The cyclic gas exchange in the diapausing pupae (DP) of the cabbage butterfly Pieris brassicae was monitored by use of simple and sensitive twin differential calorimeter combined with automatic respirometer. Usually, the periodic CO2 releases in DP occurred as large, intermittent and micro bursts (i.e. in the form of respiratory cycles). By treating the DP with low doses of the extracts of the marguerite Tanacetum roseum the large cycles of gas exchange were abolished, but the intermittent and micro bursts were preserved. These treatments did not result in any neuromuscular hyperactivity. After the treatment the body mass loss of DP increased from 1.72+/-0.16 (females (2x) and 2.23+/-0.31 (males 2x)) mg g(-1) day(-1) for the untreated pupae to 2.25+/-0.38 (females (2x) and 3.05+/-0.76 (males 2x)) mg g(-1) day(-1) for the treated ones. All the DP who survived the treatment developed into pharate stages, but adult emergence failed. The untreated and control DP kept at room temperatures (20-25 degrees C) did not initiate adult development and died after having lost more than 25% of initial body mass. It is assumed that pyrethrum, a nonhormonal agent, acts directly on the brain, stimulating the release of the prothoracicotropic hormone (PTTH).