The correct common names is the Indian meal moth, but is often called the pantry moth and sometimes the weevil moth, flour moth or grain moth.
Pantry moths are invasive pests.
Pantry moths are found across Australia and worldwide – any country with a warm climate.
The larvae are small after hatching and will grow up to 14 mm long as they go through between 5 – 7 moults. They have dark heads and a pale body which can vary a bit in colour depending on what they are eating.
Their presence in dried food if often first spotted by noticing webbing material over the top of the food.
Adult moths are up to 10mm long with a wingspan of 20 mm.
The rear half of the wing is reddish brown or grey, separated from the light grey front half by a dark band.
Adult pantry moths live only live for a week or two but the females will lay up to 300 eggs at a time.
The eggs will only hatch at temperatures above 10oC and may delay hatching in temperatures above 25oC. Eggs hatch in 2 – 14 days, depending on temperature.
The larvae move through between 5 – 7 instars. The duration of the larval stage depends on food availability and temperature. Young larvae can go into diapause if the temperature drops below 20oC. The older larvae can spin webbing, which can be seen on the food substrate and is also used for spinning their cocoons.
The larvae building their cocoons on the surface of the food or on the walls of the food container. Adults emerge after 4-10 days.
The duration of the life-cycle is very variable and can be between 30-300 days depending on the temperature. Until ideal conditions it is possible to go through up to 9 generations a year – infestations can get quickly out of control!
The Indian meal moth or pantry moth are a significant pest of dried foods in both commercial and residential situations.
Apart from damaging the food directly, they leave behind webbing and droppings. This means in most cases human food is wasted and needs to be thrown out. Animal feed may be kept, by killing the moth larvae and eggs through freezing or heating the food. However, often this is not worth the trouble.
Pantry moths will infest a wide range of dried plant based foods, such as cereals, flour, nuts & spices, dried fruit, tea and chocolate. The will also infested processed foods such as pet food (also bird seed) and even rodent bait!
It is only the larval stage that causes the damage, the adults do not feed.
In Australia, the peak pantry moth season is in the warmer moths (Jan-Mar).
The adult moths aren’t great flyers but will often be seen flying around kitchens (or near other infested areas) in the evenings.
The other key sign of an infestation is the webbing on the surface of infested food.
IMPORTANT NOTE: It is important to understand that the larvae can chew through plastic bags and indeed crawl around the thread of closed jars. So if you have a pantry moth infestation, you need to check ALL food containers.
The first step in getting rid of a pantry moth problem is to find the source of the infestation. This takes a bit of time and patience, as you need to find all the infested food and throw it out.
It can be a good idea to call a pest professional as they will know all the likely hiding places… and indeed the unlikely places… you won’t believe all the packets and apparently sealed containers that the larvae can still get into! Don’t forget the larva can check through plastic bags and crawl around the thread of closed jars!
All food cupboards should then be clean and treated with a suitable insecticide. Your pest manager will know the best (and safest) product use for this purpose.
To guard against future infestation pheromone stick traps are a good idea. These can be bought at your local supermarket or hardware store. These pheromone traps release the females sex pheromone, so will only trap males. These will help reduce the chances of an infestation, as by trapping the males it means they can’t mate, but infestations can still develop as the females can still lay eggs (assuming they have mated). So pheromone traps are probably best viewed as a monitoring device or early warning system.
For commercial situations, there are product that use the same pheromones to disrupt the mating of pantry moths, which can be very effective in preventing infestations and reducing the need for insecticide applications.