Wolbachia increases the susceptibility of a parasitoid wasp to hyperparasitism.

The success of maternally transmitted endosymbiotic bacteria, such as Wolbachia, is directly linked to their host reproduction but in direct conflict with other parasites that kill the host before it reaches reproductive maturity. Therefore, symbionts that have evolved strategies to increase their host's ability to evade lethal parasites may have high penetrance, while detrimental symbionts would be selected against, leading to lower penetrance or extinction from the host population. In a natural population of the parasitoid wasp Hyposoter horticola in the Åland Islands (Finland), the Wolbachia strain wHho persists at an intermediate prevalence (∼50%). Additionally, there is a negative correlation between the prevalence of Wolbachia and a hyperparasitoid wasp, Mesochorus cf. stigmaticus, in the landscape. Using a manipulative field experiment, we addressed the persistence of Wolbachia at this intermediate level, and tested whether the observed negative correlation could be due to Wolbachia inducing either susceptibility or resistance to parasitism. We show that infection with Wolbachia does not influence the ability of the wasp to parasitize its butterfly host, Melitaea cinxia, but that hyperparasitism of the wasp increases in the presence of wHho. Consequently, the symbiont is detrimental, and in order to persist in the host population, must also have a positive effect on fitness that outweighs the costly burden of susceptibility to widespread parasitism.

Standardized spider (Arachnida, Araneae) inventory of Hankoniemi, Finland.

BACKGROUND: During a field course on spider taxonomy and ecology at the University of Helsinki, the authors had the opportunity to sample four plots with a dual objective of both teaching on field methods, spider identification and behaviour and uncovering the spider diversity patterns found in the southern coastal forests of Hankoniemi, Finland. As an ultimate goal, this field course intended to contribute to a global project that intends to uncover spider diversity patterns worldwide. With that purpose, a set of standardised methods and procedures was followed that allow the comparability of obtained data with numerous other projects being conducted across all continents. NEW INFORMATION: A total of 104 species and 1997 adults was collected. Of these, 41 species (39%) were Linyphiidae and 13 (12%) Theridiidae. All other families had 6 or less species represented. Linyphiidae were also dominant in terms of adult individuals captured, with 1015 (51%), followed by 428 (21%) Lycosidae, 158 (8%) Tetragnathidae and 145 (7%) Theridiidae. All other families had less than 100 individuals. The most abundant species were Neriene peltata, Alopecosa taeniata, Piratula hygrophila and Dismodicus elevatus, all with more than 100 individuals. All sites had between 56 and 62 species and between 445 and 569 individuals.