Abstract:
INTRODUCTION : Temperature fluctuations are important for the distribution and
survival of insects. Rapid hardening, a type of phenotypic plasticity, is an
adaptation that can help individuals better tolerate lethal temperatures
because of earlier exposure to a sublethal but stressful temperature. Nutrition
and sex are also known to influence a species ability to tolerate thermal stress.
This study determined the effects of larval diet, adult diet, sex and hardening on
the thermal tolerance of Ceratitis cosyra (Walker) (Diptera: Tephritidae) at lower
and upper lethal temperatures.
METHODS : Larvae were raised on either an 8% torula yeast (high) or a 1% torula
yeast (low) larval diet and then introduced to one of three dietary regimes as
adults for thermal tolerance and hardening assays: no adult diet, sugar only, or
sugar and hydrolysed yeast diet. Flies of known weight were then either heat- or
cold-hardened for 2 hours before being exposed to a potentially lethal high or
low temperature, respectively.
RESULTS : Both nutrition and hardening as well as their interaction affected C.
cosyra tolerance of stressful temperatures. However, this interaction was
dependent on the type of stress, with nutrient restriction and possible adult
dietary compensation resulting in improved cold temperature resistance only.
DISCUSSION : The ability of the insect to both compensate for a low protein larval
diet and undergo rapid cold hardening after a brief exposure to sublethal cold
temperatures even when both the larva and the subsequent adult fed on low
protein diets indicates that C. cosyra have a better chance of survival in
environments with extreme temperature variability, particularly at low
temperatures. However, there appears to be limitations to the ability of C.
cosyra to cold harden and the species may be more at risk from long term
chronic effects than from any exposure to acute thermal stress.
