Biological control is taking place in fruit crops all the time, because native and naturalized populations of natural enemies overwinter on the farm and move into crops to feed on or lay their eggs into pest insects. Predators consume several insects over the course of their development. Parasites and parasitoids tend to lay eggs in their host insect, which then feed internally, develop and kill the host. Pathogens invade the body of the host insect. The impact of beneficial insects is often underestimated because it is easy to overlook and difficult to measure. It may become obvious if they are killed by broad-spectrum insecticides and pest outbreaks occur as a result. Conservation of beneficials by use of selective insecticides when pests exceed threshold levels is recommended wherever practical.
The release of lab-reared beneficials can also aid in suppressing pests. These tend to be more successful in greenhouses than in the field, but there are several instances where releases in the field have been proven to suppress or completely control key pests. For example, Neoseiulus fallacis and Phytoseiulus persimilis are tiny mite predators that feed on pest mites such as two-spotted spider mites and European red mites. N. fallacis is indigenous to the Northeast as well as available for release from reared populations in commercial insectaries. Both have been very useful tools for New England fruit growers.
Another example involves beneficial nematodes, very small roundworms that attack soil-dwelling insects. Two in particular (Steinernema and Heterorhabditis) have been mass-reared for commercial use. These seek out and penetrate their host insects, multiply within the host and kill it. They are most likely to be effective against the soil-dwelling immature stages of susceptible hosts, such as root weevils, cutworms, white grubs, wireworms, and maggots. Nematodes require moist soil conditions to survive. Consult the Resources section in the appendices of this guide for sources of further information and suppliers of beneficial organisms.