INSECTICIDE EFFICACY OF SPATIAL REPELLENT COMPOUND-METOFLUTHRIN AGAINST SUSCEPTIBLE AND RESISTANT STRAINS OF AEDES AEGYPTI

Spatial repellents (SR), include pyrethroid insecticides that are highly volatile at low temperatures and with high lethal activities against mosquitoes, mainly Aedes vectors of arboviral diseases. Of these SR, metofluthrin is widely used in various devices for repellent consumer products. This article reports the susceptibility status of Ae. aegypti Puerto Rico permethrin-resistant laboratory strain (PR) and Orlando susceptible laboratory strain (ORL) to metofluthrin and permethrin using the CDC glass bottle bioassay. The time-mortality relationships showed that the permethrin-resistant PR strain is highly resistant to both permethrin and metofluthrin compared to the susceptible ORL strain. The resistant ratio (RR) based on the killing time (KT) (KT50 -PR/KT50 -ORL) was 30- and 5- folds for permethrin and metofluthrin, respectively. The results also showed that the PR strain is less resistance to metofluthrin than to permethrin, with a three-fold RR (KT50 -PR-per/KT50 -PR-met). These results indicate the potential risk of developing cross-resistance of metofluthrin in permethrin-resistant mosquitoes. Integrated vector management in mosquito control should be considerate of how consumer products and field operations interact to accelerate cross resistance to pyrethroids.

A Maximum Dose Bioassay to Assess Efficacy of Key Insecticides Against Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae)

The whitefly, Bemisia tabaci MEAM1 Gennadius causes serious losses to Florida vegetable and ornamental production. In 2019, a maximum dose bioassay was administered to 20 field populations of B. tabaci MEAM1 collected from various economic and weed hosts across south Florida to assess insecticide efficacy. The maximum dose bioassay tests the top labeled rate of the insecticide against B. tabaci adults on treated cotton leaves in a Petri dish over a 72-h period. A susceptible laboratory colony of B. tabaci MEAM1 and a colony of B. tabaci MED were also tested. Survival over 72 h was used to produce an area under the maximum dose curve, which was used to compare insecticide effects on different populations. Overall, imidacloprid demonstrated the poorest efficacy, dinotefuran and flupyradifurone were the most effective, and bifenthrin, cyantraniliprole, and thiamethoxam tended to group together, providing intermediate control. Across populations tested, survival in whitefly adults treated with dinotefuran was 50% lower than whiteflies treated with imidacloprid, about 33% lower than whiteflies treated with thiamethoxam, bifenthrin, and cyantraniliprole, and 10% lower than whiteflies treated with flupyradifurone. Efficacy of bifenthrin was less than imidacloprid on some populations, particularly from the Homestead area. Imidacloprid and thiamethoxam had no effect on mortality of the MED population when it was tested after 22 mo in culture without exposure to insecticides, although 7 mo later, these materials resulted in some mortality for the MED population.

Effects of Spray Volume and Application Frequency on Insecticide Efficacy Against Adult Western Flower Thrips (Frankliniella Occidentalis) under Greenhouse Conditions

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major insect pest of greenhouse-grown horticultural crops. Western flower thrips causes direct and indirect damage by feeding on plant leaves, flowers, and fruits, and by transmitting viruses that can result in greenhouse producers experiencing substantial economic losses. Consequently, insecticides are used to suppress western flower thrips populations. However, issues associated with applying insecticides may affect the suppression of western flower thrips populations. Therefore, experiments were conducted under greenhouse conditions to determine the effects of the spray volume applied and application frequency on insecticide efficacy against western flower thrips adults located in transvaal daisy, Gerbera jamesonii, cut flowers. Four spray volumes (5.0, 10.0, 12.5, and 25.0 mL), two application frequencies (one or two spray applications), and three insecticides [spinosad (Conserve), chlorfenapyr (Pylon), and flonicamid (Aria)], each with a different mode of action, were tested. The insecticide treatments had the greatest effects on the mean percent mortality of western flower thrips adults regardless of spray volume or application frequency. However, in Expt. 3, the 5.0- and 10.0-mL spray volumes resulted in a higher mean percent mortality of western flower thrips adults than the 2.5-mL spray volume. Spinosad and chlorfenapyr resulted in a mean percent mortality of more than 72% for western flower thrips adults, whereas flonicamid resulted in mean percent mortality between 40% and 91%. Our study demonstrates that certain insecticides are more effective against western flower thrips adults located in transvaal daisy flowers than others, which will help greenhouse producers effectively manage western flower thrips populations.