Observations on the ecology of the cloths moths Tineola bisselliella (Humm) and Tinea pellionella L in a bulk wool store.

Abstract

Observations on the behaviour and abundance of Tineola bisselliella and Tinea pellionella were made during 1942 and 1943 in a Brisbane wool store which remained relatively undisturbed for more than three years. The store contained c. 10,000 strongly compressed. jute-covered "double dumps" of low-grade, greasy wool, stacked in large bays separated by passages. Microclimatic conditions were more equable than in the open and very favourable to the moths. Substantial vertical gradients in temperature and relative humidity resulted from insolation of the roof, but there was little horizontal differentiation. The wool tended to buffer fluctuations of these elements, both in the free air spaces and, still more, within the dumps. Larvae of Tinea were confined to loose wool protruding through breaches in the jute pack. Tineola occurred both there and within the surface 2 in. of the compressed wool under the pack. By 1943 there was estimated to be an average of c. 50 well-grown larvae per dump. Adult moths could always be seen sitting or running on the dumps throughout the stacks. The moth populations were studied by sampling with tanglefoot traps in the passages and stacks. Both species had a flight period around dusk, about half the 24-hr catch being made during the 3 hr after sunset. The peak fell earlier on cool evenings. A regression of activity on mean flight period temperature was established, a rise from 65 to 80°F doubling the catch. Females rarely fly: they normally constituted only c. 0.3 per cent, of the catch, although the sex ratio in the population as a whole was probably about 23 : 19 for Tineola and 13 : 49 for Tinea. The density of moths in flight was approximately equal in stacks and passages at a, given level, but usually increased with height. By correcting the daily catches for the effect of temperature on activity, plots of adult abundanoe against time were constructed. The two species fluctuated in almost identical fashion. Numbers were low in winter, high in spring and summer, with an indication of two to three generations per annum. From the beginning of 1943 a great decline in abundance set in, the peak for that year being a small fraction of that for 1942. The braconid Apanteles carpatus, a parasite of both moths, was also taken on the traps. It had a flight period at about the time of the daily temperature maximum. A regression of activity on temperature showed a near-quadrupling of the catch for a rise from 70 to 85ºF. A plot of adult abundance was derived as for the moths. It showed a single seasonal peak falling after the moth peaks. Several overlapping generations are postulated. The abundance ratio of Apanteles to moths rose steadily from spring to autumn in each year, but showed close agreement for corresponding seasons of the two years: there is no reason to ascribe the 1943 decline in moth numbers to the parasite. A spider, Uloborus geniculatus, became very abundant during 1943 and is believed to have been responsible for the decline of the moths, which represented its main source of food. Over the relevant period the percentage of female moths in the catch increased 40-fold, presumably as a result of the differential removal of the active males by the spider. It is calculated that in this way the number of males was reduced, by November 1943, to about 1/45 of what it would otherwise have been. The spider probably also caught adult Apanteles. It is concluded that, apart from effects of the introduction of additional species, the moths and spiders would ultimately establish some sort of equilibrium, probably at a rather low level of density. The factors favouring Uloborus in its limiting role are discussed.