Drought changes plant chemistry and causes contrasting responses in lepidopteran herbivores

The extent to which behavioural choices reflect fine-tuned evolutionary adaptation remains an open debate. For herbivorous insects, the preference-performance hypothesis (PPH) states that female insects will evolve to oviposit on hosts on which their offspring fare best. In this study, we use meta-analysis to assess the balance of evidence for and against the PPH, and to evaluate the role of individual factors proposed to influence host selection by female insects. We do so in an explicitly bitrophic context (herbivores versus plants). Overall, our analyses offer clear support for the PPH: Offspring survive better on preferred plant types, and females lay more eggs on plant types conducive to offspring performance. We also found evidence for an effect of diet breadth on host choice: female preference for 'good quality plants' was stronger in oligophagous insects than in polyphagous insects. Nonetheless, despite the large numbers of preference-performance studies conducted to date, sample sizes in our meta-analysis are low due to the inconsistent format used by authors to present their results. To improve the situation, we invite authors to contribute to the data base emerging from this work, with the aim of reaching a strengthened synthesis of the subject field.

The 1998-2002 droughts spanning the United States, southern Europe, and Southwest Asia were linked through a common oceanic influence. Cold sea surface temperatures (SSTs) in the eastern tropical Pacific and warm SSTs in the western tropical Pacific and Indian oceans were remarkably persistent during this period. Climate models show that the climate signals forced separately by these regions acted synergistically, each contributing to widespread mid-latitude drying: an ideal scenario for spatially expansive, synchronized drought. The warmth of the Indian and west Pacific oceans was unprecedented and consistent with greenhouse gas forcing. Some implications are drawn for future drought.

Individual biotic and abiotic stresses, such as high temperature, high light and herbivore attack, are well known to increase the emission of volatile organic compounds from plants. Much less is known about the effect of multiple, co-occurring stress factors, despite the fact that multiple stresses are probably the rule under natural conditions. Here, after briefly summarizing the basic effects of single stress factors on the volatile emission of plants, we survey the influence of multiple stresses. When two or more stresses co-occur their effects are sometimes additive, while in other cases the influence of one stress has priority. Further investigations on the effects of multiple stress factors will improve our understanding of the patterns and functions of plant volatile emission. Copyright 2010 Elsevier Ltd. All rights reserved.