Rapid cold-hardening and phenology in the hoverfly Episyrphus balteatus (Diptera, Syrphidae)

Mason, Philip Sydney (2007). Rapid cold-hardening and phenology in the hoverfly Episyrphus balteatus (Diptera, Syrphidae). University of Birmingham. Ph.D.

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Abstract

The effect of rapid cold-hardening (RCH) on increasing insect survival at otherwise lethal temperatures is well documented, but its relevance to maintaining insect behaviours at low temperatures remains largely uncharacterised. The hoverfly Episyrphus balteatus is weakly cold tolerant but capable of summer migration over long distances to regions in which it may not be able to overwinter in significant numbers, including the UK. RCH was investigated in the laboratory, comparing life stages, sexes, and lethal and behavioural thresholds. RCH significantly increased survival at otherwise lethal sub-zero temperatures in first and second instar larvae, and pupae, but not in eggs, third instar larvae and adults. The capacity for RCH was limited by the relationship between the freezing temperature and that at which chilling injury occurs. RCH did not affect the chill coma temperature in adults (CTmin of approximately 0.5°C), but did decrease the low-temperature threshold for flight, by more than 2°C, following hardening at 10°C for periods around 60 minutes or by gradual cooling at 0.5 and O.PCmin'1 (p<0.05). The flight threshold was significantly lower (p<0.01) in females (17.5°C) than in males (19.3°C). The results demonstrate that RCH may have real ecological implications at temperature thresholds relating to behaviour. A record of the phenology of E. balteatus at a site in the UK from 1972 to 2001 was also analysed, and significant correlations with temperature identified, including advancing flight period consistent with climate warming.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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