Conservation of Non-Pest Whiteflies and Natural Enemies of the Cabbage Whitefly Aleyrodes proletella on Perennial Plants for Use in Non-Crop Habitats

SIMPLE SUMMARY: The cabbage whitefly Aleyrodes proletella is a major insect pest of many cabbage crops. Natural enemies, in particular Encarsia tricolor as well as different hoverfly larvae and spiders, do not decrease pest populations sufficiently. The objective of this study is to promote local natural enemy populations by permanently establishing a non-pest whitefly species, which is an alternative host and additional food source when A. proletella is scarce or even absent. Therefore, the perennial abundance of the non-pest honeysuckle whitefly Aleyrodes lonicerae and natural enemies on different plants were evaluated in the open field. Wood avens Geum urbanum was the best host plant for A. lonicerae in terms of reproduction and overwintering. Most E. tricolor and spiders were also found on this plant species. In the future, G. urbanum might be used in non-crop habitats to increase natural enemy abundances in the agricultural landscape and decrease damage caused by A. proletella on adjacent cabbage plants. ABSTRACT: Aleyrodes proletella causes severe economic damage to several Brassica crops. Its naturally occurring enemies often immigrate late in the season or appear in low numbers on cabbage. This field study aims to permanently increase the local abundance of A. proletella’s natural enemies by providing the non-pest whitefly Aleyrodes lonicerae as an alternative and overwintering host/prey. Therefore, the population dynamics of natural enemies on different perennial herbaceous plants pre-infested with A. lonicerae were determined at two field locations over two winter periods. Most A. lonicerae colonized (on average 166.22 puparia per m²) and overwintered (342.19 adults per m²) on wood avens Geum urbanum. Furthermore, the abundance of A. proletella main parasitoid Encarsia tricolor (28.50 parasitized puparia per m²) and spiders (12.13 per m²) was 3–74 times and 3–14 times higher, respectively, on G. urbanum compared to the other experimental plants. Conclusively, G. urbanum pre-infested with A. lonicerae permanently promoted natural enemies of A. proletella by serving as shelter, reproduction, and overwintering habitat. A potential implementation of G. urbanum in conservation biological control strategies (e.g., tailored flower strips, hedgerows) against A. proletella are discussed and suggestions for future research are given.