Onion Thrips (Thysanoptera: Thripidae) Host Plant Preference and Performance are Mediated by a Facultative Plant Pathogen of Onion

Abstract

Insect vector and phytopathogen interactions are mediated by host plants. Insects interact with pathogens directly or indirectly and they may prefer host plants based on infection status. Performance on infected hosts varies depending on the type of pathogen involved. Species specific studies of economically important insects and phytopathogens are needed to understand how these interactions impact crop yields. Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is an economically devastating insect pest of onions (Allium cepa L., Asparagales: Amaryllidaceae) worldwide and it co-occurs simultaneously with many different pathogens. Colletotrichum coccodes (Wallr) (Glomerellales: Glomerellaceae) is a generalist fungal pathogen that attacks onion foliage, causing tan lesions and decreasing yield. Onion thrips and C. coccodes represent two important pests of onions, but the relationship between onion thrips and C. coccodes infected onions has not been studied, and it is unclear if onion thrips contribute to the spread of C. coccodes in onion fields. A four-choice test with control, artificially injured, artificially injured + symptomatic, and inoculated-symptomatic onion suggests that onion thrips distinguish between hosts based on health status. Furthermore, a two-choice test with control, inoculated-asymptomatic, and inoculated-symptomatic onion pairings revealed that onion thrips distinguish between hosts based on infection status and prefer inoculated-symptomatic hosts. In a no-choice test, onion thrips numbers increased on inoculated-symptomatic plants compared to control or inoculated-asymptomatic plants. Overall, we found that onion thrips preferred and performed best on C. coccodes infected plants.

Seasonal host shifts based on midgut residues of Protaetia brevitarsis

“…These changes in preferences may be due to biotic factors (e.g., pathogens and natural enemies), for instance, the oriental fruit moth (Cydia molesta) also shifts during their growing season from peach and apple to pear, perhaps because larval development differs on different species. Another example is when Impatiens balsamina plants are severely infected with powdery mildew, A. lucorum adults move to other species that provide a better food source [15,[30][31][32]. Abiotic factors (e.g., temperature, rainfall) often affect herbivorous insect feeding indirectly by in uencing the condition of plants and causing insects to switch to less preferred plant species [16,33,34].…”

Managing insect and plant pathogen pests with organic and conventional pesticides in onions

“…Simmons) (Pleosporales: Pleosporaceae), a destructive pathogen of the eastern production region ( Hausbeck and Werling 2018 , Hay et al 2022 ). The relationship between facultative onion pathogens and onion thrips has been the focus of various studies ( Grode et al 2017 , 2019 , Leach et al 2020 , Constancio et al 2022 ) but the influence of bio- and conventional pesticides on onion foliage and yields is not well understood. Managing 2 organisms simultaneously may be complicated by tank mixing insecticides and fungicides which may reduce insecticide efficacy ( Nault et al 2013 ).…”