HUMIDITY RESPONSES OF TROGODERMA GRANARIUM EVERTS (COL DERMESTIDAE)

The humidity responses of T. granarium were tested in humidity gradients set up in choice-chambers, each com-prising a petri-dish with the lower half divided diametrically into 2 compartments containing sulphuric-acid solutions affording different relative humidities and surmounted by a copper-gauze platform on which the insects, released centrally, could move about. Counts of the numbers in either half of the arena were made at 15-min. intervals over 2 hr. In a gradient of 20-80% relative humidity, at 20[degree]C, the average count was significantly greater on the drier side than on the moister one for larvae and adults tested in groups and for larvae and adult males, but not females tested singly; the response was greater when the insects were tested in groups. Antennectomised adults, tested at 25[degree]C in a gradient of 20-100% relative humidity, showed no response, although intact control beetles showed a significant preference for the drier side. When adults were tested in groups at 25[degree]C in a range of gradinets, from 20-10 to 20-100%, a preference for the drier side was invariably shown, the response tending to be greater and to occur more rapidly in larvae than in adults, and as the humidity gradient steepened.