Nutrition induced direct fitness for workers in a primitively eusocial wasp

Eusocial insects are characterised by a reproductive caste differentiation such that egg-laying is restricted to a small number of queens. The majority of the colony members function as non-reproducing workers and gain indirect fitness by rearing the offspring of the reproductives. In primitively eusocial species, some workers can also get direct fitness by sneaking in some eggs in the presence of the queens, replacing the queens and becoming new queens, or initiating new nests. Here we aimed to understand the factors that permit some workers to gain direct fitness and alter the number of workers doing so, using the primitively eusocial wasp Ropalidia marginata. We transplanted 12 naturally occurring colonies into large laboratory cages where there was adequate space for the workers to leave their natal nests and initiate new colonies. We compared six control colonies that we provided with ad libitum food placed near the nest to six test colonies in which we hand-fed the wasps in addition to the ad libitum food. Wasps in test colonies consumed more food, showed more aggression, replaced their queens, and initiated new nests significantly more often than those in control colonies. When considering all 12 colonies, the rates of queen replacement and nest foundation were significantly positively correlated with food consumption rates. The additional nutrition gained by hand-fed wasps appears to help workers in test colonies to develop their ovaries and lay eggs, implying that they are nutritionally castrated in control colonies.

Effects of juvenile hormone in fertility and fertility-signaling in workers of the common wasp Vespula vulgaris

In the highly eusocial wasp, Vespula vulgaris, queens produce honest signals to alert their subordinate workers of their fertility status, and therefore they are reproductively suppressed and help in the colony. The honesty of the queen signals is likely maintained due to hormonal regulation, which affects fertility and fertility cue expression. Here, we tested if hormonal pleiotropy could support the hypothesis that juvenile hormone controls fertility and fertility signaling in workers. In addition, we aimed to check oocyte size as a proxy of fertility. To do that, we treated V. vulgaris workers with synthetic versions of juvenile hormone (JH) analogue and a JH inhibitor, methoprene and precocene, respectively. We dissected the treated females to check ovary activation and analyzed their chemical profile. Our results showed that juvenile hormone has an influence on the abundance of fertility linked compounds produced by workers, and it also showed to increase oocyte size in workers. Our results corroborate the hypothesis that juvenile hormone controls fertility and fertility signaling in workers, whereby workers are unable to reproduce without alerting other colony members of their fertility. This provides supports the hypothesis that hormonal pleiotropy contributes to keeping the queen fertility signals honest.

Eusocial wasp fauna of Sulawesi Island, the central island of Wallacea (Hymenoptera: Vespidae; Polistinae, Vespinae)

Taxonomy of eusocial wasps (Polistinae and Vespinae) occurring in Sulawesi Island, the central island of Wallacea, is reviewed. Sixteen (12 polistine and four vespine) species are recognized. Polistes (Polistella) stigma, known to be widely distributed in southern Asia and Australasia, is newly recorded for Sulawesi Island. A key to the Sulawesian eusocial wasp species is provided. Their biogeographical characteristics are discussed to show that the Sulawesian eusocial wasp fauna is composed of Oriental elements.

Notes on Brood Morphology and the Development of the Neotropical Eusocial Wasp Mischocyttarus cerberus (Hymenoptera, Vespidae, Polistinae)

Mischocyttarus cerberus stands out among the most investigated species of the eusocial paper wasp, in Brazil. While the adult characteristics were relatively well reported in the earlier studies, very meager information was available regarding their immature stages. This study provides a description of the immature morphology of the general brood of M. cerberus, by studying the number of instars and analyzing the degree of influence exerted by some of the environmental factors on the individuals in the immature phases. This work involves a detailed study of 72 wasp colonies from Rio Claro and Ribeirão Preto. Using the larvae drawn from 41 nests, the number of instars was calculated; besides, the degree to which a few environmental factors could affect the immature brood development was assessed in 31 nests. Eggs showed patterns similar in terms of form and size to that of the species described earlier. The two ventral lobes, characteristic of the Mischocyttarus larvae, were fully developed only in the fifth instar. The measurements of the larval heads in the five instars found concurred with the earlier reports for most of the social wasps. Furthermore, the larval stages took longer to develop, which could be related to the greater susceptibility of the larvae to the prevailing environmental factors. From the results of our study, we concluded that the M. cerberus showed the typical developmental pattern in the immature stages of its genus.

The effect of age on non-reproductive division of labour in the tropical primitively eusocial wasp, Ropalidia cyathiformis

Division of labour among workers (non-reproductive division of labour), a characteristic feature of eusocial insects enables the efficient functioning of their colonies. In many advanced insect societies division of labour is based on age (age polyethism). Primitively eusocial insects however are believed to have a weak age polyethism. Here we investigated the role of age in non-reproductive division of labour in the tropical primitively eusocial wasp, Ropalidia cyathiformis and compared it with that in Ropalidia marginata, a congeneric species that exhibits relatively strong age polyethism. Age had a significant effect on the first performance of the four tasks studied; tasks were initiated in the sequence feed larva, build, bring food and bring building material. We measured task performance as the absolute frequency of tasks performed (FTP) and the probability of performing a task relative to other tasks (PTP) and age as absolute age in days since eclosion as well as relative age compared to nestmates. FTP varied significantly with both absolute and relative age, although absolute age explained more variance. PTP varied significantly with absolute age but not always with relative age. This is contrary to R. marginata, where more variation is explained by relative age than by absolute age. There was no trade-off between intranidal and extranidal tasks in R. cyathiformis unlike in R. marginata where the frequency of intranidal tasks decreased and that of extranidal tasks increased with age. We conclude that age polyethism is weak and less flexible in R. cyathiformis compared to that in R. marginata.