Page 528 - Biosystems Engineering

500 Cha pte r Se v e ntee n

have been discovered that show activity against nematodes, mites,
lice, aphids, and ants (Lacey and Goettel 1995). There are two other
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species of bacteria currently registered as microbial insecticides:
Bacillus sphaericus and Serratia entomophila. Bacillus sphaericus is strictly
registered for mosquito control.
Entomopathogenic viruses have been isolated from a number of
viral families, but a few from the family Baculoviridae have been reg-
istered as viral insecticides. Commercially available baculoviruses are
mostly targeted for lepidopteran hosts. The majority of baculoviruses
used as biological control agents are in the genus Nucleopolyhedrovirus.
The most widely used fungal insecticide is Beauveria bassiana to
control the maize corn borer. Other strains of B. bassiana are used to
control white flies, thrips, aphids, and mealybugs. Metarhizium aniso-
pliae spores are used to control the wheat cockchafer, and Metarhizium
flavoviride controls grasshoppers and locusts. Paecilomyces fumosoro-
seus controls white flies, thrips, aphids, and spider mites; Lagenidium
giganteum is currently used for mosquito control. These fungi gener-
ally penetrate the host with enzyme action of enzymes; death is
caused by mycelial colonization, causing starvation, or by the toxin
released.
Bioherbicides The first bioherbicide (de vine) was used in 1981, which
was a mycoherbicide based on the fungus Phytophthora palmivora. It
controls the growth of milkweed vines (Morrenia odorata) in citrus
orchards.
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Templeton et al. (1986) suggest that bioherbicides have greatest
potential for controlling (1) weeds infesting small specialized areas
where chemical herbicide development is costly, (2) weeds that have
been intransigent to chemical control, (3) crop mimics, and (4) para-
sitic weeds. Weed species may be annual (e.g., velvetleaf, Abutilon
theophrastii), or perennial (e.g., field bindweed, Convolvulus arvensis,
and dandelion, Taraxacum officinale).

Biofungicides Trichoderma harzianum is a naturally occurring fungus,
which is used as a biofungicide to protect crops from root rot and
wilting diseases caused by other harmful fungi (Fusarium, Rhizocto-
nia, Pythium, Botrytis, etc.). Gliocladium virens acts against Rhizoctonia
solani and Pythium spp., whereas Ampelomyces quisqualis protects plants
from powdery mildew disease.
Insect Hormones Insect hormones such as pheromones and juvenile,
ecdysone have been found useful in controlling insects. Pheromones that
attract males of the appropriate species are secreted by the female. If the
traps are made using synthetic analogs of female pheromones, the males
are attracted and eliminated. Similarly, molting hormone ecdysone and
juvenile hormones have been found to control insects. Juvenile hormone
should be present in the early stages to prevent early maturation, but if