Microparasite manipulation of an insect: the influence of theegtgene on the interaction between a baculovirus and its lepidopteran host

Abstract

Summary 1.Parasites and pathogens manipulate their hosts in a variety of ways that are thought to enhance their fitness. However, it is rare to be able to link such phenotypic changes to specific genes. 2. Here the effect of a single pathogen gene is examined. The ecdysteroid UDPglucosyltransferase ( egt ) gene of insect baculoviruses produces an enzyme that interferes with host moulting. 3. The effect of the egt gene was examined by comparing two baculoviruses that differed only in the expression of this gene. All three fitness traits examinedpathogenicity, infection duration and pathogen productivity -were affected by deletion of the gene. 4. Trichoplusia ni larvae in all five instars died earlier when infected with the egt -minus virus compared with those infected by the wild-type Autographa californica nucleopolyhedrovirus. 5. Unexpectedly, the egt -minus virus was more pathogenic to final instar larvae than the wild-type virus. Virus genotype and dose both influenced insect development. 6. Wild-type infected insects had a significantly higher yield of virus at death, cadaver weight and yield of virus per unit weight than those infected with the egt -minus virus. 7. The size of the virus challenge had a major influence on the outcome of the interaction. The consequences of these data for pathogen fitness are discussed.

The sf32 Unique Gene of Spodoptera frugiperda Multiple Nucleopolyhedrovirus (SfMNPV) Is a Non-Essential Gene That Could Be Involved in Nucleocapsid Organization in Occlusion-Derived Virions

“…The identification of the genetic factors that determine particular insecticidal properties of the virus may facilitate the selection of particular genotypes with desirable traits for use in bioinsecticidal products, or the development of recombinant viruses, with improved characteristics compared to the wild type [10]. The deletion of certain genes [11] or the insertion of insect-specific toxin genes [12] has been shown to increase the speed of kill of these viruses.…”

Stability of a Spodoptera frugiperda Nucleopolyhedrovirus Deletion Recombinant during Serial Passage in Insects

“…Genes have been inserted into, and removed from, NPV genomes to improve the insecticidal properties of these viruses (9,26,38), and field testing of the efficacy of recombinant virus insecticides has been undertaken (7,39,40). The findings of the present study represent a clear example of why environmental risk assessment procedures should examine the stability of recombinant baculoviruses during successive passages in insects, with the aim of identifying regions of instability and likely recombination with naturally occurring latent or persistent virus infections in the target pest insect populations.…”

Insect virus transmission: different routes to persistence

“…The egt gene affects larval-larval and larval-pupal moulting in Lepidoptera, which prolongs the larval period, often resulting in increased virus yield which is clearly likely to be beneficial for horizontal transmission of the virus [28,29]. Data from the AcMNPV-S. exigua interaction indicate that the climbing behaviour of infected larvae depends on whether they undergo a moult postinfection; information which might give further insight into the mechanism behind these changes [27].…”