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environments (3), none of which are characteristic of northeastern strawberry 

 plantings . 



Utilizing conservation techniques for native natural enemies could prove 

 more rewarding. Chief among these would be the reduction of nonselective or 

 broad-spectrum pesticide use. Despite their effectiveness on a given pest 

 species, these materials can destroy natural enemy populations, initiating a 

 resurgence and possible population explosion for certain pests, including some 

 not previously considered economically damaging. 



The effectiveness of native natural enemies is hampered by other problems 

 as well. Due to long coevolut ionary relationships, pest species likely 

 developed resistance mechanisms to most parasites, and the parasites themselves 

 may be plagued with hyperparasites . Native predators may provide some control 

 of strawberry pests. The root feeding larvae of weevils and scarabs are 

 attacked by birds and rodents, but these may themselves damage plants. 

 Predatory beetles also feed on pest larvae, tarnished plant bugs, and mites 

 (9). These predators are relatively nonspecific feeders, however, and are 

 thus less effective as control agents of a specific pest. Because they are 

 native, they will also have their own natural enemies, which will keep their 

 populations, and hence control potential, in check. 



Augmentation of natural enemies, whether native or imported, involves 

 manipulation of the population such that control of the pest species is 

 improved. Typically, this is accomplished by rearing natural enemies 

 artificially and releasing them, either inundatively or as an inoculative 

 population (3). Such approaches are usually quite expensive and may not be 

 justifiable on a minor crop such as strawberries. 



One of the most important barriers facing biological control potential in 

 strawberries is the relatively high value of the crop. Very small amounts of 

 damage may have significant economic effects due to the high cash return of 

 strawberry fruit. Therefore, when an economic injury threshold is determined, 

 it will be quite low, meaning only small pest populations need be present to 

 justify control measures (9). These thresholds may require pest numbers to be 

 below a level required for the natural predators to remain viable. This 

 condition would necessitate supplementary chemical applications, probably 

 causing greater harm to the natural enemies, or repeated inundative releases of 

 the natural enemy, much like a "biological insecticide". 



Perhaps the most promising use of biological control in strawberries to 

 date is against phytophagous mites. In California, cyclamen mite has been 

 effectively controlled with Typhlodromus species. These native predatory mites 

 can provide adequate control without manipulation, but typically not until the 

 third year of a planting. To achieve control in first and second year beds, 

 the predator must be stocked. Research also suggests that stocking young 

 fields with cyclamen mite along with Typhlodromus could improve establishment 

 and effectiveness of the predator (6). Strawberry growers were not receptive 

 to this idea, and have since adopted an annual system of production which 

 eliminates the need for such controls. Strawberry plantings in the Northeast 

 are still maintained for several years, however, allowing cyclamen mite 

 populations to reach damaging levels. Although it is unlikely that the 

 predatory Typhlodromus could successfully overwinter, inundative releases of 

 the predator at specific pest population thresholds potentially could bring 



