Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, January 12, 1995 TAG: 9501120056
SECTION: CURRENT PAGE: NRV-5 EDITION: NEW RIVER VALLEY
SOURCE: JOE HUNNINGS
DATELINE: LENGTH: Medium
While the greenhouse is an optimal environment for plant production, it unfortunately also favors insect survival and reproduction. Pest outbreaks can precipitate major losses of revenue through direct feeding damage, disease transmission and insect control-associated costs. As a result, insect control in the greenhouse and nursery industry still is largely based on routine use of agrichemicals.
But greenhouse growers want alternatives. In fact, because of concerns about insecticide resistance, environmental contamination, restrictive regulations, costs, and food and worker safety, many leading greenhouse grower organizations have made bio-control one of their highest research priorities.
Since 1991, the University of Vermont has been testing native insect-killing fungi against three major pests of greenhouse-grown ornamental and vegetable crops: Western flower thrips, sweet potato whitefly and the green peach aphid. More than 150 fungal isolates have been screened against these three pests.
Their results have demonstrated that some fungi might be used quite effectively to control insect pests. However, they have found great variation in the effectiveness of the fungi for different target pests.
How do these fungi kill insects? First, the insects must come in direct contact with fungal spores. The spores stick to the cuticle, or exoskeleton, of the insect until the spore germinates. The fungus then penetrates the cuticle to reach the inside of the insect. There, it must overcome the insect's immune defense mechanisms to establish itself and grow.
Having infected an individual, the fungus kills its hosts in one of two ways. The fungus can produce toxins lethal to the insect, or the fungus can literally eat away at the insect's insides until the insect dies. Once the insect is dead, the fungus proliferates throughout the insect cadaver.
Once an individual insect dies of a fungal infection, it can infect other insects. If conditions are favorable - high temperature and humidity levels - the fungus grows back through the cuticle and sporulates on the surface of the dead insect. These spores can then infect other, healthy insects that come into contact with them.
Vermont research thus far has focused on evaluating a range of pathogens and formulations for use on an assortment of plants, to determine which fungi are active against more than one insect pest species. At least under lab conditions, they have found several isolates to be effective at killing several insect pests.
It looks as though fungi represent a viable, ecologically acceptable alternative to chemical pesticides. Results to date have been encouraging, but agricultural researchers still have a long way to go before a commercial product becomes available.
It would be naive to expect the fungi to replace all other pest management options. But, their development as dependable and inexpensive components of integrated pest management can reduce our reliance on chemical insecticides while providing long-term benefits to growers and the environment.
Joe Hunnings is the Virginia Cooperative Extension agent for agriculture in the Montgomery County Extension Office in Christiansburg. If you have questions, call him at 382-5790.
by CNB