Polyphagotarsonemus latus (Banks)

Tarsoneme - deforming acariosis

Polyphagotarsonemus latus , commonly called tarsoneme ( broad mite ), belongs to the class of Arachnida and the family of Tarsonemidae. It is a tiny mite already damaging in very small quantities, and extremely difficult to observe with the naked eye, its size being 4 to 5 times smaller than that of tetranic mites.

P. latus is very polyphagous, it has been reported in plant species belonging to more than 60 botanical families. It parasitizes many cultivated fruit species (passion fruit, mango, papaya vine, lemon, apple, pear), vegetables (various beans, beet, cucumber, melon, squash, watermelon ...) and especially Solanaceae (tomato, but also eggplant, pepper and potato), ornamental (azalea, begonia, chrysanthemum, cyclamen, dahlia, geranium, gerbera, impatiens, lantana, pittosporum, African violet, zinnia ...) and various other plants cultivated in tropical to subtropical areas: cocoa tree, avocado, tea, coffee, cotton. Certain adventitious plants also harbor it, in particular Bidens pilosa ...

This mite is very cosmopolitan, it is reported on many continents and in many countries in tropical and sub-tropical areas (Australia, Asia, Africa, North and South America, Europe - especially in greenhouses). It is not present in France, but frequent in many departments and overseas territories. It seems very damaging on peppers in Spain in glasshouses, it was notably reported in England in the 1980s on tomatoes.
Note that this mite is not a virus vector.

It hides in the heart of plants, especially at the apex and buds.

• Nature of damage

The punctures made by P. latus are the cause of rather marked and spectacular leaf deformations, the buds and young leaves being particularly deformed. Note that these symptoms are reminiscent of those caused by hormone-type herbicides on tomatoes, and to a lesser degree those of certain viral diseases.

The leaves curl strongly, they are also wrinkled, thicker and stiffer. They sometimes have a bronze to brownish tint, and their underside has metallic reflections. Areas of brownish and suberized tissue appear under the leaves, on the petioles ...
Some plants parasitized early have their growth blocked.

The inflorescences may turn brown or take on a bronze tint, or even fall off.

The fruits are superficially corky, and sometimes show more or less marked micro-bursts. These symptoms are reminiscent of those caused by Aculops lycopersici responsible for bronzed acariosis.

• Biology

- Forms of conservation and / or alternative hosts : this mite is capable of maintaining itself all year round on different hosts, whether or not cultivated, in tropical or subtropical zones.

Stages of development: Four stages follow one another during the biological cycle of this mite: egg, larva, pupa and adult. The cycle from egg to adult is 4 to 5 days in hot periods, it is more than 7 or even 10 days if the temperatures are cooler.
The eggs, located in particular on the underside of young leaves, or even young fruits, are oval and slightly flattened and measure up to 0.07 mm. They hatch in 2 3 days and give rise to larvae little mobile , very small in size, hyaline and with 3 pairs of legs. These feed for 2 to 3 days and transform into a pupa or nymph , already showing 4 pairs of legs. The adults emerge after 2 to 3 days; they are elliptical in shape, females are up to 0.3 mm long depending on the authors while males are half shorter. They are translucent after emergence, the males gradually becoming yellowish to brown, the females yellowish-green, and have 4 pairs of legs, the fourth pair being small in the female. The latter have a lifespan of about ten days and lay an average of 2 to 5 eggs per day.

- Dispersion in culture : the adults of this mite, which cannot fly, move short distances, the males being more mobile than the females. It is mainly disseminated in the culture by the wind, the animals and the insects (in particular the whiteflies), but also the workers and their tools during the cultural operations.

- Favorable development conditions : It rather appreciates temperatures around 25 ° C and humid conditions. Generation takes place every 7 days at 27 ° C, breeding would not take place at temperatures below 13 ° C or above 34 ° C. This mite does not appreciate direct light, so it tends to colonize sheltered places.

• Protection methods

The control of P. latus is quite difficult because the presence of this mite is often detected too late in crops. Despite this, it is desirable to implement many of the protective methods proposed to control the bronzed mite on tomato:
- attempt to eradicate the first outbreak (s) by eliminating the first affected plants and / or by locally treating the latter and the surrounding plants. To be effective with regard to mites, applications must involve a large volume of mixture and this with sufficient pressure in order to access the “heart” of the vegetation. The effectiveness of the treatments should be monitored over time (note that no pesticides are authorized for tomato use in e-phy and that P. latus has developed resistance to several pesticides throughout the world);
- treat the plants before uprooting in the presence of high populations of pests;
- remove and destroy plant debris and crop residues;
- leach with water and treat the walls of shelters, posts, concrete walkways with an insecticide or a contact acaricide;
- disinfect the equipment used in the greenhouse (drip system, boxes );
- check the sanitary quality of the plants before and during their introduction into the shelter;
- weed the greenhouse and its surroundings;
- consider chemical protection *, in particular if you use auxiliaries;
- several auxiliaries have been tested to control the populations of P. latus : Amblyseius swirskii , Amblyseius barkeri ( Neoseiulus barkeri ), Amblyseius californicus ( Neoseiulus californicus ), Euseius stipulatus , Typhlonomus ovalis ...
- Certain natural substances of plant and mineral origin have also been tested against P. latus , in particular fine clay in suspension.

* Chemical control: As the number of pesticides available for a given use is constantly changing, we advise you to always confirm your choice by consulting the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of products phytopharmaceuticals and their uses, fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.