Attraction of western corn rootworm and subterranean termites to carbon dioxide with implications for pest management

Abstract

Carbon dioxide (CO2) is an attractant for larvae of the western com rootworm (WCR), Diabrotia virgifera virgifera LeConte, a major pest of com in the United States. CO2 is important to soil-dwelling termites of economic importance, but its exact role has not been determined. Elevated concentrations of CO2 prevented neonate WCR larvae from locating com roots in soil bioassays. Larvae were attracted away from com by gaseous CO2 pumped into the soil and by non-toxic CO2-emitting materials mixed into the soil. Test materials produced CO2 concentrations between 15.8 and 18.5 mmol/mol (compared to 1.7 - 2.6 mmol/mol in controls) and this was sufficient to prevent larvae from locating com roots. In field trials, CO2-generating treatments resulted in root ratings that were significantly lower than for control plants. In feeding bioassays, neonate WCR larvae fed vigorously on paper disks treated with liquid pressed from com roots or with an acetone extract of com, but not on disks treated with distilled water. Amounts of the insecticide thiamethoxam required for 50% mortality of WCR larvae were reduced 100-fold when extracts of germinating com were used to entice the neonate larvae to feed on it. Granules of spent grain, processed com cob, and clay, coated with com extract and thiamethoxam, provided better control of WCR larvae than a standard rate of Counter 20CR insecticide. The attractant CO2 improved insecticide efficacy, and CO2 plus feeding stimulants caused even greater enhancement of insecticides than CO2 or feeding stimulants alone. In field trials, com treated with CO2-generating granules containing feeding stimulants and insecticide had significantly less larval feeding damage than untreated control plants. In behavioral bioassays Reticulitermes flavipes, R. tibialis, and R. virginicus were attracted to CO2 concentrations between 5 and 50 mmol/mol. In field tests, stations containing CO2-generating baits attracted termites away from wooden fence posts. Discovery time was shorter and visitation rates were higher for the CO2-baited stations. This is the first report of attraction to CO2 for any termite species.