Activity pattern and thermal biology of a day-flying hawkmoth (Macroglossum stellatarum) under Mediterranean summer conditions

Abstract

1 The daily activity pattern and aspects of the thermal biology are described for the day-flying hawkmoth, Macroglossum stellatarum L. (Lepidoptera: Sphingidae), while foraging at a flowering population of Lavandula latifolia (Labiatae) under the dry-hot summer conditions of a southeastern Spanish locality. 2 The average abundance of M.stellatarum remained fairly constant from sunrise to about 17.00 hours (GMT), and a distinct peak occurred in the evening (18.00—20.00 hours). 3 Foraging took place over a broad range of microclimatic conditions, as described by air temperature (Ta; range 19-36°C) and solar radiation (IR; range 1–1025 Wm-2). 4 The thoracic temperature (Tth) of insects remained within relatively narrow limits (39–46°C), with the highest values occurring around noon. Variation in Tth mainly reflected differences in Ta between foraging sites and times. Tth was nonlinearly related to Ta, the rate of increase of Tth with Ta decreasing with increasing Ta. 5 The unusual tolerance of high Tth exhibited by M.stellatarum, and its enhanced thermoregulatory capacity at high Ta, enable this species to withstand the severe environmental conditions faced during diurnal foraging in the Mediterranean summer.