Author
Terence Olckers
olckerst@ukzn.ac.za
University of KwaZulu-Natal
Durban
Coauthors
Dineshen Singh, University of KwaZulu-Natal, Durban, South Africa
Abstract
Candidate agents must be compatible with weed populations in the invaded range. However, invasive populations may diverge genetically and chemically from native populations, with mismatches in the agent-weed relationship. We tested the stem-boring weevil Gasteroclisus tricostalis (Curculionidae) on Senecio madagascariensis (Asteraceae) plants from the native range (KwaZulu-Natal, South Africa) and invaded range (Australia). During no-choice tests, females displayed significantly reduced oviposition when switched from South African to Australian plants across three series of trials, resulting in 6.8 times more eggs on local plants. Furthermore, 94.4% of local plants supported oviposition, compared to only 44.8% of Australian plants. Australian plants suffered substantially higher mortality (41.4%) than local plants (5.6%), which was unrelated to larval presence. Despite this, larval recovery and survival (as a proportion of eggs laid) did not differ significantly between local and Australian plants. Generally, plant responses to larval presence did not differ significantly between local and Australian plants, with negative increments in living shoots and capitula recorded on plants that harboured larvae. Reduced oviposition on Australian S. madagascariensis may relate to higher alkaloid levels recorded earlier, but also the possibility that invasive populations originate from a different region of South Africa than originally assumed.
Keywords
Gasteroclisus tricostalis
native-range studies
no-choice testing
Senecio madagascariensis
target-plant compatibility
Highlights
Gasteroclisus tricostalis laid substantially fewer eggs on Australian fireweed plants
Larval survival was not significantly different between South African and Australian plants
Higher alkaloid levels or a genetic mismatch between plants from the two countries may be the cause