A comparison of the capacity for increase at a low temperature of foreign and Australian populations of Sitophilus oryzae (L.) and S. granarius (L.)

Abstract

The capacity for increase (ij of three populations of S. oryzae and three populations of S. granarius from Great Britain and Canada was determined over 15 and 24 weeks respectively at 15°C in wheat of 14% moisture content. The fertility of these populations at 27°C, their body weight and chill-coma threshold was also measured.With both S. oryzae and S. granarius, values of r^ for the foreign populations fell within the range previously observed when several Australian populations were reared under the same conditions. The cohort generation times (Jc) of the foreign S. oryzae populations were significantly shorter than those of the Australian populations because of the shorter immature development periods (B) of the former. Two of the foreign S. granarius populations had lower values for D than all but one of their Australian counterparts but their values of T^ were within the range previously observed for Australian weevils. When the Australian and foreign populations were considered together, the value of Xc was more strongly correlated with fertility at 27°, an optimal temperature, than with body weight in both S. oryzae and S. granarius. With S. oryzae, r^ was correlated with the chill-coma threshold of cold-acclimated weevils only. There were no correlations between r^. and chill-coma thresholds in S. granarius. It was concluded that the observed differences in r^ were related to differences in the vigour of the populations rather than to physiological differences in cold-tolerance.The likelihood of grain weevils becoming cold-tolerant as a result of grain aeration is discussed and the practical significance of differences in r^ considered.

The demography of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), submodels of age-specific survivorship and fecundity

“…The strain of S. oryzae used in this study was CLS 2, which has been maintained in laboratory culture for nearly 20 years, and which was used by Evans (1977Evans ( ,1979Evans ( , 1982 and Hardman (1978). The insects were obtained from stock cultures maintained in the laboratory at about 20°C and 12% grain moisture content.…”

“…The rice weevil, Sitophilus oryzae (L.), has been the subject of several demographicallyoriented studies (Birch, 1948(Birch, , 1953Evans, 1977Evans, , 1979Evans, , 1982Hardman, 1978;Longstaff, 1981a, b;Sharma et al, 1979). Birch's (1953) work embraced the broadest range of experimental conditions (13-35°C and 10-14% grain moisture content), but he published detailed data for only two of the sets of conditions employed, those for the remainder having been summarised by values of X, the finite rate of natural increase.…”

“…Thus, it is not possible to use much of this work for the development of a model of population growth that would seek to relate age-specific demographic parameters, such as survivorship of adults or fecundity, to environmental conditions. Evans (1977Evans ( ,1979 considered the demographic performance of 5. oryzae at the marginal temperature of 15°C, using insects collected from a wide range of sites in Australia and also overseas. Depending on whether the insects were transferred to cold conditions as adults or in the immature stages, both the shape of the survival curve and the reproductive schedule varied considerably.…”

Further studies on acclimatization to low temperatures in the grain weevils Sitophilus oryzae (L.) and Sitophilus granarius (L.)

“…At such temperatures, reproduction is inhibited in most pest species and greatly reduced in others such as the grain weevils Sitophilus oryzae (L.) and 5. granarius (L.), which have respective development thresholds of about 13 and lTC (Hardman 1978;Eastham & Segrove 1947). In con-0307-692X/8O/12OO-O371 $02.00 © 1980 Blackwell Scientific sidering the possible development of coldtolerance in grain weevils Evans (1977a,b,c;1979) examined their ability to acclimatize physiologically when transferred abruptly from 27 to 15°C. The present paper describes studies to confirm and amplify certain previous findings on thermal acclimatization in S. oryzae and S. granarius.…”