Interactions between the red imported fire ant Solenopsis invicta and the parasitoid Lipolexis scutellaris potentially affect classical biological control of the aphid Toxoptera citricida

Abstract

Abstract Lipolexis scutellaris (Mackauer), an aphidiid parasitoid of Toxoptera citricida (Kirkaldy), currently is being released in citrus groves throughout Florida in a classical biological control program. L. scutellaris is unusual in that it usually pupates in a mummy on the soil, which could make it vulnerable to predation by the red imported fire ant, Solenopsis invicta Buren, which is abundant in citrus groves in Florida. Laboratory studies found the majority (99.2 and 98.5%) of mummies containing L. scutellaris are located on the soil, in low or high aphid density treatments, respectively, which is not different (χ2, P=0.57). In the laboratory, S. invicta was presented with mummies containing L. scutellaris, which S. invicta treated differently from the positive (hot dog) and negative (sand) controls. Under laboratory conditions, S. invicta responded similarly to 1- and 9-d-old mummies. Experiments next were conducted in a citrus grove and S. invicta removed 100% of the hot dog pieces and 97.5% (first experiment) and 92.5% (second experiment) of the mummies containing L. scutellaris within 24 h from containers, indicating the ants perceived the mummies as potential food (Wilcoxon Signed Rank, P>0.1). When S. invicta and other insects were allowed access in a citrus grove to potted citrus trees containing aphids parasitized by L. scutellaris, the number of adults of L. scutellaris that emerged was 6.5-fold less (13 adults from treatment, 84 adults from control) than from control trees where insects from the soil surface were excluded (Wilcoxon Signed Rank, P=0.005); S. invicta and the Asian cockroach Blattella asahinai Mizukubo could have contributed to the reduced emergence of L. scutellaris. Collectively, these data suggest S. invicta (and other predators) could have a detrimental effect on populations of L. scutellaris in citrus groves in Florida.