Liriomyza trifoliearum Spencer, 1973 (in Spencer and Stegmaier, 1973)
This species is believed to be closely related to Liriomyza pictella (Thomson, 1868) (see Spencer, 1973).
IMPORTANT CHARACTERS
Adults
Wing length: 1.8 - 2.2 mm. Dark species. Third antennal segment rather small. Abdominal tergites dark, often with very thin yellow stripes. According to Spencer, 1973 L. trifoliearum is the darkest Liriomyza occurring on cultivated crops in the USA. The posterior spiracles of larvae and puparia having only three opening bulbs can be used to separate trifoliearum from dark specimens of Liriomyza huidobrensis.
Immature stages
Puparium dark orange-yellow, posterior spiracles each with 3 bulbs (Spencer, 1973). Cephalopharyngeal skeleton according to Hendrickson and Keller, 1983 with asymmetrical mandibles having altogether four mouthhooks of equal size. The shape resembles that of other leaf-mining Liriomyza spp. The larva causes an irregular serpentine mine. The mine is always located just below the epidermis but the frequently cross over to the opposite epidermis (Hendrickson and Keller, 1983). Pupation occurs within the leaf mine (Hendrickson and Keller, 1983).
BIONOMICS
Although not known as dangerous pest, the species received some attention in the course of the thorough investigation of the alfalfa blotch leafminer (Agromyza frontella), which share the same host plant with L. trifoliearum. The life history was investigated by Hendrickson and Keller, 1983. Above 20°C the larval and pupal development lasts 16-24 days. The longevity of the adults is 16-18 days. A female lay approximately 213 fertile eggs (N=6).
HOST PLANTS
Commonly on Medicago sativa (alfalfa, lucerne), also known from Pisum sativum L. (pea), Trifolium incarnatum L., Trifolium repens, one record from Solanum sarrachoides (Spencer and Steyskal, 1986). Furthermore L. trifoliearum was mass-reared on Phaseolus vulgaris (Hendrickson and Keller, 1983).
DISTRIBUTION
USA (California, Florida, New York, Massachusetts), Canada (Prince Edward Is.).
ECONOMIC IMPORTANCE
Liriomyza trifoliearum cannot be regarded as economic pest so far because normally the population level is too low to affect the host plants (Hendrickson and Keller, 1983). Nevertheless it can be abundant on alfalfa cultivars and may be a potential pest.
The behaviour of pupating within the mine was found to be an advantage for mass-rearing, because less moisture is needed within the breeding chambers. This prevents a heavy infestation with contaminant arthropods. Therefore, Hendrickson and Keller, 1983 employed the species to breed rather unspecific parasitoids, which were used for biological control of other species of leaf-miners.