Gargaphia decoris (Hemiptera: Tingidae) from Two South American Provenances are Equally Safe for Release Against the Invasive Tree, Solanum mauritianum (Solanaceae)

The sap-sucking lace bug, Gargaphia decoris Drake (Tingidae), was released in South Africa, and is pending release in New Zealand, for the biological control of Solanum mauritianum Scopoli (Solanaceae). Most releases were carried out with stocks imported from northeastern Argentina in 1995, but these were later augmented using stocks imported from southern Brazil in 2002 that were deemed to be better suited to the colder regions of South Africa. While the Argentinean stocks were subjected to extensive host-range testing prior to release, the Brazilian stocks were not tested prior to release. In retrospect, this was risky because of the possibility that distinct populations of the same insect species could comprise biotypes (strains) that display either major or subtle differences in host range, thus raising the possibility of non-target effects in the field. In this study, the host ranges of the two G. decoris populations were compared on an identical set of test plants, to rule out the possibility of within-species host-range variation prior to the insect's release in New Zealand. Standard host-range tests, involving seven ‘indicator’ Solanum species, failed to demonstrate any significant differences between the Argentinean and Brazilian populations in their response to the test plants in both no-choice and multi-choice arenas. Adults and nymphs from both populations performed considerably better on S. mauritianum and adults consequently displayed strong feeding and oviposition preferences for this species. There is thus no evidence of host-range variation between the two populations and we conclude that either is suitable for release against S. mauritianum.