Banana wasps

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The unique and meticulously-arranged worker formation of Apoica wasps has led to many common names: “Marimbondo-chapéu” in Brazil meaning wasp hat, “avispa girasol” in Venezuela meaning sunflower wasp, “manare” referencing a traditional basket, “avispa de leche” in Central America referencing the pale abdomen coloration, and in English the scarcely used parasol wasp. The first time I heard of Apoica, I thought the abdomens gave them a banana-like appearance, so I’ll add banana wasps as an additional common name to the internet. Before this encounter I had only seen individuals attracted to UV light traps in Costa Rica and Brazil, and for years I’ve wanted to locate a nest. Apoica is an unusual wasp because of its nocturnal habits, earning yet another common name, “media luna.” By day the wasps cover open combs in a symmetrical arrangement, a form of passive defense to deter any potential predators and protect the queen(s) and larvae that reside in the interior of the nest. At dusk Apoica exhibits explosive departure from the nest of dozens to hundreds of individuals. Departures are immediately followed by large numbers of wasps returning to the nest, obscuring the structure again. At peak activity the explosive departures and arrivals can occur at an astonishing rate of 60-200 times per hour, and studies suggest that the frequency is influenced by lunar phases with higher activity rates under a full moon.

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In comparison to other wasps in the Epiponini tribe, the ocelli of Apoica are of a substantially greater proportion, the compound eyes are larger and rhabdoms (channel-like structure in each ommatidium) wider. These adaptations are consistent with other nocturnally foraging hymenoptera such as sweat bees in the genus Megalopta — which I encountered frequently in Brazil — allowing for increased optical sensitivity in low-light conditions. However, one notable difference is that the facet number in Apoica is increased as opposed to simply enlarging the facets in nocturnal bees. Since nocturnal foraging in social hymenoptera is such a rarity, the question becomes how did this behavior evolve? In the case of Apoica it’s possible that adopting the defensive posture during the day confers such an effective defensive measure that it became advantageous for the wasps to stick around the nest for longer periods of time, eventually causing a shift in foraging patterns into crepuscular, and dimmer conditions, leading to adaptations better suited to low-light and even nocturnal foraging.

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Swarm founding in Apoica is distinct from other epiponine wasps in that the wasps do not mark substrate where gathering will occur by secreting a trail pheromone from the gaster. Instead, wasps cluster by adopting a calling posture — holding the gaster above the wings to expose sternal gland openings while remaining motionless. This suggests they may be releasing an airborne pheromone. Wasps will then groom by rubbing their legs on the gaster and wings, possibly spreading the pheromone across the body to enhance the signal strength and promote cohesion during swarm emigration. At dusk the cluster begins to diffuse slightly and emigration occurs in a similar manner to the explosive departures prior to foraging. When selecting a new site wasps will land and run across the surface flexing their abdomens upward. Once the site is of interest to most wasps, landed individuals will cease moving while still performing the calling display as wasps continue to collect on the new site.

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Apoica exhibits fixed reproduction with little morphological differentiation between females and workers, similar in size but with smaller heads and larger abdomens. Caste determination is pre-imaginal (occurring during larval development / before the imago or adult stage), and non-reproductive workers are unable to develop ovaries. Apoica nests can have a single or multiple queens, with larger colonies typically having more queens. Since workers also nourish the caste pre-determined larvae this creates an interesting scenario: according to inclusive fitness theory might workers favor larvae (or select queen-destined larvae) produced by their own mother queen? Workers have also been observed to police queens and even drive them out of the colony.

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Supposedly when a single Apoica wasp releases a drop of venom a pheromone is released, stimulating the the rest of the nest to attack the perceived threat. I’m not sure that Apoica performs any fancy defensive display such as drumming in the “guitarreros” (warrior wasps in the genus Synoeca, common name translated as “guitar players”) or even actively tracks you with a menacing look as in Polistes paper wasps. I’ve heard that in contrast to many other polistines Apoica doesn’t allow for a single touch without defending, so I refrained from touching the bananas.

Photographed in situ [1]


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