Scaptomyza flava

In captivity, the duration of the Scaptomyza flava life cycle is approximately three weeks, with an average egg to adult growth period of around 20.52 days . Eggs are laid in feeding punctures introduced to the host plant by the female. Larvae can be expected to hatch somewhere around 48 hours after the female deposits the eggs in the puncture. Once hatched, the larvae feed on the leaves as they make their way through the veins toward the petiole, then either double back on their path, or go to a new leaf. Most individuals remain in the same plant through multiple stages of development.[10] The larvae then either remain in the leaves or leave the host to pupate.[10][5]

Scaptomyza flava female

Scaptomyza flava male

Scaptomyza flava participate in anisogamous mating. When males are exposed to females in a laboratory setting, they take two to three minutes to begin mating rituals. Generally, a male approaches a female and in a display of courtship flaps his wings and touches her body with his front legs. Females then become stationary as the male mounts her, and copulation ensues. Uninterrupted copulation typically lasts around twenty minutes. After mating, the males vibrate their wings and leave the female behind, showing no further interest.[5]

Mating displays differed in frequency between mated and virgin males. Mated males are significantly more likely to practice courtship behavior and successfully mate than virgin flies. This suggests that male Scaptomyza flava are capable of learning from previous experience. This behavior has also been reported in the distantly-related male fruit fly, who are also included in the family Drosophilidae.[5] In the lab, scientists found that 90% of flies will mate once or twice, with a much smaller percentage mating three or more times.[13] Scientists have suggested that the mating patterns of S. flava are linked to their circadian rhythm.[13]

S. flava were shown to begin oviposition approximately 2.7 days after emergence, with peak oviposition happening somewhere between five and ten days post-emergence. Over a lifetime, the average female produced approximately 130 eggs, of which approximately 71 were fertilized.[13] Both oviposition and fertility peaked within the first five to ten days post-emergence, with approximately 50% of the viable eggs having been laid within the first 14 days from when the female began ovipositing.[13]

Scaptomyza flava are considered parasitoids because they live in and consume various plants.

Scaptomyza flava larvae are dependent on living plants as a food source, as opposed to other herbivorous insects that can digest decaying plant matter.[12] One benefit of this behavior is protection from pathogens, but this protection comes at the price of increased susceptibility to parasitoid attack.[10] Scaptomyza flava larvae live in and feed on plants in the family Brassicaceae, more commonly referred to as mustard plants.[7][10] Plants in the family Brassicaceae include arugula, broccoli, Brussel sprouts, bok choy, cauliflower, and turnips.[3] In New Zealand, the larvae are also known to infect gypsophila, otherwise known as baby's breath.[5]

Damage to Brassica leaf by leaf-miner

Adult females also feed on the same plants as their larvae. Instead of eating the plants from the inside out, however, they feed on the plant secretions induced by the punctures they make with their ovipositors.[10]

Herbivory is not unique to the genus Scaptomyza, occurring in many insects around the world through various evolutionary events. Specifically, herbivory in Scaptomyza is expected to have evolved between six and sixteen million years ago, with the most recent estimates placing this evolutionary event at approximately 13.5 million years ago.[6][12] The trait is associated with the split from the most recent common ancestor of Scaptomyza flava and Scaptomyza nigrita.[12]

Genetic analysis suggests herbivory evolved only once in the genus Scaptomyza. Other species in the family Drosophilidae have a strong affinity for sensing yeast, a trait that Scaptomyza flava does not possess. Scientists suggest that the loss of ability to sense yeast is associated with evolutionary events leading to the development of herbivory.[6]

The species Scaptomyza flava and Scaptomyza nigrita have specifically evolved the ability to partially metabolize glucosinolates, which are toxic chemicals synthesized by mustard plants as a defense mechanism. Other species in the family Drosophilidae are largely unable to overcome these toxins. Glucosinolates play a role in regulating stress-related genes in Scaptomyza flava, which is different from the specialized systems that other herbivores have developed to bypass the toxic effect of the chemical.[12]