Diaeretus essigellae Starý and Zuparko (Hymenoptera: Braconidae: Aphidiini), a biological control for Monterey pine aphid, Essigella californica (Essig) (Hemiptera: Aphididae: Cinarini): host-specificity testing and historical context

Abstract

The Monterey pine aphid (Essigella californica) was accidentally introduced into Australia from the northern hemisphere before being detected in Canberra in 1998. Feeding on some members of Pinaceae, including the commercially important Pinus radiata, the aphid has now spread to almost all pine-growing areas and is considered to be an important forestry pest. In 2005, a project was commissioned to import the pine aphid parasitoid, Diaeretus essigellae, into Australia and subject it to host-specificity testing with a view to releasing it as a biological control for E. californica. In 2007, the first wasp pupae arrived at Australian quarantine facilities and emergent adults were used to establish an ongoing Australian culture. Sequencing of 28S rDNA confirmed the identity of the parasitoid and showed that its closest known relative is Diaeretus leucopterus. No-choice and choice host-specificity testing was conducted using Monterey pine aphid and eight non-target aphid species as potential hosts for D. essigellae. Regardless of the testing procedure, E. californica was the only species that was successfully parasitised. This suggests that D. essigellae is highly specific (at genus or species level) and therefore, is a suitable candidate for release into pine plantations to provide control of Monterey pine aphid in Australia. Based on these data, permission to release the wasp from quarantine was granted in November 2009. Although 24 aphidiine parasitoids have been purposely or accidentally introduced to Australia, this is only the second species to have undergone host-specificity testing and in addition, is the first species released to parasitise a member of the most primitive aphid subfamily, Lachninae. This case study raises interesting questions about the basis for development/analysis of host-specificity testing of putatively highly specific biocontrol agents where close relatives of their targets either do not exist in the environment or are pests themselves.