01597nas a2200181   4500008004100000245010300041210006900144300001000213490000700223520104100230653001201271653002101283653001401304653002001318100001501338700001501353856004701368       1998                        eng d00aFactors affecting the freeze tolerance of the hoverfly <i>Syrphus ribesii</i> (Diptera: Syrphidae)0 aFactors affecting the freeze tolerance of the hoverfly iSyrphus   a21-290 v443 aLarvae of Syrphus ribesii collected from overwintering sites in the U.K. are strongly freeze tolerant with 70% survival at -35 degrees C. The cold tolerance of laboratory reared insects increased with increasing periods of acclimation at 0 degrees C, with a concurrent rise in the supercooling point (SCP) from -6.8 +/- 0.1 to -5.1 +/- 0.3 degrees C. There was 50% survival in the most cold-hardy group 72 h after brief exposures to -30 degrees C. The retention of gut contents caused a decrease in cold hardiness, with only 13% of larvae surviving 72 h after exposure to -15 degrees C, with no subsequent pupation or emergence. Wet larvae had a significantly higher SCP (-5.0 +/- 0.2 degrees C) compared to dry larvae (-7.8 +/- 0.4 degrees C), although survival of larvae was similar in both groups. There was no nucleator activity in the haemolymph of field collected larvae. The importance of these findings are discussed in relation to the freeze tolerance strategy of S. ribesii. (C) 1997 Elsevier Science Ltd. All rights reserved.10aDiptera10afreeze tolerance10aSyrphidae10aSyrphus ribesii1 aHart, A.J.1 aBale, J.S.  uhttps://syrphidae.myspecies.info/node/9442