Corn Earworm

Naming

First described in 1850 by John W. Boddie as Phalaena zea
Heliothis zea
Helicoverpa zea Boddie, 1850
Heliothis umbrosus Grote, 1862
Heliothis ochracea Cockerell, 1889
Helicoverpa stombleri Okumura & Bauer, 1969
Heliothis stombleri Okumura & Bauer, 1969

Distribution

The corn earworm is found in temperate and tropical regions of North America, with the exception of northern Canada and Alaska as it cannot overwinter in these areas. ''Helicoverpa zea'' found in the eastern United States also does not overwinter successfully. They live in Kansas, Ohio, Virginia, and southern New Jersey, but survival rate is mainly affected by the severity of the winter. Corn earworm moths regularly migrate from southern regions to northern regions depending on winter conditions. They are also found in Hawaii, the Caribbean islands, and most of South America, including Peru, Argentina, and Brazil.

Cotton earworms have also been reported from China in 2002.

The taxonomy of ''Helicoverpa'' was poorly understood for a long time. Many older works referring to "''Heliothis obsoleta''", a synonym of ''H. armigera'', are actually about ''Helicoverpa zea''.

Behavior

Males must first wait to sense a female's pheromones before they can locate her. Before males engage in flight to find a female, they warm-up by shivering the major flight muscles to reach thoracic temperature optimal to sustain flight, around 26 degrees Celsius. The thermoregulatory shivering activities of males were measured as they were exposed to different sex-related olfactory cues. Males are found to heat up more quickly in the presence of a female pheromone and take-off at a lower thoracic temperature than males who are exposed to other chemical scents. Since heating up to the right temperature leads to better flight performance than flying immediately, there is a trade-off between sub-optimal flight performance and rapid onset of directed flight. ''Helicoverpa zea'' males exposed to an attractive pheromone blend thus spend less time shivering and increase their heating rate. Thermoregulatory behavior of unrestrained moths is associated with competition for access to females, showing the ecological trade-off.

Reproduction

Eggs are individually deposited on leaf hairs and corn silks. The eggs are initially pale green in color, but over time they turn yellowish and then grey. Eggs are 0.5 mm in height and average about 0.55 mm in diameter. They hatch after 66 to 72 hours of development. Once larvae have breached the chorion, they spend up to 85% of their time emerging from their shell. In this eclosion process, the larvae work to make the exit hole larger than their heads. Larvae spend the rest of the time making a silk meshwork around the exit hole; this both helps them escape the shell and helps them find the shell afterwards so they can feed on it. After feeding on their shell, larvae rest about 3 minutes before they begin feeding on the plant material around them.Following hatching, larvae feed on the reproductive structures of the plant and usually develop through four to six instars. Initially, the young larva feed together, and this stage is their most destructive stage. Through maturation, older larvae become aggressive and cannibalistic, leaving one or two larvae per feeding site . They usually have orange heads, black thorax plates, and a body color that is primarily black. Their bodies can also be brown, pink, green, and yellow with many thorny microspines. Mature larvae migrate to the soil, where they pupate for 12 to 16 days.As the larvae mature, they become increasingly aggressive. Although they have host plants surrounding them, ''H. zea'' larvae attack and eat other insects. When presented with a second-instar larva of ''Urbanus proteus'', the corn earworm larva grasps the insect, rolls onto its side to form a semicircle, and begins feeding on the insect's posterior end. If the ''U. proteus'' begins to bite out of defense, ''H. zea'' rotates the larva 180° and uses its mandibles to puncture the head capsule, killing the insect. Then, the ''H. zea'' larva rotates the ''U. proteus'' back to its original position and continues feeding until the insect is entirely consumed. Even when presented with up to five ''U. proteus'' larvae, ''H. zea'' engages in the unique behavior, as the larvae have a higher affinity for lepidopterous prey over plant material. ''H. zea'' raised in a low-moisture environment has a lower pupal weight and a longer developmental time than those raised in environments of high moisture, so a nutritional benefit exists to such aggressive feeding behavior under such conditions.

Food

Larvae feed on a wide range of hosts, including many field crops, hence this species has been much studied.
Adult moth feeds on nectar, especially of trees and shrubs.

Predators

Sperm competition and chemicals introduced to females through mating have a negative effect on females and their lifespan. In males, production of the spermatophore, sperm, and secondary chemicals reduces their lifespan. As the number of copulations increase, the rate of mortality also increases in both sexes.Blanco, Carlos, Douglas V. Sumerford, Juan D. Lopez, Gerardo Hernandez, and Craig A. Abel. "Mating Behavior of Wild Helicoverpa Zea Males with Laboratory Females." The Journal of Cotton Science 14 : n. pag. Arthropod Management And Applied Ecology. Web. .

Migration

''Helicoverpa zea'' is a seasonal, nocturnal migrant, and adults disperse, weather permitting, when there are poor reproductive conditions. In short-range dispersal, the moths move within the crop and low over the foliage. This type of dispersal is mostly independent of wind currents. Long-range dispersal involves adults flying up to 10 meters above the ground and moving downwind from crop to crop. Migratory flights occur up to 1–2 km above the ground and can last for hours. Migration of 400 km is common for such flights as moths are carried downwind. ''Helicoverpa zea'' caterpillars are usually intercepted on produce transported by air-freight transportation. Most activity is restricted to the night-time. Some moths display vertical take-off flight, which carries them above the flight boundary layer and allows them to undertake migratory movement in upper wind systems. During mating, males engage in high-speed directed flight in search of pheromone plumes .