Recognizing the Good Bugs in Cotton - Texas Is Cotton Country ...

NPV
Disease
Nuclear polyhedrosis virus
Characteristics: Insects killed by NPV are discolored
and limp. They often hang from
leaves attached only by one or two legs.
Infected caterpillars are filled with a cloudy
liquid inside and are easily broken open
when handled. NPVs, also called baculoviruses,
are found nearly everywhere. Different
strains or “species” of virus occur and each
tends to attack only a limited number of
caterpillar species.
Hosts: NPVs infect more than 400 insect
species. Caterpillars of moths and butterflies
are commonly infected. In cotton, cabbage
loopers are often attacked by NPV while beet
armyworms, bollworms and budworms are
less commonly infected.
General Biology: The liquid released from
insects killed by NPV contains millions of
virus particles which fall onto leaves. Other
caterpillars ingest the virus particles while
feeding on contaminated leaves and become
infected. Virus particles can also enter
through natural openings in the caterpillar, or
be carried on the stinger (ovipositor) of a parasitic
wasp. Two to five days after ingesting
the virus, caterpillars become sluggish and
eat less. Death follows in 5-12 days. Shortly
before dying, the caterpillar may climb to the
top of the plant and hang by its prolegs. The
insect’s body wall is easily ruptured, thereby
releasing liquid and virus particles onto
leaves. Other caterpillars contact the virus
and the cycle is repeated.
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