Effect of developmental temperatures on Aphidius colemani host-foraging behavior at high temperature.

Temperatures experienced by insects during their adult life often differ from developmental temperatures. Yet, developmental thermal acclimation can play an important role in shaping physiological, morphological, and behavioral traits at the adult stage. We explored how three rearing temperatures (10, 20, and 28 °C) affected host-foraging behaviors and associated traits under warm conditions in the parasitoid Aphidius colemani, a key model in behavioral ecology and an important natural enemy of aphids. Developmental time was longer at lower temperatures, resulting in bigger emerging parasitoids, with higher egg-loads. Parasitism rates, emergence rates, and parasitoid survival (once placed at high temperature) were the highest for parasitoids developed at 20 °C. When exposed to 28 °C, the expression of all behavioral items (time spent walking searching for hosts, number of antennal and ovipositor contacts with hosts) was higher for parasitoids reared at 20 °C, followed by those reared at 10 °C, then those reared at 28 °C. Finally, we showed that parasitoid residence time on aphid patches was determined by both developmental temperatures and the number of host encounter without oviposition, representative of the resource quality. We revealed that developing at 28 °C did not lead to increased adult performance at this temperature, probably because of complex interactions and trade-offs between developmental costs at high temperature and optimal foraging behaviors (e.g., parasitoid size and host-handling capacities). Our results strengthen the idea that thermal developmental plasticity may play an important role in insect behavioral responses to varying temperatures, and is important to consider in the context of climate change.

Developmental Temperature Affects Life-History Traits and Heat Tolerance in the Aphid Parasitoid Aphidius colemani.

Developmental temperature plays important roles in the expression of insect traits through thermal developmental plasticity. We exposed the aphid parasitoid Aphidius colemani to different temperature regimes (10, 20, or 28 °C) throughout larval development and studied the expression of morphological and physiological traits indicator of fitness and heat tolerance in the adult. We showed that the mass decreased and the surface to volume ratio of parasitoids increased with the development temperature. Water content was not affected by rearing temperature, but parasitoids accumulated more lipids when reared at 20 °C. Egg content was not affected by developmental temperature, but adult survival was better for parasitoids reared at 20 °C. Finally, parasitoids developed at 20 °C showed the highest heat stupor threshold, whereas parasitoids developed at 28 °C showed the highest heat coma threshold (better heat tolerance CTmax1 and CTmax2, respectively), therefore only partly supporting the beneficial acclimation hypothesis. From a fundamental point of view, our study highlights the role of thermal plasticity (adaptive or not) on the expression of different life history traits in insects and the possible correlations that exist between these traits. From an applied perspective, these results are important in the context of biological control through mass release techniques of parasitoids in hot environments.

Author Correction: Citrus peel essential oil nanoformulations to control the tomato borer, Tuta absoluta: chemical properties and biological activity.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Citrus peel essential oil nanoformulations to control the tomato borer, Tuta absoluta: chemical properties and biological activity.

The repeated use of conventional synthetic pesticides in crop protection leads to resistance development by pests along with a negative impact on the environment, particularly non-target arthropods. Plant-derived active compounds, such as essential oils (EOs), play a key role in sustainably controlling pests. The lethal and sublethal activity of citrus peel EOs as emulsions and included in polyethylene glycol (PEG) nanoparticles (EO-NPs) was determined against the invasive tomato pest Tuta absoluta. Their effects on the plants were also assessed. The results showed an overall good insecticidal activity of the compounds tested, with a higher mortality through contact on eggs and larvae by EO emulsions and through ingestion on larvae by EO-NPs. The nanoformulation also significantly reduced the visible toxic effects on the plants. The data collected suggest that these natural compounds, especially when nanoformulated, could be successfully used in integrated pest management programs for T. absoluta.

Demographic traits of Eotetranychus pruni from Belgian and Tunisian orchards, in comparison with Tetranychus urticae.

Eotetranychus pruni was recorded in Belgian and Tunisian apple orchards for the first time. The aim of this study was to compare a Belgian (Vieusart) and a Tunisian strain (Grombalia), with respect to their life history and demographic traits. Furthermore, a Tunisian strain of Tetranychus urticae (Sousse) was also added to the study, in order to evaluate the potential status of the Tunisian strain of E. pruni. Experiments were carried out in the laboratory (24 degrees C) on apple leaf discs. Significant differences were noticed between the two species, with respect to development time (males), fecundity and fertility (egg hatching), but no differences could be detected between the two strains of E. pruni. Life tables were set up to describe the population statistics. The calculated intrinsic rates of natural increase (rm) appear to be rather low per se and do not correspond to those of typical "r strategic pests". The Bootstrap procedure allows us to estimate the confidence interval for these rm values. By using this method, the two Tunisian strains (T. urticae and E. pruni) appear to be quite similar, and contrast with the Belgian strain (E. pruni). The potential pest status of the Tunisian strain of E. pruni is discussed.