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Funded Project

Funding Program: Regional IPM Competitive Grants - Northeastern

Project Title: Mite Biological Control in Apples Through Distribution and Augmentation of Typhlodromus pyri

Project Director (PD): Jan Nyrop [1]

Lead State: NY Lead Organization: Cornell University

Research Funding: $99,842

Start Date: Sep-01-1998 End Date: Aug-31-2000

Site/Commodity: apples

Area of Emphasis: biological control

Summary: European red mites are significant pests in most commercial apple plantings and orchardists typically rely on chemical pesticides to control them. In addition to being costly and potentially harmful to the environment, this management strategy has not proved to be sustainable because European red mite have quickly and repeatedly developed resistance to chemical pesticides. For the first time though, biological control may be a no cost and sustainable alternative to chemical pesticides for mite control in northeast orchards. When the mite predator Typhlodromus pyri is conserved in orchards, there is no need for any chemical pesticides to control European red mite. Unfortunately, T. pyri is not common in the northeast except for in western and central New York, Nova Scotia, and a few orchards in Massachusetts and Vermont. In 1996 we began a project to introduce T. pyri from western New York into 40 orchards located throughout the northeast. The objective of this work was to determine whether populations of T. pyri capable of providing biological control could be established and sustained. Each release site consisted of a plot of six trees into which the predators were placed and a plot of six control trees. To measure the effectiveness of the releases, leaves were collected from the release and control sites and shipped to Geneva, NY 2-3 times in 1996 and 3-5 times in 1997. At Geneva predators and pest mites were collected from the leaves, counted and identified. The results from this work are very exciting. T. pyri have been recovered from 36 of 40 release locations. In 1997 these predators reduced European red mite densities, 2, 5 and 10 fold at approximately two thirds, one third, and slightly less than one third of the sites, respectively. Average numbers of T. pyri in release plots increased twofold from 1996 to 1997 (from an average of 0.17 per leaf to an average of 0.41 per leaf). At 17 locations T. pyri were recorded at over 1 per leaf in the release plots. Surprisingly, T. pyri were also found in 23 control plots, however, at densities 10 fold lower than in release plots. The results from our work over the past two years indicate that sufficient numbers of T. pyri can probably be established in most northeast orchards to realize complete biological control of European red mite. To follow up on this work, three questions should be answered. 1) Do T. pyri in northeast orchards regulate European red mite below plant damaging levels? The rational for this question is obvious. 2) Are T. pyri indigenous to the northeast more susceptible to certain pesticides than T. pyri from New York that were released into the target orchards? If this question is affirmed, then there are no climatic limits to using T. pyri as a biological control agent throughout the northeast. 3) Can improved methods of collecting and storing T. pyri and enhancing predator population increases be devised? These technologies would hasten implementation of mite biological control. To answer these questions we will do the following: 1) In 1998 and 1999 we will continue to monitor European red mite and T. pyri numbers in the release and control plots in the 41 sites where the predator has been established. In the release plots no miticides, including dormant oils, will be used. 2) Typhlodromus pyri will be collected from control plots in 7 locations and from the source orchard in Geneva, NY and bioassayed with carbaryl, azinphosmethyl, chlorpyriphos and mancozeb to determine if differences in susceptibility occur between released predators and indigenous strains. 3) We have discovered that T. pyri attempt to over winter in large numbers beneath burlap bands affixed to trees. This provides a method for collecting and storing large numbers of these predators for release into orchards. Experiments will be conducted to measure survival of T. pyri in the tree wrap bands under several conditions with the objective being to identify a procedure that can be easily used by orchardists. We have also discovered that fungi and yeasts may be important supplemental foods for T. pyri . Establishment of predator populations may be speeded if these foods were readily available. We will conduct experiments to determine whether predator population growth can be augmented by the addition of yeasts or fungi. Objectives: 1) Determine whether T. pyri will provide complete biological control of European red mite in apple orchards throughout the northeast. 2) Determine whether T. pyri indigenous to northeast apple orchards are more susceptible to certain pesticides than T. pyri from an orchard in Geneva, NY. 3) Determine the best way to store T. pyri that are in diapause so that these predators can be used to inoculate new orchards in the spring. 4) Determine whether growth of T. pyri populations can be enhanced through augmentation of yeasts or fungi. The rationale for pursuing these objectives is as follows: 1) We have convincingly shown that population of T pyri can be established in orchards throughout the northeast, that these predators persisted for a year after release, and that some of these predator populations greatly reduced pest mite densities. Because T. pyri provides complete biological control of European red mite in western and central New York and in Nova Scotia, it is likely the same will now occur throughout the northeast. If true, the need for miticides throughout this apple growing region would largely vanish. The most important question to now answer is whether biological control will in fact occur. 2) Through our previous work we discovered that T. pyri are indigenous to some orchards in the northeast. However, the incidence of this predator is lower in northeast orchards than in orchards in central New York and densities of indigenous T. pyri are lower than where New York T. pyri were released. The most plausible explanation of these patterns is that T. pyri indigenous to the northeast are more susceptible to certain pesticides than predators from New York. If this is true, then release of New York predators will almost certainly be successful and bring about biological mite control. 3) There are many acres of apples in the northeast and release of T. pyri throughout these plantings is a large undertaking. This effort could be speeded by having a method for collecting large numbers of T. pyri from apple trees and then easily placing these predators in recipient trees. We have discovered that in early fall, large numbers of T. pyri will crawl beneath bands consisting of burlap and tree wrap that are placed around the bole and large limbs of apple trees. These predators consist entirely of inseminated adult females and use the bands as over wintering sites. As many as 300 predators will crawl beneath a band 10 cm wide and 35 cm long. Unfortunately, we have also found that many of the predators beneath the bands die during the winter, most likely of desiccation. However, if a method can be found to store these predators so that minimal mortality occurs, the bands would provide a valuable tool for speeding dissemination of T. pyri throughout the northeast apple growing region. 4) We have observed that in some locations where T. pyri are released predator densities build to over three per leaf in a single year whereas at other locations, predator population growth is almost nil. Common to all of these locations was that spider mites were nearly nonexistent, so, some other food source must be present for the predators. In some cases the rapid predator population growth could be attributed to high numbers of apple rust mite (Aculus schlechtendali ); however, at other sites the food source was not observable. The only two possible nutrient sources are pollen and yeasts or fungi. Other investigators have shown that T. pyri can develop and reproduce on species of powdery mildew (Erysiphe) (Zemek and Prenerova 1997) and on apple powdery mildew, Podosphaera leucotricha (Ell. and Everh.) (Chant 1959). Eichhorn and Hoos (1990) observed that T. pyri fed on the mildew Uncinula necator (Sch.) Burr. We have conducted experiments to determine whether augmentation of pollen leads to higher predator numbers and have observed no effect from these treatments. Thus, the most likely food source is yeasts or fungi. Anecdotal evidence supports this hypothesis as release sites in apples and in grapes with either apple scab (apples) or mildew (grapes) on leaves have had the highest numbers of predators recorded. And, we have recently shown in the laboratory that T. pyri will feed and develop on naturally occurring yeasts and fungi that are antagonistic to apple scab. If applications of these microorganisms lead to higher predator growth rates, they could be used to enhance development of predator populations so that biological control will occur more quickly. Outcomes and Impacts Summary from 2001 IPM Center report European red mites (ERM) are significant pests in apple orchards and can account for 25 percent of pesticide costs in the crop each year. Orchards have been managed to produce lush, healthy trees that offer excellent yield and fruit quality, but these conditions also happen to be ideal for ERM population growth. The pesticides used for a variety of important pests often wipe out the predators that might otherwise hold ERM populations in check. To make matters worse, the ERM has developed resistance to many of the miticides once used to control it and is likely to become resistant to newer chemical controls as well. Biologically based alternatives to miticides can slow the resistance process by reducing our dependency on these chemicals. Cornell's Jan Nyrop, working with other researchers and apple growers in New England, has shown that the predatory mite Typhlodromus pyri, which controls ERM, can be used successfully throughout the Northeast. This predator eliminates the need for miticides to control ERM in orchards where it is established and conserved. Methods have been devised for collecting and moving the predator to northeastern orchards where it is not yet present. Nyrop continues monitoring to determine whether this environmentally friendly control strategy can succeed on a long-term basis. If T. pyri can be effectively established throughout the Northeast, it could save the industry more than $3.5 million in control costs each year. Publication Roda, A., J. Nyrop, M. Dicke and G. English-Loeb. 2000. Trichomes and spider-mite webbing protect predatory mite eggs from intraguild predation. Oecologia 125(3):428-435.

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