Theoretical developments are helping us to comprehend the basic parameters governing the dynamics of the interactions between generalist predators and their many pest and nonpest prey. In practice, however, inter- and intraspecific interactions between generalist predators, and between the predators and their prey, within multispecies systems under the influence of rapidly changing biotic and abiotic variables are difficult to predict. We discuss trade-offs between the relative merits of specialists and generalists that allow both to be effective, and often complementary, under different circumstances. A review of manipulative field studies showed that in approximately 75% of cases, generalist predators, whether single species or species assemblages, reduced pest numbers significantly. Techniques for manipulating predator numbers to enhance pest control at different scales are discussed. We now need to find ways of disentangling the factors influencing positive and negative interactions within natural enemy communities in order to optimize beneficial synergies leading to pest control.

We investigate the procedure of checking for overlap between confidence intervals or standard error intervals to draw conclusions regarding hypotheses about differences between population parameters. Mathematical expressions and algebraic manipulations are given, and computer simulations are performed to assess the usefulness of confidence and standard error intervals in this manner. We make recommendations for their use in situations in which standard tests of hypotheses do not exist. An example is given that tests this methodology for comparing effective dose levels in independent probit regressions, an application that is also pertinent to derivations of LC50s for insect pathogens and of detectability half-lives for prey proteins or DNA sequences in predator gut analysis.

We describe polymerase chain reaction (PCR) primers for gut analysis of aphid predators. The primers amplify aphid mitochondrial COII fragments ranging in size from 77 to 386 bp. Using these primers, we were able to distinguish six species of US Great Plains cereal aphids, including two congeners, Rhopalosiphum maidis (Fitch) and R. padi (L.), and to detect them in extracts of coccinellid and chrysopid predators. We devised a protocol for deriving half-lives of detectability for the DNA of a single aphid consumed by predators maintained under simulated field dietary and temperature conditions. Using this protocol and primers that amplify a 198-bp fragment, we determined statistically different half-lives of detectability for a single R. maidis of 3.95 h in Chrysoperla plorabunda (Fitch) and 8. 78 h in Hippodamia convergens Guerin. The detectability half-life for a 339-bp R. maidis fragment was statistically longer in C. plorabunda but not in H. convergens. The sensitivity of the assay for the 198-bp fragment is 10-7 aphid equivalents. For species-specific predator gut analysis, PCR is superior to monoclonal antibody technology, giving comparable detectability half-lives with lower expense, much shorter development times, and greater certainty of a successful outcome.

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.