Picture-winged flies (Diptera: Ulidiidae) known as corn silk flies are intensively managed with pyrethroids in fresh market sweet corn, Zea mays L., grown in Florida. The identification of alternatives to pyrethroids is needed to increase the efficacy of insecticidal management and to allow the rotation of modes of action for insecticide resistance management (IRM). This laboratory study determined the lethal and sublethal effects of six pyrethroids, five neonicotinoids, four insect growth regulators, two diamides, one spinosyn, one avermectin, and one oxadiazine on adults of the corn silk fly, Euxesta eluta Loew, following topical or ingestion exposure. For topical exposure, pyrethroids caused the highest mortality (≥89%), followed by spinetoram (50%), whereas the remaining insecticides caused <15% mortality. For ingestion exposure, spinetoram caused 95% mortality, followed by dinotefuran, clothianidin, and thiamethoxam, which caused ≥74% mortality. The further evaluation of insecticides causing <15% mortality showed that topical exposure to abamectin reduced by 61.5% the fertility of E. eluta females expressed as the number of larvae per cumulative female-day. None of the insecticides causing <15% mortality following ingestion exposure affected E. eluta fertility. This study confirms that pyrethroids represent the main commercial insecticide option for effective foliar applications targeting adult corn silk flies. Potential alternatives to pyrethroids were highly effective only through ingestion exposure, suggesting the need for the development of management tactics promoting ingestion of insecticides. This study complements pyrethroid susceptibility monitoring for the development of an IRM program in Florida sweet corn.

Wireworms (Coleoptera: Elateridae) are the main soil insect pests of sugarcane (Saccharum spp. hybrids) in Florida. Melanotus communis (Gyllenhal) is the most abundant wireworm in Florida sugarcane fields, reducing stalk populations by feeding on buds of sugarcane seed pieces and on young sugarcane plants. At-planting use of the organophosphate insecticide phorate is the main wireworm management tactic in Florida; however, phorate is a hazardous and relatively expensive insecticide. Thiamethoxam is a neonicotinoid insecticide that has potential to become registered for use on sugarcane in the United States. Previous studies suggested that thiamethoxam decreases wireworm injury to sugarcane seed pieces but does not increase wireworm mortality. The present study conducted between 2018 and 2022 aimed to comprehensively evaluate thiamethoxam for wireworm control under laboratory, outdoor, and field conditions. In two laboratory bioassays, M. communis mortality associated with thiamethoxam (3–20%) was not different than mortality for the non-treated check (0–7%), whereas mortality associated with phorate attained 93–100%. In three large container experiments conducted outdoors with controlled M. communis infestations, thiamethoxam and phorate generally protected young sugarcane plant populations at comparable levels. Insecticide efficacy was mainly associated with the protection of seed-piece buds. However, the number of recovered live wireworms was 2.7–8.0 times greater in thiamethoxam treatments than in phorate treatments. In three field experiments, young sugarcane plant populations in thiamethoxam- and phorate-treated plots were not different than those in non-treated plots. However, the at-planting application of thiamethoxam decreased the number of sugarcane thrips, Fulmekiola serrata (Kobus), by 67–89% in two experiments with thrips infestations 12 weeks after planting. Although the evaluation of insecticide efficacy under natural wireworm infestations was inconclusive, this study confirmed that thiamethoxam should be considered as an alternative to phorate if registered. However, the long-term effects of low wireworm mortality associated with thiamethoxam use should be studied.

Chlorantraniliprole susceptibility was determined in diet-incorporation bioassays for six fall armyworm, Spodoptera frugiperda (J. E. Smith), populations feeding on sweet corn, Zea mays L., in southern Florida between 2017 and 2019. The LC50 and LC90 values of these populations estimated using probit analyses ranged from 0.022 to 0.084 ppm and 0.112 to 0.471 ppm, respectively. Thus, susceptibility levels among the six field populations varied, but to a relatively small extent, with approximately fourfold differences in LC50 and LC90 values between the most and least susceptible populations. These field populations were all less susceptible than a reference population maintained in the laboratory without prior exposure to chlorantraniliprole, with RR50 values between 5.3 and 20.1 and RR90 values between 14.3 and 60.3. These results suggest reduced chlorantraniliprole susceptibility in S. frugiperda populations collected in Florida sweet corn relative to a reference laboratory population. However, field experiments in 2017 and 2019 showed that foliar applications of chlorantraniliprole reduced S. frugiperda injury and infestations to levels comparable to or lower than applications of indoxacarb, novaluron, or spinetoram. This study does not provide evidence of practical resistance to chlorantraniliprole in S. frugiperda infesting Florida sweet corn fields.

Abstract Picture-winged flies (Diptera: Ulidiidae) are the most damaging insect pests of sweet corn (Zea mays L.) produced in Florida for the fresh market. Management of these pests, referred to as corn silk flies, relies on frequent pyrethroid applications targeting adults. In response to the need for an insecticide resistance management (IRM) program for corn silk flies in this highly intensive crop system, glass vial bioassays were conducted to determine the susceptibility of 12 corn silk fly populations to the pyrethroid beta-cyfluthrin. Two Euxesta eluta Loew and nine Euxesta stigmatias Loew populations were obtained by collecting infested ears in commercial and experimental fields in 2020 and 2021. One E. eluta laboratory colony was used as a susceptible reference population.The E. eluta reference colony was the most susceptible population, with an LC50 value of 0.01 µg/vial.The E. stigmatias field populations were generally less susceptible to beta-cyfluthrin than the E. eluta field populations, with the highest LC50 values attaining 3.51 µg/vial and 0.19 µg/vial, respectively. In addition, the five E. stigmatias populations from commercial sweet corn fields were as much as 17.6 times less susceptible than the four E. stigmatias populations from nontreated fields. Results suggest that E. stigmatias is less susceptible to pyrethroids than E. eluta. Results also suggest that corn silk flies in commercial sweet corn fields are selected for reduced pyrethroid susceptibility throughout the growing season.This study successfully used the glass vial bioassay method for corn silk flies, providing a new tool to initiate an IRM program.