Eryophid tomato mites - Microscopic detection; Molecular identification (PCR and sequencing)

Information 03-09-2018. 

            The eryophids are a family of microscopic mites, phytophages, very evolved, that cause discolorations and show deformations in the plants. Among them, the brown mite of the tomato, Aculops lycopersici (Massee) is a cosmopolitan plague in Solanaceae crops, mainly in tomato (Solanum lycopersicum L.). A. lycopersici tends to abound in greenhouses and causes massive yield losses of tomato, one of the most important horticultural crops in the world.

            Eryophid mites are among the smallest arthropods on earth. The tiny size of these mites is the key to their ecological success, as it allows them to reach places small enough to be free of predators and adequate to access the plant's food resources. In agricultural crops, such mites can easily reach the state of the pest when they lack predators. The dense covers of glandular hairs protect the vital parts of the plants against many herbivorous arthropods. In the tomato, the glandular trichomes in the leaves and stems protect the plant constitutively against the spider mite of two spots or red spider, but they can also hinder predatory mites and other natural enemies. This can create a space free of competition and enemies for the tiny eriofioid mites, which seek refuge and feed between the glandular hairs. The brown mite of the Aculops lycopersici tomato represents such a case.

            Aculops lycopersici is a cosmopolitan species and causes damage to tomato crops throughout the world, with increasing incidence in the Almeria area, probably because the climatic conditions of the greenhouses are favorable for its development, especially in spring cycles, and that both temperature and relative humidity influence the growth of their populations. Aculops lycopersici feeds on epidermal cells by means of three sets of stilettos of approximately 15 μm in length, derived from the chelicerae, the runner and the infracapitulum, respectively, that surround the mouth. Through its feeding, A. lycopersici destroys the upper and lower epidermal cells, among which are the protective cells, and induces the formation of callus tissue that appears in these regions, while the plant suffers from very reduced photosynthesis and respiration. Once detected, A. lycopersici is difficult to control since it hides in the forest of tomato leaf hairs (trichomes), which protects it from predators and even chemical control.

            The symptoms begin with a yellowing of the lower leaves, extending then to the petioles of the same ones and to the stems, that are gradually drying out, originating, finally, the desiccation and death of the plant. The leaves take a yellow color at the beginning, later a silver aspect in the underside of the leaves, until they get to dry and in cases of severe attacks they end up falling. The stem has a rusty brown color. The symptoms go up through the plant, until reaching the apical areas. They can even cause the loss of the harvest, depending on the intensity of the pest. On the leaves it produces a dark bronze yellow or "old gold" color, which should not be confused with the tomato mosaic virus, which gives a yellow color and not a yellow toasted leaves. In addition the eryophids attacks old leaves, generally in the part of underneath the plant, whereas the virus begins by the young ones.

            These mites have a very short cycle, and in optimal conditions of high temperatures and low relative humidity (27° C and 30% humidity) can complete their cycle in just over a week. The life cycle of this species consists of egg states, two nymph states and adult. The eggs are transparent spherical and deposit them on the underside of the leaves. It does not present diapause so it can be found throughout the year. Adult females are the most abundant stage and frequently found in symptomatic plants. They have the basic characteristics of Eryophydae and Phyllocoptinae. This mite, like all those belonging to the Eryophidae family, has an elongated body with transverse grooves and has only two pairs of legs. The buccal apparatus is sucking type. Its size is very small, its fusiform body is 0.15 to 0.2 mm long and its color is yellowish. The prodorsal shield has a length of 40 to 50 μm, and has a broad, short anterior lobe that abruptly deviates ventrally. It is strongly sculpted with a diagnostic pattern of longitudinal striations in the shape of an hourglass, and has a pair of moderately long diverging dorsal ridges, directed backwards, near the trailing edge. The body exhibits a series of strongly differentiated rings in tergites (dorsal) and sternites (ventral). There are 25-30 tergites and more than 60 sternites, and the sternites have pointed microtubers at their posterior edges. The genital cover extends from 14-16 μm in length and is sculpted with longitudinal striations. The two pairs of legs have distinctive claw-like structures in the final part of the tarsus, called feather claws. The treatments should be carried out at the beginning of the detection of the pest since its short cycle makes it develop with extraordinary rapidity. Therefore, early detection of the pest is important. However, because of their small size, growers often detect it too late. In the IVAMI we perform the detection of eryophids in plants by means of microscopic observation and molecular identification (PCR and sequencing).

Tests performed in IVAMI:

• Microscopic observation and molecular identification (PCR and sequencing).

Recommended sample:

• Several leaves of affected plants introduced in a tight-fitting plastic container.

Conservation and shipment of the sample:

• Room temperature (less than 24 hours).

• Refrigerated (more than 24 hours).

Delivery of results:

• Microscopic observation: 24 hours (working days).

• Molecular identification: 48 to 72 hours (working days).

Cost of the test:

• Microscopic observation: Consult to