Release of a parasitic wasp for biological control of leek moth

Project Code PRR10-030

Project Lead

 Peter Mason  Agriculture and Agri-Food Canada

Objective

Release the biological control agent (Diadromus pulchellus) in areas where leek moth has become a concern, monitor its spread and impact on the leek moth, and develop educational materials for growers for integrated pest management of leek moth

Summary of Results

Background

Leek moth, Acrolepiopsis assectella, an invasive alien species from Europe, has become established in eastern Ontario as well as parts of Quebec and is continuing to expand its range. Leek moth larvae mine into the leaves of alliums (garlic, leeks and onions) damaging the plant and sometimes rendering it unmarketable.

The Pest Management Center’s Pesticide Risk Reduction Program has funded work to develop tools and information which can be used in an integrated management program (IPM) for the control of leek moth through two previous related projects. One focused on basic biology studies and the development of an IPM system (MU03-ENT2) and the second on the discovery of a biological control agent (PRR03-260). As part of this work Agriculture and AgriFood Canada researchers and collaborators from the CABI Europe - Switzerland centre identified the parasitic wasp Diadromus pulchellus as a promising biological agent. After extensive host range studies conducted in Europe and in containment facilities in Canada, a petition was submitted to the Canadian Food Inspection Agency (CFIA) and regulatory approval for release was granted.

Through this project the biological agent D. pulchellus was released for the first time in Canada. Working with the Ontario Ministry of Agriculture and Food (OMAF), Carleton University, and CABI an IPM system incorporating D. pulchellus with other reduced risk methods was developed and implemented on garlic farms in the Ottawa valley, in eastern Ontario. Extensive grower collaboration through a farmer participatory research approach was a key factor in the success of this project.

Lab and Field Experiments

Leek moth monitoring and estimate of damage

For field experiments on grower farms five blocks of garlic were planted and a portion of garlic in each block was placed under row cover. Pheromone traps were used to monitor flight patterns and numbers of adult leek moth during the growing season. Field populations of leek moth larvae and pupae were estimated through plant collections, while damage by leek moth was determined through plant dissection. In addition collections of scapes and bulbs were conducted to estimate damage to marketable products.

For all farms in 2010 - 2012 fewer plants under row cover had scape damage than without row cover. In 2012, there was no damage observed on the protected plants (row cover) at two sites. The data indicated that floating row cover provided protection to scapes and garlic plants in all years as damage was reduced under row cover compared to unprotected plants. This demonstrates that the row cover can provide protection from leek moth most likely by acting as a barrier to females trying to lay eggs.

In 2011, the results showed that when garlic was hung to dry with the stalk attached, greater damage to the bulbs occurred. However, there does not appear to be much difference in weight between garlic bulbs that were cut at the stalk and those hung with the stalk.

Rearing, releases and monitoring of Diadromus pulchellus

Leek moths were reared year round in the lab to provide host material for the biological control agent Diadromus pulchellus, as well as material for field experiments. In May numbers of D. pulchellus were increased in preparation for releases at up to four locations, the Central Experimental Farm (CEF) to test methodology and establish a local population of the parasitoid, and at three co-operator locations in the Ottawa area. Experiments to determine the effect of cold storage on fecundity were also conducted.

D. pulchellus releases were made in the Ottawa area from 2010-2012. D. pulchellus adults were released frequently from time of first generation pupation of leek moth until the end of the season. In 2010, 1337 males and females were released at two sites. In 2011, 1771 individuals were released on two sites and in 2012, 7089 individuals were released at 4 sites. More than 10,000 D. pulchellus were released over the course of the project.

Recoveries documented survival of D. pulchellus in the field for at least one complete generation during the field season. Progeny of individuals released the previous year were also recovered the following spring indicating that D. pulchellus can successfully overwinter in eastern Ontario. The results also suggest that immediate parasitism levels of almost 50% can be achieved when sufficient numbers of the biological control agent are released. Background parasitism at five locations in the Ottawa area was also established.

Farmer Participatory Research

Farmer engagement was a key element to the successful implementation and completion of the project. At the onset, five Ottawa area growers were recruited as grower collaborators to contribute to the project and the research through a farmer participatory approach. After an initial visit to explain the project and adapt the experimental set up to individual needs, collaborators were engaged through regular on-site visits and discussions during each field season. In addition annual meetings were conducted with each participant to discuss the previous year’s results and to plan for the next field season.

An end-of-project questionnaire demonstrated that participants were enthusiastic about and benefitted from the pre-project and ongoing on-site interactions. In 2010, all but one farmer was aware of biological control; however, through a combination of on-site visits, individual farmer reports and full-day information sessions, all farmers have said their knowledge and understanding has increased with respect to the leek moth problem in allium plants; the biology of the leek moth; natural enemies of the leek moth; and the role of row cover and leek moth pheromone trap monitoring and temperature data as part of an IPM program against leek moth.

All farmers said they would be willing to participate in a follow-up IPM program against leek moth and would definitely recommend participating in the program to other garlic farmers.

Knowledge and Tech Transfer

Knowledge transfer was achieved through multiple approaches, including factsheets and handouts, grower workshops as well as by the farmer participatory approach itself.

Leek moth in an emerging pest problem that will continue to impact allium production systems, particularly organic operations with few management options. This project addressed the need for reduced risk strategies by implementing a biological control option for management of leek moth.

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