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Insect social parasites, like other parasites, may benefit from inhibiting their host from reproducing (complete or partial parasitic castration) because they can then exploit more of the host's resources for their own reproduction. In particular, social parasites that kill or expel the host queen need to prevent host workers from reproducing; this is a common worker response to the absence of their queen. Indeed, host workers would benefit from detecting the presence of the parasite and investing in direct and indirect fitness. Studying whether and how social parasites control host worker reproduction can provide information about the degree of integration of the parasite in the host colony and help identify factors regulating workers' reproductive decisions in social insects. We investigated whether the paper wasp social parasite, Polistes sulcifer, suppresses Polistes dominula (host) worker reproduction as efficiently as the dominant host female does in queen-right colonies by comparing worker reproductive efforts in parasitized and non-parasitized (control) colonies. Our results show that 6 weeks after usurpation of their colony by the social parasite, parasitized workers (1) had more developed ovaries than control workers and (2) laid more eggs as soon as the opportunity arose. This reproductive readiness of parasitized workers was not apparent 2 weeks after colony usurpation. This suggests that P. dominula workers have evolved means to react to social parasitism, as occurs in some ants, and that the parasite has only limited control over host reproduction. [ABSTRACT FROM AUTHOR]

The chemical integration strategies of facultative social parasites of social insects have not received the scientific attention they deserve, even though there is considerable research being done on the strategies of obligate social parasites. We simulated intraspecific nest usurpations in the social paper wasp, Polistes biglumis, by dividing each nest into two parts and putting one half in the care of the original foundress and the other half in the care of a usurper. After 8days, we removed and killed foundresses and usurpers, and later tested the responses of naïve, sister-offspring to them. In each half-colony, the offspring were more tolerant to the female that was last on the nest, regardless of whether she was the foundress or a usurper. This suggested that usurpers had the chemical means to be tolerated by the host offspring. Comparisons between the epicuticular hydrocarbon profiles of foundresses and usurpers showed that usurpers were neither chemically insignificant nor transparent, nor were they mimetic, as obligate parasites often are. Instead, usurpers had chemical profiles richer in methyl-branched hydrocarbons than those of the foundresses. Analyses of the hydrocarbon profiles of nest paper revealed that usurpers supplemented host nests with their own hydrocarbons, a sort of nest marking. As a result, the chemical profiles of the host nests became qualitatively more similar to those of the usurpers. These chemical strategies illustrate that branched hydrocarbons play a role as semiochemicals and that facultative parasites may not all be on the main pathway to obligate parasitism. [ABSTRACT FROM AUTHOR]

Insect social life is governed by chemicals. A great number of studies have demonstrated that the blend of hydrocarbons present on the cuticle (CHCs) plays a pivotal role in intra- and inter-specific communication. It is not surprising, therefore, that social parasites, specialized in exploiting the costly parental care provided by host workers, exploit the host chemical communication system too. Throughout their life cycle, social parasites intercept and break this CHC-based code. Recently, however, several polar compounds (mainly peptides) have been found in addition to CHCs both on the cuticle and on the comb surface of social insects, and their semiochemical role has been demonstrated in some circumstances. In the present study, we used the paper wasp social parasite-host system Polistes sulcifer (Zimmerman)-Polistes dominulus (Christ) to evaluate the relative importance of the CHC5 and polar compounds in two different steps of the host exploitation process: host nest detection by the pre-usurping parasite and parasite chemical integration into the host colony. After separating the polar and apolar fractions of the host nest as well as those of pre- and post-usurpation parasites, we carried out laboratory assays based on the binary choice model. Our results show that nest polar compounds neither are used by the parasite to detect the host's nest nor play a role in parasite chemical integration into the host colony. In contrast, we demonstrate that CHCs are fundamental in both steps, thus confirming their primary role in social insect life and consequently in social parasite-host interactions. [ABSTRACT FROM AUTHOR]

Coevolutionary theories applied in the study of host–parasite systems indicate that lineages exhibit progressive trends in response to reciprocal selective pressures. Avian brood parasites have generated intense interest as models for coevolutionary processes. Similar to avian cuckoos, Polistes wasp social parasites usurp a nest and exploit the parental care of a congeneric species to rear their own brood. In the present study, we show a coevolutionary arms race in the daily activity pattern in a Polistes host–parasite pair. We measured the daily activity rate, in constant laboratory conditions, of both host and parasite females during the period in which nest usurpations occur. The parasites showed a hyperkinesis in the middle of the day. As the field observations suggested, this mid-day activity is used to perform host nest usurpation attempts. Timing the usurpations allows the parasite to maximize its usurpation attempts during daytime when the host defence is lower. A field comparison of host presence on the nest in two populations with different parasitism rates showed that populations under strong parasitic pressure exhibit timing counteradaptations to optimize nest defence. This study provides the first example of a mutual coadaptation in timing activity in a parasite–host system. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 399–405. [ABSTRACT FROM AUTHOR]

In animals, restlessness is a strategy to fulfil a goal within a narrow seasonal window when ecological and physiological constraints require the performance of certain fundamental events. Although restlessness can be expected in parasitic species that have their biological cycle similar to that of the host, no ‘urge to parasitize’ has thus far been demonstrated in any host-parasite pair. The paper wasp, Polistes sulcifer, is a social parasite that has lost the nest-building ability and marked by the absence of the worker caste; it depends on a congeneric host species to reproduce. Host colony usurpation is successful when it occurs in a well-defined seasonal window. The short time available for host-nest usurpation might lead to parasite restlessness that overlaps this period. Under controlled laboratory conditions, we demonstrated that the parasite females exhibit ‘usurpation restlessness’ during the period in which field usurpations occur. Additional experiments showed that both this period and laboratory temperature influence the parasite’s ‘urge to usurp’. [ABSTRACT FROM AUTHOR]