Economic Injury Level of Thrips tabaci (Thysanoptera: Thripidae) on Welsh onions (Allium fistulosum L. var) in the Early Transplanting Stage

Abstract

This study was conducted to develop economic injury level (EIL) of onion thrips, Thrips tabaci, on welsh onion (Allium fistulosum L. var) in the early transplanting stage. The changes of welsh onion biomass, yield loss, and T. tabaci density were investigated according to the inoculation periods of T. tabaci. In the early transplanting stage of welsh onion, the yield loss (%) increased with increasing inoculation periods: 17.0, 53.3, 38.4, and 80.8% yield loss in 5, 10, 15, and 20 d inoculation periods, respectively. The relationship between Cumulative Insect Days (CID) of T. tabaci and yield loss (%) of welsh onion was well described by a nonlinear logistic equation. Using the estimated equation, EIL of T. tabaci on welsh onion was estimated to 30 CID per plant based on the yield loss 12% (an empirical gain threshold 5% + marketable rate 93% of welsh onion). ET was calculated to 24 CID, which corresponds to 80% of EIL. Until a more defined EIL-model is developed, the present results should be useful for T. tabaci management in early growth stage of welsh onion. The effect of T. tabaci attack on the yield of welsh onion in late growing season (120 days after transplanting) was also examined. The yield of welsh onion increased at a low population density of T. tabaci and decreased at higher densities, showing a typical over-compensatory response.

Thelytokous Reproduction of Onion Thrips, Thrips tabaci Lindeman 1889, Infesting Welsh Onion and Genetic Variation among Their Subpopulations

“…Insects 2022, 13, 78 2 of 12 Onion thrips is a cosmopolitan species with a wide host range, allowing it to have genetic diversity due to different hosts in various local regions [6]. For example, to control the thrips, foliar spray of chemical insecticides including spinetoram resulted in both regional and temporal variations in its efficacy in USA [7].…”

“…Welsh onion is cultivated in most agricultural farming areas in Korea, where T. tabaci causes serious direct feeding damage [12]. A flight behavior analysis has shown that T. tabaci performs both dispersal and migratory displacement, leading to its wide habitat range in Korea and other countries [13].…”