Efficacy of Bacillus thuringiensis Strain 407 versus Synthetic Pesticides in Controlling Sugar Beet Pests under Open Field Conditions

DOI 機関リポジトリ (HANDLE) オープンアクセス

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In sugar beet fields of West Eurasia and North Africa, including Egypt, the beet moth Scrobipalpa ocellatella, cotton leafworm Spodoptera littoralis and beet armyworm Spodoptera exigua are commonly major and serious pests causing irreparable damage to beet plantation. However, frequent use of synthetic pesticides can harm beneficial insects in the agroecosystem and should preferably be avoided in terms of environmental protection and safety. This study aimed to evaluate the impact of Bacillus thuringiensis (Bt) strain 407 in comparison to major chemical insecticides, chlorfenapyr (Pestpyr) and methomyl (Goldben), on the populations of the above–mentioned pests and their associated natural enemies in the field. Our results showed that the densities of S. ocellatella were remarkably higher than those of S. littoralis and S. exigua in two successive growing seasons. Within the first week of application with both chemical pesticides, numbers of pests were dropped and its population size reduced by 95 – 100% though reduction percentage tended to decline with time. Bt application was equally effective in reducing the three pest species after 7 or 10 days of application though it had less effectiveness in the earlier days due to a time–delayed impact. The major natural enemy predators, i.e., the green lacewing Chrysoperla carnea, Coccinella septempunctata and C. undecimpunctata, disappeared completely three days after chemical application and remained few during the study period. By contrast, reduction of the predators compared to control plots was markedly small in study plots with Bt application, indicating use of Bt conserved the predator populations. Thus, multiple sprays of Bt may be useful in sugar beet production, which can solve the dilemma between pest control and beneficial natural enemy conservation.

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