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Planet Earth

Moths Fondly Remember Plant Species Where They Lost Their Virginity

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Think real estate decisions are hard for humans? Imagine if the house you lived in were also your singles bar, your babies' nursery, and your shelter from large animals trying to eat you. And, while you were growing up, your food source, as you nibbled away its floors and shingles. Moths face all these pressures each time they settle down on a plant. That may be why at least one type of moth uses pleasant associations to help with its choices. The plant species where an individual loses its virginity becomes a favorite.Spodoptera littoralis, or the Egyptian cotton leafworm, lives throughout Africa and in parts of Europe. As a caterpillar it's a pest feared by humans, munching through crops voraciously. It's not picky—the insect feeds on plants from more than 40 different families. Earlier studies showed that S. littoralis's experiences as a very hungry caterpillar can influence the kinds of plants it prefers as an adult moth. So Magali Proffit, a researcher at France's Centre d’Ecologie Fonctionnelle et Evolutive (CEFE), and her coauthors asked a not-so-obvious next question: are the moth's likes and dislikes also shaped by its sexual experiences? The researchers studied moths that had emerged just two days earlier. As caterpillars, these individuals had grown up eating a potato-based laboratory diet, so they hadn't learned to like any leaves better than others. To start, the scientists compared just two plants: cotton, which (as you might have guessed from its name) the cotton leafworm naturally enjoys; and cabbage, which it's not as fond of. They put groups of moths in enclosures with either cotton plants, cabbage plants, or no plants at all, and let them mate freely. Afterward, the researchers tested the moths' preferences in two ways. When female moths were ready to lay their eggs, the researchers gave them access to both cotton and cabbage plants and let them choose egg-laying sites. Male moths, meanwhile, were put in a wind tunnel that wafted female moth pheromone toward them. They could choose to land on either a cotton or cabbage plant for the mating they thought was about to take place. In both cases, moths that had lost their virginity without any plants around inherently preferred cotton. Moths that had mated on cotton plants still preferred it. But moths that had mated on cabbage were more likely to choose cabbage for their future egg-laying and mating needs. When the experiment was repeated in a G-rated form—moths simply hung out on different plants, rather than mating on them—this effect disappeared. The researchers also compared cabbage to cowpea, a plant that S. littoralis loves even more than cotton. This time they also raised the caterpillars on either cowpea, cabbage, or the standard lab diet. When the caterpillars became moths, the researchers repeated the mating experiment just as before. Regardless of its diet as a caterpillar, mating on cabbage still increased a moth's preference for cabbage plants. Growing up eating a tasty plant can make a moth like that plant a little more, the researchers found. But nothing sways a moth's opinion like its first mating experience. It's not clear why this is. For males, a plant where you've mated before might be a surer bet for future trysts. For females, maybe successfully mating on a certain plant species tells a mom that her offspring can live there without being preyed on. In general, the authors write, being flexible about favorites is a good thing for insects. A moth that can modify its preferences based on life experiences—both positive and negative—will probably survive longer than a moth that can't change its mind. And a little nostalgia for past romance apparently doesn't hurt.

Image: by Andy Reago & Chrissy McClarren (via Flickr). NOTE: This is a related moth species and not the exact species used in the study.

Proffit, M., Khallaf, M., Carrasco, D., Larsson, M., & Anderson, P. (2015). ‘Do you remember the first time?’ Host plant preference in a moth is modulated by experiences during larval feeding and adult mating Ecology Letters, 18 (4), 365-374 DOI: 10.1111/ele.12419

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