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Lepidoptera / Noctuidae
Helicoverpa armigera conferta
(Previously known as Heliothis armigera)
Found throughout New Zealand, tomato fruit worms are caterpillars that chew holes into flower buds and fruit. They also chew patches out of unfolding leaves, causing plants to be stunted.
Tomato fruit worms feed on a very wide range of host plants, so they can cause a lot of damage and defoliation when their population builds up.
When feeding on tomato fruit, they’re commonly referred to as ‘tomato fruit worm’; but when feeding on sweetcorn they’re commonly referred to as ‘corn earworm’. Overseas, these names describe different species, but in NZ it’s actually the same miscreant causing the trouble in both cases.
The caterpillars that cause the damage are the larvae of ochre-brown nocturnal moths. Because the moths are usually found in the tropics, their range in NZ is partly constrained by frost; but the moths are capable of long-distance flight so they rapidly expand South during warmer weather.
Caterpillars range in colour from light green, to red, to almost black and often have light stripes along their back and sides. Tomato fruit worm pupates below ground to get through the winter, emerging as adult moths between November and March.
When feeding on tomato fruit, they usually hide under or around the stalks.
In sweetcorn, the most serious damage occurs when the larvae chew the ears and corn kernels. To add insult to injury, the caterpillars leave behind moist skin castings, which can result in mould and leave the corn prone to diseases.