Baculoviruses provide alternatives to chemicals for controlling insect pests and can be applied by spraying. Baculoviruses have a limited host range, but work relatively slowly. They are dissolved in the midgut of insect larvae to release infectious virions which enter gut epithelial cells and begin to replicate. Replication in other organs causes extensive tissue damage and eventually death. This process can take 4-5 days, but in the field may last for more than a week, allowing the larvae to feed for longer and thereby damaging the host plant. Baculovirus expression vectors expressing foreign genes, such as those for insect-specific toxins, hormones or enzymes, might alleviate this problem. We have now constructed a recombinant baculovirus derived from Autographa californica nuclear polyhedrosis virus containing an insect-specific neurotoxin from the venom of the North African (Algerian) scorpion, Androctonus australis Hector. The neurotoxin acts by causing specific modifications to the Na+ conductance of neurons, producing a presynaptic excitatory effect leading to paralysis and death; it has no effect in mice. Expression of the neurotoxin by the virus causes a reduction in the time required to kill the host insect.

IMPROVEMENT of biological pesticides through genetic modification has enormous potential and the insect baculoviruses are particularly amenable to this approach1,2. A key aim of genetic engineering is to increase their speed of kill, primarily by the incorporation of genes which encode arthropod or bacterially derived insect-selective toxins3–11, insect hormones12,13 or enzymes14,15. We report here the first, to our knowledge, field trial of a genetically improved nuclear polyhedrosis virus of the alfalfa looper, Autogmpha californica (AcNPV) that expresses an insectselective toxin gene (AaHIT) derived from the venom of the scorpion Androclonus australisl6–18. Previous laboratory assays with the cabbage looper, Trichoplusia ni, demonstrated a 25% reduction in time to death compared to the wild-type virus, but unaltered pathogenicity6 and host range19. In the field, the modified baculovirus killed faster, resulting in reduced crop damage and it appeared to reduce the secondary cycle of infection compared to the wild-type v

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The host range of a multiply enveloped nuclear polyhedrosis virus (NPV) (Baculoviridae) isolated from the cabbage moth, Mamestra brassicae (Lepidoptera: Noctuidae), was determined by challenging a wide range of insect species with high (106 polyhedral inclusion bodies) and low (103 polyhedral inclusion bodies) doses of the virus. The identity of the progeny virus was confirmed by dot blotting. Analysis of 50% lethal dose was carried out on selected species, and the progeny virus was identified by using restriction enzyme analysis and Southern blotting. Other than the Lepidoptera, none of the species tested was susceptible to M. brassicae NPV. Within the Lepidoptera, M. brassicae NPV was infective to members of four families (Noctuidae, Geometridae, Yponomeutidae, and Nymphalidae). Of 66 lepidopterous species tested, M. brassicae NPV was cross-infective to 32 of them; however, 91% of the susceptible species were in the Noctuidae. The relevance of host range data in risk assessment studies is discussed.