Egg clumping, host plant selection and population regulation in Cactoblastis cactorum (Lepidoptera)

Abstract

Since the successful control of prickly pear cactus by Cactoblastis cactorum in Australia, populations of plants and moths have persisted at low densities in open woodland sites. A contagious egg distribution causes overcrowding of larvae on some plants but insures low levels or no attack of other plants. This prevents extinction of plants and insects. Cactoblastis moths choose plants with characteristics which may increase the success of their larvae. Field observations and cage experiments indicate that large, green cactuses near previously attacked cactuses receive more eggs. Plants which are actively photosynthesizing are also more attractive as oviposition sites. These oviposition preferences contribute to the observed contagious egg distribution.While open woodland Opuntia and Cactoblastis populations fluctuate around an equilibrium, pasture populations may better be described by the "hide and seek" model, with the woodland populations serving as refuges. Average plant quality and variation in quality are suggested as important components in the dynamics of this system.

Travel costs, oviposition behaviour and the dynamics of insect–plant systems

“…Previous suggestions about the effects of such behaviour on the stability of exploitative systems have been contradictory (compare Hassell 1980;Taylor 1988;Cronin and Strong 1999), and ours is the first model to address these effects explicitly. Aggregation of clutches is of interest, among other reasons, because it has been offered as an explanation for stability in the successful biological control of Opuntia by Cactoblastis (Myers et al 1981). Although previous studies have largely considered aggregation as a fixed behaviour, travel-costs arguments suggest that (like clutch size), aggregation behaviour might be under selection to respond to plant density.…”

“…Johannesen and Loeschcke 1996) and could play an important role in determining the outcome of herbivore-host plant interactions (e.g. Myers et al 1981;Zwölfer and Völkl 1997).…”

Effects of changes in atmospheric carbon dioxide on the location of hosts by the moth, Cactoblastis cactorum

“…The interaction between the pyralid moth Cactoblastis cactorum and the cactus Opuntia stricta has attracted considerable attention because the introduction of the plant to Australia led to a major ecological problem, and because the subsequent introduction of the moth resulted in one of the best-documented cases of successful biological control (Dodd 1940;Myers et al 1981;Osmond and Monro 1981;Robertson 1987;Hosking et al 1994). In particular, there is indirect evidence for the involvement of the detection of CO 2 gradients in oviposition site selection by C. cactorum.…”

“…The boundary layer is CO 2 depleted if the plant is actively assimilating. Finally, plants that had received sunlight during the day are preferred as oviposition sites during the following evening (Myers et al 1981).…”

Enemies Hypothesis: A Review of the Effect of Vegetational Diversity on Predatory Insects and Parasitoids

“…Reeve & Murdoch (1986) found that effective control of the California red scale had been achieved by a parasitoid because the scale was able to find a spatial refuge in the interior of trees, thus preventing extinction of both species. In Australia, Myers et al (1981) found that refuges are important in continued control of the prickly pear cactus by enemies. Kareiva (1985Kareiva ( ,1987 found that vegetational patchiness leads to increased outbreaks of aphid populations in the field, apparently by interfering with searching and aggregation behavior of predatory coccinellids.…”