has been suggested to act as a plant defense system. The aim of the present investigation was to study the insecticidal potentialities of Pergularia tomentosa latex at different concentrations, alone or in combination with the penylacetonitrile (PAN), on the 4th instar larvae of Locusta migratoria. The obtained results showed that the latex revealed an interesting insecticidal activity against L. migratoria larvae, resulting in a mortality reaching 96.49 %, 6 days after treatment. Toxicity bioassays revealed that PAN, associated with the latex, is able to accelerate and to increase the mortality rate. Pheromone-based treatment affected the health of treated insects by significantly reducing their respiratory rhythms. PAN was shown able to alter, quantitatively and qualitatively, the larval blood cells as expressed by the significant decrease in the number of the differential haemocyte counts (prohemocyte, plasmatocytes and granulocytes) and the important cell lysis.