facebook   twitter   mail  

The Nelson Photo News

 

46

The Battle For The Pastures

There's a war being waged in Nelson, and upon its outcome could depend the future prosperity of New Zealand. The enemies are grass grubs; the forces for good, the Entomology Division of the D.S.I.R.

Nelson is the headquarters of the division, which is primarily responsible for all the research of insects, excluding the veterinary and forestry fields. At present, a considerable proportion of the research effort is being devoted to the study of insects affecting pastures, since the grasslands are of prime importance as a source of overseas earnings. Although the division has substations at Auckland, Palmerston North and Lincoln, scientists in the Nelson group are concerned with insect problems throughout the country. including sub-antarctica and off-shore islands.

But it is towards the control of the grass grub that about 50 per cent of research effort is directed. The grass grub is no new problem. A native insect it has thrived on the improved pastures, following the clearing of the forest, for more than 100 years. It is now so well established throughout New Zealand, that the country's grasslands are seriously threatened. It is at the grub stage that "Costelytra zealandica" damages the pastures, for the grubs below the earth's surface feed on the grass roots, destroying the grass at its source. The adult beetles which fly in November are not responsible for any appreciable feeding damage, but are vital to the life history of the species in that they lay the eggs which carry the infestation from one cycle to. the next.

In this photographic feature we will cover but a small segment of the battle being fought against grass grub and another pest, porina, by the various sections of the division. Each section is working towards control of the grub, but along different lines. The insecticide section concentrates on control through insecticides; biological control is investigating the possible use against grass grub of natural enemies, and the ecology section studies the relationship of insects to their environment. The other section, systematics, works in with all three and specialises in the classification of insects according to their relationships.

×

Close-ups taken by division photographer Barry Eykel of a grass grub and egg and the adult beetles.

×

Samples of grubs are taken from a pasture by a field team.

×

The division (ringed) established in The Wood area in 1937. Within four years it is to be shifted to Auckland.

47

On this page we show a part of the work of the insecticide section. Its first task is to evaluate possible new insecticides for the control of grass grub and porina caterpillars. For the last 15 to 20 years, DDT has been reasonably effective against both, but now it is less satisfactory because insects are developing a resistance to it, and because of a problem of minute quantities of DDT appearing in farm produce in the form of residues. The section now has to find insecticides to deal with the problem. To this end it receives new insecticides from all parts of the world for experimentation.

×

Section leader, Mr Peter Fenemore, displays trays of insecticide-treated soil containing grubs. The trays are kept in incubators at a constant temperature.

×

A fairly new procedure for the section is the radio-active labelling of grubs. The grubs are fed with different amounts of radio active material to see how long the material lasts in the grubs. The section is also assessing the possibility of radio-actively labelling grubs so they can later be traced in the field. Here, Mr Fenemore checks the amount of radio-activity in a particular grub.

×

Batches of caterpillars await treatment by technician, Mr David Perrott.

×

A close-up of a micro-drop applicator which measures minute drops of insecticide. In this case, porina caterpillars are treated with differing amounts of insecticide for study.

48

Biological Control

The other three pix show some of the work of the biological control section. This section deals with the use of the natural enemies of closely-related white grub species in other countries to control the grub in New Zealand, and also with the. possible use of insect diseases. Although over 20 potential parasites and predators have been tested in Nelson over the last few years, none has thus far looked likely to succeed in the New Zealand field.

These pictures also depict some other facets of the work of the biological control section.

×

Technician Christine Wells in a rearing room. Here the insecticide section is rearing house flies and using them to measure the quantity of insecticide in a sample by the effect produced.

×

A grub is inoculated with milky disease for laboratory study.

×

Another view of the procedure, carried out by Dr Michael Fowler.

×

At right, technician John Biss prepares smears of treated grass grub body tissues for the presence of the milky disease.