Book Review: Parasites in Social Insects by P. Schmid-Hempel

Abstract

Princeton University Press, 1998. $85.00 £60.00 (hbk) (xi+409 pages) ISBN 0 691 05923 3In his meticulously researched review, Schmid-Hempel presents a fascinating insight into the world of social insects and their battle with a broad spectrum of parasitic organisms. It is a Herculean effort at summarizing the literature (as mentioned on the cover) and is an ideal reference source on parasites of social insects (especially Appendix 2, which lists all reported associations between parasites and social insects). It is an extremely good book that will be of value to anyone interested in parasite–host interactions.The groups of parasitic organisms affecting social insects are described and the author discusses the interactions against an evolutionary, ecological and behavioural background. From fungus-infected larvae (still used in Chinese medicine to cure opium addiction) to trematode cercaria that attach themselves to the ‘brains’ of ants and induce behavioural changes enhancing their transmissibility, the reader can marvel at the wealth of illustrated biological phenomena.One cannot avoid comparing some of these phenomena to other socially organized communities, such as humans, especially when such terms as ‘suicide’, ‘STDs’, ‘slavery’ and ‘seduction’ are mentioned. Parasites are normally confronted with the problem of how to gain access to their host, and the strategies and tactics deployed to try and achieve this fill an entire chapter. The example of inquilinism, an advanced case of social parasitism whereby the parasite forces the host colony to look after its progeny and often brutally dominates or even kills the host queen, contrasts sharply with the subtle entry points for viruses and bacteria and displays the variations observed in entering populations of social insects.Some of the classical works in this field [eg. Bailey, L. and Ball, B.V. (1991) Honey Bee Pathology. (2nd edn) Academic Press; Holldobler, B. and Wilson, E.O. (1990) The Ants. Springer-Verlag] have clearly shaped the theoretical framework that constitutes the heart of the discussion in which host–parasite dynamics are considered. The author argues the need for considering colonies rather than individuals when studying these dynamics. With this in mind, models describing the dynamics of microparasitic infections in social insects (mainly honey bees) are presented and show that parasite dynamics in a population of social insects is largely driven by horizontal transmission between colonies.Seasonal dynamics of infections in discrete generations are described and modified to account for the dynamics of colonies and infection within a season, assuming equilibrium of the epidemic at the end of the season and constant infection rate over the years. With these and other assumptions likely to be violated, a rather complex dynamic would hold, and models might have to rely on numerical simulations, which the author makes some reference to.A particularly commendable aspect of the book is that the author identifies many critical gaps in the study of host–parasite interactions and dynamics where more research is needed to clarify patterns, expectations and estimates of necessary parameters and rates, to enable more elaborate description of the dynamics in social insects ‘exposed’ to parasitic infections. The remainder of the book considers the co-evolution between host-resistance and parasite virulence and how parasitism may have influenced the evolution of different levels of sociality. Again, interesting ecological and evolutionary concepts abound and invite some re-thinking of traditional concepts in parasite–host interactions.Unfortunately, information on the economics of parasitic infections in beneficial social insects is lacking, and other aspects, such as research exploring the potential of using parasites to our advantage (eg. bioprospecting for antibiotics), could have broadened the scope of the book, but a Glossary and Subject, Host, Parasite and Author index are convenient additions.Being the first of its nature, Parasites in Social Insects introduces the reader to the intricacies of the most successful lifestyles in the living world–sociality and parasitism. It is certainly a ‘must’ for those interested in the evolution and ecology of parasite–host interactions.