Impact of conventional insecticides on two bollworms and their indirect effects on the ectoparasitoid, Bracon brevicornis (Wesmael) (Hymenoptera: Braconidae)

• Main Authors: Mervat A. Kandil, Hemat Z. Moustafa
• Format: Article
• Language: English
• Published: SpringerOpen 2019-12-01
• Series: Bulletin of the National Research Centre
• Subjects: Pectinophora gossypiella; Earias insulana; Toxicity; Etofenprox and Chlorpyrifos; Indirect effect of insecticides; Bracon brevicornis
• Online Access: https://doi.org/10.1186/s42269-019-0250-3

Abstract Background Cotton bollworms such as Pectinophora gossypiella and Earias insulana are serious pests which destroy the cotton plant, and Bracon brevicornis is a parasitoid which attacked the larvae of bollworms. Results In this study, experiments were performed to investigate and evaluate the toxicity of etofenprox and chlorpyrifos insecticides against newly hatched larvae of Pectinophora gossypiella and Earias insulana. Some biological aspects of compound effects on larval and pupal duration, percentage of mortality, and percentage of adult emergence which resulted from treated newly hatched larvae were studied. The results revealed that LC50 was 0.7 and 0.87 ppm when P. gossypiella was treated with etofenprox and chlorpyrifos, respectively, while LC50 was 0.09 and 0.73 ppm when E. insulana was treated with etofenprox and chlorpyrifos, respectively. The obtained results showed that the percentage of mean larval mortality was 65.0 and 63.0% for treated P. gossypiella, while it was 71.0 and 66.0% for treated E. insulana. The corresponding figure for pupal percentage mortality was 8.0 and 10.0% for treated P. gossypiella, but it was 5.0 and 2.0% for treated E. insulana, with etofenprox and chlorpyrifos, and a prolongation effect in larval and pupal development (total immature stage) resulted from treated both bollworms as follows: 35.5 and 32.4 days for treated P. gossypiella compared with 21.9 days in control and 34.7 and 23.2 days for treated E. insulana compared with 23.1 days in control. The indirect effect of etofenprox and chlorpyrifos on the total immature stage of Bracon brevicornis was 18.2 and 19.5 days compared with 14.3 days in control when B. brevicornis parasitized on P. gossypiella larvae while it was 19.8 and 20.6 days compared with 15.2 days when B. brevicornis parasitized on E. insulana larvae. Conclusion The life cycle of B. brevicornis after parasitism on P. gossypiella and E. insulana larvae treated with etofenprox and chlorpyrifos were increased than the control larvae.