Helicoverpa zea

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. 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 H. zea. == Lifecycle and description ==

Eggs Eggs are individually deposited on leaf hairs and corn silks (not in reference given). They hatch after 66 to 72 hours of development. Larvae Following hatching, larvae feed on the reproductive structures of the plant and usually develop through four to six instars. Through maturation, older larvae become aggressive and cannibalistic, leaving one or two larvae per feeding site (See Interfamilial Predation). They usually have orange heads, black thorax plates, and a body color that is primarily black. Mature larvae migrate to the soil, where they pupate for 12 to 16 days. Pupae Larvae pupate 5 to 10 cm below the soil surface. Adults Adults have forewings that are yellowish brown in color and have a dark spot located in the center of their body. Adult moths collect nectar or other plant exudates from a large number of plants, and live for 12 to 16 days. Females can lay up to 2,500 eggs in their lifetime. == Economic impact ==

Damage The corn earworm is a major agricultural pest, with a large host range encompassing corn and many other crop plants. H. zea is the second-most important economic pest species in North America, next to the codling moth. Control Two kinds of control measures have been advocated since the 19th century. Pesticides are one method by which corn earworm populations are controlled; however, since they have been widely used, the insects have become resistant to many pesticides. Strains of maize have been genetically modified to produce the same toxin as the bacterium, and are referred to as Bt-corn. == Survival ==

Natural enemies More than 100 insect species prey on H. zea, usually feeding on eggs and larvae. Some plants emit a blend of chemicals in response to damage from H. zea, which attract parasitic insects. When the wasps find damaged host plants, they hover around and then search for the host with their antennae. When the females find their prey, they use their antennae to position themselves and deposit eggs into the host. The braconid wasp Microplitis croceipes, which deposits its eggs inside a living caterpillar, is also an important parasitoid of both H. zea and the related species Heliothis virescens. When larval densities are high, a fungal pathogen, Nomuraea rileyi, can cause an outbreak of disease. However, pupal mortality is high not because of predators, but because of harsh weather conditions, collapsing pupal chambers, and disease. Larval predation 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. ==Movement ==

Migration Helicoverpa zea is a seasonal, nocturnal migrant, and adults disperse, weather permitting, when there are poor reproductive conditions. Migration of 400 km is common for such flights as moths are carried downwind. Most activity is restricted to the night-time. By preparing themselves for a major change in environmental conditions, they can increase reproductive success. == Feeding ==

Host plants Helicoverpa zea has a wide host range, attacking vegetables that include corn, tomato, artichoke, asparagus, cabbage, cantaloupe, collards, cowpea, cucumber, eggplant, lettuce, lima bean, melon, okra, pea, pepper, potato, pumpkin, snap bean, spinach, squash, sweet potato, and watermelon. Various signs reveal the presence of these moths. Corn Helicoverpa zea earns its nickname the corn earworm for its widely known destruction of cornfields. Soybeans Helicoverpa zea is the most common and destructive pest of soybean growth in Virginia. == Mating ==

Pheromone production A hormone produced in the brain of the female moths controls sex pheromones. The hormone is released into the hemolymph to stimulate pheromone production. Pheromone biosynthesis-activating neuropeptide (PBAN) is a peptide that regulates pheromone production in moths. It acts on the pheromone gland cells using calcium and cyclic AMP. Although the photoperiod regulates the release of PBAN to some extent, the chemical signals from the host plant supersede the effect from the time of day. Female moths often become depleted of sex pheromone after mating within 2 hours of separation from the male. The pheromonostatic peptide (PSP), a protein 57 amino acids long found in the male accessory gland, is what causes depletion of the female's sex pheromone. This capability in males has been selected for because it increases the reproductive fitness of those that carry it, since other males will not be attracted to a female without a sex pheromone; thus, the female will bear only the first male's offspring. When females are infected with the virus Helicoverpa zea nudivirus 2, they produce 5 to 7 times the amount of sex pheromone than uninfected females. Mortality Sperm competition and chemicals introduced to females through mating have a negative effect on females and their lifespan. Flight behavior Males must first wait to sense a female's pheromones before they can locate her. ==Gallery==

File:Tomato fruitworm.jpg|Tomato fruitworm eating an unripe tomato File:Cotton bullworm.jpg|A cotton bollworm eating a boll image:Bulletin (1904) (20419732502).jpg|Bollworm eggs attached on the silks of an ear of corn image:Bulletin (1904) (20240335660).jpg|Corn bud and tassel image:Bulletin (1904) (20419753042).jpg|1) Tobacco plant; 2) Green tomato fruit; 3) Green peach; 4) okra pod. 5) Cowpea pod. == References ==