ABSTRACT
Interactions among seed-feeding insects are well noted in the literature, with many of these interactions being asymmetrical and causing a disadvantage for one of the species involved. While often effective, the use of the cumulative stress approach to biological control (where multiple natural enemy species are released) may increase the risk of interaction, which may lead to less effective biological control programs. Spotted knapweed (Centaurea stoebe ssp. micranthos (Gugler) Hayek) is an invasive plant that causes damage in rangelands and pastures. In Arkansas, two biological control agents for spotted knapweed, Larinus minutus Gyllenhal and Urophora quadrifasciata Meigen, are established. Both species attack the capitula of spotted and diffuse knapweeds. There is potential for interactions between these species, and this could affect the efficacy of the biological control program. To evaluate these potential interactions, we collected spotted knapweed capitula weekly from three sites in Arkansas from 2010 to 2012. Capitula were monitored for emergence of L. minutus and U. quadrifasciata, and the effect on seed reduction was analyzed. Over all three years, L. minutus and U. quadrifasciata were present in 35.8% (492) and 22.8% (313) of the capitula, respectively. We determined that the occurrences of L. minutus and U. quadrifasciata were not independent of each other, and that L. minutus is more effective at reducing spotted knapweed seed production than U. quadrifasciata within individual capitula. Seed production in capitula with both natural enemies present was no different from capitula with L. minutus.
ABSTRACT
Coccinellids have been widely used in biological control for over a century, and the methods for using these predators have remained virtually unchanged. The causes for the relatively low rates of establishment of coccinellids in importation biological control have not been examined for most species. Augmentative releases of several coccinellid species are well documented and effective; however, ineffective species continue to be used because of ease of collection. For most agricultural systems, conservation techniques for coccinellids are lacking, even though they are abundant in these habitats. Evaluation techniques are available, but quantitative assessments of the efficacy of coccinellids have not been done for most species in most agricultural crops. Greater emphasis is needed on evaluation, predator specificity, understanding colonization of new environments, and assessment of community-level interactions to maximize the use of coccinellids in biological control.
ABSTRACT
Dipper samples of Anopheles quadrimaculatus immatures from stocked enclosures in Arkansas rice fields were used to develop regression equations relating dipper sample counts to absolute density. Confidence limits were developed for mean number of immatures collected at each density and stadia, including combined stadia. These data can be used to estimate absolute density from mean dipper count. Distribution of rice field immatures approximated but did not fit the Poisson distribution. Sample size was calculated for 10, 25 and 50% of the true mean, at various levels of Type I and II error. A sample size of N = 6,424 was necessary to detect differences within 10% of the true mean, with 5 and 10% probability of Type I and II error, respectively.