Host Specificity and Biology of Spodoptea pectinicornis (Lepidoptera: Noctuidae), a Biological Control Agent of Waterlettuce (Pistia stratiotes)

The noctuid Spodoptera pectinicornis (Hampson) from southeast Asia was studied in quarantine for potential use as a biological control agent of the floating aquatic weed waterlettuce, Pistia stratiotes L. Host-specificity tests were conducted on 70 plant species in 32 families. First instars fed slightly on 5 plant species and moderately on 1. Third instars fed slightly on 7, moderately on 5, and heavily on 3 plant species. In all tests, no larvae lived longer than 6 days or developed to the next stage except those on impatiens (Impatiens balsamina L.). In whole-plant tests of impatiens, larvae fed for several weeks, but were unable to complete development. In multichoice oviposition tests, moths laid over 70% of their egg masses on waterlettuce, 21% on nonplant surfaces, four masses on eggplant (Solanum melongena L.), and one mass each on 4 other plant species. No eggs were laid on impatiens. The inability of larvae to develop to the next stage except on whole plants of impatiens, on which they did not advance to the pupal stage, and the nonchoice of impatiens for oviposition indicate the safety of S. pectinicornis for release. Species from genera with mostly polyphagous members should not be rejected from consideration as biological control agents of weeds without testing. Areas other than the apparent center of origin should also be explored to discover newer insect-plant associations. Information on the biology of S. pectinicornis is also presented.