Abstract
Biological control of weeds in Vanuatu began in 1935, with the introduction of the tingid Teleonemia scrupulosa to control Lantana camara. To date, nine biological control agents have been intentionally introduced to control eight weed species. Seven of these agents have established on their respective hosts while an eighth, Zygogramma bicolorata, an agent for Parthenium hysterophorus has only recently been released and establishment is unlikely. The fate of a ninth agent, Heteropsylla spinulosa, released for the control of Mimosa diplotricha is unclear. Six other biological control agents, including Epiblema strenuana which was first detected in 2014 on P. hysterophorus on Efate have spread into the country unintentionally. Control of the target weeds range from inadequate to very good. By far the most successful agent has been Calligrapha pantherina which was introduced to control Sida acuta and Sida rhombifolia. The beetle was released on 14 islands and managed to spread to at least another 10 islands where it has effectively controlled both Sida spp. Control of the two water weeds, Eichhornia crassipes by Neochetina bruchi and N. eichhorniae and Pistia stratiotes by Neohydronomus affinis, has also been fairly good in most areas. Two agents, T. scrupulosa and Uroplata girardi, were released on L. camara, and four other agents have been found on the weed, but L. camara is still not under adequate control. The rust Puccinia spegazzinii was first released on Mikania micrantha in 2012 and successfully established. Anecdotal evidence suggests that it is having an impact on M. micrantha, but detailed monitoring is required to determine its overall impact. Future prospects for weed biological control in Vanuatu are positive, with the expected greater spread of recently released agents and the introduction of new agents for P. hysterophorus, L. camara, Dolichandra unguis-cati and Spathodea campanulata.
Highlights
For many farmers in Vanuatu and the South Pacific in general, weeds are a major problem, outcompeting or smothering food crops, and decreasing food security and income
This paper reports on the biological control agents introduced into Vanuatu and provides an update on their distribution within Vanuatu and their status in controlling their respective target weed species
Insect biological control agents for the terrestrial weeds were reared on potted plants of their respective hosts in organzamesh screened, aluminium-framed cages (90 × 45 × 45 high cm), using methods similar to those used by the research organisation from which the particular biological control agent was imported
Summary
For many farmers in Vanuatu and the South Pacific in general, weeds are a major problem, outcompeting or smothering food crops, and decreasing food security and income. Conventional control of weeds is not always feasible, as herbicides are expensive and beyond the means of most subsistence farmers, while manual control through slashing or hand-pulling is labour intensive (Orapa 2001, Day et al 2012). Both means of control require constant follow-up, as not all plants are killed or plants can regrow from fragments left behind following slashing. Biological control of weeds was first undertaken in Vanuatu in 1935, with the introduction of the tingid, Teleonemia scrupulosa Stål (Hemiptera: Tingidae) to control Lantana camara L. sens. Teleonemia scrupulosa had been originally introduced into Hawaii in 1902 (Swezey 1923), before being released into Fiji and from there into Vanuatu (Winston et al 2014)
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