Mean development rates under cycling temperature regimes (both alternating and sinusoidal regimes) have been found to be either accelerated, decelerated or unaffected when compared to development at constant temperature regimes with equivalent means. It is generally accepted that this phenomenon is a consequence of the non-linearity inherent in the temperature-rate relationship of insect development and is known as the rate summation, or Kaufmann, effect. Some researchers invoke an additional physiological mechanism or specific adaptation to cycling temperatures resulting in a genuine alteration of development rate. Differences in development rates at constant and cycling temperatures may have important implications for degree-day (linear) population models, which are used in bath pest management and ecological studies.
Larvae of Aglais urticae L. (small tortoiseshell), Inachis io L. (peacock), Polygonia c-album L. (comma) and Vanessa atalanta L. (red admiral) (Lepidoptera: Nymphalidae) were reared at constant (10, 15, 20, 25, 30°C) and alternating (20/10, 25/15, 30/10, 30/20°C) regimes. Development rates under the alternating regimes used were found to differ from those under equivalent constant temperatures in a pattern suggestive of the Kaufmann effect: in all species development at 20/10°C was faster than at 15°C, and for three species development at 30/20°C was slower than at 25°C. The exception was A. urticae. A similar pattern was found for growth rate and pupal weight. The results are discussed with respect to cycling temperature theory and degree-day modelling., Simon R. Bryant, Jeffrey S. Bale, Chris D. Thomas, and Lit
Modality in the supercooling points of cold tolerant but freezing intolerant terrestrial arthropods has proved a pragmatically reliable means of distinguishing between summer and winter cold hardiness in such species. This paper proposes an ecologically realistic method of modal analysis which may either be used in lieu of the traditional separation of supercooling points into "high" and "low" groups, or as a complementary assessment of the risk of freezing mortality. Instead of a posteriori determinations of modal break points, animal supercooling points are assigned a priori to one of four categories of cold hardiness: (1) summer cold-hardy; (2) semi-cold-hardy; (3) cold-hardy; and (4) winter cold-hardy. Each category is identified by the temperature range within which arthropods can be expected to freeze. The temperature ranges assigned to each category are based on a conservative, but realistic, assessment of the temperatures at which animals can be expected to freeze at a given point in the season. The approach has greater discriminatory power than traditional bimodal descriptors (i.e."summer" and "winter" cold-hardy), as well as allowing animal supercooling points to be related to the temperatures they actually experience in their habitats. Thus, for example, animals considered "summer" cold-hardy according to conventional analysis may actually be "semi-cold-hardy" with supercooling points well within the safety margin of minimum ambient temperatures.
The development of the Western Flower Thrips (Frankliniella occidentalis Pergande; Thysanoptera: Thripidae) was studied at six temperatures between 10 and 35°C. Developmental rate increased linearly as rearing temperature increased. It was estimated that 268 degree-days, above a threshold temperature of 7.9°C, were required to complete development from egg to adult. These data were related to records of field temperatures in the West Midlands region of the UK, to estimate the potential number of generations per year that could complete development in outdoor conditions. Using this data, a maximum of between three and five generations could have developed annually between 1986 and 1995, (in the absence of factors impairing continuous development). The application and relevance of this data as an indicator of the potential range of F. occidentalis is discussed.
In order to manage the risks posed to domestic crop production by quarantine pests such as Thrips palmi, their potential to establish in a new environment must be assessed. The thermal requirements for development of T. palmi were determined and compared with UK temperatures, to estimate its potential for development under UK conditions. Temperature and rate of development of T. palmi from egg to adult were linearly related between 15 and 30°C, allowing calculation of an overall threshold of 10.1°C, and a sum of effective temperatures of 194 degree-days. In the UK, development of T. palmi would be possible outdoors during the summer when a maximum of up to four or five generations could occur. Comparison of these data with those of the recently established and biologically similar pest, Frankliniella occidentalis, shows that establishment of T. palmi in the UK is unlikely to be limited by an inability to complete the life cycle during the favourable season., Jamie R. McDonald, Jeffrey S. Bale, Keith F.A. Walters, and Lit