Contents - Faperta

262 Biotechnological Approaches for Pest Management and Ecological Sustainability
Baculoviruses Expressing Insect Diuretic Hormones
The genes for juvenile hormone (JHE) esterase and diuretic hormone have also been
expressed in baculoviruses (Maeda, 1989; Hammock et al., 1990; Bonning and Hammock,
1996). Proteases that perforate the insect cell membranes and hasten systemic spread of
infection have also been expressed in NPVs (Harrison and Bonning, 2001). Baculoviruses
expressing insect diuretic hormone that affect insect morphogenesis have also been developed
(Maeda, 1989). Hammock et al. (1990) developed a recombinant NPV expressing
juvenile hormone esterase. Excessive levels of JHE reduced feeding and delayed the development
of insect larvae. Baculoviruses expressing JHE with point mutations designed to
increase stability have been found to be more effective than wild-type JHE. A more
dramatic effect has been obtained by selecting the viral gene egt (which codes for UDP
glycosyl transferase, needed for production of the insect molting hormone ecdysterone)
(O’Reilly and Miller, 1991).
Expression of Entomopoxvirus in Bacteria
A virus-enhancing factor (EF) from Mythimna separata (Walk.), entomopoxvirus, has been
successfully expressed using an Escherichia coli Escherich expression system, pGEX-2T
(Hukuhara, Hayakawa, and Wijonarko, 2001). The EF enhanced the fusion between the
PsunMNPV and the cultured insect cell line, SIE-MSH-805-H. The resulting lysates
of transformed E. coli cells enhanced PsunMNPV infection when treated with either
trypsin or thrombin. The EF enhanced Pseudaletia unipuncta (Walk.) (M. separata) multinucleopolyhedrovirus
(PsunMNPV) infection in larvae of the armyworm, P. unipuncta.
Effect of Insecticides on Biological Activity of Baculoviruses Expressing Neurotoxins
The effect of deltamethrin has been studied on the larvae of L. sericata, H. virescens, and
T. ni infected with A. californica NPV expressing mu-Aga-IV from A. aperta and AsII from
A. sulcata (Popham et al., 1998). Co-application of deltamethrin conferred no advantage
in fi eld applications of recombinant baculovirus. Application of pyrethroids probably will
have no adverse effect on recombinant virus effi cacy unless it deters larval feeding and
virus acquisition.
Role of Baculoviruses in Pest Management
To prolong the insecticidal activity of the recombinant baculoviruses expressing neurotoxins,
it is important to ensure continued production of the neurotoxin through appropriate
regulatory elements or by increasing the copy number of the target gene. It is still too early
to assess how such engineered viruses will fi t into integrated pest management (IPM)
programs. Insect pathogenic viruses usually attack a narrow taxonomic range of insects
and must be ingested to have an effect. Even if the range of insects that a virus can affect
is broadened by genetic engineering, the recombinant viruses may affect the predatory
and parasitic insects if the virus is infective to them. Although most researchers would
like to produce an engineered organism that cannot survive on its own in the wild, there
is some concern that new traits in engineered viruses may be passed on to other more
competent viruses or the “disarmed” engineered viruses might mutate to a more independent
form. How much environmental damage such a virus might cause has to be determined.
The most important challenge to biotechnology with regard to insect viruses is the
development of methods for mass production that do not require live insect hosts. If right