Lessons from Unsuccessful Attempts to Establish Spodoptera pectinicornis (Lepidoptera: Noctuidae), a Biological Control Agent of Waterlettuce

Abstract

We released nearly 332 000 Spodoptera pectinicornis individuals for biological control of the floating aquatic weed Pistia stratiotes (waterlettuce) at 22 sites in Florida during December 1990-December 1997. Predation (by boat-tailed grackles, fire ants, and spiders) and Allee effects (resulting from rapid dispersal of adults) prevented populations from persisting during early attempts. These efforts consisted of small releases at multiple sites, with no nurturing of the introduced populations. Modification of our initial approach resulted in a series of release strategies that consisted of multiple releases at fewer sites and employed progressively more intensive nurturing of the introduced populations. The most successful strategy incorporated: (i) cages to restrict adult dispersal and exclude flying predators; (ii) plant-free zones around the cages to exclude crawling predators; (iii) enhancement of the nutritional quality of waterlettuce in the cages; and (iv) frequent inoculation of the cages with laboratory-reared insects. Use of this strategy resulted in several provisionally-established S. pectinicornis populations, numbering as much as 23.5 S. pectinicornis individuals m -2 , and produced up to seven post-release generations. Unfortunately, all of these incipient populations declined until S. pectinicornis was undetectable. We conclude that field populations of this moth no longer persist in Florida, and offer an introspective assessment of how this project might have been improved.