During the past four decades, several species of aphidophagous Coccinellidae became established in North America, including Coccinella septempunctata, Harmonia axyridis, Hippodamia variegata, and Propylea quatuordecimpunctata. After their
establishment, unknown circumstances favoured a rapid increase in population densities and distribution of H. axyridis and C. septempunctata at localities hundreds and thousands of kilometers from their release sites. Propylea quatuordecimpunctata and Hippodamia
variegata have spread more slowly after becoming established in northeastern North America. Comparative studies based
upon allozyme variation in these four introduced species and in six native North American species of ladybird beetles revealed no
significant differences in genetic diversities. Genetic variation, assessed by allelic diversity and heterozygosity, was uncorrelated
with the establishment and spread of these predatory species in North America. All ladybirds studied show a remarkable degree of
dispersion with little detectable population subdivision.
The laboulbenialean fungi occur throughout the world and are closely associated with a range of arthropods, including many coleopteran hosts. Throughout the summer of 2004, coccinellids were collected from a Bluegrass savanna woodland ecosystem, dominated by blue ash Fraxinus quadrangulata and Chinkapin Oak Quercus muehlenbergii, and the adults were examined for the presence of Hesperomyces virescens using binocular and scanning electron microscopy. Over 80% of adult Harmonia axyridis, a species previously reported as having a persistent association with the fungus, were infected. No significant differences were observed in incidence on male and female hosts, however, the distribution of fungus differed between sexes. Female H. axyridis had a greater percentage of infection on their elytron compared to other parts of their body whilst male infection was concentrated around their elytra, legs and abdomen. Although infection rates were significantly lower, we report, for the first time, the presence of this fungus on the hosts Cycloneda munda, Brachiacantha quadripunctata and Psyllobora vigintimaculata. This is the first study documenting the incidence of this insect-associated fungus with these native coccinellids of North America. In the samples collected from the Bluegrass savanna, two species (Coleomegilla maculata and Hyperaspis signata) were not infected by this fungus.
The community of predators within agroecosystems has the potential to restrict aphid populations, especially early in the season before exponential increases in density and prior to the arrival of specialist natural enemies. Although direct observations of predation, laboratory feeding trials and manipulative field studies have been used to estimate levels of biological control exerted by different species (or potentially negative interactions between them), it is often difficult to extrapolate results to naturally occurring interactions in the field.
Over 100 investigations have utilized gut-content analysis to estimate aphid predation rates by predators. Throughout the last century, gut dissection, which enables the visual identification of aphid body parts, has been used in over 50% of studies although accurate identification and quantification of predation is difficult. Other techniques have included radio-labelling of prey, dissection of faecal samples, electrophoresis, stable isotope analysis and use of polyclonal antisera. In recent studies of invertebrate predation, monoclonal antibodies have been the most frequently applied technique but advances in molecular biology have enabled the detection of species-specific DNA sequences. The use of these applications to quantify predation by aphidophagous predators will be reviewed, with emphasis on potential sources of error and difficulties of quantitative interpretation. Despite the considerable focus currently directed towards molecular approaches, antibody-based techniques are likely to remain an important tool for studying predation rates of pests in the field, especially when antibodies have already been developed. However, the study of multiple predation events within complex generalist predator food webs is only likely through the detection of species-specific DNA sequences using molecular techniques.