Insect Courtship and Reproductive Biology

– Daniel Heald

15 February 2021

Falling on the day after Valentine’s Day, it was apt that KRMB’s first meeting of the year should have a presentation on Insect Courtship and Reproductive Biology delivered by Daniel Heald. Daniel’s PowerPoint presentation outlined the intricacies of both courtship and reproduction in the world of insects. He commenced by explaining how Springtail females judge whether a male is suitable by engaging in a bout of head butting with the male to test his strength. For Velvet Worms (Onychophora), while mating has been observed in only a very few species, it is clear that modes of copulation are also diverse. Some species show dermal-haemocoelic (body cavity) insemination, in which sperm deposited in proteinaceous packages (spermatophores) on the skin of females, make their way into the haemocoel through a lesion in the body wall across the haemolymph to the ovary. Other species mate in a more common fashion, with delivery of spermatophores via direct contact between male and female genitalia. Copulation is truly bizarre in some Australian species in which spermatophores are transferred to the female by species-specific, ornate structures on the heads of males. The sole published study to date of genetic paternity indicates complex patterns of fatherhood among embryos within and between the two uteri in a female. Given complex female reproductive anatomy, such as long-term sperm-stores (spermathecae) and mysterious accessory pouches and ciliated funnels associated with them, there are major questions about female control of paternity and sperm competition.

There are many ways in which males attempt to attract mates. For example, a tiny European species of aquatic freshwater insect, Micronecta scholtzi a very small water boatman just 2 mm long, rubs its penis against its abdomen (a process known as stridulation, which serves to attract a mate), the chirping noise created can be up to 99.2 decibels. Other insects present Nuptial Gifts to prospective mates. For example, Dance Flies, also called Balloon Flies or Dagger Flies, are predatory Diptera that are members of the family Empididae. Empididae is characterized by their long, pointy mouth parts and their extravagant mating rituals. If a fly can be charming, the Dance Fly is certainly the one that is most likely to be. During the breeding season, swarms of male Dance Flies will gather together and perform for nearby females while carrying delicate, especially crafted silk balloons. These balloons are called nuptial gifts and a successful male will pass his balloon to his partner during mating and they will often tumble to the ground together. When it comes to romance, Rhamphomyia longicauda, often known as the Long-tailed Dance Fly, switches things up. Most often in the animal world, it’s the females who do the choosing and the males who do the wooing, but those roles are reversed for Dance Flies. Females don’t hunt, so they rely completely on nuptial gifts provided by males for nutrition. The females fly in groups at dusk and dawn waiting for males to bring food to them. To make themselves appear more desirable, females fill their abdomens with air to advertise their eggs as being more mature than they may truly be, a characteristic that males seek out. Mating takes place in flight, and males bear the weight of both the nuptial gift and the female while she feeds upon it. So, just how large can a female get without becoming too heavy to hold onto in flight? To test this question, researchers studied a wild population to see whether the wing loading of males (i.e., wing area relative to body mass) was related to the mass of the female Dance Flies they ultimately mated with. Contrary to their hypothesis that males with higher wing loading would select smaller females, the researchers found the opposite. This indicates that male Long-tailed Dance Flies don’t experience the same load-lifting constraints that other Dance Flies do. When it comes to Long-tailed Dance Flies finding a date, being bigger is better.

A new study says the male water strider (Gerridae) creates tiny ripples in the water that actually lure predatory fish. The male will keep tapping his legs against the water’s surface until the female agrees to mate. In strider copulation, the male mounts the floating female from above, so the female is more at risk from predators since she’s on the water’s surface. This menacing pickup tactic, the study says, likely started after females evolved a “genital shield.” This insect chastity belt means that mating happens only with female consent, but the male’s high-stakes game of chicken doesn’t give the female much choice. The more quickly she gives in, the less likely she’ll be fish food. When all else fails, insects may try an aphrodisiac to make a partner willing to copulate. Male Queen Butterflies dust prospective mates with an aphrodisiac produced by “hairpencils,” brush-like appendages on the tip of the abdomen. If his magic dust works, she will fly to a nearby plant. He dusts her once more to be sure she’s ready, and if she is, they consummate the marriage. On the other hand, insects sometimes employ anti-aphrodisiacs to turn away suitors. Certain ground beetle females produce methacrylic acid, a potent anti-aphrodisiac that not only repels males, which can knock them out for several hours. Male Mealworm Beetles apply anti-aphrodisiac pheromones to their female partners after mating, to make them less attractive to other males.

Daniel then went on to say that male Soapberry Bugs heavily outnumber females, so competition among males to find a mate is fierce. Males will take extreme measures to ensure their seed is passed on to the next generation and will stay connected to their female partners for up to 11 days as a way of guarding their mate from copulating with another male. Some males will even stay connected with the female until she is ready to lay her eggs. Being clingy pays off for these guys. In Honeybees, the young queen bee leads drones on a high-speed chase; only the fastest get a chance to mate and die. In a mid-air mating, the male Honeybee’s penis explodes with ejaculation, and the eviscerated male falls from the sky to die alone in the shrubbery. Quite a few bees have sperm that turns into a solid plug. It’s a DIY chastity belt that prevents mating with multiple partners. In some insects, the plug is also a meal. Mormon Crickets attach a blob of protein to their sperm packet, which the female eats. It’s the equivalent of a snack bar for a pregnant mother; the female gains nutrition from the plug. Size does matter; the female chooses males on how big their spermatophore (sperm packet) is. Up to 27% of a male Mormon Cricket’s weight can be transferred during mating in a sperm package.

Daniel then concluded his presentation by explaining that mating can be risky for the males of some species. For instance, a female Praying Mantis will often start eating the male during the act of mating. Females of the Orb Weaver spider, Leucauge mariana, will cannibalize males if their sexual performance is poor. They use palpal inflations to determine sperm count and if the female deems sperm count too low, she will consume the male. For Nursery Web Spiders, the male brings the female a gift of a prey item wrapped in silk. The female inspects the parcel, and if she accepts, he mates with her while she unwraps and eats the meal. Research shows that the male often lies, if he gets hungry before he brings the gift, he sucks out the food and presents a beautifully wrapped exoskeleton. Sometimes they don’t even bother with an exoskeleton and use a twig. Sometimes the females weighs it but is still fooled by how pretty the wrapping is. When she finds out, the relationship ends – immediately. The audience members thanked Daniel for his very informative and entertaining presentation.

Colin Prickett