assessment: field release of genetically manipulated baculoviruses
Baculoviruses are a group of viruses that kill particular insects including
crop pests. The value of wild type baculoviruses as sprayable, environmentally
safe, biopesticides has been well established. However, their commercial
competitiveness with chemical insecticides would be further improved by
genetic engineering to incorporate genes which would lead to swifter death
or cessation of host insect feeding. It is also perceived that the practical
use of genetically modified baculoviruses depends on a satisfactory outcome
to thorough assessment of the risks of release.
Approach and methodology
Assessing the risk of release of a genetically modified baculovirus depends
on a sound knowledge of the ecology of the wild type from which it was
derived. Ecological deviations in the recombinant virus can thus be identified.
The wild type baculovirus Autographa californica nuclear polyhedrosis
virus (AcNPV) and its recombinant clone (AcNPC/p1OZ) were studied. The
wild-type and recombinant were both infective in both a pest of pine forests
(Pine beauty moth) and a pest of agricultural crops (Cabbage moth). Extensive
field observations identified ecological aspects suitable for study in
severely contained simulated ecosystems (microcosms) specially developed
for the purpose. The behaviour of wild type viruses and the recombinant
were studied in microcosms.
Main findings and outcome
Cabbage moth and Pine beauty moth NPVs were infective in 4 of the 14 Lepidoptera
families. Each of four NPV clones had different infectivity levels which
were up to four and a half times greater than those of the wild type.
In the field, baculoviruses can persist in the soil for at least 3 years.
Opilionids are the main agents of local dispersal, they excrete active
viruses for 100 hours after ingestion. Birds are a second major pathway
by which baculoviruses are spread; 40% of individuals and 9 out of 15
bird species studied excreted active virus. Cabbage moth virus was recovered
20 km from the point of introduction. In microcosms containing field crops,
simulated rain also dispersed baculoviruses. Between 1 and 10% of baculoviruses
remained on plants but the soil contained the remaining 90 to 99%. No
baculoviruses were found in percolation water. Air flow, rain splash,
parasites and aphids all dispersed viruses. Despite similar levels of
infectivity of wild type and recombinant viruses, less recombinant baculoviruses
were produced in microcosms. Recombinant baculoviruses were less persistent
than the wild type.
Despite baculoviruses having many alternative lepidopteran hosts, field
infections were not found in alternative hosts, suggesting little risk
of environmental disturbance. In vivo cloning of Pine beauty moth
NPV gave many distinct clones, which allowed selection for recombinant
work. Recombinant baculoviruses were less productive and persistent in
a microcosm than the wild type: Higher NPV doses gave lower progeny NPV
yields in microcosms.
April 1987 - December 1989
Institute of Virology and Environmental Microbiology
Biologische Bundesanstalt für Land- und Forstwirtschaft