I. Introduction: European red mite (ERM) (photo 1-45) is a major tree fruit pest, especially in the eastern U.S., and is considered by many growers to be their most important and sometimes most difficult pest to control. The mite was introduced to North America from Europe in the early 1900s and is now established in most fruit growing areas.

II. Hosts: ERM will attack a number of different fruit crops and can cause extensive injury if left uncontrolled. Apple is usually the most important host, but ERM will also attack cherry, nectarine, peach, pear, plum, and prune.

III. Description: ERM overwinters as a fertilized egg (photo 1-46). It is oval, bright red, and has a small stalk arising from the top, approximately the length of the diameter of the egg. Overwintering eggs are deposited in groups on roughened bark, especially around buds and fruit spurs. Summer eggs are globular, somewhat flattened, and pale green, almost white to greenish-amber when first deposited, but slowly change to a reddish-orange just before hatch. Six-legged larvae hatch from the eggs and are initially a pale orange, darkening to a pale green as they feed. Larvae molt to eight-legged protonymphs which are variable in color from a pale green to reddish-brown, with the dark green predominating. Pale spots at the base of bristles are very faint, if present at all. Protonymphs molt to deutonymphs which vary from an amber color to a dark green, with dark green predominating. Pale spots are distinct at the base of bristles. The eight-legged adult female mite has a globular body and is approximately 1/64th inch (0.4 mm) long, bright red to velvety brown, and has four rows of white hairs on her back. The adult male mite is smaller, has a pointed abdomen, and is straw-yellow to reddish-yellow.

IV. Biology: Overwintering egg hatch in the spring is closely correlated with apple bud development and first occurs when 'Delicious' buds are in the prepink stage; hatch continues throughout the bloom period. Larvae immediately move to the young foliage and begin to feed. Before the mites transform to each succeeding stage, they go through a short quiescent period. Adult mites usually appear by petal fall. Female mites live up to an average of 18 days and each female is capable of laying approximately 35 eggs during her life span. The rate of development is temperature dependent. Under ideal hot conditions (average 80º F; 26.7º C), a life cycle may be completed in 10 to 12 days, however, a generation normally takes 20 to 25 days to complete. Eight to ten generations can occur during a normal growing season. ERM populations usually peak in July. Females begin laying overwintering eggs in early to mid-August.

V. Injury: ERM injures the tree by feeding on leaves, destroying chlorophyll, and increasing respiration. This is accomplished by insertion of the mite's mouth parts into the leaf cells to withdraw the contents. All motile stages feed on the foliage. The lower leaf surface is preferred, but both leaf surfaces are attacked when populations are high. All apple varieties are susceptible to attack, but mites appear to increase faster and to higher densities on 'Delicious' and 'York'. A characteristic brown foliage, starting as a subtle cast to the green leaf, but becoming bronze in severe cases, results from heavy mite feeding (photo 1-47). The most serious injury occurs in late spring and early summer when trees are producing fruit buds for the following season. Moderate to heavily injured trees (that is, with 750 mite days or more or with 43 motile mites per leaf) produce fewer and less vigorous fruit buds. Mites feeding on leaves also reduce their ability to manufacture enough photosynthates for desirable sizing of fruit. Injury effects from mite feeding are more severe during periods of drought stress. Late season high populations of mites can cause further indirect downgrading of fruit by depositing overwintering eggs on the fruit themselves, especially in the calyx end.

VI. Monitoring: Select trees of the same cultivar (e.g., ‘Delicious', ‘Stayman' or ‘York') randomly scattered throughout the block. Collect five to ten leaves of middle age (i.e., from the middle of a fruit spur) from each tree and count the total number of motile mites on each leaf. Mite populations should be monitored on a weekly basis, especially during periods of rapid buildup. Using figure 1, estimate the projected production per acre (harvested bushels) for the affected block. Select the threshold line on the figure for the appropriate time of the growing season. For a given time of the growing season and a given estimated crop load, if mites per leaf exceed the threshold then some control is needed, either by Stethorus punctum (see below) or by application of miticides. If you are using the alternate-row-middle (ARM) system of spraying to make your miticide applications, reduce the action threshold to one-half the value in the figure since you are only spraying one-half of the tree. These levels apply to healthy, vigorous trees with mite damage occurring only after June 4. If the mite population does not exceed the action threshold, it should be reassessed within one to two weeks.

If the mites per leaf exceed the action threshold, the Stethorus population should be assessed by determining a predator-to-mite ratio. To calculate predator-to-mite ratios, divide the number of Stethorus adults and larvae counted in three minutes by the number of motile mites per leaf. For example: 25 Stethorus adults and larvae divided by ten motile mites per leaf equals a predator-to-mite ratio of 2.5.

VII. Management: If the predator-to-mite ratio is less than 2.5 and the action threshold has been reached, then a miticide application is justifed. The miticides that are likely to be the most effective for summer application in West Virginia are Pyramite and Kelthane. The orchard should be checked again five to seven days after application to determine if retreatment is necessary. If the predator-to-mite ratio is only slightly less than 2.5, a half spray (ARM application) may be sufficient to allow Stethorus to become abundant enough to provide biological control.

Stethorus punctum (Leconte)

I. Introduction: Stethorus punctum (SP) is usually the most important and frequent predator of spider mites observed in fruit orchards throughout the mid-Atlantic region. This lady beetle is native to North America and was first identified in 1852. Research conducted annually since 1967 in Pennsylvania has provided much of the basic biology and management information for using this predator as the cornerstone of integrated mite management programs for deciduous fruit crops.

II. Hosts: SP is strictly a predator of plant-feeding mites, particularly the spider mites important to this area, the European red mite, Panonychus ulmi (Koch) and twospotted spider mite, Tetranychus urticae Koch. Studies have indicated that areas in the orchard having an average of at least two to five mites per leaf are necessary to keep SP active, and that eight to ten mites per leaf are needed in these "pockets" to encourage the beetle to reproduce. Beetles feed on all stages of mites, and the adult can consume approximately nine motile mites per hour, or about 75 to 100 motile mites per day. Third and fourth instar SP larvae can consume up to eight mites per hour.

III. Description: SP adults (photo 1-133) are oval, convex, uniformly shiny black, and covered with sparse, fine yellowish to white hairs. Adults reach a length of 1/16 inch (1.5 mm). Eggs are very small in size [1/64th inch (0.37 mm)], pale white, and oval (photo 1-134). They become blackish just before the larva emerges. The larva is gray to blackish and has many long-branched hairs and black patches. They have 13 segments, exclusive of the head. As the larva matures it becomes reddish, at first on the edges of the body, and entirely just prior to pupation (photo 1-133). SP pupae are uniformly black, small, flattened, and somewhat pointed on the posterior end (photo 1-135). With magnification, lines representing abdominal segments can be seen. Wing pads are prominent and the entire body is covered with yellow hairs. For a short period after it is formed the pupa is reddish-orange. The emerging adult is also reddish-orange during the first few hours after emergence from the pupal case before turning black.

IV. Biology: SP overwinters as an adult beneath the trash cover ("duff") under fruit trees and in other protected habitats near the orchard. Adults can be found in the leaf litter immediately surrounding the trunks of fruit trees, in large numbers along the herbicide strip, and occasionally in the drive row. Recent research indicates the distribution of SP to be closely associated with the leaf litter distribution in the orchard. The number of SP overwintering outside the orchard is unknown, but they have been found along fence rows and adjacent wooded areas. It is advisable not to disturb the area in the herbicide strip near the trunk of the tree from November 1 to mid-April. Adults begin to emerge at the tight cluster stage of apple development, with peak emergence from the pink to bloom stage. Adult emergence is usually complete by the petal fall stage. Adults will continue to feed in the orchard until September to late October. They are very active when in fruit trees and if disturbed will often fall to the ground. They are good fliers and thus tend to concentrate where prey is plentiful and to disappear when the mite population becomes low.

During early May females begin to lay eggs on the leaves of fruit trees. Egg-laying occurs from May to mid-August. Eggs are laid singly on their sides, with between one and ten per leaf, depending on mite density. Most of the eggs are laid close to the primary veins of the leaf and adhere tightly, with 95 percent on the under surface of the leaf and 5 percent on the upper surface. After an approximate five-day developmental period, the larva emerges from the egg and starts to feed on all stages of mites present. Peak periods of larval activity are dependent upon mite density, but in south-central Pennsylvania they occur during mid to late May, late June to early July, and mid-August. After feeding for about 12 days and development through four larval instars, the mature larva fastens itself to the leaf and remains there in a motionless state for 24 to 48 hours before pupation. The pupal stage lasts an average of five days. Although pupae are constantly in the trees, the peak pupal periods are late May, early to mid-July, and late August. SP produces three generations per year in south-central Pennsylvania. The average period from the time the egg is laid to the appearance of the adult is 23 days. Adults feed for an average of 25 days before beginning to lay eggs. This time lag between emergence and egg-laying is of little consequence because there is such an overlapping of active adults in the trees at all times.

V. Injury: This insect does not injure the fruit or foliage.

VI. Monitoring: The SP population should be estimated by walking slowly around the periphery of each tree and counting the number of adults and larvae (photo 1-133) that can be observed within three minutes. Take care not to count pupae (photo 1-135) since they do not feed. Furthermore, empty pupal skins will cling to leaves for some time after adult emergence; therefore, counting pupae could lead to an overestimate of the SP population. If small or trellis trees are examined, two to three trees can be collectively observed within a three minute period. Monitoring for this predator should be conducted before leaves are inspected for mites. Refer to the section above on the European red mite for making management decisions regarding the success of biological control.

VII. Management: In order to preserve SP populations, consideration must be given to the toxicity of insecticides when making selections for pest management. Pyrethroid insecticides should be limited to the early prebloom period, preferably no later than the 1/2-inch green stage of apple bud development. Sevin, when used for thinning, has generally been disruptive to SP populations; however, the XLR PLUS formulation has been less toxic than wettable powder formulations in some tests. Once established and reproducing in an orchard, SP will tolerate low rates of Lannate (up to 6-8 oz/acre of 90 SP). Even this rate may keep populations from becoming established in some situations.

Credits: Text prepared by H. W. Hogmire, 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). Prepared in July, 1997.

Web Site Author: Alan R. Biggs
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