Context-Dependent Behavior, Reproduction and Brain Structure in Newly-Established Colonies of the Primitively Eusocial Wasp, Mischocyttarus mexicanus

Reproductive division of labor is the most distinctive characteristic of the social Hymenoptera; some individuals reproduce and others forego their own reproduction to raise non-descendant offspring. In species where females are reproductively totipotent and lack morphologically distinct castes, there is potential for reproductive conflict because more than one female in a colony may attempt direct reproduction. I focused my dissertation research on a subtropical population of the primitively eusocial paper wasp, Mischocyttarus mexicanus, to investigate the initiation, establishment, and development of the colony before the emergence of adult offspring. Female M. mexicanus exhibit variation in behavior and task performance, and switch between reproductive and non-reproductive roles. These changes in behavior and reproduction may be influenced by social context. In three studies, I investigated the role of social context on reproduction, behavior, and brain structure. In the first study, I tested the role of body size, reproductive potential, and immediate egg-laying potential on the reproductive tactic employed by females. I found that large females either became solitary foundresses or became part of a group-initiated colony. In contrast, small females left their natal colony and pursued joining other colonies. This joiner tactic is unique to this population and has not been observed in temperate zone populations. I also found that subordinate females had the potential to lay eggs if given the opportunity. This suggests an incentive to remain in a colony for future opportunities of direct reproduction. In the second study, I investigated the effect of three variables on non-nestmate acceptance: non-nestmate age, stage of colony development, and non-nestmate aggressive behavior. I demonstrated that non-nestmate acceptance was context-dependent. Both non-nestmate age and stage of colony development had an effect on the proportion of accepted non-nestmates. Although, non-nestmate aggressive behavior did not affect non-nestmate acceptance, it did trigger an aggressive response from colony nestmates. In the third study, I assessed the relationship of Mushroom Bodies (MB) volume, the brain neuropils associated with learning and memory, to environmental conditions and social interactions. I compared MB volume of newly-established colonies initiated by solitary foundresses to groups of foundresses. In addition, I performed laboratory experiments to differentiate between the effect of environmental conditions and social interactions. I found a positive relationship between MB volume and environmental conditions including light intensity and foraging experience. In contrast to previous studies, I found no association between MB volume and social interactions. Ovary development was positively correlated with MB development. This result suggests that although reproductive dominance is established in newly-initiated colonies, social dominance may not yet be established. In summary, my studies found an effect of social context on behavior, adoption of reproductive tactics and brain structure in colonies of M. mexicanus during the offspring pre-emergence phase.</p

Parasitism and predation of the planthopper Tagosodes orizicolus (Homoptera: Delphacidae) by a dryinid parasitoid in Costa Rica

We analyzed the effect of predation and parasitism by the native dryinid Haplogonatopus hernandezae as a natural enemy of the rice pest Tagosodes orizicolus under controlled conditions in an insectary in Costa Rica. We found no change in the proportion of T. orizicolus nymphs that were fed upon, parasitized, and that showed no apparent damage throughout the adult stage in H. hernandezae, which favors a stable control of the pest. The percentage of T. orizicolus nymphs that were parasitized (37 %) and preyed upon (36.5 %) was similar, eliminating 73,5 % of the total nymphs causing damage to the rice plants (N = 1 099). Of the total 324 parasitized nymphs, female nymphs were more parasitized than male nymphs (95 % and 5 % respectively) and dryinids developed more successfully in female host nymphs. These tendencies did not change with dryinid age. Survival of dryinids was higher in female T. orizicolus, both for larvae that emerged from the host and pupated, and for pupae that moulted to adults. In cages where the nymphs had no contact with dryinids we found a higher amount of males than females (57.44 ± 28.5 vs 45.22 ± 25.85). In contrast, when the nymphs were in contact with dryinids, the sex ratio was two females to one male reaching adulthood since the dryinids fed more on male nymphs (N = 692). Our results indicate that female dryinids prefer to oviposit in female T. orizicolus nymphs and prey on males. Reproduction by parthenogenesis, acceleration of the development in an insectary with controlled conditions and eficiency of H. hernandezae as a parasitoid and predator indicate that this dryinid is an effective biological control agent of T. orizicolus. Rev. Biol. Trop. 57 (Suppl. 1): 203-211. Epub 2009 November 30

Supplementary material 2 from: Tribull CM (2015) Phylogenetic relationships among the subfamilies of Dryinidae (Hymenoptera, Chrysidoidea) as reconstructed by molecular sequencing. Journal of Hymenoptera Research 45: 15-29. https://doi.org/10.3897/JHR.45.5010

Previously, the only published phylogenetic analysis of Dryinidae was a morphological analysis of just 32 characters. Herein, I present the first analysis of molecular sequence data examining the relationships among several of the major subfamilies of Dryinidae. A total of 77 specimens of Dryinidae from seven subfamilies, two specimens of Chrysis (Chrysididae), one specimen of Cleptes (Chrysididae), and one specimen of Sclerogibba (Sclerogibbidae) were examined utilizing molecular sequence data from nuclear 18S and 28S genes and mitochondrial Cytochrome Oxidase Subunit I (COI) and Cytochrome b (Cytb) genes. Dryininae were rendered nonmonophyletic due to the placement of Thaumatodryinus, which was sister to the remainder of Dryininae and Gonatopodinae. To establish monophyly of Dryininae, Thaumatodryininae were resurrected for Thaumatodryinus