Evaluation of chlorpyrifos and Beauveria bassiana as a strategy in the Egyptian sugar beet fields: impact on Spodoptera littoralis (Boisduval) and its associated predators populations and the sugar beetroot yield

Abstract Background The susceptibility of pests and natural enemies to conventional insecticides is a critical element in judging the success of integrated pest management programs implementing biological control as a tactic. In this study, the susceptibility of the cotton leafworm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) to an organophosphorus insecticide (chlorpyrifos) and the entomopathogenic fungus Beauveria bassiana was evaluated through field applications during two successive sugar beet seasons. The populations of the coccinellid, chrysopid, and formicid predators were estimated to indicate pesticide risk assessment strategy. The root and sugar yields were compared during the whole experiment to emphasize the impact of both control strategies on the pre-harvest loss in this strategic crop. Results Results indicated that over the course of the two seasons of the investigation, chlorpyrifos significantly reduced the population density of S. littoralis and its associated predators. It showed a detrimental effect on S. littoralis larval population than untreated areas, causing an overall reduction of 97 and 92% during the 1st and 2nd seasons, respectively. The biopesticide based on entomopathogenic fungus Beauveria bassiana caused an overall reduction of S. littoralis , reaching 96 and 65% during the 1st and 2nd seasons, respectively. Meanwhile, B. bassiana slightly affects the population of predators compared to insecticide-free areas, so it was recommended for application in sugar beet fields without providing considerable risk to the associated insect predators. The sugar beetroot production and its sugar content increased significantly in both treatments during the two growing seasons compared to non-treated plots. Conclusion Chlorpyrifos is not recommended for pest control; instead, B. bassiana is considered an effective biopesticide in the Egyptian sugar beet fields infested with S. littoralis as part of an integrated pest management program. Their effect was direct through reducing pest population and indirectly increasing the sugar beetroot production and increasing its total sugar content. Hence, both the sugar beetroot quality and quantity were improved favoring the microbial agent over the chemical insecticide in application for mitigating the chemical hazards toward the associated predators.