Combating Wasps in New Zealand

New Zealand Journal of Agriculture, Volume 81, Issue 5, 15 November 1950, Page 459

Combating Wasps in New Zealand

By

C. R. PATERSON,

Apiary Instructor, Department of Agriculture,

Hamilton, and C. R. THOMAS, Plant Diseases Division, Department of Scientific and Industrial Research, Auckland.

ASPS of the species Vespula germanica were first discovered in ** New Zealand in the Waikato district several years ago. These wasps, which are common in England and European countries, appear to have become permanently established in the central part of the North Island in spite of all measures taken to eradicate them. Their control, however, is desirable, as there will be seasons favourable to their establishment when they may become a nuisance to the public, especially to domestic fruit growers and beekeepers. Every endeavour should be made to locate nests and to destroy them, and to assist in this destruction the Department of Agriculture will issue 10 per cent. D.D.T. powder free on application.

EXPERIENCE gained over the last 5 years in a close study of the wasp Vespula germanica (previously Vespa germanica) has shown that it is practically impossible to eradicate once it has become established in a district. It is also unfortunate that its spread to other districts cannot be controlled because of the many ways hibernating queens may be carried about. Queens have been found in raincoats, packing cases, trucks of coal, logs, trucks of timber, wire holes in concrete fencing posts, muslin covering on rolls of bacon, bundles of sacks, and even travelling cases. Flying queens before and after hibernation may also be wind-borne for a considerable distance into new territory.

An effective control can be carried out if the public will destroy all nests discovered and kill any queens that may be found in hibernation or on the wing. Life History It is desirable that the life history of the wasp should be understood. Young queen wasps of the species Vespula germanica ■ are raised in autumn, and after mating they hibernate singly or in groups in dark, sheltered corners. With the exception of newly emerged young queens, all the community, including old queens, die in autumn and the old nests are abandoned. However, a small percentage of these nests remain active throughout winter, and it is the

inhabitants of these over-wintered nests that cause a considerable amount of concern to beekeepers.

In spring the young queen awakens and immediately searches for a suitable place (usually a cavity in a dry earth bank) to begin building her nest. The wasps protect their many tiers of brood cells by building a bag of several layers of fragile paper made from wood pulp prepared by their jaws and placed securely in position. Only a few cells made of the papery material are built at first and a single egg is laid in each. When these eggs hatch the resulting grubs are fed by the queen on a diet of masticated insects of all kinds, including flies and caterpillars, which she catches herself. As each grub grows, the queen builds up the cell walls hexagonally and also begins other cells round them in which more eggs are deposited.

Worker Wasps Emerge

About 28 days after the first eggs are laid worker wasps emerge from the cells. The new arrivals enlarge the nest, build additional new combs, and extend the paper walls sufficiently to develop second and subsequent batches of larvae. Worker wasps develop in rapid succession, and soon the queen has a large army of assistants and is relieved of all her earlier duties except that of egg laying. As the nest is enlarged the worker wasps excavate to provide adequate room. This work is done with their mandibles and the bulk of the spoil is carried out and dumped well away from the entrance. All the new arrivals are workers (imperfect females) until late in the season or in early autumn, when numbers of males and young queens are produced.

Surplus Workers

Throughout spring and early summer they feed almost exclusively on other insects, but by February, when the nest has become well established, there are usually more workers than are necessary to maintain the normal economy of the nest. At this

time and until late in the autumn before the workers, males, and the old queen die, these wasps, because of their fondness for sweets, including jam and ripe fruit juices, become a great nuisance to housewives and beekeepers and in home orchards. Beehives receive considerable attention from these wasps and any weak colonies are likely to be slowly robbed of their honey. The wasps do not store honey or other sweets in their nests, as no food is required for consumption in winter. By May, when the young queens bred in autumn leave the nest and fly away to hibernate, there is a decided slackening off in the activity of the wasps. The outside paper covering of the ordinary wasp nest is light greyish. Nests may be located by watching the regular flight of the wasps in any direction, especially near ground level or toward the entrance to a hole in the ground. The sides of an earth bank where conditions are likely to be fairly dry are favoured for the building of nests.

Unlike the honey bee, which dies once it loses its sting, the female wasp can sting repeatedly. It is unfortunate that these insects have become established in New Zealand, and though they are regarded in other countries as being more a nuisance than a pest, in New Zealand it is desirable to control them. That can be done only by the vigilance and prompt action of the .public in locating nests and by suitable arrangements for their destruction. Where to Look for Hibernating Queens As each nest left undestroyed may produce hundreds of queens in autumn, it is worth while knowing where to look for queens once they have gone into hibernation. The following are some of the places favoured by these queens:— 1. Underneath loose bark on semidecayed trees. In 1948 around Hamilton thousands of queen wasps were discovered in such hibernating places.

2. Under sacks hanging on a fence or piles of sacks in a shed. 3. Underneath tile roofs or between roofing iron and sarking. 4. Under stack covers. 5. In coats or clothing hanging up in ope-n sheds. 6. Under piles of stacked timber. Where to Look for Nests Nests can be found in a great variety of places, sometimes even in buildings. Gullies, river-banks, and drains appear to offer the most suitable places for the queens to begin a nest in spring. Although a nest may be several feet long, the only indication that it exists is a small opening (about 2in. in diameter) from which wasps can be seen coming and going. Because these small openings are very difficult to find, the observer has to be guided by the flight of the wasps to a particular spot. It is surprising

how many nests can be located by watching carefully and then following the main direction of flight until a point is reached where it is quite easy to see them entering a hole in the ground.

Control Measures

Much experimental work has been carried ■ out . in an endeavour to improve the control measures used in the past, but at present the only effective means of control appears to be based on the destruction of queen wasps and established nests before queens have had time to hatch out.

Queens can be caught easily during hibernation. While flying around in spring, they can be knocked down with a fly swat or tennis racket.

Nests once discovered can be dealt with by dusting D.D.T. powder well into the opening. It has been found that unless a nest has been disturbed previously powder can be applied quickly with very little risk of the operator’s being, stung. The application of this powder can be made during the daytime, when the wasps are flying in and out, or it may be left until evening, . when activity has quietened down.

For D.D.T. to be effective it is essential that it should be well distributed inside the opening, because the wasps must come in contact with the powder. A second . application is sometimes needed a week or so later where the wasps have found a track out which is free of D.D.T. Applying the powder by a tube as illustrated gives efficient distribution. If the tube is loaded before approaching the nest,' only a second or two is required to administer the dose. Hundreds of nests have been treated in this manner without operators being stung.

■». To assist the public in the destruction of every possible nest the Department of Agriculture will issue free a supply of 10 per cent. D.D.T. powder to anyone notifying nests. Supplies and information will be available from the nearest office of the Depart- - ment. The. public should endeavour to destroy' every nest and should kill hibernating queens immediately. If this is neglected, it is possible that in some seasons wasps will be so numerous that great inconvenience and annoyance may be caused to everyone; their stings are painful, and in autumn they are very persistent in their search for sweets such as jam, ripe fruit, and honey.

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COMBATING WASPS IN NEW ZEALAND