Biopesticides - Pesticides: Evaluation of Environmental Pollution - page 593

them, the cannibalizing grasshoppers get a much greater dose of the disease-causing
organisms than through the initial Nosema application.
19.6 Viruses Biopesticides
Microbial biopesticides known as baculoviruses are a family of naturally occurring
viruses known to infect only insects and some related arthropods. Most are so specific in
their action that they infect and kill only one or a few species of Lepidoptera larvae (cater-
pillars), making them good candidates for management of crop pests with minimal off-
target effects. Baculoviruses used as microbial biopesticides consist of DNA surrounded
by a protein coat (nucleocapsid), which is itself embedded in a protein “microcapsule” or
occlusion body (OB) that provides some protection from degradation in the environment.
Depending on the virus, OBs may contain a single nucleocapsid (a granulovirus, GV) or
multiple nucleocapsids (nucleopolyhedrovirus, NPV).
Upon ingestion by a susceptible caterpillar, OBs are dissolved within the alkaline mid-
gut, releasing nucleocapsids, which infect the cells lining the midgut. The viral DNA rep-
licates in the nuclei of the host cells and then spreads throughout the body of the larvae,
essentially turning it into a “virus factory.” The infected insect stops feeding within a few
days, dies and disintegrates, releasing billions of new OBs, which can be ingested and can
cause new infection of the neighboring larvae.
The granulovirus of the codling moth Cydia pomonella (CpGV) is a good example of a
commercially successful viral insecticide. First discovered in the 1960s, it is now the active
ingredient of about half a dozen products sold worldwide. Often used in conjunction
pheromone-based mating disruption, CpGV limits codling moth populations and dam-
age in pome fruits while preserving the beneficial insects and minimizing the chemical
residues. Although accepted for use in organic farming, most CpGV applications occur in
conventional orchards where its unique mode of action can minimize the risk of resistance
to chemical insecticides.
19.7 Yeast Biopesticides
A variety of yeasts have been investigated for their usefulness in controlling plant
diseases. Nonpathogenic Cryptococcus and Candida species naturally occur on plant tis-
sues and in water. Isolates from a variety of crops have been investigated for their bio-
control capacities. For example, C. olephila Strain O, first isolated from golden delicious
apples, has been developed into an effective biopesticide for the control of postharvest
fruit rots. It is applied to apples and pears after harvest—but before storage—to control
particular fungal pathogens. The yeast serves as an antagonist to fungal pathogens
such as gray mold ( Botrytis cinerea ) and blue mold ( Penicillium expansum ) that cause
postharvest decay.
Candida oleophila strain works primarily through competition for nutrients and precolo-
nization of plant wound sites. However, there is evidence that it produces enzymes that