Quantifying pathways of energy transfer between plants, pests, and beneficial insects is a necessary step toward maintaining pest stable agroecosystems in the absence of chemical subsidies. A diet switching experiment utilizing a predatory ladybird beetle, Hippodamia variegata (Goeze), evaluated the use of naturally occurring stable C and N isotopes as an economically feasible and safe method for quantifying pathways of energy flow within agroecosystems. Stable isotope values of the ladybird beetle Coleomegilla maculata lengi (Timberlake) collected from an agroecosystem were used to estimate the relative amount of C and N derived from agricultural plants and incorporated by ladybird beetles based on mass balance equations. At the beginning of the diet-switching experiment δC and δN values of H. variegata (-12.0‰ and 6.3‰, respectively) differed by -0.2‰ and 2.9‰ from the aphids that were provided exclusively as their diet. These data are consistent with previous estimates of trophic level isotope effects. After switching the diet of H. variegata to an alternative food, isotope values of H. variegata gradually shifted toward expected values for individuals fed this diet (-22.9‰ and 8.8‰ for δC and δN values, respectively). Isotope values of another ladybird beetle, C. maculata, collected from the field indicated that in May, alfalfa and maize (pollen) obtained in the previous year contributed 32% and 68% of the C or N to the diets of these individuals and in August, 52%, 6%, and 42% of the C or N assimilated by these insects was derived from alfalfa, wheat, and maize, respectively. These data are consistent with expectations based on the relative abundance of C. maculata in various crops during the season. The field and laboratory data are a clear indication that isotope values are sensitive to dietary changes on a relatively short time scale (days) and provide a strong basis for the use stable C and N isotope to trace energy flow patterns of these beneficial organisms within agroecosystems.

A monitoring system established within an array of cultivated and uncultivated habitats was used to characterize the first 5 yr of establishment of the exotic multicolored Asian lady beetle, Harrrwnia axyridis (Pallas), in an agricultural landscape of southwestern Michigan. Population trends over time were summarized for II species of resident cocci nell ids before ,md after the arrival of H. axyridis. In addition, annual population increase, habitat utilization patterns, and within-season population fluctuation for H. axyridis were analyzed. H. axyridis became a dominant coccinellid species in the landscape 4 yr after its arrival. Adults of this species were found in all habitats monitored, including early secondary succession, poplar plantation, alfalfa, soybean, corn, and winter wheat. Significant population peaks were observed early and late in the season, depending on the habitat. Resident species that appear affected by the establishment of H. axyridis are Brachiacantha ursina (F.), Cycloneda /nunda (Say), and Chi/acarus stigma (Say). However, to attribute the decline on the numbers of those species to H. axyridis will require further assessment.

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International trade is widely acknowledged as a conduit for movement of invasive species, but few studies have directly quantified the invasion risk confronting individual locations of interest. This study presents estimates of the likelihood of successful entry for alien forest insect species at more than 3,000 urban areas in the contiguous United States (US). To develop these location-specific estimates, we first utilized historical merchandise imports and insect incursions data to estimate an annual US rate of alien insect species establishment. Next, we used historical pest interception data to calculate the proportion of all insects arriving at US ports of entry that are associated with forest hosts. We then combined these results to estimate a nationwide establishment rate specifically for alien forest insects. Finally, we employed international and domestic commodity flow networks to allocate this nationwide rate to individual US urban areas. For 2010, we estimated the nationwide rate as 1.89 new alien forest insect species per year. While the establishment rates observed at most urban areas were low (\0.005 new species/year), for a few select areas the rates predict new alien forest insect species establishments every 5-15 years. This national-scale assessment provides a realistic depiction of humanassisted establishment potential in the US as well as functional inputs for quantitative models of invasion. Overall, these analyses support broad-scale biosecurity and management strategies.

Aphidophagous coccinellids (ladybeetles) are important providers of herbivore suppression ecosystem services. In the last 30 years, the invasion of exotic coccinellid species, coupled with observed declines in native species, has led to considerable interest in the community dynamics and ecosystem function of this guild. Here we examined a 24-year dataset of coccinellid communities in nine habitats in southwestern Michigan for changes in community function in response to invasion. Specifically we analyzed their temporal population dynamics and species diversity, and we modeled the community’s potential to suppress pests. Abundance of coccinellids varied widely between 1989 and 2012 and became increasingly exotic-dominated. More than 71% of 57,813 adult coccinellids captured over the 24-year study were exotic species. Shannon diversity increased slightly over time, but herbivore suppression potential of the community remained roughly constant over the course of the study. However, both Shannon diversity and herbivore suppression potential due to native species declined over time in all habitats. The relationship between Shannon diversity and herbivore suppression potential varied with habitat type: a positive relationship in forest and perennial habitats, but was uncorrelated in annual habitats. This trend may have been because annual habitats were dominated by a few, highly voracious exotic species. Our results indicated that although the composition of the coccinellid community in southwestern Michigan has changed dramatically in the past several decades, its function has remained relatively unchanged in both agricultural and natural habitats. While this is encouraging from the perspective of pest management, it should be noted that losses of one of the dominant exotic coccinellids could result in a rapid decline in pest suppression services if the remaining community is unable to respond.

Changes in species assemblages of predatory coccinellids in response to landscape structure (habitat diversityand patchiness) was studied in a southern Michiganlandscape during 1989-1990. Three sites with different mosaics of cultivated (alfalfa,com, wheat) and uncultivated (deciduous, field succession) habitats were sampled for coccinellid species using yellow sticky traps. The landscape at each site was characterized using the Berger-Parker index for habitat diversity and a relative patchiness index for habitat fragmentation. Relative abundance, species richness, species dominance, and the Kendall coefficient were used to analyze and compare species assemblages among sites. Principal component analysis (PCA) was used to extract factor components per species and site scores, which were compared with landscape indices using the Pearson correlation coefficient. Thirteen species of coccinellids were caph1redduring the 2 yr of weekly sampling. Of these species, Cocci nella septempunctata (L.) was the dominant species in the landscape and was equally abundant in the 3 sites. Coleomegilla maculata lengi Timberlake was more abundant in the site that had a com habitat, whereas Cycloneda munda (Say),Chilocoms stigma (Say),and Brachiacantha ursina (F.) were more abundant in the site that had a deciduous habitat. Overall, the site with a deciduous habitat had higher species richness. There were significantdifferences in species composition between the site with a deciduous habitat and the other 2 sites. Differences observed among sites were Significantlycorrelated with the presence of uncultivated habitats in the landscape.