Mar 13, 2017

Crop Protection WCRC WCRC1
Abstract                                                                         Back to Table of contents

Insect pathogenic baculoviruses offer a means of pest control that is safe to non-target organisms and environmentally benign.  Control of insect pests on cotton with baculoviruses as an alternative to, or in conjunction with, chemical insecticides has been attempted or recommended in at least 19 countries.   In all cases the targets for control have been lepidopteran species.

Reported results have been variable but in many cases application of baculoviruses has resulted in control similar to that obtained with chemical insecticides.  A study of examples of successful use of viruses to control insect pests of cotton allows conclusions to be drawn on the requirements for effective control.  These include a robust formulation, well placed and accurate timing of application and use against appropriate targets.  Poor control has usually been a result of application against unsuitable targets, formulations of unknown quality or failure to integrate the use of baculoviruses with other control agents in order to control the complex of pests normally encountered on cotton.

Future developments include the use of genetically modified baculoviruses with increased speed of action or wider host range, as well as the possibility of in vitro methods of production.  These will increase the potential market for use in developed countries.  However, their suitability for many developing countries may be questioned where the use of locally-produced, indigenous virus strains for cotton pest control can be economically advantageous and sustainable.

Conclusion and Future Developments

Baculoviruses can undoubtedly provide effective control of cotton pests.  However, their use should be limited to appropriate conditions and cannot, in most instances, totally replace chemical insecticides.   Effective control has been achieved where baculoviruses have been used as part of an IPM system.  For example, in Egypt control of S. littoralis could be achieved with NPV, but early season control of thrips and later season control of P. gossypiella relied on the use of chemical insecticides (for P. gossypiella pheromones could also be employed).  In Thailand, IPM demonstration plots have shown that of the 15 chemical sprays used on cotton, four to six sprays could be replaced with NPV to control H. armigera during the middle of the season (Ketunuti and Prathomrut, 1989).   Room (1979) described a pest management system to control Heliothis spp. in Australia, where similar cotton yields were obtained from a crop treated with four virus sprays and four chemical insecticide sprays, as were obtained from a crop treated with 11 chemical insecticide sprays.

Poor control of large larvae, high density populations of larvae and cryptic pests, along with the time lag from infection to death, currently limit the use of baculoviruses in cotton cropping systems.  The last factor is being addressed through two routes; first the addition of low doses of chemical insecticides which in some cases have been shown to synergize baculoviruses (Biache and Chaufaux, 1986; Renou, 1987), and second, genetic engineering of baculoviruses, where foreign toxin genes are inserted into the viral genome resulting in faster kill and/or cessation of larval feeding on infection (Possee, 1993).  It has also been suggested that genetic engineering techniques could be used to broaden host range (Hawtin and Possee, 1993).  These approaches will broaden the range of applications of virus.  However, both of the approaches may be questioned.  The effect of sub-lethal insecticide doses in a formulation on development of resistance of the insect to the chemical is not fully known.  While genetically modified baculoviruses have yet to be registered and testing requirements at present are considerably more severe than for naturally occurring viruses (Wood and Hughes, 1993).  Moreover, many of these genetically modified baculoviruses will need to be produced in vitro.   Whereas effective large-scale production of baculoviruses can only, at present be achieved in vivo, improvements in in vitro  production technology may result in this becoming economically attractive for developed countries (Granados et al., 1987).  However, the suitability of the technology for developing countries may be questioned where one of the advantages of baculoviruses is the ability to produce them locally at low cost, using indigenous strains.

Finally, we should consider the commercial development of viral insecticides.  Heliothis spp. NPV was  registered for commercial use as Elcar® in the mid 1970's (Ignoffo and Couch, 1981).  However, although generally accepted as a technical success, it could not compete with the newly marketed pyrethroid insecticides and production was discontinued in 1982 (Winstanley and Rovesti, 1993).  However, the increasing problems of chemical insecticides, highlighted in the introduction to this review, as well as an increasingly effective environmental lobby and improved virus formulations are likely to lead to a increasingly favourable climate for the commercialisation and use of viral insecticides.  A number of viruses are now being used commercially and competing in terms of cost with chemical insecticides (Winstanley and Rovesti, 1993; Jones et al., 1993).

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