Reduced insecticide susceptibility among populations of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) in strawberry production

Abstract

Chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is a major, economically important, and recent invasive pest of strawberries and other horticultural crops in United States. Several conventional insecticides are used for S. dorsalis management, and resistance development threatens loss of few available tools. Hence, our objectives were to: (1) determine the susceptibility of S. dorsalis to commonly used conventional insecticides: spinetoram, acetamiprid, cyantraniliprole and bifenthrin, and (2) establish LC 50 and LC 90 dosages for spinetoram against S. dorsalis. Sampling of S. dorsalis populations was conducted twice in seven strawberry fields in Florida during the strawberry field season between 2019 and 2020. Leaf-disc bioassays were performed with field collected populations along with a susceptible 2-year-old laboratory culture of S. dorsalis. Overall, at highest recommended rate the percent mortality of late season S. dorsalis populations from five out of seven collection sites was lower (~41%) than average mortality observed with early season populations (~72%).Populations from at least four out of seven sampling sites exhibited significantly lower mortality than the laboratory susceptible culture in late season. The LC 50 and LC 90 values for spinetoram for the susceptible laboratory population were 0.026 and 8.64 ppm, respectively. On the other hand, LC 50 values of field collected populations to spinetoram varied with resistance ratios ranging from 6 to 269 fold as compared against the laboratory strain. Our results suggest that susceptibility of S. dorsalis to commonly used insecticides in strawberries varies significantly between early and late season populations within the same crop season. The efficacy of bifenthrin against S. dorsalis was particularly low (~ reduced to half in late season), especially among field collected populations. Our results indicate an urgent need to incorporate other pest management strategies, as well as effective rotation programs to reduce selection for resistance among populations of S. dorsalis in strawberry production.

Real-Time Detection and Classification of Scirtothrips dorsalis on Fruit Crops with Smartphone-Based Deep Learning System: Preliminary Results

“…Traditional methods, such as visual inspection and sticky traps, are ineffective, especially in cases of low population densities or hidden infestations. Chemical control is also limited because S. dorsalis has developed resistance to several insecticides [ 8 ] and the use of broad-spectrum pesticides can harm beneficial insects and disrupt ecosystems [ 9 ].…”