Nucleopolyhedrovirus interactions with their insect hosts.

It is clear from this brief review that our understanding of the molecular cross-talk between insects and their baculovirus pathogens is still very limited. Studies in cell culture have taught us a great deal about the basic baculovirus molecular machinery and how it is regulated, and in many cases this information has been predictive of what occurs in infected insects. Frequently, however, studies in cell culture do not adequately predict the infection process in insect hosts, as demonstrated by viral mutants (some of which were discussed in this review) that behave identically to wild-type virus in cell culture but differ markedly in larvae. More baculovirus studies, therefore, need to be conducted in vivo if we are to improve our understanding of the complex interactions between baculoviruses and their hosts. Conducting baculovirus studies in insects (or at least in primary cell culture) also offers the opportunity to address questions that reach beyond the baculovirus community in significance. For example, almost all of our knowledge of viral fusion mechanisms comes from infection of cells in culture where the pH is neutral or acidic and the temperature is constant at 27 degrees or 37 degrees C. An answer to the question of how the ODV envelope fuses with the microvillar membrane of columnar epithelial cells in the highly alkaline midgut environment at low temperatures will not only be important for an improved understanding of baculovirus infection in the natural world, but will also constitute a new chapter on viral entry mechanisms. Similarly, the answer to the question of how baculovirus nucleocapsids move basally within microvilli promises to involve factors and/or a mechanism not yet described by cell biologists, and so will constitute a valuable contribution to both baculovirology and cell biology. There are many more such examples of biological mechanisms that can be uniquely explored within the context of baculoviruses and their insect hosts, some of which have been highlighted in this review. As more and more young investigators realize the importance of combining a knowledge of virology, molecular technology, and insect biology, however, many of the outstanding mysteries will be solved.