Getting the most out of Eretmocerus hayati, an effective natural enemy of silverleaf whitefly
Silverleaf whitefly (SLW) is a considerable pest of vegetable production. It has a broad host range and is able to develop resistance to insecticides rapidly. To reduce reliance on insecticides CSIRO imported and new species of parasitoid, Eretmocerus hayati, and began releasing it in November 2004 (HAL final report VG06029). It established well and has since spread to all major vegetable production areas in Australia where SLW occurs. Following post-release evaluation CSIRO identified that while it was highly effective, grower management practices could either assist or hinder the parasitoid’s effectiveness. This research focused on how to get more out of the parasitoid, and better silverleaf whitefly (SLW) control by investigating: what management practices and decisions influence the abundance and distribution of the parasitoid; what features of the landscape influence the capacity of the parasitoid to achieve early colonisation of at-risk crops; and why the introduced E. hayati provides better control than the native E. mundus. Results were used to provide guidelines to growers that help to integrate control options for SLW. These guidelines were summarised in a user guide which identified a set of practical approaches that growers could adopt and integrate into their farming practice. The guide was prepared in consultation with growers so that the content and layout made sense to them. Conducting surveys of grower practices, laboratory and field experiments on growers’ properties we show that several years post-release of E. hayati: – SLW has significantly decreased in all areas with the worst year being 2006 for Lockyer, 2004 for Bundaberg, and 2008 for Burdekin. – Growers that improved their farm hygiene had a significant reduction in SLW problems. – Broad spectrum insecticide to manage insect pests on whitefly host crops is still very prevalent and these insecticides are deadly to the parasitoid. The more that they are used the worse the grower ranked their whitefly problem. – There are limited chemical options to control SLW that are also soft on E. hayati. The extensive use of imidacloprid should be an indication to look for alternatives. – E. hayati lives longer and is more fecund than the native E. mundus. – E. hayati has the potential, when not disrupted by broad-spectrum insecticide, to cause a 100 fold decrease in silverleaf whitefly numbers. – E. hayati disperses by flying at distances of tens of metres, flying and wind at distances of hundreds of metres, and primarily wind at distances of kilometres. – Seasonal crop rotations have the potential to get E. hayati into crops faster and keep silverleaf whitefly populations lower for longer These findings show that E. hayati has had a significant impact on SLW populations. With E. hayati now available for inundative release, future R&D should focus on assisting growers with its integration into the full complement of pest management decisions for SLW susceptible crops. We also found that E. hayati adults survived 4.5 days longer and produced three times as many progeny as E. mundus and so may help explain why E. hayati performs better in the field in Australia, than E. mundus.