Comparison between eggsticks of two cactophagous moths, cactoblastis cactorum and melitara prodenialis (Lepidoptera: Pyralidae)

Abstract

The invasive cactus borer Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) now cooccurs with a species of borer native to North America, Melitara prodenialis Walker (Lepidoptera: Pyralidae), in the southeastern United States. Because C. cactorum damages native species of pricklypear (Opuntia) often through population outbreaks, it is necessary to distinguish this species from the native cactus borer that has reduced impact on pricklypear populations. Cactoblastis cactorum and M. prodenialis eggs are laid one on top of another to form eggsticks that resemble cactus spines. Both moth species utilize the same host plant species in the Opuntia genus, and during larval life stages it is easy to distinguish the two species. Determining species identification based on eggs alone, however, has been difficult. Yet, it is impractical to wait for eggs to hatch and larvae to develop to determine species identification for research or monitoring purposes. Several objective, quantitative differences were found between the two species that can be used in laboratory identification to train research assistants or invasive management personnel for the field. Based on the data, we provide a dichotomous key to distinguish the eggsticks of these two species.