The Indianmeal moth (Plodia interpunctella), also spelled Indian meal moth and Indian-meal moth, is a pyraloid moth of the family Pyralidae. Alternative common names are weevil moth, pantry moth, flour moth or grain moth. The almond moth (Cadra cautella) and the raisin moth (Cadra figulilella) are commonly confused with the Indianmeal moth due to similar food sources and appearance. The species was named for feeding on Indian meal (the cornmeal and maize flour from maize), with Indian in the New World sense; it does not occur natively in India. It is also not to be confused with the Mediterranean flour moth (Ephestia kuehniella), another common pest of stored grains.
P. interpunctella larvae (caterpillars) 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 Indianmeal 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".References in Savela, Markku (2009): Markku Savela's Lepidoptera and Some Other Life Forms – Plodia. Version of 9 April 2010. Retrieved 10 April 2010.
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 (unjustified emendation) Plodia castaneella (Reutti, 1898) Plodia glycinivora (Matsumura, 1917) Plodia interpunctalis (Hübner, 1825) Plodia latercula (Hampson, 1901) Plodia zeae (Fitch, 1856) Tinea castaneella Reutti, 1898 Tinea interpunctalis Hübner, 1825 Tinea interpunctella Hübner, Tinea zeae Fitch, 1856 Unadilla latercula Hampson, 1901
The common name, "Indianmeal moth", for this species was coined by Asa Fitch, an entomologist employed by the state of New York in the 19th century. In a report published in 1856, Fitch discussed the species, noting that the larvae had been observed to infest stores of cornmeal, which at the time was referred to as "Indian meal".Fitch, Asa (1856) First and Second Report on the Noxious, Beneficial and other Insects of the State of New York. C. Van Benthuysen, Albany, USA.
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 Indianmeal 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
Indianmeal moths feed on plants, grains, and other human food products.
Plant-based foods Moths feed on many plant-based foods including dry pet food (plant based), 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 Indianmeal moths are also known to cannibalize larvae. This often leads to viral granulosis infections spreading through an Indianmeal 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 Indianmeal 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 (400–475 nm) rather than UV light (10–400 nm) is dominant and attracts the moths. Blue light's role in the Indianmeal 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 Indianmeal 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.Lyon, William F. (2006): Ohio State University Insect and Pest Fact Sheets – . Version of 31 August 2006.
Diapause 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 Indianmeal 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 (Lacertilia) Rodents (Rodentia) Spiders (Arachnida) Other cannibalistic Indianmeal 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."Biological Control of Stored-Product Pests" Midwest Biological Control News (University of Wisconsin)
Diseases Baculoviruses are double-stranded DNA viruses commonly used as biological control agents for the Indianmeal 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 Indianmeal moths are developing a resistance to many kinds of biological agents, such as the granulosis virus. Use of pest-control agents can cause resistance to these agents to be selected for in populations of Indianmeal moths. In populations exposed to the granulosis virus, it was found that the moths were 96 times more resistant to the virus; this led to the prohibition of many such biological agents.
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 Indianmeal 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 Indianmeal 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.
Female–male interactions
Female pheromones
In the Indianmeal moth, mating occurs a few days after the adult moth emerges from the silk cocoon. Mating rituals are largely limited to pheromones release by the female. There are four identified (via mass spectrometry techniques) primary pheromones in the female pheromone blend: (Z,E)-9,12-tetradecadienyl acetate, (Z,E)-9,12-tetradecadienal, (Z,E)-9,12-tetradecadienol, and (Z)-9-tetradecenyl acetate. These pheromones are attractants to male moths. Removing any one component of the blend reduces the activity of the pheromone and the number of males attracted. Other components of the pheromone blend are also known but their functions are unclear. It has been suggested the reason for having so many components to the pheromone is that it ensures species specificity.
Male pheromones
Male moths also release pheromones. After approaching the female from the back, the male releases a pheromone from wing glands located at the base of each forewing. These pheromones induce the female to remain stationary in the acceptance posture (raised abdomen between wings) which facilitates copulation.
Copulation and multiple mating