Biological control of soil insect pests in field crops

Project Code BPI08-010

Project Lead

Peggy Dixon - Agriculture and Agri-Food Canada

Objective

To evaluate fungal biocontrol agents against several soil insect pests, establish the economics and risk reduction potential of a biocontrol/IPM (Integrated Pest Management) regime incorporating fungal pathogens to manage these pests and apply for label expansion or registration of promising agents

Summary of Results

Background

Soil insect pests such as cabbage root maggot (Delia radicum; Diptera: Anthomyiidae) and the seed corn maggot complex (Delia platura and Delia florilega; Diptera: Anthomyiidae) can cause extensive damage to crops across Canada. Among the crops affected are large-acreage crops like canola, as well as high value brassica vegetables, including broccoli, cauliflower and rutabaga. These pests are difficult to manage with conventional methods. Traditional chemical controls are not effective on the juveniles in the soil, due to poor penetration of the topsoil layer, and thus insufficient concentration of active ingredients. Other, more effective methods such as fumigants, pose risk to environmental and human health. Further to this, several pest control products are being phased out as a result of re-evaluation. Therefore, there is an urgent need for new, integrated methods to manage these pests. Various integrated approaches have been reviewed in the project PRR06-690 and entomopathogenic fungi have been identified as a potential solution as part of an IPM strategy. These fungi have been shown to progressively diminish insect pest populations through natural host-pathogen interactions in the soil, thus providing an effective and sustainable approach.

The main objective of this project was to test the effect of commercially available biopesticides registered for use against other insects either in Canada or elsewhere on the pest species Delia radicum, the cabbage maggot, and Delia platura, the seedcorn maggot, in order to identify promising candidates for the management of these challenging pests.

Approaches

A two phased approach was taken for the efficacy trials with test products: first a laboratory screening assay was set up to evaluate the impact of various products in vitro, then potted plant trials were conducted with the most promising products.

Six different entomopathogen products or formulations were tested in the phase one screening trials. Initially, the assays were done by dipping 2nd instar larvae in a spore solution, then placing them on sterile sand in petri dishes with rutabaga as a food source. This method proved problematic and was replaced by drenches, where spore solutions were applied to the surface of sterile sand in plastic cups with 2nd instar larvae and cubes of rutabaga as a food source. Some dose-response experiments were conducted using 2nd instar cabbage maggot larvae, while a separate study was conducted using cabbage maggot adults.

Greenhouse potted plant trials were done with cauliflower seedlings in plant pots containing sifted, unsterilized field soil. The two most promising products, both based on the entomopathogen Metarhizium anisopliae strain F52 (Met 52), were tested against cabbage maggot eggs and 1st instar larvae (seedcorn maggot was not available at the time). Data collected were % recovery of maggots in the pots, root damage ratings, and cauliflower dry weights.

Results

A total of 1,980 larvae, 1,600 eggs and 90 flies of Delia spp. were tested in dip, drench and spray bioassays and in potted plant trials.

The laboratory drench method with one formulation of Met 52 resulted in about 40% mortality of D. radicum larvae and about 32% mortality of D. platura larvae at a product rate of 1 x 106 cfu (colony forming units) per gram of soil and of 70% at 1 x 107 cfu per gram of soil. The other products killed only a small proportion of larvae in the drench bioassay.

Due to methodological problems, the results from the potted plant trials were highly variable, with very poor larval recovery. No definitive conclusions can be drawn regarding the efficacy of the tested products.

The most promising result from this project is the ability of M. anisopliae strain F52 to kill 70% of D. radicum in the drench assay.

The registrant of Metarhizium anisopliae strain F52 has developed and registered an improved liquid formulation of the strain since this project was concluded. Given the promise shown by the biological control strain, it may be warranted to include this new product in a future field screening or in a project aiming to integrate a number of tools or approaches to develop an IPM approach for the management of cabbage maggot.

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