No abstract

SUMMARYOxygen convective uptakes in gas exchange cycles were directly recorded in early diapause pupae of Pieris brassicae L. (Lepidoptera; Pieridae) by means of O 2 coulometric respirometry. This method was combined with flow-through CO 2 respirometry, the two systems being switchable one to the other. During recording with both systems, measurements were also taken with infrared actography. The pupae displayed short discontinuous gas exchange cycles lasting 40-70min. No true C phase was found by flow-through measurements; instead, flutter opening of the spiracles with discrete convective O 2 uptakes began shortly after the O phase whereas CO 2 release was suppressed by the inward directed passive suction ventilation. The F phase was characterized by a series of small CO 2 bursts (flutter events). Between these bursts, novel sub-phase 'miniflutter' was observed, which consisted of six to 10 miniature inspirations without any CO 2 emission. During the flow-through measurements, oxygen convective uptakes were indirectly recorded by the infrared actograph as sudden extensions (lengthening) of the abdominal segments at each spiracular microopening.

Supercooling point (SCP) and cold-hardiness of the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae) were investigated. Mature eggs from the oviduct were supercooled on average to )28.0°C and from oilseed rape buds to )24.4°C; first instars were supercooled to )21.0°C and second instars to )16.8°C. Despite their high supercooling ability, none of the eggs survived 24 h exposure to )2.5°C. The supercooling ability of adults varied significantly among feeding and non-feeding beetles: high SCPs prevailed during the whole warm period, being about )12°C; low values of SCP of )20°C dominated in non-feeding beetles. In spring and autumn, beetles displayed the same acclimation efficiency: after 1 week of exposure at 2.0°C with no access to food their SCPs were depressed equally by about 3°C. Meligethes aeneus beetles have a different response to low temperatures depending on the season. The lowest tolerance was found in reproductively active beetles after emergence from overwintering sites; the time needed to kill 50% of individuals (Ltime 50 ) was 56.2 h at )7°C and the lower lethal temperature needed to kill 50% (Ltemp 50 ) after 24 h exposure was )8.6°C. Cold hardiness increased from midsummer to midwinter; Ltime 50 was 80 h in August, 182.8 h in September, and 418.1 h in January. Lethal temperature after 24 h exposure was )9.1°C in August and )9.8°C in September. In February, after diapause, the beetles started to loose their cold tolerance, and Ltemp 50 was slightly increased to )9.5°C. Hibernating beetles tolerated long exposure at )7°C well, but mortality was high after short exposure if the temperature dropped below )9°C for 24 h. Despite the season, the beetles died at temperatures well above their mean SCP; consequently, SCP is not a suitable index for cold hardiness of M. aeneus.

Abstract. Discontinuous gas exchange (DGE) is the main (23 individuals) breathing mode in resting adult Platynus assimilis. Few of the beetles tested (13 individuals) displayed a pattern of cyclic gas exchange or CGE. The burst of CO2 release in DGE and CGE was always accompanied by abdominal pumping (active ventilation or V). Seven individuals displayed a pattern of continuous respiration, characterized by regular abdominal pumping. Resting metabolic rate (RMR) in continuously breathing beetles was higher than in those using DGE and CGE. After treatment with sub-lethal doses of alpha-cypermethrin DGE ceased. Treated beetles were characterized by continuous pumping and almost regular periods of activity. RMR increased significantly after treatment with a pyrethroid.

Gas exchange patterns of adult male Pterostichus niger Schaller after hydration (i.e. given access to food and water) are compared in dry air [5-7% relative humidity (RH)] and moist air (90-97% RH) by means of flow-through CO 2 respirometry combined with infrared probe actography. Of thirty beetles examined, slightly more than 50% showed continuous gas exchange and are not considered further. Of the remaining beetles, the majority (approximately 71%) display a pattern of cyclic gas exchange in both dry and moist air (i.e. CO 2 gas is released in bursts, with a low level of CO 2 release during the interburst periods). A minority of the beetles (four out of 30) are found to exhibit discontinuous gas exchange in both dry and moist air; this is characterized by three clearly separated states of the spiracles: closed (C), flutter (F) and open (O) phases. The pattern of cyclic gas exchange is associated with weak abdominal pulsations. After switching from moist to dry air, a small modulation of the discontinuous gas exchange cycles (maximum mean CO 2 production rate) occurs, providing no clear support for the hygric theory of discontinuous gas exchange in this species (i.e. that it serves to restrict respiratory water loss).