Male wasps tag females, create harems
In a lengthy study conducted at SFU, an unusual wasp courting method has been unearthed. Particular parasitoid male wasps of the species Ooencyrtus kuvana — no longer in size than the thickness of a nickel at two millimetres long — build a harem of virgin females through a pheromone-antenna tagging system, which better propagate the male wasp’s genes into the next generation of his offspring. “I assumed that [this tagging] was normal behaviour, or that I would see it in other insects and arthropods, but I haven’t seen anything like this in any other species,” said graduate student Kelly Ablard, head of the research team looking at O. kuvanae.
This past December, Ablard defended her PhD thesis at SFU, where she has analyzed O. kuvanae for the last six-and-a half years as a component of her degree. This particular discovery, however, was not an intentional one. It took over three years to run appropriate and conclusive tests. “My thesis was met with a lot of resistance,” said Ablard, “people were quite skeptical about it.” Her current findings have been published in the journal Behavioural Processes, New Scientist, and Canadian Geographic.
The study examined the harem gathering and guarding technique of the male wasp in both competitive and lax environments. By tapping his left antenna to hers, a male wasp tags an unmated female with an individual-specific, signature pheromone that marks her as taken and allows him to relocate her for later mating. After a female has been tagged, she will only reproduce with the wasp that tagged her: her mate. “The males recognize their own individual pheromone, and the females that they tag recognize only the male that marked them,” noted Ablard. “That in itself is amazing. It’s almost like giving your loved one an engagement ring.”
In non-competitive situations, the harem-gathering technique was not observed in Ablard’s wasps. Instead, male wasps mated with a female immediately upon finding her, referred to as the mate-at-once strategy. Ablard discovered that choice of tactic depends on rivalry posed by other male wasps, the distribution of females around him, and the health of the wasp in question. Wasps that employed harem gathering and guarding techniques tended to be faster than their mate-at-once counterparts and, as a result, are likely healthier.
By tagging virgin O. kuvanae females as permanently taken,harem gathering and guarding males can later revisit multiple tagged females, versus the less often-mated females of a mateat- once male, and mate withthem at his leisure without worries of competition from other wasps. This allows the owner of a harem to pass his genes onto the next generation in a larger volume. “Mate-at-once males will end up passing on their genes, maybe not as much as a harem gatherer, but they can still coexist with this type of male,” said Ablard. Evolutionarily, harem gathering and guarding is largely beneficial: mate-at-once males lose out on the mating opportunities.
A single mating takes one and a half minutes on average, and in a larger group where males are vying to mate with as many females as possible, “Time is critical,” said Ablard.
