Submitted to: Basic and Applied Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/29/2009
Publication Date: 12/15/2009
Citation: Szendrei, Z., Greenstone, M.H., Payton, M.E., Weber, D.C. 2009. Molecular gut-content analysis of a predator assemblage reveals the effect of habitat manipulation on biological control in the field. Basic and Applied Ecology. 11:153-161. Interpretive Summary: In the biological control of pests, it is important to determine not just if natural enemies are present, but to what extent they are suppressing the pests of interest. However, it is difficult to tell whether insect predators are consuming significant numbers of insect pests, because of their small size, infrequent and often hidden feeding activities. The polymerase chain reaction (PCR) can detect pest DNA in the guts of insect predators, allowing researchers to determine which predators are eating the pest of interest, without disturbing the predators and prey in the crop field. Predators respond to management changes in crops, such as mulches and tilling the soil. To learn how mulching versus tillage of the potato crop changed predation of Colorado potato beetle (CPB), we grew potatoes in two separate years with or without tillage, the non-tilled crops having either rye or vetch mulch. Predators were sampled and tested by PCR for whether they had consumed the pest, CPB. Although mulched crops had lower pest numbers, this was not due to higher predator numbers or predation (pest feeding), because predators were neither more abundant, nor more likely to have consumed the pest, according to the mulch treatment. By adjusting the prey detection in each of the predators, based on how fast they digested the prey pest, we were able to rank two predatory stink bugs and a carabid (ground) beetle as most important predators, whereas the more abundant spotted pink lady beetle was much less likely to consume CPB. This information is important to entomologists and pest managers designing farming systems to conserve natural enemies of CPB.
Technical Abstract: Despite growing evidence that habitat manipulation can alter predators’ impact on target prey consumption, few studies have directly examined the effect of habitat context on conservation biological control in the field. Because of contradictory evidence in the literature for the outcome of habitat manipulation on herbivore suppression, we used molecular gut content analysis method to evaluate the efficiency of an entire predator assemblage in situ. We investigated the effect of habitat manipulation in potato fields in 2006 and 2007, by systematically collecting predators from plots with different mulch treatments. Field-collected predators were then tested for DNA (PCR of Cytochrome Oxidase I sequence of 214 bp) of the target prey, Leptinotarsa decemlineata, using species-specific primers to evaluate predator gut contents. Concurrently, L. decemlineata larval abundance and plant damage were recorded from the experimental plots. Predator species abundance and diversity were not influenced by habitat complexity treatments, while L. decemlineata density was highest in plots without mulch. Predator gut content analysis revealed that the highest incidence of predators positive for L. decemlineata DNA was in plots without mulch, where target prey abundance was the highest. Therefore the lower prey abundance in mulched plots does not seem to be due to predation. The most abundant species in the predator assemblage was Coleomegilla maculata, which had the lowest proportion of L. decemlineata in the gut. Podisus maculiventris, Perillus bioculatus, and Lebia grandis were less abundant but had a higher incidence of target prey DNA in the gut. These proportions of positive detection were adjusted using detectability half-life corrections based on laboratory marker disappearance studies for each of the major predators.