Larvae of the white butterfly (Pieris rapae) eat the leaves of cruciferous crops such as cabbage and broccoli. Adult white butterflies are cream with black spots on the wings, and are a common sight in summer. The yellow, bullet-shaped eggs are attached to the underside of brassica leaves. Larvae are covered in fine hairs, and are pale yellow-green when young, darkening to dull green with a thin orange stripe as they mature. The parasite Cotesia rubecula was introduced to New Zealand in 1993 to help control them.
The diamondback moth (Plutella xylostella) is small and slender, with a row of yellow, diamond-shaped markings visible on the wings when they are folded along the body. Eggs are laid singly or in batches on the underside of brassica leaves, and hatch into greyish-green larvae which grow to about 10 millimetres in length. These caterpillars feed on brassica leaves, leaving many small holes.
Potato tuber moth
The potato tuber moth (Phthorimaea operculella) is a major pest of potatoes in some places. It has slender grey-brown wings which are heavily fringed with hairs. Eggs are laid on potato foliage or exposed tubers. The pink or greenish larvae grow to approximately 10 millimetres long and bore into the tubers, making them unsaleable.
The tomato fruitworm or corn earworm (Helicoverpa armigera) affects many plants, including tomatoes and maize. The damage done by caterpillars to flowers and fruit causes considerable financial losses. Adult moths have brown-to-orange forewings, while the caterpillars are variable in colour, ranging from pink to green to dark brown. The caterpillars move in a looping motion, devour leaves, and eat into tomatoes and corn cobs. Two parasites, Cotesia kazak and Microplites croceipes, have been introduced to control tomato fruitworms.
Thrips are mobile insects that rasp the surface of fruit and leaves, puncturing plant cells to suck the sap. Affected leaves take on a silvered appearance. Thrips also transmit diseases.
The endemic New Zealand flower thrips (Thrips obscuratus) infests several stonefruit, including nectarines, apricots, plums and cherries. Their feeding causes russetting on fruit. Greenhouse thrips (Heliothrips haemorrhoidalis), first found in New Zealand in the 1930s, has a wide host range that includes avocados and citrus fruits. Onion thrips (Thrips tabaci) attacks vegetable crops including onions, lettuces and tomatoes.
Mites are not insects, but belong in the same taxonomic class as spiders and have eight legs. They are tiny and often too small to see.
Two species known as spider mites damage horticultural crops by feeding on plant juices, and their presence puts export crops in quarantine. The two-spotted spider mite (Tetranychus urticae), named for the spots on its back, is a ubiquitous pest that attacks orchard and greenhouse crops. The mites produce a large amount of webbing on the foliage they eat, and heavy infestations make leaves look bronzed. The European red mite (Panonychus ulmi) is predominantly an orchard pest and causes leaf discolouration.
The predatory mites Typhlodromus pyri and Galendromus occidentalis can reduce populations of these pests.
Aphids and mealybugs
Various species of aphid and mealybug suck plant sap, and heavy infestations may inhibit and distort new plant growth. They produce sticky secretions on which sooty mould can grow and diseases spread. Three species of mealybug (Pseudococcus longispinus, P. calceolariae and P. viburni) infest grapevines and spread leafroll virus, a significant disease in vineyards.