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United States Department of Agriculture

Agricultural Research Service

Title: Mortality and Feeding of Late Instar Trichoplusia Ni Larvae Fed a Wild Or Recombinant Strain of the Nuclear Polyhedrosis Virus of Autographa Californica (Acmnpv)

Authors
item Ignoffo, Carlo
item Garcia Jr, Clemente

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 1996
Publication Date: N/A

Interpretive Summary: Safe, viral insecticides have been genetically engineered in attempts to make them more effective against a damaging insect pest. We tested a genetically engineered virus against cabbage loopers to find out whether cabbage loopers would die quicker and do less feeding than cabbage loopers exposed to a non-engineered native virus. Our laboratory tests demonstrated that cabbage looper, exposed to the genetically improved vira insecticide, do die quicker (ca. 26% quicker) and did less feeding (ca. 10% less) than the non-engineered virus. Although the genetically engineered virus performed better than the native virus additional enhancement may be necessary to ensure an earlier, consistent high level of efficacy.

Technical Abstract: Baculoviruses have been genetically engineered to enhance the rate of mortality and thereby, hopefully, reduce feeding damage inflicted by populations of pest insects. Prior results using recombinant viruses, with an insect-selective-toxin insert, has increased the rate of larval mortality ca. 25 to 50% and reduced feeding ca. 35 to 60%. Our objective was to determine the extent and rate of mortality of 5th-instar larvae of Trichoplusia ni exposed to a wild (AcC6) or recombinant strain (AcAaIT) of AcMNPV and relate mortality to feeding. Early 5th-instar larvae were used to simulate a worst-case-scenario when larvae are approaching full growth and at a stage, prior to prepupation, when most feeding will be done. The rate of mortality of 5th instar larvae exposed to the recombinant AcAaIT virus was significantly faster than with the wild AcC6 strain. Initial mortality occurred after 2 days for larvae exposed to AcAaIT and after 3 days for larvae exposed to AcC6. The AcAaIT strain killed 5th instar T. n larvae 26.3 + or - 4.7% faster than the AcC6 strain. The extent of feeding (based on fecal weights) of late-instar larvae exposed to AcAaIT was significantly less than the controls in all three experiments and significantly lower than the wild AcC6 strain in only one experiment. The reduction in feeding for larvae exposed to AcAaIT when compared to the control or AcC6 was 13.2 + or - 0.6% and 8.5 + or - 2.6%, respectively. There was no significant differences in fecal weights between the untreated larvae and larvae exposed to the AcC6 strain. The difference in fecal weight between AcC6 and the untreated larvae averaged 5.0 + or - 2.0%.

Last Modified: 8/22/2014
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