Control effect of four commercial natural enemy species against Frankliniella intonsa in forcing strawberry cultivation after the spring season

Abstract

We evaluated the control effect of four commercial natural enemy species against thrips, mainly Frankliniella intonsa (Trybom), and the suppression of thrips-mediated fruit damage after the spring season in forcing strawberry (Fragaria × ananassa Duch.) cultivation for three years from 2022 to 2024 in Shizuoka Prefecture, Japan. In 2022, Amblydromalus limonicus (Garman and McGregor) (50,000 individuals/10 a) and Haplothrips brevitubus (Karny) (15,000 individuals/10 a) were released. A. limonicus showed no effectiveness against thrips, and this natural enemy was not found in flowers, which are the main habitat of thrips. H. brevitubus appeared to suppress thrips larvae. In 2023 and 2024, each natural enemy species was released three times at one-month intervals. All natural enemy species suppressed thrips; however, the rate of fruit damage varied depending on the species. In 2023, the ratio of thrips-damaged fruits to total harvested fruits was significantly lower, in the following order: Amblyseius cucumeris (Oudemans) (700,000 individuals/10 a) < A. cucumeris (350,000 individuals/10 a) = Amblyseius swirskii Athias-Henriot (50,000 individuals/10 a). The rate in 2024 was significantly lower, and in the following order: A. cucumeris (350,000 individuals/10 a) < A. swirskii (50,000 individuals/10 a) = H. brevitubus (15,000 individuals/10 a). These results suggest that A. cucumeris provides the best control against thrips on strawberries. This effect may be primarily attributed to the high release rate of A. cucumeris. However, it is necessary to use other control measures after late May because even A. cucumeris could not suppress the increase in damaged fruits after this period.