Phenology and Egg Production of the Cactus Moth (Lepidoptera: Pyralidae): Comparison of Field Census Data and Life Stage Development in the Field

Abstract

Natural phenology and development of the cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), was studied under field conditions in St. Marks National Wildlife Refuge, St. Marks, FL, from July 2006 to September 2007. Pads of cactus (Opuntia stricta Haw. [Cactaceae]) were visually surveyed weekly for presence of moth immature stages. Adult male C. cactorum populations were surveyed using a pheromone lure and wing style sticky traps. The field census data identified 3 generations per year which generally occurred in August to September, October to April, and May to July. Numbers of eggsticks peaked in midAugust, midOctober and midApril. High numbers of early larval immatures (1st to 3rd instars) were recorded in October 2006, May 2007 and September 2007. High numbers of late-stage larvae (4th to 5th instar) were recorded in September to October 2006, December to January 2006, June to July 2007. Peak numbers of Cactoblastis male adults occurred approximately in midOctober 2006, April to May 2007, and July to August 2007. Pupae were cryptic and difficult to sample. Development in field cages was studied by introducing cohorts of moth eggs on potted cactus plants (Opuntia ficus-indica (L.) Mill.) into the field at approximately the same times they were found to occur naturally. During the course of each generation, the potted plants were returned to the laboratory for determination of moth lifestage. Body weights and lengths also were recorded. In the field cages, 3 generations were observed and these coincided with the populations that were observed in the open field. However, the generations were more clearly defined because eggs were introduced as cohorts and most insects were recovered. Measurements of larval head capsules and body lengths show that development in the winter generation is slower than that of the summer and fall generations, although peak measurements are approximately identical in all 3 generations. Female pupae weighed 225.25 (± 4.8 SE) mg which was significantly heavier than males weighing 138.01 (± 5.5) mg. Pupal weights differed according to generation, but there was no effect on adult weight. Female adults weighed 130.3 (± 11.3) mg, compared with males, which weighed 60.81 (± 2.4) mg. Adult sex ratio was approximately 1:1. Male adults appeared to have emerged earlier than females in the fall generation.