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

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.

Mitogenomic analysis of diversity of key whitefly pests in Kenya and its implication to their sustainable management

Whiteflies (Hemiptera: Aleyrodidae) are devastating agricultural pests of economic importance vectoring pathogenic plant viruses. Knowledge on their diversity and distribution in Kenya is scanty, limiting development of effective sustainable management strategies. The present study is aimed at identifying whitefly pest species present in Kenya across different agroecological zones and establish predictive models for the most abundant species in Africa. Whiteflies were sampled in Kenya from key crops known to be severely infested and identified using 16S rRNA markers and complete mitochondrial genomes. Four whitefly species were identified: Aleyrodes proletella, Aleurodicus dispersus, Bemisia afer and Trialeurodesvaporariorum, the latter being the most dominant species across all the agroecology. The assembly of complete mitogenomes and comparative analysis of all 13 protein coding genes confirmed the identities of the four species. Furthermore, prediction spatial models indicated high climatic suitability of T. vaporariorum in Africa, Europe, Central America, parts of Southern America, parts of Australia, New Zealand and Asia. Consequently, our findings provide information to guide biosecurity agencies on protocols to be adopted for precise identification of pest whitefly species in Kenya to serve as an early warning tool against T. vaporariorum invasion into unaffected areas and guide appropriate decision-making on their management.

Investigation on the Relationship between Morphological and Anatomical Characteristic of Savoy Cabbage and Kale Leaves and Infestation by Cabbage Whitefly (Aleyrodes proletella L.)

The cabbage whitefly (CW), Aleyrodes proletella (L.) (Hemiptera: Aleyrodidae), is an important pest in Brassica oleracea L. crops. Little is known about the mechanisms of resistance to CW of savoy cabbage and kale cultivars. Light microscopy (LM) and scanning electron microscopy (SEM) analysis were used to determine the relationship between the morphological and anatomical features of savoy cabbage (Brassica oleracea L. convar. capitata (L.) Alef. var. sabauda L.) and kale (Brassica oleracea L. convar. acephala (DC.) Alef. var. sabellica L.) leaves and host suitability to colonization by CW. Two kale cultivars, “Redbor” and “Starbor”, and two savoy cabbage cultivars, “Gloriosa” and “Alcosa”, that differed in the degree of infestation by A. proletella were taken for histological analysis. The lowest infestation by all forms of A. proletella was observed on savoy cabbage cultivar “Alcosa” and kale cultivar “Starbor”. The reduced colonization by cabbage whitefly may be related to the structure of the epidermis and the anatomical features of the leaf. The leaves of “Starbor” and “Alcosa” had more folds in the epidermis, less numerous but larger stomata, and a more compact mesophyll structure compared to “Redbor” and “Gloriosa”. In both analysed species, there was no clear relationship between the thickness of the abaxial epidermal layer, thickness of the lamina, number of vascular bundles, and degree of infestation by the cabbage whitefly. This study identified promising sources of resistance to A. proletella among cultivars of savoy cabbage and kale. Varying infestation by CW was associated with morphological and anatomical characteristics of leaves. Further study is needed to confirm the relationship between insect resistance and leaf surface and morphological characteristics of leaves in a broader range of Brassica spp.

Manipulation of landing behaviour of two whitefly species by reflective foils

Whiteflies are major pests on several vegetable and ornamental crops. Landing behaviour is strongly influenced by wavelength (nm) of reflected light from ground and surrounding vegetation. This paper deals with manipulation of whitefly landing behaviour in semi-field greenhouse experiments using background foils, either white foils with high reflection of short wavelength radiation or green foils reducing contrast between target plants and background (soil). The reactions of two different whitefly species were compared to detect possible differences between specialist (Aleyrodes proletella) and generalist (Trialeurodes vaporariorum) species. Dual-choice experiments were performed in a greenhouse using ice-lettuce, Lactuca sativa var. capitata (T. vaporariorum) and broccoli, brassica oleracera var. Italica P (A. proletella) as model plants. The results show strong impact of the white reflective foil in controlling landing behaviour of both species, whereas the effect of the contrast-minimising foil was much lower. Light influence was stronger on generalist than on specialist species. Mechanisms behind these effects and opportunities for inclusion in an integrated pest management strategy are discussed.

Importance of Antixenosis and Antibiosis Resistance to the Cabbage Whitefly (Aleyrodes proletella) in Brussels Sprout Cultivars

The cabbage whitefly Aleyrodes proletella (L.) (Hemiptera: Aleyrodidae) is an important pest of a wide range of vegetable Brassicas. Since the control of this pest is still challenging, new approaches such as the use of resistant cultivars are required. For this, we screened 16 commercialised Brussels sprout cultivars for resistance against this species. Antibiosis was tested with no-choice experiments in a climate chamber, using reproduction, mortality, longevity, developmental time and weight as parameters. Antixenosis was screened in three choice experiments with circular design in a greenhouse to detect cultivar preferences. A field trial with both antibiosis and antixenosis tests was done to verify results under natural conditions. Finally, for several cultivars, also the leaf glucosinolate concentrations were analysed. Cabbage whiteflies showed on certain cultivars significantly increased mortality, prolonged developmental times and reduced weights. Besides, some cultivars were significantly less infested. However, the incidence of antibiosis and antixenosis as well as the glucosinolate patterns were partly inconsistent. Although a number of moderately resistant cultivars could be identified, the detected resistance is certainly not strong and consistent enough as an exclusive measure of a plant protection strategy but might become a component of a multi-layered strategy against cabbage whiteflies.