Insect Note #S-3

Problems with sap beetles in strawberry fields have been reported over the years and they appear to be on the increase in North Carolina. Correct identification, cultural control and management tactics are outlined in this insect note and should be followed to prevent unnecessary damage by sap beetles.

Strawberry fruit are susceptible to attack by at least nine species of sap beetles. In North Carolina, at least three species of importance include the strawberry sap beetle and two species of picnic beetles.

Damage

The injury is primarily direct, as cavities are eaten in the fruit. The beetles can also disseminate rot orgaminsms from diseased to nondiseased fruit Larval feeding is less obvious, as it occurs in decomposing fruit. However, worm-infested fruit is of major concern to growers and consumers

As berries begin to ripen adult sap beetles are attracted to fields. They attack ripe diseaseed or damaged fruit by boring into the teeny and devouring it. On some berries sap beetles enter from the underside by eating a hole where the fruit contacts soil or mulch. The perennial matted row culture system seems to be more susceptible to attack by beetles than the annual or plastic mulch system

Hosts

Hosts of sap beetles include ripening fruits ant vegetables of apples, peaches, melons, cucumbers, tomatoes sweet corn, brambles, grapes and sweetpotatoes. Any decaying sweet, fruit ant vegetable are attractive, and can serve as reservoirs for sap beetles.

Description

Adult: Strawberry sap beetle is a small, oval, brown ant slightly mottles beetle less than 1/8 inch long. Picnic beetles are larger and may have four orange blotches on their back. All sap beetles have short elytra and thus the terminal segments of the abdomen are exposed

Eggs: Small, whitish and are laid singly on various stages of fruit.

Larva: Mature larvae are 1/8 to 3/8 inch long depending on species. Creamy, white larva has a stout body with 3 pairs of short legs near the front. Pupae: Brown pupae are found just under the soil surface.

Life History

Adults leave overwintering sites in wooded areas and ditch banks in late spring when daily high temperatures exceed 60°F. This is usually when fruit begin to ripen. Adult beetles attack fruit throughout the harvest period, with populations more abundant as the season progresses. Sap beetles are usually more severe on farms that have many crops serving as host reservoirs. When fruit are disturbed, adults fall to the ground and move quickly. Adults are long lived, mate and lay eggs in suitable fruit. Eggs hatch in a few days and larvae feed on and in fruit for a week or two. Larvae fall to the ground and burrow into the soil to pupate. Pupation lasts some 10-14 days and adult beetles emerge, mate, feed and seek out overwintering sites in woods near host fields. There are probably two generations each year of strawberry sap beetle and multiple generations of picnic beetles.

Management

Integrated pest management strategies and tactics include crop and land rotation, sanitation measures for all planted and native fruits and vegetables in the area, proper strawberry bed management and renovation, growing berries on bare soil with a minimum of straw mulch and moisture or by growing on the annual plastic mulch system, providing good disease control during wet weather, avoiding mechanical damage, harvesting and removing mature fruit as well as damaged or diseased culls, prompt removal of sound berries from the field, covering with a mesh screen to keep beetles out and timely sprays of insecticides around field margins when daily high temperatures exceed 60°F in the spring. Beetles can be monitored using several trap designs and baited with an attractant. Several natural enemies exist but are usually not effective in preventing damage and do not offer practical control. Early maturing varieties and those that produce firm fruit appear to escape beetle attack.

Control

Cultural control is useful in reducing sap beetle populations. Avoidance of damage to developing fruit, good disease control programs, prompt harvesting of fruit and removal and destruction of all damaged, diseased and over-ripe fruits are effective tactics. Similarly, sanitation with other fruit and vegetables in the area will help keep populations from building. Bare soil, less straw mulch and dry conditions discourage sap beetles. Also prompt removal of foliage and bed renovation after harvest together with rototilling the middles to disturb pupation sites will help break the cycle. Insecticides may be used but are not as effective as the cultural control measures just described. Insecticides effective against adult beetles include Sevin, malathion, Guthion and methoxychlor. Frequent and thorough applications are needed during the early period of adult activity. Danitol or Brigade as a drench with high volumes of water is moderately effective against small larvae. Be sure to follow pesticide label directions for best results.

THE USE OF TRADE NAMES IN THIS PUBLICATION DOES NOT IMPLY ENDORSEMENT OF THE PRODUCTS NAMED OR CRITISM OF SIMILAR ONES NOT MENTIONED.

Prepared by:
K. A. Sorensen, Extension Entomologist
11/96/mw/100/d:2
Revised: 02/17/05