Facultative bacterial endosymbionts are associated with many arthropods and are primarily transmitted vertically from mother to offspring. However, phylogenetic affiliations suggest that horizontal transmission must also occur. Such horizontal transfer can have important biological and agricultural consequences when endosymbionts increase host fitness. So far horizontal transmission is considered rare and has been difficult to document. Here, we use fluorescence in situ hybridization (FISH) and multi locus sequence typing (MLST) to reveal a potentially common pathway of horizontal transmission of endosymbionts via parasitoids of insects. We illustrate that the mouthparts and ovipositors of an aphelinid parasitoid become contaminated with Wolbachia when this wasp feeds on or probes Wolbachia-infected Bemisia tabaci AsiaII7, and non-lethal probing of uninfected B. tabaci AsiaII7 nymphs by parasitoids carrying Wolbachia resulted in newly and stably infected B. tabaci matrilines. After they were exposed to infected whitefly, the parasitoids were able to transmit Wolbachia efficiently for the following 48 h. Whitefly infected with Wolbachia by parasitoids had increased survival and reduced development times. Overall, our study provides evidence for the horizontal transmission of Wolbachia between insect hosts by parasitic wasps, and the enhanced survival and reproductive abilities of insect hosts may adversely affect biological control programs.

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The intensity of sperm competition determines how much reproductive effort should be invested in sperm. One important factor affecting sperm competition in internally fertilizing organisms is the mating frequency of females, since it determines the extent of competition between ejaculates. In simultaneous hermaphrodites, energy spent on sperm has to be traded off against energy expended on ova production. By extending an existing model, we consider how the number of matings affects sperm competition and, thus, sex allocation in internally fertilizing simultaneous hermaphrodites. We then go on to explore the consequences of two common characteristics of hermaphroditic mating systems, namely, sperm digestion and reciprocal insemination. Since sperm digestion reduces the competitive ability of a given ejaculate, it selects for increased sperm investment. As a result, the amount of sperm digested and male allocation can enter a coevolutionary cycle in which both will increase up to the point of equal investment in male and female gametes and in high rates of digestion. Because of this high degree of sperm digestion, fitness through the male function becomes more dependent on the amount of resources invested in sperm than on the number of matings. As a result, sperm digestion reduces Bateman's principle. Hence, hermaphrodites with sperm digestion should be less likely to display traits that increase the number of matings. Once ejaculates are large and costly, animals insisting on reciprocal sperm transfer will be favored since they receive some compensation for their investment. Under reciprocity, an even higher investment in sperm is favored. This is the result of the compensation received in the form of the partner's ejaculate and a nuptial gift effect by increasing a partner's production of eggs.

When organisms are tightly bound in interspecific interactions over long evolutionary times, the diversification of the partners is rarely independent. The symbiotic partner (i.e., the "hostassociated" organism that lives part or its entire life cycle on another organism) is often constrained by the speciation of its hosts. There are numerous examples of phytophagous insects and parasites that specialize and phylogenetically track their host (Ehrlich and Raven 1964; Janz and Nylin 1998; Lopez-Vaamonde et al.

pollinator (Ceratosolen galili) has been reported to be rarer than the pollinator (Ceratosolen arabicus) in drier areas due to lower desiccation tolerance. Both species are closely related and utilise the same oviposition sites on Ficus sycomorus. We used ecological niche modelling to determine whether C. galili covers the range of F. sycomorus and whether it is consistently rarer than C. arabicus. We examined emergence times, critical thermal limits, desiccation and starvation tolerances of the wasps. The suggested rarity of C. galili relates to lower abundance in certain months and at certain localities but a similar number of occurrence records within the distributional range (except in arid regions, e.g. Namibia). In contrast to C. galili, C. arabicus has a wider thermal range, lives longer under hydrating and dehydrating conditions and is a nocturnal flier. The synergistic effect of physiological tolerances and flight time differences exacerbate the less favourable conditions available to C. galili during flight and location of receptive figs. These factors enable C. arabicus to survive for longer than C. galili, meaning that they are more likely to disperse to trees that are flowering further away in space and time.Combining correlative and mechanistic approaches has aided us in understanding the ecological niches of these species. 3Physiology, species abundance patterns and distribution A complex and varied set of factors may determine the range limits of a species, and the abundance structure across its range. Fine-scale changes in the distribution of suitable microclimates may lead to changes in population size and colonization rate and to changes in distribution (Wilson et al. 2009). The physiological tolerances of species may be one driver of has become a model system for investigating numerous evolutionary and ecological questions (Janzen 1979, Wiebes 1979, Wang et al. 2008. In these mutualisms, the tree depends on the wasp for the dispersal of pollen and for seed set, while the wasp depends on the tree for offspring development (Wang et al. 2008).In contrast to externally feeding insects, fig wasp pollinators are expected to occupy most of the geographical ranges of their hosts because of their intimate host associations (Wiebes 1979, Weiblen 2002. A shift in the host's distribution must entail a concomitant shift in the distribution of the pollinator for the mutualism to persist and vice-versa. If the host plant becomes extinct, the wasp will also become extinct unless it is able to shift to a new host plant. A species that has a greater starvation tolerance would be able to search for longer (i.e. able to resist starvation for longer) and would be more likely to find a suitable host (see also Kjellberg et al. 1988).In addition, the wasps may be more susceptible to unfavourable environmental conditions at certain times of the day. For example, a temporal structuring of emergence times may allow nocturnally emerging individuals to survive unfavourable seasons while diurnally emerging individuals suc...