Various attempts have been made to control weeds by introducing insects to attack them. The most notable attempts at control have concerned the following:

Gorse by a seed weevil (Apion ulex); ragwort by the seed fly (Hylemyia seneciella), the leaf miner (Phytomyza atricornis), and the cinnabar moth (Tyria jacobaeae); St. John's wort by the beetle (Chrysolina hyperici); Mexican devil weed by the gall fly (Procecidochares utilis); manuka by blight caused by the coccid, Eriococcus orariensis.

Virus:

The white butterfly (Pieris rapae) is attacked by a virus to such an extent that it plays an important part in field control of this pest.

Bacteria:

Naturally occurring bacterial diseases materially help to control the diamond-back moth (Plutella maculipennis).

Fungi:

Fungi play a role in control of the diamond-back moth. The fungal parasites of the genus Cordyceps attack subterranean grass caterpillars and other hepialid caterpillars and change the body of the caterpillars into the so called “vegetable caterpillars”.

Nematodes:

These are of no importance as yet in New Zealand but are known to attack grass grubs (Costelytra zealandica).

Most of the pests of plants, animals, or man are recent introductions, almost without exception having been introduced unwittingly by man over the last 150 years.

Control

Chemicals: The use of insecticides is controlled by the Agricultural Chemicals Board. Some chemicals are prohibited and regulations are made from time to time governing the use, application, and rates of insecticides.

The following pests in New Zealand are known to have become resistant to insecticides.

Housefly (Musca domestica) against DDT and Dieldrin; Blowfly (Lucilia sericata) against Dieldrin; Leaf roller (Austro-tortrix postvittana) against DDD; European red mite (Panonychus ulmi) against organo-phosphorus sprays; Two-spotted mite (Tetranychus telarius) against organo-phosphorus sprays; Midge (Chironomus zealandicus) against Dieldrin.

Biological control: The following are some of the cases of attempted control of insect pests by specially introduced insect enemies which have shown a worth-while degree of success.

Woolly aphis (Eriosoma lanigerum) by Apelinus mali; Cottony cushion scale (Icerya purchasi) by the ladybird, Vedalia cardinalis, and the fly Chryptochaetum iceryae; Gumtree scale (Eriococcus coriaceus) by the ladybird Rhizobius ventralis; White butterfly (Pieris rapae) by the pupal parasite (Pteromalus puparum).

Plant resistance to pests: Some resistant plants have been introduced, notably apple stocks resistant to woolly aphis and grape stocks resistant to phylloxera. Plants have been bred for resistance to insects especially brassicas, beans, and cereals.

Anoplura: Lice. Small dorso-ventrally flattened, wingless animal parasites. 60 species. The majority are biting lice (Mallophaga) and are found on native birds. Introductions in recent times include the common sucking and biting lice of farm and domestic animals.

Coleoptera: Beetles and weevils. Forewings modified to tough elytra or wing cases. 4,500 species. The most abundant are the weevils, carabs, rove beetles, longicorns, leaf beetles, and click beetles. Most well-known families are represented, but there are relatively few chafers, jewel beetles, stag beetles, and ladybirds. The most interesting ones are the huhu beetle and its grub, the giraffe beetle, and the grass grub beetle and its larva. Introduced species include the “cosmopolitan-stored-products” beetles and weevils and the furniture and timber borers.

Collembola: Springtails. Small wingless insects with a jumping organ. 230 species. New Zealand has a large fauna most of which live in debris at soil level. Some of the largest individuals of the order (up to 10 mm in length) occur in New Zealand.

Dermaptera: Earwigs. Elongate with abdominal forceps. 3 species. Little is known about the endemic fauna. The introduced European earwig is common in gardens and orchards.

Diptera: True flies. Two-winged insects. 1,850 species. Most of the well-recognised families are represented. Some are particularly numerous and more species are known than in Australia. Such families are the crane flies, gnats, midges, kelp flies, dance flies, and tachinids. Other families are worthy of note because of their very weak representation, viz.: beeflies, fruit flies, and louse flies. Some families are absent such as the wasp flies and March flies. Of special interest are the New Zealand glow worm and the salt-water mosquito.

Ephemeroptera: Mayflies. Delicate insects with three long caudal filaments. 20 species. Common near freshwater lakes and streams throughout the country.

Hemiptera-Heteroptera: True bugs. Sucking insects with forewings hardened bassaly. 85 species. Poorly represented in most of the well-recognised families. The largest families and those of most importance are the shield bugs, assassin bugs, and capsid bugs. Of special interest are the shield bugs, back swimmers, water boatmen, and the primitive Peloridiid bugs. A recent introduction is the Nezara or green vegetable bug. The bed bug is rare.

Hemiptera-Homoptera: Aphids, cicadas, hoppers, scale insects. Sucking insects, usually phytophagous. 300 species. Families well represented are the cicadas, leaf hoppers, scale insects, and mealy bugs. Endemic aphids are rare, but 47 species are recent immigrants and are particularly abundant. The place of the aphids in the endemic insect fauna of New Zealand is taken by the more primitive psyllids. Of special interest are the large green and black cicada and the many scale insects. Introduced hoppers include the passionvine hopper and the green hopper, both of which are indigenous Australian species.

Hymenoptera: Ants, bees, ichneumons, wasps. Usually “wasp-like” insects with stiff clear wings. 350 species. Although much of the fauna has not been studied, it appears that the order is poorly represented in New Zealand. There appears to be no endemic sawflies or horntails, few sand wasps and no social wasps, no social bees and few solitary bees. The best represented families are the ichneumon and braconid parasites. Of special interest are the blind ants, mason wasp, and the large ichneumons. Accidental introductions include the European wasp, the Tasmanian wasp, and many species of pest ants. Honey bees and bumble bees have been deliberately introduced.

Isoptera: Termites. Social insects with distinct castes; wings long and narrow. 10 species. The two endemic species are dry wood termites, and damage trees, logs and fence posts. Australian termites (8 species) have been accidentally introduced and some have become serious pests.

Lepidoptera: Moths and butterflies. Two pairs of wings bearing scales. 1,500 species. The major point of interest is the paucity of butterflies. Only 15 species occur, but some additional species have been accidentally introduced in recent years or are occasional immigrants which do not become permanently established. Recent introductions are the white butterfly and the monarch or wanderer, while the blue moon butterfly is an occasional visitor. There are no naturally occurring skippers or swallow tails and only few admirals, blues, and coppers. Moths are well represented by many grass moths, case moths, leaf miners, leaf rollers, plume moths, and noctuids. Of special interest are the monarch butterfly, the puriri moth, and the porina moths and its caterpillar – the subterranean grass caterpillar. “Cosmopolitan-stored-products” moths and clothes moths are well established.

Mecoptera: scorpion flies. Long-winged insects with a snout. 1 species.

Neuroptera: Lace wings, ant lions. Two pairs of membraneous wings with many cross veins. 13 species. Poorly represented in New Zealand. Most species belong to the brown lace wing family or the ant lion family. Of special interest is the large ant lion.

Odonata: Dragonflies and damselflies. Usually large slender insects with two pairs of large wings. 13 species. Although poorly represented, they are conspicuous members of the insect fauna and their aquatic larvae are numerous in most streams and lakes. Of special interest is the large black and yellow dragonfly.

Orthoptera: Cockroaches, crickets, grasshoppers, mantids, stick insects, wetas. 80 species. Most families are well represented but there are relatively poor numbers of species of endemic cockroaches, mantids, crickets, mole crickets and grasshoppers. The wingless stick insects and wingless wetas are important elements in the fauna. Of special interest are the Maori bug, bush cockroach, large stick insect, bush weta, cave weta, giant tree weta, true locust, and the katydid. Introduced forms are in many cases well established and include the German and the American cockroaches, the praying mantid, and the field cricket.

Plecoptera: Stone flies. Sluggish four-winged aquatic insects. 25 species. Fairly common insects around freshwater streams. Most species belong to widespread Southern Hemisphere families.

Protura: Proturans. Minute wingless soil insects without jumping organs. 2 species. Only recently discovered in New Zealand.

Psocoptera: Procids, booklice. Very small insects winged or wingless. 20 species. Of interest is the wide representation of well-known families. The cosmopolitan booklice is well established and is a pest in houses and museum collections.

Siphonaptera: Fleas. Wingless laterally flattened parasites. 6 species. Endemic species occur on a native bat and on a penguin. Cosmopolitan man and animal fleas are well established.

Thysanoptera: Thrips. Small insects with short, very slender fringed wings. 11 species. About 20 recent introductions are well established and many are important plant pests.

Thysanura: Bristle tails, silver fish. Wingless insects with long caudal cerci. 5 species. Endemic species fairly rare. The introduced European silver fish is common in houses.

Trichoptera: Caddis flies. Mothlike with hairy wings. 120 species. Abundant insects always associated with water. Larvae are an important source of trout food. Of special interest is the salt-water breeding caddis fly.

The following orders of insects appear to be absent from New Zealand: Embioptera (web spinners), Zoraptera, Strepsiptera (stylops).

Araneida: Spiders. Two divisions to body and eight legs. Most well recognised spider families are represented. Of particular interest is the poisonous katipo spider, the nursery spider, and the South Island trap-door spider.

Acarina: Mites and ticks. Small head, six legs in young stage, eight in adult. Endemic representatives belong to most suborders. Introduced forms are the Eriophyid and Tetranychid mite pests of plants, the Tyroglyphid mites of stored products, and the mite parasites of animals. No serious tick problem occurs on cattle.

Phalangidea: Harvestmen. Spiderlike, no body divisions, very long legs. Mostly found in sheltered places. Some large forms are present.

Speciation has proceeded at a normal rate, but owing to the relatively small size of the land mass of New Zealand and the lack of variations in the major habitats, the number of species in any group is not great. During the Pleistocene period when glaciation occurred in parts of New Zealand, it is probable that many endemic species then became extinct. The present-day absence of many groups of tropical or subtropical insects could also be due to their extinction in the glaciation periods.

The original natural cover of the New Zealand land mass before the human era was forest, tussock grasses, and sparsely covered or bare mountain lands. Through the replacement of vast areas of the forests by introduced grasses, many endemic species of insects, mites, and spiders are probably extinct. Insects abound in all habitats from the shore line to the high mountain regions. There are several associated with salt water, such as the salt-water breeding mosquito, the marine caddis fly, and marine mites. In the littoral zone, New Zealand has a rich community of insects and other organisms which live on decaying seaweed and seashore debris. Kelp flies are important New Zealand members of this community. Salt-water marsh lands have a distinctive and peculiar fauna including some species which tend to a subapterous condition. The forested areas provide a multitude of different ecological habitats. The North Island rain forest associations differ from the southern beech forests and some insect orders show distinct segregation of species in the two areas. Native tussock grasses still occur over extensive areas but the insect fauna of these areas has not been seriously studied. Some insects are found in the alpine areas, and such organisms as mites, springtails, harvestmen, and micro insects abound in forest litter. Intensive studies have been made on some of these insects and the conclusions drawn from such studies have been used in formulating theories on the past geography of New Zealand. Fresh-water lakes and rivers have an abundant fauna of bugs, beetles, flies, and caddis flies. Off-shore islands in many instances still retain much of their original vegetation and are important as localities of species which have become extinct on the mainland. Sub-Antarctic islands vary from the barren rocks of Bounty Islands to the tussock and low stunted forest of Auckland Islands. The insect fauna of these islands is sparse and is a peripheral one of the New Zealand subregion.

The New Zealand fauna is one of the most interesting in the world. It includes many unexpected elements and likewise lacks certain well known and otherwise widespread groups.

The New Zealand land mass may be described as subcontinental, in so far that it is probably a remnant of a more extensive land mass, but it has been isolated for a long time. Hence it has had no connection with other land masses which received many of the more advanced groups of animals and plants after its isolation. Thus mammals and other more recently evolved groups did not have access to New Zealand and this is reflected in the insect fauna. The long isolation has permitted the continued existence of primitive insects which might otherwise have become extinct through competition. The insect fauna shows some relationships to the fauna of South America and to New Caledonia, but overall most authorities regard it as being basically a peripheral one of the Australian region, for the reason that the majority of the components of the fauna have close relationship to Australian forms and also because some Australian elements are lacking often without any valid or obvious reason. Possible temporary or partial land connections with the Antarctic in the south and New Caledonia, New Guinea, north Australia in the north during the Mesozoic and early Tertiary may have made possible insect immigration from both these areas. There appears to be a faunal relationship with Tasmania due to a common source in Antarctica, and a relationship with Queensland and the lands to the north of Australia.

The uniqueness of some of the elements of the New Zealand fauna is shown in many groups. The primitive Peloridiid bugs are well represented and restricted to the southern areas of Australia and Chili and to New Zealand. This restricted distribution to southern lands is exemplified also by other families of bugs, and by some midges and beetles. Whether such a distribution points to a southern continental connection between land masses or whether it can be explained as the persistence of relics of former world-wide distributions followed by extinction in the northern continents, is still a matter for contention amongst zoogeographers.

The distance between Australia and New Zealand of 1,000–1,200 miles is not prohibitive for minute or flying insects. Such insects could make successful journeys across this distance when assisted by the prevailing westerly movement of the weather systems. There seems little doubt that successful dispersal across the Tasman Sea and South Pacific has been effected, at least over the past 20,000 years, and that successful establishment of many of the insects involved has occurred in New Zealand.

Man has been responsible for the introduction, either accidental or otherwise, of many insects into New Zealand over the last 150 years. Approximately 1,100 such species are known. A large number of these introduced insects have become pests of man, of his crops, or of his animals.

Insects:

The number of species known to occur in New Zealand is approximately 10,000. On the basis of a world census (1,000,000 species described and 2,000,000 species estimated), a figure of about 20,000 species may be close to the actual number for New Zealand. The last complete census of New Zealand insects was compiled in 1926 when the total was 8,150 species. This was a fair approximation although many undescribed species were included in that number. Some orders have been studied extensively since that time and, as a result, the number of species known has increased. The groups which have been most seriously studied in recent years are the spring-tails, wetas, aphids, scales, bugs, caddis flies, beetles, flies, and moths. Catalogues of species have been compiled in recent years for Diptera, Coleoptera, and Trichoptera.

Spiders:

A census of species in 1946 revealed that 304 species were known. Since that date some additions have been made and the total number of species now known is approximately 390.

Mites:

Ninety-nine species were listed in 1952. Lack of serious study in many groups of mites makes it apparent that the number occurring in New Zealand may well be far in excess of 100.

Harvestmen:

Recent study of this group has revealed a fauna of more than 160 species.

The main methods of controlling insect pests are:

By Chemicals: Since 1945, when DDT was introduced commercially to New Zealand, there have been many types of organic insecticides produced, the number growing with each year. DDT is the most common, about 1,200 tons of technical material having been used for control of grass grub, Costelytra zealandica (Wh.), in 1960–61. DDT is one of the chlorinated hydrocarbons; others of this class are DDD, lindane, dieldrin, and aldrin. The chlorinated hydrocarbons are nerve poisons, the first symptoms in poisoned insects being tremulousness of the entire body and its appendages, a condition known as “DDT jitters”. The second large class of organic insecticides contains the organophosphates, such as parathion, malathion, and gusathion. This group also includes insecticides that are systemic in their action, that is, they are taken up in the sap stream of the plant to which they may be applied and may kill insects (aphids, for example) through their feeding on the sap of the plant. Systox and metasystox are examples of such insecticides. Organophosphates are also nerve poisons, but they have a specific action which is not possessed by the chlorinated hydrocarbons. They inhibit the formation of cholinesterase, which is an enzyme necessary to the normal functioning of nerve tissue. Other organic insecticides that have appeared in recent years are the carbamates, such as sevin, and crotonates, such as karathane (acaricide).

Lead arsenate, once a very important insecticide, is now much restricted in use as is lime sulphur. Petroleum oils are still used, but there is now a tendency to rely on lighter fractions at or soon after bud movement instead of the older winter oils. Insecticides of plant origin, such as nicotine, derris, and pyrethrins, are still considerably used. An insecticide of vegetable origin new to New Zealand is ryania, which is just now being tried experimentally against codling moth, Cydia pomonella (L.). There are also fumigants, such as hydrocyanic-acid gas and methyl bromide, which are used to treat, for example, infested grain and similar materials.

A phenomenon that has appeared throughout the world since the advent of DDT is insect resistance to insecticides. Through repeated applications of chemical, certain insects, especially those with short life cycles, produce strains upon which the chemical is no longer effective. In New Zealand instances of this have appeared in the European red mite, Panonychus ulmi (Koch); the leaf roller, Epiphyas postvittana (Walk.); and the leaf hopper, Edwardsiana australis (Frogg.).

By Biological Means: This is commonly called “biological control”. Insect pests are controlled by parasites or predators, usually purposely introduced from overseas. New Zealand appears to be particularly suited for this kind of work as many of our pests are introduced species that have entered the country without their natural enemies. Several examples of this kind of control will be given: (1) The ladybird, Rodolia cardinalis (Muls.), on cottony cushion scale of citrus; (2) Aphelinus mali (Hald.) on woolly apple aphid, Eriosoma lanigerum (Hausm); (3) The parasites Pteromalus puparum (L.) and Apanteles glomeratus (L.) on white butterfly, Pieris rapae (L.); (4) The parasites Angitia cerophaga (Grav.) and Diadromus collaris (Grav.) on diamond-back moth, Plutella maculipennis (Curt.); (5) The parasite Prosactogaster demades (Wlk.) on pear midge, Dasyneura pyri (Bouche); (6) The parasite Habrolepis dalmanni (Westw.) on the golden oak scale, Asterolecanium variolosum (Ratz.); (7) The latest successful case is the control of the oak leaf miner, Lithocolletis messaniella (Zell.), by the parasites Apanteles circumscriptus (Nees), and Enaysma splendens (de L.).

In addition to insects, there are other agents of biological control, such as protozoa, bacteria, nematodes, virus, and fungi. The viruses are especially interesting because there are native species which are quite potent. In particular, there is one on white butterfly, Pieris rapae (L.), that, in the North Island at least, helps largely to control this pest on field crops of crucifers. At present it comes rather later in the season than is desirable and attempts are being made to introduce it earlier into the field. Then there is a bacillus, namely, Bacillus thuringiensis, (Berl.), produced commercially, which has some promise of controlling certain pests; it might, for example, be a satisfactory control of white butterfly and diamond-back moth on crucifers.

By Breeding of Resistant Varieties of Host Plants: The outstanding example of this is the resistance shown by Calder variety of swede to the cabbage aphid, Brevicoryne brassicae (L.). There is also a variety of rape into which this resistance to the aphid has been bred from the swede. And there are indications that some varieties of carrot are more resistant than others to the rust fly, Psila rosae (F.), and the aphid Cavariella aegopodii (Scop.).

By Sterilisation in Cold Storage: This method is applied to sweet oranges imported from South Africa. In the latter country there are the two species of fruit flies, the Mediterranean species, Ceratitis capitata (Weid.), and the South African species, C. rosa (Karsch.). It has been found that under certain conditions of transport at 31°F in the cold chambers of ships none of this fruit-fly material survives the journey from South Africa.

By Arranging Suitable Planting Dates: Seedling crucifers, especially in the South Island, if present when the adult beetles of the grass grub, Costelytra zealandica (Wh.), are about, are liable to be severely damaged. In this instance the pest is known as the “turnip fly”. The remedy is to delay planting until the main flights of the beetle are over, this safe period being usually about Christmas or the end of December.

Hygiene: The proper disposal of vegetable rubbish in which house flies could breed is of the utmost importance. Other control methods are mechanical measures by using heat, cultural practices or management, and by legislation (quarantine).

The chemical method is probably the commonest and main means of insect control, especially in such crops as fruit, vegetables, and tomatoes, but it has some disadvantages. First, the materials used are usually poisonous to human beings and leave residues on food; secondly, they cause resistance to chemicals to appear in certain plant pests, thus making controls more difficult; and thirdly, they are usually harmful to insect agents of biological control. It appears to be advisable, therefore, to make the most of the biological as well as the chemical method. It is important today that they should be “integrated”; that is, the chemical method should not be used so that it eliminates the biological one; rather, the aim should be to make control the sum of both methods.

by William Cottier D.SC., Late Director, Entomology Division, Department of Scientific and Industrial Research, Nelson.

• Plant Protection in New Zealand, Atkinson, J. D., et. al. (1956)
• The Diseases of Farm Animals in New Zealand, Reid, H. A. (1923)
• D.S.I.R. Bulletin No. 120 (1956), “Bibliography of New Zealand Entomology”, Miller, D.
• N.Z. Dept. of Agriculture Bulletin, No. 244 (1951), “Grass Grub and Grass Caterpillar Control”, Kelsey, J. M.
• Ent. Res. Sta. Publication No. 14 (1955), “Control of Grass Grub and Subterranean Caterpillar”, Kelsey, J. M.

There have been recorded many introduced pests of grain, dried fruit, cereal food, flour, cocoa, carpets, animal skins, etc., and even of books. These occur in the orders Coleoptera, Lepidoptera, Orthoptera, Thysanura, Hemiptera, Diptera, and Psocoptera.