White-speck Moth

Appearance

The true armyworm has a distinct migration pattern in which they travel north in the spring and south in the fall to ensure that mating occurs in a favorable environment in the summer. While progressing through the life cycle stages of egg, larva, pupa, and adult, this species must avoid attack from predatory bugs, birds, wasp and fly parasitoids, and bacterial and fungal diseases. As polygamous insects, females release sex pheromones and choose multiple males as mates. The production and release of the pheromones are influenced by temperature, photoperiod, and the juvenile hormone. Hearing is an important sense for the true armyworm, necessary for mating and evading bat predation.

Naming

"M. unipuncta" males can distinguish females of their own species from those of other species by recognizing the contents of the female sex pheromone. One study looked at how "M. unipuncta" males responded to lures containing their own pheromone and to lures containing the sex pheromone of a sympatric species known as "Sesamia nonagrioides." When -11-hexadecenal, a component found in the sex pheromones of "S. nonagrioides" females, was added to the lures, the "M. unipuncta" males were less attracted. Therefore, the males' ability to detect certain acetates in the pheromones serves as a reproductive isolating mechanism and prevents cross-species mating.

Behavior

In a given year, there can be two to three generations, each generation requiring 30–50 days to complete.When females are ready to mate, they release sex pheromones through a behavior known as calling. On average, this behavior is displayed around 4–6 days after emergence; age of calling onset is determined by ambient temperature and photoperiod. Low temperatures and short photoperiods delay the calling period, but higher temperatures and long photoperiods trigger calling period sooner after emergence These are consistent with the yearly changes in the behavior of "P. unipuncta": the moth is in migration in the fall and spring seasons, and "P. unipuncta" prefer to mate in the summer. Females can mate about 5 or 6 times in their lifetime.

Reproduction

Larvae feed and damage on a variety of Graminae and other crops.

⤷  "Hordeum vulgare" – barley
⤷  Maize – corn
⤷  Oats
⤷  Rice
⤷  Rye
⤷  Sorghum
⤷  Sugarcane
⤷  Wheat
⤷  Alfalfa
⤷  Artichoke
⤷  Bean
⤷  Cabbage
⤷  Carrot
⤷  Celery
⤷  Cucumber
⤷  Lettuce
⤷  Onion
⤷  Parsley
⤷  Pepper
⤷  Sweet potato
Larvae feed and damage on a variety of Graminae and other crops.

⤷  "Hordeum vulgare" – barley
⤷  Maize – corn
⤷  Oats
⤷  Rice
⤷  Rye
⤷  Sorghum
⤷  Sugarcane
⤷  Wheat
⤷  Alfalfa
⤷  Artichoke
⤷  Bean
⤷  Cabbage
⤷  Carrot
⤷  Celery
⤷  Cucumber
⤷  Lettuce
⤷  Onion
⤷  Parsley
⤷  Pepper
⤷  Sweet potato

Predators

Many species feed on armyworm larvae. These include ground beetles, who share the same habitat in the soil, in addition to predatory bugs, ants, and spiders. The bobolink, a small type of blackbird, has been nicknamed the "armyworm bird" in North America because of its predation on armyworms. Other birds that pose a predation risk are crows and starlings.

Migration

"P. unipuncta" are seasonal migratory moths that travel north in the spring to escape high temperatures and south in the winter to escape cold temperatures. It has been shown that females reared in high temperatures mated less often, and those that did copulate experienced a 10-fold decrease in fertile egg production compared to females reared in temperate conditions. This could indicate an evolutionarily beneficial reason for this migratory behavior. Females flying in the spring northern migration were found to have developed ovaries and mating experience whereas females flying in the fall southern migration were found to have little or no reproductive organ development. This lends further support to mating being favored in the summer months.