SUPPRESSION OF <I>DIAPREPES ABBREVIATUS</I> IN POTTED CITRUS BY COMBINATIONS OF ENTOMOPATHOGENIC NEMATODES WITH DIFFERENT LIFESPANS

Abstract

El-Borai, F. E., J. D. Zellers, and L. W. Duncan. 2007. Suppression of Diaprepes abbreviatus in potted citrus by combinations of entomopathogenic nematodes with different lifespans. Nematropica 37:33-41. Two experiments were conducted to test the hypothesis that augmenting entomopathogenic nematode (EPN) communities with short-lived EPN species can gradually reduce biological control of insect larvae by partially displacing longer-lived EPN species. Citrus seedlings growing in pasteurized soil mix were infested with Steinernema riobrave (Sr; short-lived) and S. diaprepesi (Sd; long-lived), either alone or in combination in both experiments, and with Heterorhabditis zealandica (Hz; short-lived) alone or combined with Sr or Sd in the second experiment. Larvae of the weevil Diaprepes abbreviatus were added to the pots periodically and plants were grown for up to 8.5 months in the first experiment and 13.6 months in the second. No interactions (P ≥ 0.05) occurred between any treatment in either experiment. In the first experiment, the average weight of plants treated with Sd or Sd + Sr was greater than that of untreated controls (P < 0.01), but the main effect of Sr was not significant. The growth and survival of the citrus plants in the second experiment and the suppression of weevil larvae were greatest in the treatment combinations that contained Sd. Plant weights in all treatments containing Sd were greater than those of positive controls (P ≤ 0.01) and did not differ from those of negative controls (no weevils). Treatments with Sr also produced plants that were heavier than the positive controls, but lighter than the negative controls (P ≤ 0.05). Augmenting pots with Hz did not significantly affect plant weight or insect suppression. Steinernema diaprepesi was the only EPN species recovered by baiting soil with insect larvae at the end of either experiment. Neither experiment supported the hypothesis. Indeed, the long-lived Sd revealed a remarkable ability to invade adjacent pots where it became the dominant species.