Does Multiple Mating Help Spotted Lanternflies Spread?
By Paige Embry
Although the spotted lanternfly (Lycorma delicatula) is called a fly and looks like a moth, it is neither. It is of the order Hemiptera, and like other members of its clan—aphids, cicadas, stink bugs, scales, bed bugs—it has piercing-sucking mouthparts.
Indeed, spotted lanternflies are sapsuckers extraordinaire, as well as swarm feeders, and highly successful invaders. Native to Asia, spotted lanternflies (SLFs) were first found in the United States in Pennsylvania in 2014 and have spread to at least 14 states in less than 10 years. Nadège Belouard, Ph.D., a teaching assistant at the University of Rennes in France, studies SLF, including during her previous role as a postdoctoral researcher at the Integrative Ecology Lab in the Department of Biology at Temple University.
“Ubiquity is common in invasive species—that’s part of what makes them thrive and spread in new environments, but I think the spotted lanternfly is particularly good at it,” Belouard says. “In infested areas, you will find them everywhere. A tree in a park? Yes. A pole in a train station? Sure. A hedgerow in a farm? Definitely. Flying by your office window on the fifth floor of a building? Yes!”
Not all species that arrive someplace new survive and prosper. New colonies are begun by a limited number of individuals, so the resulting gene pool is small, potentially limiting adaptability or fitness due to inbreeding. Females that produce offspring from multiple fathers, however, can help maintain a robust gene pool. Belouard and Temple colleague Jocelyn Behm, Ph.D., investigated the role of multiple paternity—individuals from more than one father in the same egg mass—in spotted lanternflies, reporting their findings in August in Environmental Entomology.
For the experiment, the duo collected 248 female SLFs from 24 sites in 2020 and another 42 females along with their egg masses in 2021. They used these females (and the eggs) to investigate several questions: Did females mate with multiple males? Was there multiple paternity? Did multiple mating vary with distance from the introduction site? Did larger, and theoretically more fecund, females have more mates?
To determine if multiple mating happened, the researchers dissected the spermatheca (sperm storage sac) of each female. When SLFs mate, the males deliver the sperm in a tidy package—a kind of biodegradable baggie. They use parts of their genitals to make the transfer, and bits often remain in the female. Those bits don’t plug up the female, but losing them may prevent the males from being able to mate again. Finding more than one spermatophore (sperm package) or more than two male genital bits (they tend to be left behind in pairs) meant the females had mated more than once. Using these criteria, 231 out of the 267 mated females had mated once, 33 had mated twice, and three had mated three times.
However, multiple mating doesn’t equal multiple paternity. Of the female and egg-mass pairs with evidence of multiple mating, only some showed signs of multiple paternity. Surprisingly, the offspring from egg masses with multiple fathers didn’t show evidence of greater genetic diversity than those with just one, but this result is not conclusive. It might be due to the low diversity in alleles, or gene variations, at the DNA sites used for the genetic testing. Belouard says, “Finding low genetic diversity at neutral markers, like the microsatellites [short, repetitive DNA segments] that we used, doesn’t mean that the genetic diversity is low at important, selected genes, which could bring game-changing variants in new environments.”
Belouard and Behm hypothesized that the “presumed advantage” of multiple paternity for species entering a previously uncolonized area would lead to an increase in multiple paternity as one went further from the original point of colonization, but they found the opposite. They aren’t sure why, but they speculate whether male availability plays a role. Because males may only be able to mate once (due to loss of genital parts during mating) and females can mate multiple times—might there be a shortage of males to mate with females on the fringes of an invasion? For instance, in a population with an even male-to-female ration, if males can only mate once but females can mate multiple times, not all females would be fertilized. “It brings up a lot of new questions!” Belouard says.
The authors also hypothesized that males would be attracted to more fecund (reproductively capable) females. If so, females that lay more eggs would be more likely to have multiple mates. For invertebrates, size often correlates with fecundity, so the researchers measured wing length as a proxy for body size. They found that the females that had larger egg masses were indeed more likely to have multiple mates, but neither larger egg masses nor having multiple mates correlated with wing size.
These experiments could be a first step for finding ways to control spotted lanternfly. “An interesting follow-up experiment would be to test which female traits attract males and verify whether they are able to mate just once, for example with mating trials,” Belouard says. “With that, new management techniques could be developed: trapping techniques designed specifically for males at the onset of mating season, with attractive pheromones, visual or auditory cues, would considerably reduce the possibility of reproduction for females.”
Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.