Monitoring Red Imported Fire Ant (Hymenoptera: Formicidae) Foraging Behavior and Impact on Foliage-Dwelling Arthropods on Soybean Produced Under Three Ant Suppression Regimes

Abstract

The red imported fire ant, Solenopsis invicta Buren, has been reported to contribute to the biological control of key arthropod pests in soybean, Glycine max (L.) Merrill, and other crops. Solenopsis invicta also has been implicated as a major disrupter of biological control and a direct crop pest associated with reduced yields. In 2000 and 2001, fire ant foraging, survival of sentinel lepidopteran eggs and pupae, seasonal abundance of common foliage-dwelling soybean arthropods, and crop yield were assessed under three different fire ant suppression treatments at two test sites in Tift Co., GA. The treatments included an untreated control, hydramethylnon ant bait, and hydramethylnon bait in combination with the broad spectrum insecticide chlorpyriphos. Fire ant foraging was reduced in the chemically-treated plots in comparison to the control, based on fire ant numbers on hot dog baits after a 1-h field exposure in the early morning. Survival of soybean looper, Pseudoplusia includens Walker, eggs in 2000 and corn earworm, Helicoverpa zea Boddie, eggs in 2001 was lower in the untreated plots after a 24-h field exposure, where S. invicta foraging rates were high. Soybean looper pupal survival was 34 and 88% lower on foliage and the ground, respectively, in the control compared to those with reduced fire ant foraging. The seasonal abundance of foliage-dwelling soybean arthropods was primarily unaffected by the fire ant suppressing treatments. However, in 2001, green cloverworms, Hypena scabra F., and spiders were significantly lower (38.6 and 40.5%, respectively) in the chlorpyriphos plus hydramethylnon bait treatment in comparison to the other treatments. Season-long suppression of fire ants had no effect on soybean yield. The results of this study suggest that S. invicta, at naturally-occurring levels, is an active predator on some common soybean lepidopteran pests.