African red mite

English name: African red mite

Scientific name: Eutetranychus africanus (Tucker)

Pest group: Mites

Order: Actinedida

Family: Tetranychidae

Description and life cycle

Mites are small and with the naked eye they are hardly visible as small reddish or brown dots on the leave surface. An easy way to observe them is shaking an infested leave above a sheet of white paper. Use a small hand lens to observe their behavior on the leaves.

The small size of mites makes it difficult for farmers or field workers to recognize the them. Inexperienced observers may easily confuse mites with other small animals that live on the leaves, such as thrips. Correct identification is also important because not all mites are pests. Several predatory mites can be found on the leaves as well and these are beneficial as natural enemies of the red mites.

The body of the female mites is 0.3 to 0.4 mm long and 0.3 mm wide, dark red or brown close to black in color. It has a round to oval shape.

The male is light brown and slightly smaller than the female. The front side is widest and the back side rather pointed. Their body length is about 0.3 to 0.4 mm and the width about 0.3 mm.

Mating starts as the male finished molting and becomes an adult. It will start looking for a third instar larva female and when it finds one it will wait for the final molting of the female. Mating then takes place immediately and 1-2 days after mating the female will start to produce eggs.

The development of both the males and females takes about 9 days, including about 5 days for the egg stage and around 1.5 day for each of the 3 larval instars. Males live only for 1.5 days and females live for around 8 days during which period they lay on average 14 eggs.

Host plants

Besides on durian, African red mite can be found on a wide range of hosts including: papaya, tangerine, pomelo, lime, leech lime, Citrus sinensis, jackfruit, breadfruit, horse-radish, cassava, cotton, soybean, cowpea, castor bean, watermelon, garden pea, and hibiscus.

Plant damage and plant compensation

African red mite is an important pest of durian in Thailand, especially during the cool season (late October to early March). It sucks leave juice at the upper surface of leaves. The pest multiplies rapidly during hot and dry weather conditions.

The infested leaves show whitish spot where the mites were feeding. The leaves become pale and do not have a glossy green like normal leaves. The trees can tolerate quite a number of mites, but heavy infestations may result in durian leaves falling down, which will affect the development of flowers and fruits.

Natural enemies

Several predatory mites belonging to 3 different families can control the African red mite: Phytoseiidae, Stigmaeidae and Cunaxidae. But in durian orchards were insecticides are used frequently, these predatory mites rapidly disappear.

Other important predators of African red mite include lacewings (chrysopids), larvae and adults of lady beetles (coccinellids), spiders, and long leg fly (Dolichopus sp.)

Also a number of entomopathogenic fungi such as Hirsutella thompsoni Fisher are found to be controlling this pest.

In Thailand, the use of a predator mite, Amblyseius longispinosus (Evans) to control African red mite has been studied. It was found that this predatory mite can play a role in control, but its use is only practical in orchards with low or no pesticide use.

....we need an paragraph on how farmers can recognize predatory mites and distinguish them from the red mites....

predatory mites move faster...

Management and control practices

Prevention activities

	Conserving the natural enemies is crucial to keep red mite populations under control. In a healthy orchard, especially the predatory mites, but also coccinellid beetles and spiders are efficient predators of red mites. Natural enemies can be preserved by avoiding the use of pesticides.
	Maintain ground cover in the orchard, including weeds, as this provides alternative sites for predatory mites.

What can be done when African red mites are present in the field

	Water jet spraying. Spray water into the tree to increase humidity during the dry season. This can decrease red mite quantity.
	Installation of sprinkler on the top of the tree for water spraying will help reduce numbers of red mites.
	Release of mass reared predatory mites (Amblyseius longispinosus (Evans))
	As a last resort the use of pesticides is an option, but this should be done only after careful observations.  Earlier manuals on Durian give for this pest an ETL of 25% infested mature leaves. A leaf is called "infested" if it contains more than 5 living mites. But the decision to spray should not be based only on counting the pest. If predators such as predatory mites, lady beetles and lacewings are present in the field it is better to use water jet spraying.  Acaricides containing hexythiazox, propargite or amitraz are effective against red mites. Of these three, hexythiazox is relatively safe for the farmer (lowest toxicity) and also in its effect on natural enemies this is probably the best choice.

Points to remember about African red mites

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Links

Eutetranychus africanus