Strawberry pollen as a source of UV-B protection ingredients for the phytoseiid mite Neoseiulus californicus (Acari: Phytoseiidae)

Combined nighttime ultraviolet B irradiation and phytoseiid mite application provide optimal control of the spider mite Tetranychus urticae on greenhouse strawberry plants

BACKGROUND

Tetranychus urticae is a hard-to-control pest of greenhouse strawberry production. Nighttime ultraviolet B (UV-B) radiation using light reflection sheets (LRS) has been applied as a physical method to control T. urticae through direct ovicidal effects (the UV method). However, because strawberry leaves grow more densely, UV-B radiation fails to reach the lower leaf surfaces inhabited by spider mites; therefore, a complementary method is required. We propose the supplemental application of phytoseiid mites in greenhouse strawberry production. We evaluated the control effects of UV-B irradiation, phytoseiid mite application and their combined use. The effects of UV-B irradiation on the degree of overlap relative to the independent distributions (ω) between predators and prey were also analyzed.

RESULTS

The UV method alone maintained low T. urticae density levels from November to February; however, mite populations increased from March onward. Phytoseiid mite application in January and February without UV-B irradiation resulted in a temporary increase in spider mites in March and/or April. By contrast, combined application of the UV method and phytoseiid mites had a greater control effect during the strawberry growing season. The ω values were higher for the UV method compared with no UV-B irradiation, suggesting that UV-B irradiation increased phytoseiid mite foraging rates.

CONCLUSION

The release of phytoseiid mites compensated for the shortcomings of the UV method, and UV-B irradiation promoted predation by phytoseiid mites by increasing the behavioral numerical response. Consequently, combined application of UV-B irradiation and phytoseiid mites is optimal for T. urticae control in greenhouse strawberry production. © 2023 Society of Chemical Industry.

The flashy red color of the red velvet mite Balaustium murorum (Prostigmata: Erythraeidae) is caused by high abundance of the keto-carotenoids, astaxanthin and 3-hydroxyechinenone

The red velvet mite, Balaustium murorum (Hermann), is a pollenophagous free-living mite with a flashy red body. This mite occurs in early spring and lives on sunny surfaces of human-made structures, such as concrete. Hence, it is inevitably exposed to a harsh environment due to solar ultraviolet-B (UV-B) radiation and radiant heat, which cause oxidative stress via the production of reactive oxygen species. The spider mite Panonychus citri that resides on upper leaf surfaces accumulates synthesized keto-carotenoids to protect against oxidative stress. Therefore, we evaluated carotenoid composition in the red pigment of B. murorum. To identify major carotenoids, we performed a high-performance liquid chromatography analysis of intact and de-esterified pigments of B. murorum females. The flashy red pigments of B. murorum consisted of the highly abundant keto-carotenoids astaxanthin and 3-hydroxyechinenone (60 and 38% of major carotenoids, respectively), and a small amount of β-carotene (2%). Although P. citri is an astaxanthin-rich species, the astaxanthin concentration (per protein) in B. murorum is 127-fold that in P. citri. Due to their high antioxidant activities, those keto-carotenoids probably contribute to the survival of B. murorum in the harsh environment caused by solar UV-B radiation and radiant heat in inorganic habitats.

Dual purpose: Predatory hoverflies pollinate strawberry crops and protect them against the strawberry aphid, Chaetospihon fragaefolii

BACKGROUND

Predatory syrphids are an important functional group due to their potential for providing multiple ecosystem services. Adults feed on nectar and pollen, and can be effective pollinators, while larvae are voracious predators that can reduce aphid pressure. Still, little research has addressed their potential dual function in agroecosystems. In this study, we assessed the potential of two predatory hoverflies, Eupeodes corollae and Sphaerophoria rueppellii, for delivering concurrent pollination and biological control of Chaetospihon fragaefolii in greenhouse strawberries.

RESULTS

Both hoverfly species effectively pollinated strawberry flowers of two different varieties ('Elsanta' and 'Sonsation'), resulting in an increase in high-quality marketable fruits, a reduction of fruit deformities, and higher number of seeds per fruit compared to pollinator-excluded fruits. S. ruepellii had a significantly longer flower handling time than E. corollae, which translated to a more efficient pollination expressed as higher seed numbers per fruit after a single flower visit. By contrast, flowers that were open to multiple visits were more effectively pollinated by E. corollae, suggesting that E. corollae is potentially a better cross-pollinator than S. rueppellii. In addition, both hoverfly species suppressed aphid populations in strawberry (var. 'Sonata'), with S. rueppellii and E. corollae reducing aphid populations by 49% and 62%, respectively.

CONCLUSION

Predatory syrphids can concurrently contribute to pollination and biological control in strawberry in a greenhouse setting. © 2022 Society of Chemical Industry.