D3319: Alate trapping reveals Solenopsis invicta (Hymenoptera: Formicidae) reproductive flights in hot summer months in Coachella Valley, CA

Red imported fire ants (Solenopsis invicta) have expanded to the heavily irrigated golf courses and suburbs of Coachella Valley, CA, where they are actively managed by the Coachella Valley Mosquito and Vector Control district. Their reproductive flight phenology has not been studied in CA, unlike in the temperate southeastern U.S. where it is correlated with rainfall. Knowledge of when most mating flights occur and correlating it to predictive environmental cues can improve efficacy of bait applications. We monitored temperature, humidity, and flight activity in the arid climate of Coachella Valley. An easily dissembled alate trap was designed to rest above S. invicta nests, causing minimal disturbance. In May 2022, 4 traps each were installed in 2 separate, sprinkler irrigated urban areas with active infestations. Traps were surveyed for alates every week over 15 months, ending in August 2023. Temperature and relative humidity (RH) at trap height was recorded hourly. Over 2000 alates were collected across all traps. Alates were caught in all traps at both sites from May through October 2022 and February through August 2023. Flight activity, indicated by the trapping frequency of at least one alate caught/week, was most prevalent from June through September with 10 - 30 flights per month. During weeks with intensive flight activity (≥10 alates caught) average temperatures ranged from 20.3 to 41.4 degrees C with 17.4 to 83.1% RH. Weeks with lower or no catch experienced minimum temperatures below which S. invicta have been observed foraging in CA. Implications will be discussed.