Research Projects

Behavior and Management of Rhagoletis Flies in Michigan Fruit Crops

Kirsten S. Pelz

Introduction

The blueberry maggot fly, Rhagoletis mendax (Diptera: Tephritidae), is one the most important late-season pests of Michigan blueberries. Larvae of each species develop inside host fruit, rendering the fruit unmarketable. Under USDA regulations, there is zero tolerance for infestation by these pests and detection of one infested fruit in a standard sample leads to rejection of that load. Proposed restrictions on the use of organophosphate and carbamate insecticides by the EPA in response to the Food Quality Protection Act of 1996 present a challenge for pest management. Growers apply 3-5 applications of broad-spectrum insecticides to control flies before they lay eggs. These older insecticide chemistries have strong contact activity and thus are effective at killing flies as they move around in the field or orchard. In contrast, the lethal action of all newer insecticide chemistries primarily occurs through ingestion. Unfortunately, adult flies generally do not feed extensively and so flies must be enticed to consume a lethal dose of the newer insecticides to prevent larval infestation of fruit.

Bait-and-Kill

The development of a bait-and-kill approach to fruit fly control is promising since it harnesses the behavior of the fly to lead it to the toxic bait. An insecticide-bait formulation, GF-120, has recently been registered for control of blueberry maggot but little is known about its efficacy this blueberry pests.

Objectives:

1) Determine the effectiveness of insecticide bait sprays for control of blueberry in small-plot trials.
2) Determine fruit fly responses to insecticide-bait formulations under field conditions.

Results:

Objective 1: Our recent research in 2002 and 2003, funded by Michigan State University Project GREEEN, has shown that the newly-registered baited formulations can provide almost complete control of infestation (Table 1). In these experiments, we compared the activity of two formulations of a new insecticide, spinosad, for protection of blueberries and apples against blueberry maggot in unmanaged blueberry fields. The active ingredient, spinosad, was tested in two formulations, SpinTor and GF-120. Infestation in both the SpinTor and GF-120 plots was significantly lower than that in untreated or bait-treated plots. Fruit infestation in the two insecticide treated plots did not differ significantly.

Table 1. Effect of treatments on percentage (mean ± SEM) of fruit infested with blueberry maggot puparia in 2002 and 2003.

Means ± SEM followed by the same letter are not significantly different.

Objective 2: In 2003, we conducted observations of blueberry maggot interacting with droplets of GF-120, water, or protein-bait applied to blueberry bushes to determine how flies respond to the bait formulations under field conditions. The results of these observations showed that there was no significant difference in the number of flies that visited bushes treated with GF-120, water, or protein-bait. However, flies spent significantly more time in close proximity to droplets of GF-120 or bait than to water. This data suggests that GF-120 only arrests flies that land near the bait droplets, but does not attract them.

Summary and Future Directions

GF-120 shows promise an effective alternative to carbamate and organophosphate insecticides for control of blueberry maggot. However, with zero tolerance for infestation, improving this strategy is a priority. Experiments in 2004 will focus on further increasing the efficacy of this product through the addition of attractants such as ammonium acetate and ammonium carbonate. In addition, the baited insecticides are prone to washing off in the rain; therefore, we hope to increase the rainfastness of GF-120 through the addition of non-polar additives, such as paraffin wax.

Funding

This research is supported by Michigan State University’s Project GREEEN.