Abundances of thrips on plants in vegetative and flowering stages are related to plant volatiles

Western flower thrips (WFTs),Frankliniella occidentalisPergrande, and onion thrips (OTs),Thrips tabaciLindeman, are two cosmopolitan insect pests of agricultural and horticultural plants. Understanding the occurrence and development of thrips on plants is crucial for identifying suitable plants that can be used for developing a "push-pull" strategy against thrips. In this study, the dynamics of WFTs and OTs on plants (Allium fistulosumL.,Medicago sativaL.,Luffa cylindrica(L.) Roem.,Ocimum basilicumL., andSchizonepeta tenuifolia(Benth.) Briq.) were investigated for two consecutive years (2018-2019). Throughout the survey, the abundances of both thrips species were strongly associated with plant species and plant phenology; both thrips species were present at relatively high densities onM. sativabut very low densities onO. basilicumandS. tenuifolia. Populations of both thrips species greatly increased during plant flowering. A Y-tube olfactory test was used to study the effects of plant volatiles in mediating thrips behaviour and showed that volatiles ofM. sativawere attractive to both thrips species whether emitted by the plant in the vegetative or flowering stage, while volatiles ofO. basilicumandS. tenuifoliawere repellent to thrips. Additionally, because of the presence of a high number of floral chemicals, both thrips species exhibited a greater preference for volatiles emitted by plants in the flowering period over those emitted by plants in the vegetative period. Our observations indicate that plant species and flowering status play an important role in the abundance dynamics of thrips and that the volatiles of flowering plants attract thrips more strongly than volatiles emitted by vegetative plants. These findings can facilitate the screening of attractive/unattractive plants for developing push-pull strategies to control thrips.