Zonosemata electa Say Diptera Tephritidae

Natural History

Distribution. This native pest occurs throughout the eastern United States west to Texas and Kansas. However, it is most abundant along the east coast, from Massachusetts to South Carolina. In Canada its distribution apparently is limited to southern Ontario.

Host Plants. Pepper maggot develops successfully only in plants in the family Solanaceae. The vegetable crops injured are pepper and eggplant. Tomato has been reported to be a host, but this is rare. Solanac-eous weeds that sometimes support pepper maggot are horsenettle, Solanum carolinense; silverleaf nightshade, S. elaeagnifolium; groundcherry, Physalis sp.; and possibly others. Insects developing in horsenettle are considerably smaller than those developing in pepper, indicating that pepper is a superior host (Foott, 1968a; Judd et al, 1991).

Natural Enemies. Few natural enemies have been documented. The wasp Opius sanguineus (Ashmead) (Hymenoptera: Braconidae) has been reared from pepper maggot infesting horsenettle in Ontario, but not from maggots in crop plants.

Life Cycle and Description. So far as is known, there is a single generation throughout the range of this insect. The puparia overwinter, with adults emerging in June and July. The egg and larval stages are relatively brief, which require a total of only a month, and new puparia are formed and enter diapause during July-September.

  1. Females insert eggs into fruit. The egg is unusual in shape, primarily elongate-oval but with one end narrowed, tapered, and curved. Altogether, the egg resembles crooked-neck squash. The stalk of the egg may be visible by close examination in the ovipo-sition slit. The whitish egg measures 2.0-2.2 mm long. The width is about 0.30-0.35 mm at the bulbous end and only about 0.05 mm at the narrow end. Duration of the egg stage is about 8-10 days. The total fecundity of females is reported to average about 50 eggs, but some females produce up to 200 eggs.
  2. The larva is typical in form for flies—a cylindrical body with the posterior end wide and blunt, and tapering gradually to a narrow, pointed head. Body length increases from 1.5 mm at hatching to 10-12 mm at maturity. The color changes from translucent white, when the larva is young, to opaque white and then yellowish at maturity. The larva feeds on the central fleshy region of the fruit, occasionally eating young seeds. Mean development time for larvae is about 18 days under field conditions, (range 12-22 days).
  3. The larva exits the fruit at maturity and drops to the soil, where it forms a puparium. The puparia are usually found within the upper 5-10 cm of soil, and persist from late summer or autumn until the next summer. The puparia are oval, measuring about 6-8 mm long and 2.8-4.2 mm wide, and flattened dorsoventrally. They are yellowish-brown to medium-brown.

Pepper maggot larva (left) and puparium (right).

Adult. The head, abdomen, and legs of the adult are pale yellow. The thorax is bright yellow and bears brownish stripes. The last abdominal segment bears a pair of small black dots. Dark bands cross the transparent wings, and the distal bands forms a "V" shape. The eyes are green. Males measure about 6.5 mm long, females about 7.5 mm. The adults often mate within the first day of emergence, but mate repeatedly. The pre-oviposition period is 6-7 days. Adults live about 20-40 days.

The biology of pepper maggot was given by Peterson (1923), Burdette (1935), and Foott (1963). Foott (1968b) described rearing procedures. Keys to adults were presented by Bush (1965) and Foote et al. (1993). An excellent summary of biology and management in Canada was presented by Howard et al. (1994).

Damage

Oviposition punctures occur on small fruit, usually with a diameter of 1-3 cm. As the fruit expands, the area around the puncture sinks, forming a shallow dimple. The larva normally burrows in the soft, central tissue or core, which becomes brown in color. Sometimes mining of the epidermal area is evident. Usually only a single maggot develops in each pepper, but several may develop within each eggplant. In the absence of controls, infestation levels of 90% were recorded, but this pest occurs only sporadically.

Damage by pepper maggot to peppers is similar to injury inflicted by pepper weevil, Anthonomus eugenii Cano. However, larvae of pepper weevil have distinct heads, unlike pepper maggot. Also, pepper weevil is found only to southern states whereas pepper maggot occurs in northern areas.

Management

  1. The adult populations can be monitored with yellow-sticky traps. Traps placed along the margin of fields indicate presence of flies, though they appear not to be reliable indicators of density. It is difficult to detect larvae in fruit until they produce an exit hole at maturity.
  2. Insecticide applications are often recommended for pepper fields if adults are present. Foliar applications of insecticides usually are made at weekly intervals.

Cultural Practices. Sanitation is important in pepper maggot management. Removal and destruction of rotten and infested fruit is recommended to prevent future infestations. Alternate host such as horsenettle should be removed. Relocation of pepper fields to distant sites also is a helpful precaution.

Host-Plant Resistance. Some pepper varieties, particularly the thick-walled bell and cherry types,

Pepper maggot larva (left) and puparium (right).

are most susceptible to injury, whereas the thin-walled pepper varieties are not preferred for oviposition and somewhat resistant to larval feeding.

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