Research and IPM

Characterize the genetic variation of Hyalopterus populations in California to determine their invasion history and relation to ancestral populations in the Mediterranean.

Test the compatibility of distinct Aphidius biotypes against Californian Hyalopterus to identify the best source of parasitoids from the Mediterranean for introduction to California.

This research project has assisted us in determining the most effective native parasitoids for introduction against mealy aphid, and in the development of a methodology that may be used to conduct future natural enemy explorations in other biocontrol systems.

Multiple genetic markers were examined in mealy aphids collected from California and the Mediterranean. These data indicate the presence of three host adapted species within Hyalopterus that are specific to the host plant from which they were collected. Aphids sampled from plum share one genetic pattern, aphids sampled from almond share a second, and aphids sampled from peach share a third. Interestingly, we have found that apricot trees act as a shared resource for each of the three species, and even permits some hybridization, at least between the plum and almond associated species.

Mealy plum aphids in California are of the same species as the Mediterranean plum group, thus indicating that only H. pruni is an invader. Based on genetic markers, we have identified Spain or Tunisia as the likely source of invasive mealy aphids, and have discovered an entirely separate introduction of aphids in eastern North America.

Genetic analysis of the mealy aphid's native parasitoid, Aphidius transcaspicus, has revealed substantial population structure, but no evidence of host plant associated species like those found in Hyalopterus. Virulence experiments showed no differences in parasitism rates or offspring sex ratio among A. transcaspicus from Spain, Morocco, Israel, and Cyprus, and instead indicated that female size was a better predictor of parasitism success.

DNA sequences from four genes and genotypes for nine microsatellite markers were examined for mealy aphids collected from California and the Mediterranean. These data indicate the presence of three host adapted species within Hyalopterus that are specific to the host plant from which they were collected. Aphids sampled from plum share one genetic pattern, aphids sampled from almond share a second, and aphids sampled from peach share a third. Interestingly, we have found that apricot trees act as shared resources for each of the three species, and even permits some hybridization, at least between the plum and almond associated species.

Mealy plum aphids in California are of the same species as the Mediterranean plum group. Based on microsatellite genotyping and a shared mutation at the mtDNA 12S gene, we have identified the western Mediterranean as a likely source of invasive mealy aphids.

Genetic analysis of the mealy aphid's native parasitoid, Aphidius transcaspicus, has revealed several regional strains, with no evidence of cascading host plant effects on parasitoid population structure. Behavioral assays indicate that parasitoids from Greece seem more aggressive toward invasive H. pruni than Cypriot and Israeli populations. More extensive experiments will help guide the search for the most effective source of parasitoids for biological control introductions.

DNA sequences from a single gene for mealy aphids collected from California and the Mediterranean indicate three major groups, or potential species, within Hyalopterus. These groups differ based on the host plant from which the aphids were collected. Aphids sampled from plums share one genetic sequence, aphids sampled from almonds share a second, and aphids sampled from peaches and apricots share a third. Mealy plum aphids in California have the same DNA sequence associated with the Mediterranean plum group. Based on initial microsatellite genotyping, we have tentatively identified Spain as a likely source of invasive mealy aphids, and confirmed that "plum type" genotypes are found on multiple host plants in the Mediterranean.

DNA sequences from the mealy aphid's native parasitoid, Aphidius transcaspicus, show little population structure. Initial microsatellite genotyping from Mediterranean populations, however, has revealed three main regional groups. Parasitoids from Spain and Tunisia are similar, with parasitoids from Greece and Italy forming two distinct groups. Though genetic variability in A. transcaspicus is relatively low compared to H. pruni, parasitoid populations appear to have greater geographic population structure. More extensive genotyping will help guide the search for the most effective source of parasitoids for biological control introductions and elucidate the potential for future host-plant shifts or expansions of the mealy aphids in California.

DNA sequences from a single gene for mealy aphids collected on prune in California's Central Valley, and on plum, almond, peach, and apricot from Spain and Greece indicate the presence of three major groups, or potential species, within the genus Hyalopterus. These groups are based largely on the host plant from which the aphids were collected: aphids sampled from plum share one genetic sequence, aphids sampled from almond share a second, and aphids sampled from peach and apricot share a third. Examples from the aphid group on plum were also found on all other host plants, suggesting that 'plum' aphids have the potential to utilize multiple host plants. Mealy plum aphids in California also share the same DNA sequence associated with the plum group in the Mediterranean.

More detailed experiments are currently being developed to determine the geographic sources of the mealy plum aphids in California and the extent of variation associated with its parasitoid, Aphidius transcaspicus, in the Mediterranean. This will help guide the search for the most effective source of parasitoids for biological control introductions, and elucidate the potential for future host-plant shifts or expansions of the mealy aphids in California.