Indianmeal moth
The Indianmeal moth, also spelled Indian meal moth and Indian-meal moth, is a pyraloid moth of the family Pyralidae. Alternative common names are hanger-downers, weevil moth, pantry moth, flour moth or grain moth. The almond moth and the raisin moth are commonly confused with the Indian-meal moth due to similar food sources and appearance. The species was named for feeding on Indian meal or cornmeal, and does not occur natively in India. It is also not to be confused with the Mediterranean flour moth, another common pest of stored grains.
P. interpunctella larvae are commonly known as waxworms. They are not the same species as the waxworms often bred as animal feed. Rather, they are a common grain-feeding pest found around the world, consuming cereals, fruits, and similar products. Substantial efforts have been taken in the United States to control the moth's damage to grain crops.
The larvae of this species have the ability to bite through plastic and cardboard so even sealed containers may be infested. Once found, the moths are difficult to eradicate.
The last larval instar is also able to travel long distances before pupating; so a new infestation site may develop far from the last pupation site. In addition to food sources, this species can reproduce and pupate on clothing and any source of clothing must be inspected to prevent reinfestation.
Distribution and habitat
Plodia interpunctella is found on every continent in tropical habitats, excluding Antarctica. Within the United States, the moth is most commonly found in Florida, where it thrives in the tropical habitat. The moth lives in a wide range of conditions, making it a persistent pest. It is often found at food storage facilities worldwide, specifically in grain bins or grain storage buildings.Taxonomy and etymology
The Indian-meal moth is the only known living species of the genus Plodia. It is closely related to the genera Cadra and Ephestia, which include other pest species like E. kuehniella, also known as the "flour moth".The species has been described under a number of junior synonyms, which may occasionally still be found in non-entomological sources.
- Ephestia glycinivora Matsumura, 1917
- Ephestia glycinivorella Matsumura, 1932
- Plodia castaneella
- Plodia glycinivora
- Plodia interpunctalis
- Plodia latercula
- Plodia zeae
- Tinea castaneella Reutti, 1898
- Tinea interpunctalis Hübner, 1825
- Tinea interpunctella Hübner,
- Tinea zeae Fitch, 1856
- Unadilla latercula Hampson, 1901
Description
Adults are in length with wingspans. The distal two thirds of their forewings are generally reddish brown in color with a copper luster. They can also be bronze or dark gray. The more proximal parts of the wings are yellow-gray or white-gray, with a dark band at the intersection between the proximal and distal regions. The hindwings, in general, are uniformly gray.The eggs of the Indian-meal moth are white, ovate, and very small. It is difficult to see them with the naked eye. Newly hatched larvae are equally difficult to see. They are mostly off-white in color, have brown heads, and develop through five to seven larval instars. When these larvae mature, they measure about long. Larvae also have three sets of legs near the head and five sets of prolegs protruding from the abdomen. The legs help the larvae move over long distances in order to find pupation sites.
Food resources
Indian-meal moths feed on plants, grains, and other human food products.Plant-based foods
Moths feed on many plant-based foods including dry pet food, birdseed, cereal, soup mixes, bread, pasta, rice, flour, spices, dried fruits and nuts. There is strong evidence that the northern Manitoba wheat supports the development of the moth. Other optimal diets include sultanas, American yellow corn and almonds. Groundnuts and maize meal, on the other hand, result in a longer development time for the moths.Non-plant foods
Indian-meal moths are also known to cannibalize larvae. This often leads to viral granulosis infections spreading through an Indian-meal moth population. Healthy larvae are picked more often than unhealthy larvae for cannibalism. There appears to be no kin discrimination and siblings can be eaten by caterpillars.Foraging flights
Though Indian-meal moths generally do not migrate over long distances, they do engage in long-distance foraging flights. These flights take place during the twilight hours during which blue light rather than UV light is dominant and attracts the moths. Blue light's role in the Indian-meal moth foraging behavior has recently been harnessed as a form of pest control since it is attractive to the moth.Life history
Eggs
Usually the life cycle of an Indian-meal moth colony starts in a location where grain is present. The temperature within a grain bin must exceed. The eggs of the moth are grayish white and have a length between. Eggs can be laid directly on the food source singly or in groups of between 12 and 30. A mature female may lay between 100 and 300 eggs at a time.Larvae
Larvae begin to hatch in approximately two to fourteen days. The larvae have between five and seven instars. Newly hatched larvae feed on grain while more mature larvae feed on grain germ. The larvae are an off-white color, but can be pink, brown, or greenish. They are about 12 mm long and have prolegs for movement. Fully-grown larvae are able to spin webs and leave silk threads in their path of travel. Mature larvae that make silk also make threaded cocoons.Adults
The pupae are often seen on grain surfaces and on the walls of grain bins. The adults emerge in four to ten days. They then mate and the cycle begins again. The entire life cycle of this species ranges between 30 and 300 days. A typical life cycle is 50 days. Under optimal conditions a life cycle can be as short as 28 days but cooler winter months prohibit this. Seven to nine generations of moths can live in a year.Diapause
is defined as a delay in animal development due to certain external factors and can end once the adverse environmental conditions wear off. The duration of diapause can vary in Indian-meal moths. Diapause is especially prevalent late in the breeding season. During the egg stage, if the temperature of the moth's environment exceeds, it can cause a delay in hatching. In the moth's early larval stage, temperatures of below can cause a similar diapause. Different strains of P. interpunctella have differing tendencies to enter diapause.Enemies
Predators
- Nocturnal insectivores: birds, bats, and owls
- Lizards
- Rodents
- Spiders
- Other cannibalistic Indian-meal moths
Parasites
- Habrobracon hebetor is a parasitoid wasp that is commonly used in biological control. The adult wasp finds and paralyzes the Indian meal moth's larva with a sting. After immobilizing the larva, the wasp deposits its eggs on the host's body. After hatching, the wasp larvae feed on the host moth larva; their gut enzymes denature the host's blood proteins, ultimately killing it.
Diseases
- Baculoviruses are double-stranded DNA viruses commonly used as biological control agents for the Indian-meal moth and are considered parasites. They come from a family of viruses that are limited to insects as hosts. Baculovirus isolates have been often isolated from other Lepidoptera. At sub-lethal dosages, baculoviruses decrease reproductive capacity in terms of egg viability and production.
Immunity
Regulations prevent the use of many pesticides near food sources, so these pests are highly suitable for control with natural predators.
Mating
Male–male interactions
Sperm competition
Females mate multiple times, so sperm competition could be an important aspect of male–male competition for being reproductively successful. Males have a limited number of sperm and allocate it depending on various factors. Male Indian-meal moths ejaculate a greater amount of sperm to females that have mated multiple times previously. This is to ensure a greater chance of success in sperm competition in the females' storage organs. Males also ejaculate more sperm when mating with a younger female.Food and pupation site competition
The most common type of competition in Indian-meal moths is due to a lack of food. This competition can change the timing of male and female emergence, reducing the chance of early males finding females to mate with, which could encourage emigration. This is considered a form of male–male competition because males that emerge at an appropriate time are more likely to be reproductively successful with the surrounding females.Males are also involved in finding pupation sites. If the larvae do not find pupation sites in the food layer, they may wander long distances to find one. This competition to find a pupation site affects males more than it does females, it indirectly impacts females as well because it results in a delayed population of males to mate with.