Irja Kivimägi

Relative attractiveness of Brassica napus, Brassica nigra, Eruca sativa and Raphanus sativus for pollen beetle (Meligethes aeneus) and their potential for use in trap cropping

Oilseed rape (Brassica napus) is a valuable crop, attacked by several insect pests, of which the pollen beetle (Meligethes aeneus) is one of the most widespread and important in Europe. The relative attractiveness for the pollen beetle of Brassica nigra, Eruca sativa and Raphanus sativus was compared with that of spring oilseed rape, to assess the potential of these plant species as trap crops for the pest. At early growth stages, B. nigra and R. sativus were more attractive to over-wintered adult pollen beetles than B. napus. At the bud and flowering stages, B. nigra was the most attractive while E. sativa was the least attractive. At flowering, B. nigra was more attractive for oviposition than the other species. Thus, of the species tested, B. nigra has the most potential as a prospective trap crop to protect spring oilseed rape before flowering when it is at its most vulnerable developmental phase, due to its faster development and its acceptability both for feeding and oviposition to overwintered pollen beetle adults. Raphanus sativus was accepted both for feeding and oviposition, but pollen beetle larvae failed to develop in its flowers; it therefore has the potential for use as a dead-end crop. At the end of the growing season, both E. sativa and R. sativus, as late-flowering species, attracted the new generation of pollen beetles and thereby have potential to extend the effectiveness of a trap-cropping system at this time.

Gas exchange patterns of Pterostichus niger (Carabidae) in dry and moist air

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 CO2 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. CO2 gas is released in bursts, with a low level of CO2 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 CO2 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).

Supercooling ability and cold hardiness of the pollen beetle Meligethes aeneus

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 (Ltime50) was 56.2 h at −7 °C and the lower lethal temperature needed to kill 50% (Ltemp50) after 24 h exposure was −8.6 °C. Cold hardiness increased from midsummer to midwinter; Ltime50 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 Ltemp50 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.

The length of discontinuous gas exchange cycles in lepidopteran pupae may serve as a mechanism for natural selection

Gas exchange is studied in diapausing pupae of Mamestra brassicae L., whose larvae are reared under identical conditions. The release of CO2 gas is recorded with infrared gaseous analyzers. Oxygen convective uptake into the tracheae and oxygen consumption rates are recorded by means of a constant‐volume coulometric respirometer. Outputs from both of these respirometry systems are combined with infrared actographs. All 3‐month‐old pupae of M. brassicae display a pattern of discontinuous gas exchange (DGE) cycles of CO2 gas release by bursts, although the lengths of these cycles varies between individuals. Some pupae exhibit long DGE cycles of at least 20 h in duration, with negligible CO2 gas release during interburst periods, and there is presumed to be a convective gas exchange at this time. As a result of a partial vacuum inside the tracheae, a large oxygen convective uptake always occurs at the start of the spiracular opening phase. Other pupae have short DGE cycles of less than 3 h in duration, with elevated CO2 gas release during the interburst period, when gas exchange is predominantly diffusive. The spiracular open phase in these pupae consists of frequent separate convective bursts of CO2 gas release, with the opening–closing rhythms of the spiracles, which are considered as O phase fluttering. The pupae with long DGE cycles exhibit extremely low metabolic rates and very low total water loss rates, whereas those with short DGE cycles have higher metabolic and total water loss rates. The pupae with long DGE cycles live approximately twice as long as those with short cycles; thus, the present study demonstrates that long DGE cycles confer a fitness benefit on pupae as a result of a lower metabolic rate associated with water economy, conferring on them a longer life.

Seasonal cold adaptation dynamics of some carabid beetle species: Carabus granulatus, Pterostichus oblongopunctatus and Platynus assimilis

Abstract Cold-hardiness can be measured by supercooling points – the temperature at which spontaneous freezing occurs. Seasonal changes in supercooling point were assessed in field-collected predacious carabid beetle species: Carabus granulatus L., Pterostichus oblongopunctatus L. and Platynus assimilis Payk. (Coleoptera: Carabidae). Supercooling ability of these beetles changed seasonally. The tested carabid beetles proved to belong to freeze-avoiding cryotype.