Potential Arthropod Targets for Biological Control in the Midwest

The North Central region of the United States has a long history of biological control of arthropod pests dating from entomologist C.V. Riley's pioneering efforts in Missouri in the 1870s. Numerous programs have since followed, including extensive efforts at biological control of European corn borer, cereal leaf beetle and alfalfa weevil, which resulted in numerous establishments and control successes. Current biological control efforts within the region target more than 40 arthropod pests or pest complexes in nearly all commodities and types of habitats.

A variety of criteria may be utilized in selecting target pests for biological control programs, including biological, economic and logistical factors. Specific target selection criteria and quantitative methods have been developed for both arthropod and weed targets. In practice, these methods are probably best applied to a limited range of potential target pests. A 1992 survey of researchers and Extension specialists at Midwestern universities was used to evaluate the potential for biological control of various arthropod pests in the North Central region of the United States. The purpose of the survey was to identify regionally important target pest species for which there was a high probability of successful biological control. The survey results are intended to assist researchers and decision makers in targeting pests for collaborative biological control efforts in the North Central region.

Surveys were conducted in 10 commodity/specialty areas: field crops, forest, fruit, greenhouse, medical/veterinary, rangeland, stored grains, turf, vegetables and woody ornamentals. A total of 100 responses were received from 48 scientists from nine of the 13 North Central states. Respondents rated the importance of each pest in their state and the potential for successful biological control. In each commodity/specialty area, one or more targets were identified that have regional importance and for which biological control techniques have a high potential for success.

The survey indicates a substantially positive view of the potential for successful use of biological control to manage arthropod pests in the North Central region, with one or more pests in each of the commodity/specialty areas that respondents agreed were amenable to biological control.

Arthropod Targets Ranked Highest in Importance and Potential for Biological Control in the Midwest

In field crops, the European corn borer and the alfalfa weevil were identified as regionally important pests with a high potential for successful biological control. Both of these pests have been the target of extensive biological control efforts. In some parts of its range, the alfalfa weevil is currently considered to be under biological control. The corn borer continues to be a problem, but results of this survey indicate that respondents remain optimistic about additional biological control solutions.

Conifer sawflies and the forest tent caterpillar emerged from this survey as important pests of forest systems for which biological control approaches could be effective. The orange-striped oakworm and the European pine shoot moth, which ranked rather low in regional importance, were also considered good targets for biological control. This survey preceded the spread of the pine shoot beetle, a pest of current widespread concern for which biological controls are being investigated. It is anticipated that both the importance and potential for success ratings for this pest will change rapidly as new information is gathered.

In fruit production systems, the European red mite and two-spotted spider mite were both identified as regionally important pests for which biological control has a high potential for success. Methods to conserve the natural enemies of these pests are already being implemented in many fruit production systems. Tentiform leafminers and San Jose scale were somewhat less important regionally but showed a high probability for success.

Greenhouse pests were uniformly ranked high in potential for successful application of biological control. All of the greenhouse pests had a potential for success ranking exceeding 6.5 on the 1-10 scale. This probably reflects a history of past successes in applying biological control in these more controlled environments. Two-spotted spider mites, sweetpotato and greenhouse whiteflies, green peach aphid, fungus gnats and shore flies all were considered important pests for which biological controls have a high probability of success.

The next three groups of pests medical/veterinary, rangeland and stored products had lower response rates than the other groups. This undoubtedly reflects the limited distribution of rangeland in the region. In the other cases, the relative lack of specialists in these groups probably resulted in the lower response rates. In the medical/veterinary group, only the house fly and the stable fly received high rankings for both importance and potential for success. Too few responses were received for the rangeland pests to give accurate rankings. Of the stored products pests, only the Indian meal moth was both of widespread importance and viewed as a good candidate for successful biological control.

Billbugs, sod webworms and Japanese beetles are the turf pests of widespread importance for which biological control tactics were deemed to have a high probability for success. The European chafer was also ranked high in probability for success but is not a problem in many states in the region.

Several important caterpillar pests were among the vegetable insects identified as pests of widespread concern for which biological controls offer good probability for success, including the imported cabbage worm, cabbage looper and the European corn borer. The diamondback moth was also highly ranked in potential for success but is of less widespread concern.

The largest group of pests identified was in the category of woody ornamentals. In this group, respondents identified eight insects for which the probability of success exceeded 7. Some of these were of widespread concern, such as euonymous scale and other scale insects. Others were of much more local concern, such as the imported willow leaf beetle and the tulip tree aphid. Considerable differences in the distribution of the host plants of these insects within the region account for the fact that few pests were important throughout the region.

Although this survey information should be used cautiously (survey respondents may have different expectations for "success," new pest introductions may occur, or pest status may change over time), it is hoped that this list of potential targets for biological control will prompt discussions and collaborative efforts among researchers and Extension staff members and various state and federal institutions in the region. If targets of common interest occur, then the biological, ecological and logistical factors necessary for success can be evaluated and promising targets pursued in collaborative efforts.

- Doug Landis and Michael Haas, Michigan State University

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