A mite very often met with by bulb growers is the bulb-mite (Rhizoglyphus hyacinthi), now found in most parts of the world. Although this mite may possibly be able to attack practically all tubers or bulbs, it is commonly found infesting narcissus, hyacinth, tulip, crocus, and Easter lily; it is especially abundant in bulbs with loose scales, and has been found to be capable of attacking healthy tissue. The life-history of this species is complicated at times by the development of additional stages; one of these—the hypopus—is of particular interest, as it shows more activity than the others, and attaches itself to the bodies of insects, and is so transported. The mite develops from egg to adult within a period of nine days under favourable conditions, or as long as six weeks at other times. All stages of the bulb-mite occur at the same time in infested bulbs, which become soft and rotten. The adult mites ([Fig. 13], 10) are smooth, yellowish-white, tinged with pink, and have legs and mouth-parts reddish. Symptoms of their presence are to be found in stunted growth and yellowing leaves, failure of flower development, reddish spots on bulb scales, or a softening of the bulbs. All seriously-infested bulbs should be destroyed, and the ground where they were grown treated with calcium cyanide. For the treatment of bulbs, they should be immersed for ten minutes in a two per cent. solution of formalin heated to 122 deg. Fahr., or simply in water at a temperature of 131 deg. Fahr.
FIG. 13.
(1) Five stages in mite development: (1) Egg, (2) larva, (3) nymph, (4) older nymph, (5) adult mite. (6) European red mite and (7) egg of same. (8) Brown mite. (9) Common red spider. (10) Bulb mite. (11) Pear-leaf blister mite. (12) Common woodlouse. (13) Garden millepede. (14) Garden slug. (15) Garden snail. (16) Bulb eelworm. (17) and (18) Immature and mature beet eelworm. (19) and (20) Immature and mature root knot eelworm.
Another group of mites of importance to the horticulturist is that of the blister mites; they are so minute—measuring about a hundred-and-fiftieth of an inch long—as to be invisible to the unaided eye. Though so minute, however, their damage to foliage is characteristic and conspicuous, so that their presence is easily detected. The most important blister mite in New Zealand is the pear-leaf blister mite (Eriophyes pyri); it differs from the other mites described above in having a long and cylindrical body, with only two pairs of legs crowded at the head end, the elongate abdomen having the appearance of being composed of innumerable segments ([Fig. 13], 11). This mite lives in colonies in blisters formed on the leaf, and sometimes on the leaf petioles. In the spring the yellowish-green blisters will give the upper surface of an infested leaf a spotted appearance, and as the season advances these blisters become reddish and finally brown; in the case of severe infestation, the blisters become so crowded as to merge into masses.
During the winter the mites lie in the shelter of the bud scales; as soon as the foliage begins to develop in the spring the over-wintering mites attack the leaves, each mite forming a blister, in which it produces a colony of young. The offspring then migrate from the parent blister and form blisters for themselves, and this goes on until autumn, when the last generation of mites migrates for the winter to the shelter of the bud scales.
Owing to the mites being protected within the leaf blisters, summer sprays are not effective as a means of control, which can be effected, however, by spraying with lime-sulphur in the autumn, when the mites are taking up their winter quarters, and again at bud movement in the spring.
Woodlice.
Woodlice are so well known, that but little description is necessary here. However, the following features are of interest. They belong to the group of animals known as the Crustacea, which also includes the crabs; these animals breathe by means of gills, and are usually aquatic, but some forms, such as the woodlice, have become adapted to a life on land. In outline ([Fig. 13], 12) the woodlice are more or less oval, with the upper surfaces somewhat arched, and the lower flat; the body is divided into several segments, which may enable the animals to curl up in the form of a pill. There is a distinct head, bearing a pair of antennæ and the mouth-parts, followed by seven large thoracic segments, to each of which a pair of legs is attached; finally, the remaining six segments are more or less crowded together, and constitute the abdomen.