Management of the European apple sawfly using a parasitic wasp
Project Code: PRR10-060
Charles Vincent - Agriculture and Agri-Food Canada
- Determine the susceptibility of Lathrolestes ensator to pesticides commonly used in conventional apple orchards and establish its potential as a biological control agent.
- To disseminate the parasitoid into three minimally sprayed orchards where the European apple sawfly is established.
- To develop recommendations for the incorporation of L. ensator for the management of the European apple sawfly into orchard Integrated Pest Management (IPM) that supports the survival and activity of the parasitoid.
Summary of Results
The European apple sawfly, (EAS), is an insect pest accidentally introduced into North America in the late 1930’s that has become established in southwestern Quebec, eastern Ontario, Nova Scotia and parts of New Brunswick. The larvae feed on apple fruit early in the season causing a ribbon-like scar on the fruit at harvest. The larvae may also bore into the core of the fruit and create a large exit hole plugged with frass. Fruit that have this secondary type of damage tend to drop in June. Larvae damage more than one fruit in a cluster.
At the time of the initiation of this project, the EAS was managed by insecticide applications at pre-bloom to control other spring feeding insects and at post bloom by the timely application of the organophosphate insecticide azinphos-methyl (AZM). At the time, AZM was the only product registered for EAS control and moreover, it was scheduled for phase-out by the end of 2012. With the impending phase-out of this material, there was a recognized need for alternative control products for both conventional and organic orchards. This project was initiated under the Agriculture and Agri-Food Canada (AAFC) National Strategy to reduce the risks from the use of organophosphate pesticides in pome fruit orchards.
Lathrolestes ensator, an ichneumonid wasp parasitoid specific to the European apple sawfly, had been imported from Europe and released from 1995-1999. The parasitoid became established in minimally sprayed orchards at AAFC Frelighsburg, Quebec, and had been shown to provide as much as 64% larval parasitism of EAS populations. Similar to its host, L. ensator has one generation per year and has an obligatory diapause. Adult L. ensator emerge in June, shortly after the fruit set stage of apple. To establish its potential as a biological control agent, additional studies were required to determine the susceptibility of this parasitoid to insecticides used in conventional programs and how it could effectively fit into integrated pest management programs.
Two apple orchards at AAFC Frelighsburg, Quebec were used as sources of the parasitoid for distribution to other orchards and for the laboratory studies. The parasitoids were collected in apple fruitlets infested with parasitized EAS larvae. This is the most successful way to handle the parasitoid and results in a minimal mortality of the parasitoid during transfer activities and a synchronised emergence of the parasitoid with its host the following year.
Laboratory testing to evaluate the susceptibility of the parasitoid to insecticides commonly used in conventional orchards was planned for years 2011 and 2012 of the study. In spring 2010, fruitlets showing secondary sawfly damage were collected from source orchards. The percent parasitism of the EAS in the fruitlets was determined by dissection to be up to 80%. Fruitlets were placed on sandy soil beneath trees in an unsprayed apple orchard at AAFC, Frelighsburg to allow the obligatory diapause of both host and parasitoid during the winter. In the spring of 2011, parasitized pupae were separated from the sandy soil by sifting and put on clean sand to allow emergence of L. ensator adults in a rearing room with a temperature regime simulating outside conditions. To test for susceptibility to insecticides, adults were to be collected upon emergence and placed in contact with dried residues of insecticides on inner surfaces of Petri dishes. Similar tests were planned for 2012, using fruitlet collections occurring in 2011.
Fruitlets showing evidence of EAS infestation and with known rates of EAS parasitism (24-80%) were introduced into each of three recipient orchards in Kentville (Nova Scotia), Mountain (Ontario) and Magog (Quebec) in 2010. The recipient orchards had previously confirmed European apple sawfly infestations and were under pest management programs with minimal pesticide use. The establishment of the parasitoids was evaluated in 2011 through the dissection of 100 fruitlets from recipient orchards. Releases were planned for 2011 and 2012, however they were not conducted due to insufficient availability of L. ensator.
In May 2010, successive freezing during the flowering of apple in Frelighsburg resulted in an unusually low fruit set. Dissections of fruitlets collected in 2010 and 2011 from the Mountain and Kentville orchards revealed zero or trace levels of EAS injury with no signs of the parasitoid. Although fruitlets from the Magog orchard were not examined, EAS was found to be present through the use of sticky traps.
Harvesting of the EAS pupae for laboratory studies in the spring of 2011, yielded only 10 viable parasitoid pupae, which was insufficient for testing susceptibility to pesticides.
Although fruit production was normal in spring 2011, the number of fruitlets showing evidence of EAS attack in source orchards, was abnormally low. The low levels of EAS in 2011 and corresponding low availability of the parasitoid, resulted in insufficient numbers of the parasitoid available for further distribution to recipient orchards in 2011 and for laboratory testing in 2012. As a result the project had to be prematurely terminated. While the source orchards at Frelighsburg are no longer available due to the closure of this AAFC site, in years previous to this project, the parasitoid had been introduced into other organic orchards in Quebec which might provide a source of the parasitoid for future studies with this promising biological control approach.
Since this project was initiated, additional reduced risk pesticides have been registered for the management of EAS. Growers follow an integrated approach that includes monitoring and the use of action thresholds to determine the need and timing of sprays for this insect pest.
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