Chaetocnema ectypa Horn Coleoptera Chrysomelidae

Natural History

Distribution. Desert corn flea beetle is western in distribution. It is generally considered damaging only in the southwestern states of New Mexico, Arizona, and California. However, it has apparently spread north to Canada, where Beirne (1971) reported it from British Colombia starting about 1949, and where it occasionally causes severe damage to corn.

Host Plants. Desert corn flea beetle is known principally as a pest of corn, but it readily attacks other grass crops such as barley, sorghum, sudangrass, sugarcane, and wheat. Occasionally, it has been reported to feed on non-grass crops such as alfalfa, bean, cantaloupe, and sugarbeet. Native and weedy grasses are suitable hosts, and include such species as wild barley, Hordeum leporinum; saltgrass, Distichlis spicata; Johnsongrass, Sorghum halepense; and hairgrass drop-seed, Sporobolus airoides. Wildermuth (1917) reported that the adults could be found feeding on the above-ground plant parts, and larvae on the roots, whenever the plants were actively growing.

Natural Enemies. Natural enemies are poorly known. Wildermuth (1917) found some general predators such as ground beetle larvae (Coleoptera: Carabi-dae), and parasites such as a mite, Pymotes sp. (Acari: Tarsonemidae) and a wasp, Neurepyris sp. (Hymenop-tera: Bethylidae) attacking corn flea beetle in Arizona, but their importance is uncertain.

Life Cycle and Description. Desert corn flea beetle has been reported to have three generations regularly in Arizona, with part of the population undergoing a fourth generation. First generation adults, which result from the reproduction of the overwintering beetles, appear in early June, followed by the second generation adults in mid-July and the third in mid-September. Generations overlap considerably and all stages are present through most of the year. The time required for a complete generation is about 46 days, though this may vary from 31 to 79 days depending on weather.

  1. The eggs are about 0.35 mm long and 0.15 mm wide and whitish. They are unusual among flea beetle eggs in that they are bean shaped. Eggs are deposited at or near the surface of the soil, sometimes being attached below-ground to the plant stem. They usually are deposited singly, but groups of up to six eggs have been observed. The eggs require, on average, 5.8 days to hatch. However, the hatching time varies from as little as three days in the summer to 15 days in the spring.
  2. The larvae initially are only about 0.8 mm in length, but eventually grow to about 4 mm. They are whitish, although the head capsule and anal plate are straw-colored. The larval development time is about 32 days, but it may vary from 20-47 days depending on temperature. The mature larva, as it pre-

Desert corn flea beetle egg.

Desert corn flea beetle egg.

Desert corn flea beetle larva.

Desert corn flea beetle larva.

pares for pupation, creates a small cell in the soil. The larva becomes thicker in form and shortens to about one-half its former length prior to pupation. The prepupal period typically is about 3-4 days.

  1. The pupa resembles an adult beetle in appearance, but initially it is white and gradually turns brown. The pupa measures about 1.5-2.0 mm long. Duration of the pupal stage averages 5.6 days (range 3-12 days). Pupation occurs near the soil surface under wet conditions, but as deep as 10 cm in dry soil.
  2. The adult flea beetles are shining black, measuring 1.5-2.0 mm long. The adult bears parallel rows of small punctures on the elytra. The hind femora are greatly enlarged. Beetles are mature and copulation commences about 4-6 days after emergence. Egg deposition begins about 4-5 days after copulation. Adults commonly live a month or more, and produce 40-80 eggs. Desert corn flea beetle apparently overwinters above-ground, among organic debris and weedy grasses. The latter is important as a food source when the weather warms. However, the number of adults observed above-ground during the winter months is very low, so the possibility of some beetles overwintering in the soil should not be ruled out.

Damage

As is the case with most flea beetles, adults feed on foliage, while larvae attack the roots. Adults tend to create long narrow feeding strips, caused by removing epidermis between the parallel veins of grasses. They do not usually eat completely through the leaf. The

Corn Flee Beetle
Adult desert corn flea beetle.

time and site of feeding varies. During cool weather, the beetles are most active during the heat of the day, but in hot weather feeding is limited to cooler periods. Beetles often work their way down to the growing point of the grasses and feed on the most tender young tissue.

The larvae consume rootlets completely, but create grooves in, or burrow within, larger roots. Sometimes the entire root system is tunneled, or the roots entirely severed. Early planted corn is especially susceptible to injury.

Management

This insect is not considered as a major pest, and planting-time applications of insecticide to the soil, or foliar applications post-planting, usually prevent or remedy problems. However, elimination of dense stands of weedy grasses such as Johnsongrass and saltgrass will deprive the insects of alternate hosts and do much to alleviate problems. Damage by larvae can be minimized with adequate irrigation.

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