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In a new study, researchers observed the patterns of fruit flies during reproduction. The research team discovered that when it comes to laying eggs, the flies are a lot pickier than one would assume. The team found that if the flies have many fruit options, they would generally choose to lay their eggs in citrus fruits.

The researchers composed of Marcus Stensmyr from Lund University and Bill Hansson from the Max Planck Institute for Chemical Ecology explained that the fruit flies' decision to lay eggs on citrus fruits is based on basic survival instincts. Fruit fly larvae and young fruit flies tend to be food for parasitoid wasps. Parasitoid wasps, however, have an aversion to citrus. Therefore, by laying their eggs on citrus fruits, the eggs have a higher chance of surviving by avoiding parasitism.

"When it comes to egg-laying, flies are more picky than previously thought," said Stensmyr. "They are not indiscriminately using any old fruit encountered, but show a clear preference towards citrus."

The researchers also explained that citrus fruits have a very distinctive smell that is made up of a combination of chemical ingredients. These ingredients, specifically limonene, help flies differentiate between a citrus fruit, such as an orange and a non-citrus fruit like an apple. The flies have a receptor called Or19a, which guides them to the chemicals. The researchers found that flies without this receptor are incapable of picking out an orange from an apple. The researchers stated that based on their findings, people might want to think twice before leaving their citrus fruits outside of the refrigerator for too long

The study, "Olfactory Preference for Egg Laying on Citrus Substrates in Drosophila," was published in Current Biology.