RESUMEN
Fast and effective monitoring and surveillance techniques are crucial for the swift implementation of control methods to prevent the spread of Huanglongbing, a devastating citrus disease, and its invasive psyllid vector, Asian citrus psyllid, Diaphorina citri, into South Africa, as well as to control the native vector, African citrus triozid, Trioza erytreae. Monitoring for citrus psyllid pests can be improved by using semiochemical odorants to augment already visually attractive yellow sticky traps. However, environmental variables such as temperature and humidity could influence odorant release rates. Five field cages were used to test the ability of a selection of odorants to improve yellow sticky trap efficacy in capturing citrus psyllids. Environmental effects on odorant loss from the dispensers were also investigated. The odorants that most improved yellow sticky trap captures in field cages were then tested under open field conditions alongside lower concentrations of those same lures. Gas chromatography-mass spectrometry was used to calculate odorant release rates as well as to determine if any contamination occurred under field conditions. None of the odorants under field cage or field conditions significantly improved psyllid capture on yellow sticky traps. Temperature influenced odorant loss, and release rate from polyethylene bulbs decreased over time. Based on these results, the use of unbaited yellow sticky traps seems to be the most effective method for monitoring of Huanglongbing vectors.
RESUMEN
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.
