Rhizoglyphus callae Oudemans R robini Claparede Bulb mites

Bulb mites are generally common but usually secondary pests of bulbs, corms and tubers; hosts include many ornamentals (e.g. freesia, gladiolus, hyacinth, iris, narcissus and tulip), vegetables (e.g. beet, onion and potato) and various other crops. The mites often invade diseased or damaged tissue and, once established, can cause considerable damage, especially in lifted bulbs being stored under warm conditions; the inside of severely infested bulbs, for example, often turns completely black and powdery. Unlike Rhizoglyphus callae, R. robini (a more frequently reported, slightly larger species with shorter body hairs) tends to favour relatively healthy hosts. Attacks can also occur in the field; the mites may then invade the growing points, so that emerging leaves become distorted and sometimes develop ragged or saw-tooth edges (the latter is also a symptom of attack by bulb scale mite, Steneotarsonemus laticeps, p. 262).

BIOLOGY

Bulb mites are associated mainly with stored crops or stored crop products, especially where conditions are damp or mouldy. Their development is favoured by warmth and high humidity, and the mites will breed continuously and multiply rapidly whilst conditions remain suitable. Development from egg through a larval and two nymphal stages to adulthood takes from 1 to 4

weeks according to temperature. A dispersal stage, known as the hypopus, may appear in some populations. These individuals cling onto passing insects, such as small narcissus flies, Eumerus spp. (p. 177 et seq.), and then may be carried to other breeding sites.

DESCRIPTION

Adult 0.7 mm long, translucent-whitish, very shiny, with brownish internal markings; body globular, with several long hairs extending back beyond the tip of the hysterosoma; legs reddish-brown, short and stumpy. Egg 0.2 x 0.1mm, hyaline-whitish, smooth and shiny. Hypopus 0.3 mm long, dark brown; legs short, robust and each terminating in a large claw.

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