Brett Miller, a Biosecurity Officer with the Northland Regional Council, says guava moth (Coscinoptycha improbana) has a voracious appetite for the fruit of many of the region’s trees – feijoa in particular.
Mr Miller says guava moth larvae have little chance of being exposed to insecticides because they burrow directly into fruit, so targeting the leaf litter they live in during the cocoon phase of their life cycle is a better alternative.
Guava moths are a problem because their caterpillars infest and eat fruit and also contaminate it with their excrement.
Although feijoa is one of the guava moth’s favourite foods in Northland, it also attacks a wide range of fruit including citrus, macadamia, loquat, plums, peaches and nashi and can move from species to species as its fruit ripens.
Mr Miller says fallen fruit, leaf litter and soil beneath trees plays an important part during the cocoon phase of the moth’s life cycle.
“With feijoa now beginning to form on the many trees dotting the region, it’s a good time to ensure leaves and other debris beneath fruit trees is removed and burned. As the feijoa season gets into full swing, it’s also important to do the same with any unwanted fallen fruit too.”
He says burning is important because composting material does not always kill the moths.
Mr Miller says guava moth was first found at Ahipara and Kaitaia in 1997 but has subsequently reached as far south as Whangarei. It is originally thought to have blown across the Tasman Sea.
Adult guava moths are about one centimetre long and cream in colour, overlain with black and white speckles. They are so similar to other moths it takes microscopic analysis with a trained eye to positively identify them.
Moths lay their tiny eggs in cracks at the end of fruit. Caterpillars then emerge from the eggs and burrow into ripening fruit to feed and grow. More than one larva can be found in each piece of fruit but infestation is not normally total for all fruit on a tree while some trees can miss out on being infested altogether.
When infected fruit ripens and falls to the ground, the fully-grown larvae leave the fruit and move into surrounding leaf and soil litter to build a camouflaged cocoon about 8mm long. After about a fortnight (depending on temperature), the adult moth emerges to lay more eggs and the cycle continues.
However, studies have found that guava moth do not move far from fallen infested fruit to make their cocoons, hence the advice to rake up and remove fallen fruit, leaves and soil debris.
Meanwhile, Mr Miller says adult guava moths can also be caught using special sticky traps available from plant shops. The small and relatively inexpensive traps are baited with caps that have been impregnated with scents that sexually attract the moths.