Collembola Dermaptera

COLLEMBOLA Introduction

Springtails are 0.75-6 mm long, wingless and soft-bodied insects. The abdominal segments are fused and there are not more than six segments visible. Antennae have 4-8 segments. The common name is derived from a forked structure, the fur-cula, which helps to propel them through the air. The fur-cula is on the fourth ventral abdominal segment, and when at rest it is folded under the abdomen. Jumps are made by forcefully extending the furcula downward and backward to strike the substrate, which lifts the insect. The jumping ability is strongly developed in terrestrial springtails, which jump to escape from predators. Entomobrya dorsalis is 2 mm long, but it can travel a distance of more than 16 cm. When disturbed, most springtails can be airborne within 50 ms, and Allacmafusca takes only 12 ms to respond with a jump. On the ventral side of abdominal segment 1 there is an eversible vesicle, called the collophore. This hold-fast structure provides for water absorption from moist substrates. Eyes are reduced to 1-8 ommatidia or absent. Mouthparts are mandibulate or suctorial and styletlike. Collembola have simple metamorphosis and the immature stages resemble the adults.

Mating behavior ranges from males randomly placing stalked spermatophores in the environment for females to discover, to males and females involved in elaborate courtship and mating involving a stalked spermatophore, or direct transfer to the female. Females do not retain sperm during ecdysis, and must collect a spermatophore after each molt to continue to lay fertilized eggs. In Sminthurus viridis, the male deposits spermatophores and the female takes it up alone, or with a little encouragement from the male. Males in Sminthuridinae and Bourletiellinae have clasping organs on their antennae, and these are used in mating. The male Sphaeridia pumilis, after some preliminary courtship, clasps the antennae of the female and positions her ventral surface to his, then transfers a drop of sperm to the female. Copulation lasts for 15 min or more.

Eggs are smooth and spherical, usually yellowish white, and deposited singly or in small batches directly on a moist substrate. Eggs are sometimes laid on top of those deposited by conspecific females. Up to 10 000 eggs may accumulate in a single site in laboratory populations of Proisotoma minuta. Single eggs may be covered with liquid fecal material from the female. Hatching is in 20-26 days; fecundity is based on nutrition and access to a male, and may be 400 eggs. Firststage immatures are white with dark pigment in the region of the eyes if present. There are 6-8 molts before nymphs achieve maximum size; development is completed in about 48 days. Full-grown springtails live for about 15 days. There are multiple generations per year. There is a tendency for gregariousness and massing of large numbers of adults and nymphs for short periods. This behavior is usually associated with abundant food, favorable environmental conditions, or migration.

Pest status is due to their presence in small or large numbers indoors and outdoors, and to the ability ofsome species to cause dermatitis. Springtails inhabit moist locations and most feed on decaying plant material, fungi, pollen, algae, and arthropod feces. Several species occur in commercial sites, and cause damage to cultivated mushrooms and greenhouse plants. Those that occur in households are associated with moist or wet conditions, but some species have protective scales on their body and can persist in dry environments. Conditions favorable for springtails indoors include high humidity, mold, mildew, or other wet or moist organic matter. Species that occur outdoors may move when conditions are unsuitable. About 20 species have been reported indoors. Entomobrya nivialis is a small, cosmopolitan species and ithas been reported to cause human dermatitis.

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