Plant bug parasitoid established in Ontario strawberry production areas

The tarnished plant bug, Lygus lineolaris, is a major concern in strawberry production areas across Ontario. Tarnished plant bug adults and nymphs feed on all parts of the plant by sucking sap, destroying embryos within seeds and preventing fruit tissue growth beneath the seed. The resulting misshapen berries are known as "cat faced" and are unmarketable. In Ontario Lygus completes two full generations and a partial third generation per year in southern Ontario and has adverse impacts on strawberry production throughout the growing season: first-generation nymphs cause severe economic damage to June bearing cultivars, while second-generation nymphs are the major limiting factor on later day-neutral cultivars.

Following the example of organic strawberry growing in California, an IPM strategy has been developed by scientists from CABI Europe - Switzerland in collaboration with Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) and Agriculture and Agri-Food Canada (AAFC), combining trap cropping, classical biological control and a reduced-risk approach using chemical control. Adapting this strategy to Ontario strawberry farms was started in 2007 and has continued in 2008. The initiative was funded by AAFC's Pesticide Risk Reduction Program, to reduce the risks from pesticides used in the agriculture and agri-food industry.

As part of the IPM approach, several hundreds of the European parasitic wasp Peristenus digoneutis, were released at several locations in eastern and southern Ontario for biological control of tarnished plant bugs. In spring, the female wasp injects a single egg into each tarnished plant bug nymph and its larva feeds inside the young tarnished plant bug. After 7-10 days the mature larva leaves the dying plant bug nymph and drops to the ground, where it pupates. A second generation of the wasp emerges in July parasitizing the summer generation of the plant bug. Peristenus digoneutis had previously been introduced to the northeastern USA where it has been shown to reduce plant bug field populations in alfalfa. Since its first release P. digoneutis has dispersed naturally into Canada, where it is now present in plant bug populations in Quebec, parts of Ontario and Nova Scotia.

The inundative releases under this project, from insects mass reared at AAFC in London, Ontario, were intended to enhance the spread of the parasitoid throughout the province and to allow its impacts to be realised much sooner in Ontario's strawberry fields. After consecutive releases of P. digoneutis in strawberry growing areas of southern and eastern Ontario, the analysis of plant bug samples collected showed that that the wasp is now well established at several sites in eastern and southern Ontario Records of P. digoneutis at strawberry sites where the wasp was not released suggest that P. digoneutis already naturally dispersed throughout parts of Ontario. At all release sites a promising increase in parasitism was observed soon after the first releases in 2007. However, it is too early to state whether P. digoneutis has already reduced Lygus populations in Ontario and whether the IPM approach has been successful. In the northeastern United States, it took almost ten years before a significant impact of P. digoneutis was recognized and Lygus populations collapsed.

Ongoing work to encourage population build up and assess impact is needed. In addition, surveys in other parts of Ontario would help to identify areas where the parasitoid is not yet present, and releases would help to accelerate the dispersion and establishment of P. digoneutis.

For more information on the "Lygus IPM in Ontario strawberries" project please visit: www.cabi.org/ProjectsDetail.asp?ProjectID=382

Figure 1: Parasitic wasp attacking tarnished plant bug nymph (photo credit Tim Haye)

Figure 2: Releasing parasitic wasps into an alfalfa field. (photo credit Peter Mason)

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