Population ecology of Dactylopius confusus (Homoptera: Dactylopiidae)

Abstract

Field and laboratory studies were conducted to investigate the biology, ecology, and population dynamics of the native cochineal insect Dactylopius confusus (Cockerell) (Homoptera: Dactylopiidae) and the insect's potential as a biological control agent for pricklypear, Opuntia spp. (Cactaceae). Development, survivorship, and reproduction of D. confusus were monitored at constant temperatures of 26(DEGREES) and 22(DEGREES)C. Development was more rapid and fecundity was greater at 26(DEGREES) than at 22(DEGREES), but percent survival was similar at both temperatures. Generation time, T(,c), was 61 days at 26(DEGREES) and 83 days at 22(DEGREES). Net reproductive rate, R(,o), was 201 at 26(DEGREES) and 141 at 22(DEGREES).Spatial distributions of D. confusus and its hosts, Opuntia spp., were aggregated. Approximately one-third of the plants were infested by D. confusus. Colonies occurred more often near the plant base and in areas of dense grass cover. Both D. confusus and the similar native cochineal, D. opuntiae (Cockerell), exhibited distinct differences in survival and generation time on different Opuntia hosts. Of nine Opuntia species/semispecies evaluated, four were comparable hosts for D. confusus, one resulted in less survival, and four gave low survival or were not suitable hosts. D. opuntiae survived equally well on four hosts but also adequately utilized the other five hosts. Dactylopiid generation time was inversely related to host suitability for most insect/host relationships examined. The primary limiting factor to D. confusus density was predation. The most abundant predator was Laetilia coccidivora (Comstock) (Lepidoptera: Pyralidae), and two common predators were Leucopis bellula Williston (Diptera: Chamaemyiidae) and Hyperaspis trifurcata Schaeffer (Coleoptera: Coccinellidae). When predators were excluded, D. confusus density increased significantly, resulting in increases in Opuntia mortality and reductions in new growth. No parasites or pathogens of D. confusus were found. Abundance of D. confusus on a range site subjected to prescribed burning increased during the first postburn season but was similar to that on an unburned site in subsequent seasons. Reductions in pricklypear infestation during the first postburn season appeared to result more from fire damage than from increased D. confusus population density. Application of insecticides to deter predators had no effect on D. confusus density.