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Stethorus punctum - Spidermite Destroyer (Coleoptera: Coccinellidae)

Stethorus punctum eggs D.Asquith	Larva L.Hull	Adult L.Hull

Appearance

Stethorus is a tiny (1.5 mm), oval, convex, shiny black lady beetle, covered with sparse, fine yellowish to white hairs. The white, oval eggs are less than 0.5 mm long, and turn blackish just before the larvae emerge. They are laid singly, usually on the underside of leaves near the primary vein, on their sides and adhere tightly to the leaf. The newly hatched larva is gray to blackish and has many long-branched hairs and black patches. As it matures, it becomes reddish, at first on the edges of the body, and just prior to pupation the entire larva turns reddish. The larva has 13 segments, plus the head. The pupae are black and flattened, somewhat pointed on the posterior end, with the entire body covered with yellow hairs.

Emerging adults are reddish-orange for a few hours after emerging from the pupal case before turning black. Adults can be found in the leaf litter immediately surrounding the trunks of fruit trees, in large numbers along the herbicide strip (the area under the tree canopy that is often cleared by use of herbicides) and occasionally in the drive row.

Habitat

Fruit orchards, strawberry fields, crops attacked by spider mites. This species, first identified in 1852, is native to North America and is found throughout the mid-Atlantic region and also in the Midwest, although it is not as predominant there as in the mid-Atlantic region.

Pests attacked

Stethorus punctum is strictly a predator of plant-feeding mites, particularly the spider mites such as the European red mite and the two-spotted spider mite, and especially the eggs.

Life cycle

Stethorus overwinters in the adult stage beneath leaves and other organic matter under fruit trees and in other protected habitats near the orchard, such as fence rows or adjacent wooded areas. Adults begin to emerge at the tight cluster stage of apple development with peak emergence from the pink to bloom stage. Emergence is usually complete by the petal fall stage. Adults remain active in the orchard until September to late October. Egg laying occurs in most areas from May to mid-August. Eggs are laid close to the primary veins of the leaf and adhere tightly, with 95 percent on the undersurface of the leaf and 5 percent on the upper surface. The larva emerges after approximately 5 days.

The larva passes through four larval stages in about 12 days, feeding on all stages of mites. The mature larva fastens itself to the leaf and remains in a motionless state for 24 to 48 hours before pupation which lasts about five days. The peak periods of larval activity are dependent upon mite populations. There are usually three overlapping generations per year. The average period from egg deposition to the appearance of the adult is 23 days, and the adults feed for an average of 25 days before beginning to lay eggs. Females lay 1 to 10 eggs per leaf depending on mite density.

Relative Effectiveness

When Stethorus are used as a low-level preventive biocontrol they are released at anywhere from 200-500/acre. These beetles consume all stages of mites; adults can consume 75 to 100 mites per day and large larvae can devour up to 75 mites per day, so they quickly lessen an outbreak of spider mites. They are one of the most important and frequent predators of spider mites in fruit orchards. Adults are very active when in fruit trees and if disturbed they will often fall to the ground. They are good fliers, and therefore tend to concentrate in areas of the orchard where mites are plentiful and disappear when the mite population becomes low. There must be 2-5 motile mites per leaf to keep S. punctum in an orchard, and "pockets" of 8-10 mites per leaf are required for reproduction.

Conservation

Because adults overwinter in the leaf litter immediately surrounding the trunks of fruit trees, it is advisable not to disturb the area under the tree from November 1 to mid- to late April. Recent studies indicate the distribution of S. punctum to be closely associated with the leaf litter distribution in the orchard.

Pesticide susceptibility

In one study, fenoxycarb was ovicidal in the laboratory and disrupted the larval-pupal molt in the field. Abamectin was toxic to S. punctum larvae and adults in the laboratory and methomyl was toxic to adults. Teflubenozuron was toxic to the pupal stage in the field; along with fenoxycarb, this IGR caused late-season increases of phytophagous mite populations in field trials. Tebufenozide was not toxic to all S. punctum stages in the laboratory and field. S. punctum was tolerant to all organophosphate insecticides tested.

References:

Larry Hull (1995), Know Your Friends: Stethorus punctum, Midwest Biological Control News Online. Vol.II, No.12. www.wisc.edu/entomology/mbcn/kyf212.html

Biddinger, D. J. and Hull, L. A. 1995 Effects of several types of insecticides on the mite predator, Stethorus punctum (Coleoptera: Coccinellidae), including insect growth regulators and abamectin. Journal of Econ. Ent., 88: 2, pp. 358-366.

Fruit Insect Focus for July 1997, Kearneysville Tree Fruit and Education Center, West Virginia University, H.W. Hogmire, ed. (Modified from the original text in the Mid-Atlantic Orchard Monitoring Guide (original text by D. G. Pfeiffer, L. A. Hull, D. J. Biddinger, and J. C. Killian (European red mite), and L. A. Hull and R. L. Horsburgh (Stethorus punctum).

Adapted from:

website © Cornell University, Last modified May 1, 1998. Suggestions, corrections, and/or comments are appreciated: http://www.nysaes.cornell.edu/ent/biocontrol/predators/stethorus_p.html