Liriomyza huidobrensis (Blanchard, 1926)
INTRODUCTION
Recent molecular research found evidence for a cryptic species within the species complex previously known as Liriomyza huidobrensis (Scheffer, 2000, Scheffer and Lewis, 2001, Scheffer et al., 2001). For this species the old name Liriomyza langei was resurrected. Both species are at present not distinguishable by external characters. Therefore until further research this description can be applied to both Liriomyza species which can be separated by molecular characters only (Scheffer et al., 2001).
Most probably there are differences in geographical distribution, host preferences and other biological characteristics. This question will be subject of future work.
Hence, the taxonomy of the difficult species group previously consisting of bryoniae, strigata and huidobrensis increased in complexity.
The species is closely related to Liriomyza strigata and Liriomyza bryoniae. No morphological characters available for the separation of the adults of bryoniae and strigata. Although the color patterns can be variable, huidobrensis is generally darker than bryoniae and strigata with both vertical bristles normally on dark cuticle. The combination of the mines being associated with veins and midrib and the peculiar aedeagus are a good diagnosis outside of Europe.
IMPORTANT CHARACTERS
Adults
Wing length: 1.7 - 2.25 mm. Color patterns can be variable, anepisternum can be dark, except for a yellow narrow dorsal section. Third antennal segment with brown tip, orbits dark.
Inner and outer vertical bristles on dark cuticle but the surrounding of the outer one is darker than that of the inner. Frontorbits normally slightly darkened but sometimes completely yellow, frontorbital bristles often located on dark patches. Frons yellow.
Male genitalia
Surstyli with single curving spine (Spencer, 1973).
Immature stages
Similar as Liriomyza bryoniae.
BIONOMICS
The larva feeds primarily as a leaf miner but on peas it may also feed on the outer surface of young pods. The mine is frequently associated with the midrib and lateral veins but can also be irregularly serpentine and, particularly when several larvae are present in a single leaf, can form a secondary blotch (Spencer, 1973). The larvae generally prefer the spongy mesophyll (Parrella et al., 1985), which is an unusual behaviour among the economically important Liriomyza species.
The life-cycle was examined by Parrella et al., 1981, Prando and da Cruz, 1986, Carballo et al., 1990 and Hincapie et al., 1993: The larval and pupal development lasted from about 15 to 23.5 days. According to Prando and da Cruz, 1986 and Hincapie et al., 1993 a female lay about 100 - 130 eggs under laboratory conditions but Parrella et al., 1981 observed as much as 250 eggs per female. Likewise the life-span of the females varies according to the studies between 7 and 30 days.
Generations follow in quick succession as long as growing conditions of the host-plant provide suitable food.
HOST PLANTS
Highly polyphagous species with records of at least 14 plant families (Spencer, 1990 but see also Wei et al., 2000).
Crop plants attacked include Beta vulgaris L., Spinacia oleracea L., Lactuca sativa L. (lettuce), Cucumis melo L. (melon), Pisum sativum L. (pea), Vicia faba L. (broad bean), Allium cepa L. (onion), Linum usitatissimum L. (lineseed), Capsicum annuum L. (pepper), Lycopersicon esculentum L. (tomato). Solanum tuberosum L. (potato), Apium graveolens L. (celery) and some ornamentals, e.g. Gerbera and Chrysanthemum.
Already Spencer, 1973 mentioned that within huidobrensis some local preferences regarding the host plants could be found.
DISTRIBUTION
As mentioned above the former species.
Liriomyza huidobrensis is recently subdivided into two species. That leads to some uncertainty about the distribution of both species.
The present state is that huidobrensis is native from South America and subsequently spread to Central America (Scheffer, 2000, Scheffer and Lewis, 2001). From the nineties onwards (in many European countries it was recorded in 1989) the species was spread around mainly by human trade with cut flowers.
At present huidobrensis can be expected in all tropical and subtropical regions of Europe, Asia and Africa, where reliable host plants are cultivated. In temperate regions the species is usually restricted to greenhouse cultures. However, the species is not yet known from North America and Hawaii, where the new separated species Liriomyza langei was recorded. Up to now both species are not known to occur sympatrically. Further studies are required.
ECONOMIC IMPORTANCE
The plants are damaged both by larval feeding and the feeding punctures of females. L. huidobrensis can be a serious pest, substantial damage has been recorded from many of the known host-plants. Damage can sometimes result in complete crop loss. Problems with huidobrensis were reported from both, areas, where the species seems to be native and from those areas, where the leaf miner was introduced (References from South America and Europe). Due to their unusual mining habit, at low population densities huidobrensis causes more harm to the host plant than the other important pest trifolii (Parrella et al., 1985). However, at high population densities the difference is less obvious.
Apparently, the infestation of huidobrensis and other Liriomyza species is often the result of indiscriminative use of insecticides, applied either against the agromyzids themselves or other noxious insects. This is because many naturally occurring parasitoids are more vulnerable to insecticides than their hosts. Thus, the support of parasitoids seems to be a promising attempt to control huidobrensis and other Liriomyza pests. Especially in greenhouses through inoculative release of parasitoids a good control can be achieved (Parrella and Keil, 1984, van der Linden, 1991). In Europe several parasitoid species are commercially available. However, in many cases the careful application of modern insecticides might be inevitable.