INSECT DRAMAS.

Timaru Herald, Volume CXXV, Issue 18652, 22 August 1930, Page 13

INSECT DRAMAS.

PARASITES BRED FOR EXPORT The layman does not look for drama in entomology, which he is inclined to regard as a very matter-of-fact science; but if he cared to plumb some of the secrets of the Farnham Royal Parasite Laboratory, founded by the Imperial Bureau or Entomology three years ago in a charming country house in the heart of “Beechy Bucks,” I fancy he would encounter another “insect play” quite as fascinating as Capek’s (writes a correspondent). Here for example is one little drama disclosed by a visit there recently. Far away in Western Canada a pest known as the wheat stem sawfly hes been inordinately busy, to the detriment of crops. At present experts out there are “dosing” the wheat with a liberal supply of a certain parasite which destroys that particular pest. This parasite, by the thousand, has actually been bred for export in the charming country house at Farnham Royal. Before this invaluable work could be inaugurated corn stubble containing the sawfly, together with its p:\rasite, had to be brought over from Europe. Why Europe? Because there the two insects are found inhabiting the same plant. Not so in Canada, curiously enough. When the sawfly attacks grass in Canada the parasite is there to attack it in turn; but, for some unexplained reason, the parasite will not follow its host into the corn! A pretty caprice of Nature calculat- i ed to elude the entomologist! But the entomologist—that is the Farnham Royal expert—merely says: “Very well, Master Sawfly, since there are no parasites to spoil your little game in Canada, we’ll just have to get some from Europe, breed them up, and send them there.” And that is what Farnham Royal has done and is doing. Saving Apple Crops Dr George Salt, in the absence of the Superintendent, Dr W. R. Thompson, indicated many such little dramas of the insect world in a tour of the laboratories, insectories, and garden. One room, for instance, was devoted almost entirely to the Ascogaster and Ephialtes, to minute parasites which prey on the codlin moth, the first upon its j egg, the second upon its larva. This codling moth does a lot of damage to apple crops, notably in Canada, Australia and Cyprus. At Farnham Royal it is encouraged to do as much damage as it can. It lays its eggs on paper; each egg is “mounted” on a fragment smaller than a piece of confetti, and the fragment is carefully pinned to the apple so that there shall be no mistake about the larva emerging and doing its work. While it is doing its work the parasites get busy doing theirs, and are painstakingly “harvested” for export in the process. “You see,” remarked Dr Salt casually, “each parasite destroys between 100 and 200 moths; the moth multiplies 100 times each generation; with these 300 trays each containing fifteen apples, we can turn out about 10,000 parasites in each generation. We get two generations a year, and hope to get three. That will give us an output of 15,000 to 20,000 parasites.” And across the wide seas these parasites go to enlarge , the bounty of Dominion and Colonial orchards—sometimes in cold storage, sometimes cosily packed in strips of corrugated cardboard, each corrugation forming a safe “cell.” In “constant temperature” chambers, automatically controlled and humid as the tropics, we found cultures of the friendly parasite Microbracon, which had come all the way from Egypt together with its host the pink bollworm pest, which battens on cotton. The parasite passes through one generation here, and then its progeny is sent out to Barbados. Parasites’ Foster-Mother. Remarkable, indeed, seemed the case of another friendly parasite, Trichogramma, which was being reared to combat the sugan cane borer pest in the West Indies. Farnham Royal had no natural host, the Borer itself, to work upon, so it was rearing these parasites on an artificial host, a species of flour moth, which served as a kind of fostermother. The eggs of this moth looked little bigger than specks of dust, but those in which the parasite was busy showed black instead of white. “We can produce about 500 of these a day, and there is a six to twenty fold increase per generation,” was Dr. Salt’s comment. “One man in Barbados, Mr R. W. E. Tucker, liberated no fewer than 26,000,000 of these beneficial parasites last year.”

An important part of the Farnham Royal reasearch is, of course, devoted to finding parasites which, while being beneficial in one particular way, will not be harmful in others, in which case the cure might be worse than the ill. One insect was found, for example, which attacked blackberry right enough, but went on to attack apple and raspberry also. Naturally, he was relegated in favour of a certain beetle which bores into the stem of the blackberry and stops at that. Either in “lab” or outdoor insectory which shields plants and pests from all interference, the life history of every insect is patiently studied, and subsequently recorded. The wo ’y -aphis, which infests apple trees, the scale of the hawthorn twig, the fluted scale of the citrous fruits, a

moth which attacks larch trees—parasites or predators to fight these and other pests—were being sedulously cultivated for export. Pet Parasite. Perhaps the most remarkable creature at Farnham Royal is Rhyssa, an insect with a thin, flexible ovipositor which can actually penetrate the hard wood of the silver fir tree, using its body as a lever. In New Zealand silver firs are frequently spoilt for use by the activities of a pest, Sirex, the larva of which bores imo the wood. But it has to reckon with the uncanny instinct and power of Rhyssa, who divines the presence of the larva beneath the surface, drives its ovipositor deep into the wood, stings the larva, and lays its own egg in the concealed tunnel. Rhyssa, accordingly, has become a special “pet” at Farnham Royal, and is on view in a glass case. In addition to its director, Sir Guy Marshall, and its superintendent, Farnham House is staffed by four entomologists, two botanists, a secretary, Mr R. C. Jeffery, a few garden hands and a carpenter, who is continually fabricat- ; ing new devices for keeping the insect ! family safe and sound as it emerges into the light of research. To date it has shipped some 363.000 beneficial insects of twenty-one different species to a dozen different countries. At present it has seventy-two separate projects in hand; it is always I being approached to undertake new ' ones for some remote part of a DominI ion or Colony.