FOR TEE FARMER.

Manawatu Standard, Volume LX, Issue 225, 21 August 1940, Page 12

FOR TEE FARMER.

SMELL ORGANS OF INSECTS. (Written fur the “Alanawatu Standard.*') The extreme development of the olfactory organs of many creatures, both with and without backbones (vertebrates and invertebrates), plays an important part in their struggles tor existence. However delicately the sense of smell has been developed among the quadrupeds, especially the dogs and Che weasel group, it is far inferior to that of many insects, as may bo readily observed. This is an essential compensation for having no hearing, and with eyes capable of seeing only short distances and then without discrimination. Insects need a sense that will detect both friends and enemies and guido them long distances and unerringly to food. The organs of smell in the unthropo’ida (which group includes the invertebrate animals having locomotary appendages! are the antennae. This fact has been questioned and controversy has arisen over it, but it is now generally admitted, for experiments clearly indicate that with these often peculiar and highly developed head appendages removed there is no apparent reception of odours no matter how particularly enticing Thu antennae are. used also as feelers, anti perhaps tor detecting disturbances in the air as caused by a slowly approaching enemy. Considering the nature of its transmission the power of smell as possessed by insects rivals the acute sense of hearing in many quadrupeds, and the sight of tho most highly developed eybs, far surpassing tho eyes of all vertebrates.

THE BUTTERFLY'S ALERTNESS. ' Tho most extreme exartiple that lias been observed concerns the emergence of a female moth from a wild cocoon taken to the heart of a great city, and the visitation within a few hours at night of many males that had come from suburban sections more than three miles away—this on a still night, and the visitors drifting in from many directions. Close observation out of doors will determine that insect antennae are put to mo6t important uses; not only tho saving of life, but also its prolongation and its propagation. The honey and flesh-loving diptera, tho butterflies and certain hymonoptera, are the best examples for study. Watch a bee-lly alight among plants not yet in flower, and with a sudden shift of the breeze see him discern a honey blossom a few feet away. The insect slowly faces about toward the desired object,' turns a little too far, then back again; its pendant antennae with the central erect bristles slowly moving back and forth, then it suddenly makes a beeline for the delectable object. Blow and meat flies alighting upon a covered bundle of moat crawl about to find tho hoped-for opening and cleSrly follow the lead of tho extended and wavering smellers. Approach with most deliberate motion an alert butterfly perched with ready wings jiwaiting a playful invitation from one of its sporting iellows. The creature cannot hear you, and its lack of intelligence does not permit it to recognise your form by sight as a possible enemy. It may select your hat or shoulder or log as its next perching place. Nevertheless, it becomes aware of your presence as something unusual, an'd possibly menacing and this by scent alone. PERFUME AN' AID. Fully as important as the detection of food, or tho discovery by this means of an enemy, is the sense of smell _to most insects as a guide to propagation. Courtship with most species- is not a matter of attractiveness to the eye, but is one of agreeable odours. Has the female of the genus homo, with her use ot various perlumes, retained the tendency through a long-time inheritance from an ancestral type that likewise branched off to the insect ? As an argument for tho antennae: Many male insects that court females that do not seek the males possess antennae far more complicated and much larger than the antennae that scent to be needed by the egg-laying sex. Witness tho feathershaped smellers of certain moths and those of the male mosquitoes and allied gnats, the extended and thicker antennae of male scale insects, and the forked or singlebranched horns of male saw-flies and certain beetles. Where tho females do as much of the seeking and the courting as do the males, or where they do all the seeking, as for example the female long-horned grasshoppers, the antennae are alike in the sexes, and, moreover, there are other uses which may govern this. Most interesting and convincing .are actual experiments. The removal of the antennae clgso to the head by a sharp pair of scissors docs not scorn to annoy tho ineect to any considerable degree after a timo; the organs arc not at all vital, nor is the nervoue construction such as to cause the creature actual pain. However thickened the basal joints may be, which is common, the attachment is generally slender. It is possible, indeed probable, that tho palpi, especially when large, are also used for smelling. They are primarily feelers at close quarters used for sampling food or recognising friends, and thus thev must bo receptive of odours. In spiders, which have no antennae, the well developed palpi are probably the only organs of smell. But these most intelligent little creatures do not possess a fine sense nf detecting odours, for one will climb its silken thread to the human hand that suspends it and not until the hand is reached will the spider become alarmed and drop. AN EXPERIMENT WITH BLOWFLIES The antennae aro generally made up ol many joints, the terminal ones often larger, giving a knobbed or clubbed appearance, as in the butterflies, many beetles, most bees and wasps, water and nerve-winged flies, and certain bugs. They aro often many-branched, or they possess extraordinary length, as observed as the crickets and long-hornedgrass-hoppers. The writer caught in his insect net thirty-one blowflies attracted to a piece of tainted meat. Sixteen of these wero deprived of their antennae and all wero turned loose in a largo room. The meat was placed on a table. They * flew about, mostly in an effort to escapo through tho screened 'windows, but eventually the continued urge to deposit their eggs made them seek the common medium Thirteen of these flies soon found the meat, but all of these thirteen possessed antcnriao and only one of those without those organs found it eventually, although quite by accident. Five of the flies without antennae were put under a screened cover and coming into contact with bits of meat greedily sipped the juices and laid their eggs thereon. NO ANTENNAE—NO LOVE. Eight freshly emerged females of a common yellow butterfly and five males were liberated in a screened room where a bunch of red clover was placed on tho floor in tho centre of the room. The antennae of four of the females and three of the males were clipped off close to the head. Within less than an hour all the four females whceo smellers were intact had peen unable to withstand the near odour of the natural food plant of their larvae and had laid eggs on the clover. The oilier four had not found it although when the plants were placed in the window sill and, in their flopping about theso specimens without antennae happened to alight on it, all four promptly laid their eggs also. The two males with antcnnao promptly responded to tho lover-like tendency and began paying courr to some of the females, while those with their antennae missing could not even be lured by sight until an enchantress happened to come near. Many years ago a noted entomologist took a nunifier of inotlis to a district where no other of the same species existed. The female moths were confined in transparent jars by means of netting. As a check on this group, other females wore placed under inverted glass jars whose lower ends were buried in tin* sand. Male moths of lho same species were then released at various distances. They were soon able to find their way to the jars whose mouths were obstructed only by netting; but, they did not succeed in locating those with hermetically scaled openings. Nevertheless, the female moths had- all the time remained clearly visible through both kinds of jars. Further to demonstrate how fully these insects depend on their acute sense of smell, a thing coating of shellac was placed on the antennae of several male moths. Even though they were brought almost within touch of the females they now paid no attention to them. Blinded moths, how- | ever, having undamaged antennae experienced no difficulty in. finding the females.