High-temperature responses of Myzus persicae and its parasitoid Aphidius gifuensis in relation to heat level, duration and developmental stage.

BACKGROUND: Understanding how parasitoids respond to temperature is crucial for improving biological control strategies under the context of global warming. This study examined the suitability of Myzus persicae and its parasitoid Aphidius gifuensis to varying temperature conditions, as well as the stage-specific response of A. gifuensis to high temperatures. RESULTS: High temperatures had a significant impact on the both M. persicae and A. gifuensis. When exposed to 36°C, M. persicae developed more slowly and produced smaller adults compared to control, regardless of the duration of exposure (2, 4 or 6 h); additionally, the survival rate of M. persicae nymphs sharply decreased under these conditions. Exposure to 36°C for 4 h negatively impacted the development of A. gifuensis. Female parasitoids exposed to 32°C developed into smaller adults, whereas males exposed to all three temperature levels were smaller compared to control group. Female parasitoids exposed to high temperatures, regardless of the specific heat level and duration, exhibited reduced longevity and decreased fecundity. None of the parasitoids exposed to 36°C for 6 h daily developed into adults. Heat treated during early developmental stages (2 and 4 days old) had a greater influence on parasitoid development, whereas heat treatment at 4 and 6 days old had a more significant impact on its fecundity. CONCLUSION: High temperatures not only directly affected the performance of A. gifuensis, but also exerted indirect effects by influencing the quality of the host aphids M. persicae. The deleterious effects of high temperature on larvae can persist into the adult stage, affecting the longevity and reproduction of adults. These findings are important for the utilization of A. gifuensis in the control of M. persicae in warming environments. © 2024 Society of Chemical Industry.

Parallel evolution of behaviour during independent host-shifts following maize introduction into Asia and Europe.

Maize was introduced into opposite sides of Eurasia 500 years ago, in Western Europe and in Asia. This caused two host-shifts in the phytophagous genus Ostrinia; O. nubilalis (the European corn borer; ECB) and O. furnacalis (the Asian corn borer; ACB) are now major pests of maize worldwide. They originated independently from Dicot-feeding ancestors, similar to O. scapulalis (the Adzuki bean borer; ABB). Unlike other host-plants, maize is yearly harvested, and harvesting practices impose severe mortality on larvae found above the cut-off line. Positive geotaxis in the ECB has been proposed as a behavioural adaptation to harvesting practices, allowing larvae to move below the cut-off line and thus escape harvest mortality. Here, we test whether the same behavioural adaptation evolved independently in Europe and in Asia. We sampled eight genetically differentiated ECB, ACB and ABB populations in France and China and monitored geotaxis through the entire larval development in artificial stacks mimicking maize stems. We find that all ECB and ACB populations show a similar tendency to move down during the latest larval stages, a behaviour not observed in any European or Asian ABB population. The behaviour is robustly expressed regardless of larval density, development mode or environmental conditions. Our results indicate that maize introduction triggered parallel behavioural adaptations in Europe and Asia, harvest selection presumably being the main driver.

[Effects of temperature and density on the mortality and reproduction of cotton aphid Aphis gossypii].

A laboratory cotton leaf disc experiment was conducted to study the effects of different temperature (32, 34, 36, 38, and 40 degrees C) and density (5, 25, 50, and 75 individuals per dish) on the mortality and reproduction of Aphis gossypii. With the increase of temperature, density, and culture duration, the cumulative mortality of A. gossypii presented an increasing trend. The parameters estimated by complementary log-log (CLL) model showed that the beta value decreased with the increase of density, indicating that the effects of temperature weakened with increasing density. The gamma value, a parameter for the time effect of temperature, changed with culture duration, indicating that the morality of A. gossypii was co-affected by the temperature and culture duration. The two-way ANOVA analysis of variance showed that temperature and density had significant effects on the fecundity of A. gossypii, and there existed interactive effect. At 32-36 degrees C, the reproduction rate of A. gossypii decreased with the increase of density, but at 40 degrees C, no significant difference was observed in the reproduction rate under different densities, suggesting that the density effect was weakened with increasing temperature, i. e., the contribution of temperature and density to the survival and reproduction of individual varied with the ranges of the temperature and density. This study could provide reference for the monitoring and forecasting of A. gossypii population and for the improvement of pests control.

[Effects of high temperature on the mortality and fecundity of two co-existing cotton aphid species Aphis gossypii Glover and Acyrthosiphon gossypii Mordvilko].

Aphis gossypii and Acyrthosiphon gossypii are the coexisting species on cotton plant, with their abundance differed within and among years. To explore whether the abundance difference was related to the different responses of the two aphid species to high temperature, a laboratory experiment was conducted to assess the mortality and reproduction of the two aphid species at high temperatures 32, 34, 36 and 38 degrees C. With the increasing temperature and prolonged exposure period, the cumulative mortality of the two aphid species increased, and Acyrthosiphon gossypii had a higher cumulative mortality than Aphis gossypii. The daily mortality of the aphids could be well simulated by complementary log-log (CLL) model. The median lethal temperature of the two aphid species estimated by CLL model decreased with prolonged exposure period. Under the same exposure period, the median lethal temperature of Aphis gossypii was higher than that of Acyrthosiphon gossypii. Within the range of 32-38 degrees C, the reproduction rate of the two aphid species decreased with increasing temperature, but Aphis gossypii had a significantly higher reproduction rate than Acyrthosiphon gossypii, indicating that at the temperature higher than 32 degrees C, Aphis gossypi had higher tolerance against high temperature than Acyrthosiphon gossypii, and consequently, had more competitive advantage under global warming.