Liriomyza trifolii, known generally as the American serpentine leafminer or celery leafminer, is a species of leaf miner fly in the family Agromyzidae.
L. trifolii is a damaging pest, as it consumes and destroys produce and other plant products. It commonly infests greenhouses and is one of the three most-damaging leaf miners in existence today. It is found in several countries around the globe as an invasive species, but is native to the Caribbean and the Southeastern United States.
Description
L. trifolii are relatively small flies for their family. The adults typically measure less than 2 mm in length. They are mostly yellow in color, although parts of the abdomen and thorax are dark brown or grey. They typically have yellow legs. A key distinction between L. trifolii and their very similar relatives, L. sativae, are L. trifolii's dark, matte mesonotum.
L. trifolii typically have a wingspan of 1.25 to 1.90 mm. Their wings are transparent and have veins in a similar pattern to that of flies in the Phytomyzinae subfamily.
Distribution
Originally, L. trifolii was solely found in Caribbean countries and the southeastern United States (specifically concentrated in southern Florida). However, export of produce and other vegetative goods from these areas has led to the dispersion of L. trifolii to several countries in Asia along the Pacific Ocean, as well as Europe, California, and certain parts of Canada. This human-facilitated dispersion occurred mostly after L. trifolii became resistant to certain insecticides and therefore were not killed off by the exports' treatment with insecticides before and after transport.
Habitat
L. trifolii are naturally found in tropical and subtropical regions. However, they frequently infest greenhouses and can now be found as an invasive species in a wider variety of climates. Because of this human-facilitated dispersion, L. trifolii can now be found in more temperate climates than they naturally would, although their development and survival is not as successful in the cooler climates.
Life History
Compared to other flies, L. trifolii have a relatively brief life cycle, ranging from 21 to 28 days in habitats they are native to. Because of this, there can be multiple generations of L. trifolii within one year in warm climates. Additionally, the rate of development for L. trifolii has been shown to be temperature-dependent. Maximum pupal survival rates and oviposition rates were shown to occur at 30˚C.
Eggs
The eggs are typically about 1 mm long, 0.2 mm wide, and oval in shape. Initially after oviposition, the eggs are clear, but they become creamy white in color as time goes on. Eggs are laid just below the surface of the leaf; when the larvae hatch, they mine their way out of the leaf as they feed, hence the name "leaf miner". The eggs frequently fall victim to parasitoid wasps.
Larval Instars
The larvae of L. trifolii are unique from those of many other flies in their shape, as the body of L. trifolii larva does not taper at the head end. The larvae are uniform in thickness at both their anterior and posterior ends but additionally have a pair of spiracles at the posterior end. They do not have legs and are initially clear in color, but gradually become yellow as they mature.
The larval instars are differentiable by the lengths of the body and mouthparts. The first instar is recognizable by a mean body length of 0.39 mm and a mouthpart length of 0.10 mm. For the second instar, the mean measurements are 1.00 mm (body) and 0.17 mm (mouth). For the third instar, the mean measurements are 1.99 mm (body) and 0.25 mm (mouth). The fourth instar is a non-feeding stage and thus is usually disregarded.
Pupa
Typically, at the end of the larval phase, L. trifolii drop to the soil to pupate after exiting the leaf mines they have created. Initially, the puparium is yellow, but it grows to become a darker brown over time. The puparium is typically less than 2.3 mm long and 0.75 mm wide.
Adults
Adult female L. trifolii tend to live around 13 to 18 days. Male adults typically only live 2 to 3 days because they are unable to puncture plants and thus have difficulty feeding. As previously described, both males and females are typically around 2 mm in length with a wingspan around 1.25 mm. After chewing a fan shape into the leaf of their host plant, adults feed on exuding sap of the host plant on which oviposition will occur.