The Release of the Parasitoid Trichogramma evancens to Control the Pink Bollworm Pectinophora gossypiella (Saunders) and the Side-Effect of Certain Insecticides on It

Abstract

The present study was conducted to evaluate the effectiveness of the parasitoid Trichogramma evenecens (Hymenoptera, Trichogrammatidae) as a potential biological control agent upon the laid eggs of the pink bollworm Pectinophora gossypiella (Saunders) (PBW) in cotton fields. The effect of releasing Trichogramma evenecens, the application of the insecticide spinetoram (Radiant ® ) and their combination on the yield of cotton was considered. Meanwhile, the side-effect of certain insecticides on the parasitoid Trichogramma evanescens was involved. The toxic side-effects of these insecticides that have been recommended for controlling insect-pests attacking cotton plants namely gama-cyhalothrin, chlorpyrifos, spinetoram, methoxyfenozide and thiamethoxam were tested on the parasitized eggs of the Angoumois grain moth Sitotroga cerealella (Olvier).The results showed that the parasitoid T. evancens efficiently parasitized PBW Pectinophora gossypiella eggs. Parasitism percentage and the cotton yield were greatly affected by releasing T. evenecens at the rate of 33000 parasites/fed./release; thus decreasing the infestation of PBW and consequently increasing cotton yield. The efficiency of spinetoram was compared with the release of T. evanescens when they were separately used or when they were combined. The combination of releasing T. evanescens and application of spinetoram was superior to control PBW. Herein, the highest rate of infestation was recorded in the untreated check (9.3 and 15.5%); gradually decreased by the release of T. evanescens alone up to 3.4 and 5.0%, spinetoram alone (2.8 and 3.2%) and spinetoram with T. evanescens release (1.2 and 2.1%) in 2009 and 2010, respectively. The increase of cotton yield was the highest in case of releasing T. evanescens with the application of spinetoram during both seasons (8.5 and 8.2 Ken. / Fed., respectively). Chlorpyrifos and gamacyhalothrin were extremely toxic and adversely affected the exposed parasitized eggs of the grain moth S. cerealella (Olvier) since they caused complete inhibition (100%) of adults emergence in the treated parasitized egg of 48, 96 and 192 hrs old post-parasitisation, while more than 80% inhibition of adult emergence from the eggs of 24 hrs old was occurred. Methoxyfenozide was the least toxic and safer compound compared with the other tested ones.