The Indian meal moth is a frequent stored products invader, and a pest that professional pest managers should be well versed in managing.
Far from being an occasional pest, Plodia interpunctella, the ‘pantry moth’ – or more correctly, the Indian meal moth – is a truly global pest found in warm climates around the world. In Australia it is found in all states including Tasmania, so pest managers need to be familiar with its habits and the potential control measures.
The Indian meal moth is the only moth in its genus and despite its name, it’s not actually a native of India. Its common name was given by a 19th-century US entomologist who described the larvae infesting cornmeal. At the time, cornmeal was sometimes referred to as ‘Indian meal’, thus the name.
The adult moths are easily identified. They are up to 10 mm long with a wingspan of up to 20 mm. The distal (rear) half of its forewing is reddish brown, bronze or dark grey, which is separated from the lighter (proximal) front half of the wing by a narrow dark band. Although easily identified, they are often only seen when disturbed. However, they do occasionally go on foraging flights to search for new food sources. If they do take to the wing, they do so during twilight hours, when they can be seen flying slowly around the kitchen. Although Indian meal moths can be present year round, the peak season for infestations is in late spring and summer, when the warmer temperatures speed up their life cycle.
Pantry moths can infest all manner of dried plant foods – cereals, grains, flour, spices, nuts, dried fruit, tea and chocolate. They will also infest pet food, bird seed and rodent bait! It is the larvae that do all the damage, and although they can be hard to spot, they leave behind their tell-tale webbing on the surface of infested food.
Female moths will lay hundreds of eggs near a potential food source. One of the important points to note about the pantry moth is that the larvae are capable of chewing through plastic and cardboard, and can even crawl around the threads of closed screw lids! Even unopened packets can be penetrated by pantry moth larvae. That said, the source of infestation in most cases is through infested, often unopened product being brought into the house.
Dealing with a pantry moth infestation follows a tried and tested process. Firstly, carry out a thorough inspection to identify all infested food. It is important to make sure it’s a comprehensive inspection – don’t assume the infestation is just in one cupboard. Make sure you check all food storage and pet food storage cupboards, and inspect under appliances and cupboards for any spilled food. If you don’t identify all infested food, it is very likely the problem will persist.
Once all the infested food has been identified, it should all be bagged, sealed and thrown into the bin. If the customer really wants to keep some of the food (!), for example the pet food, exposing the food to heat above 40ºC for a couple of hours will kill all the eggs and larvae present – placing food in black plastic bags in the sun for a couple of hours will do the trick.
All food cupboards should be vacuumed and thoroughly cleaned. The caterpillars can crawl some distance away from the food to pupate and the pupae can often be spotted in the top corners of cupboards or even on ceiling cornices. Once the cupboards are clean, they can be sprayed with a residual insecticide to kill any eggs present and provide protection against future infestation.
To make it difficult for larvae to attack food, all opened food packages should be placed in thick plastic or glass containers with tight-fitting lids. If you or your customer have any concerns about incoming food packages, they can always be placed in a freezer for a few days, just in case.
If the location has a history of recurring infestations, it may be a good idea to leave behind some pheromone sticky traps. Although these are primarily used as monitoring stations (so customers can contact you if they notice moths in the trap), they can be very effective in preventing an infestation, as they contain a female sex pheromone that lures male pantry moths and therefore prevents them from breeding.
Often homeowners will not realise they have a pantry moth infestation, as the moths often infest the hidden, unused food packets at the back of cupboards. So when visiting for another service, keep your eyes open for pupae near the ceiling and moths flying around the kitchen later in the afternoon for a potential upsell opportunity.