Sr. Bryant et al., Modification of the triangle method of degree-day accumulation to allow for behavioural thermoregulation in insects, J APPL ECOL, 35(6), 1998, pp. 921-927
1. The ability to predict insect development in field situations is fundame
ntal to pest management programmes and in the understanding of insect pheno
logy, Basic modelling techniques, however, fail to take into account behavi
oural thermoregulation by larval or nymphal insects, which has been shown t
o result in substantial increases in body temperature relative to ambient,
particularly in species which bask.
2. The triangle method of degree-day accumulation formulated by Sevacherian
, Stern & Mueller (1977), which incorporates daily maximum and minimum air
temperatures, is modified here to include thermoregulation data in the form
of a linear body/ambient temperature relationship and daily sunshine hours
.
3. Using developmental and larval thermoregulatory data for the nymphalid b
utterfly Aglais urticae (small tortoiseshell), it was calculated that there
was a mean increase of 75% in the availability of degree-days for larval d
evelopment, for the period April to September inclusive (using 10 years of
meteorological data for Birmingham, UK).
4. Implications for this species' phenology was demonstrated by constructin
g a simple model. By taking larval thermoregulation into account, the modif
ied method performed better than the original triangle method in predicting
patterns of adult emergence: it is suggested that without larval thermoreg
ulation, A. urticae would typically be univoltine in central England, where
as it actually achieves two generations per year.