Paul J. Ode

Covering sex allocation, sex determination and operational sex ratios, this multi-author volume provides both a conceptual context and an instruction in methods for many aspects of sex ratio research. Theory, statistical analysis and genetics are each explained and discussed in the first three sections. The remaining chapters each focus on research in one of a wide spectrum of animal, plant and microbial taxa, including sex ratio distorting bacteria in invertebrates, malarial parasites, birds, human and other mammals, giving critical appraisals of such research. Sex Ratios: Concepts and Research Methods is primarily intended for graduate and professional behavioural and evolutionary ecologists in this field, but it will also be useful to biologists building evolutionary models, and researchers analysing data involving proportions or comparisons across phylogenetically related species.

Abstract Climate warming is considered to be among the most serious of anthropogenic stresses to the environment, because it not only has direct effects on biodiversity, but it also exacerbates the harmful effects of other human‐mediated threats. The associated consequences are potentially severe, particularly in terms of threats to species preservation, as well as in the preservation of an array of ecosystem services provided by biodiversity. Among the most affected groups of animals are insects—central components of many ecosystems—for which climate change has pervasive effects from individuals to communities. In this contribution to the scientists' warning series, we summarize the effect of the gradual global surface temperature increase on insects, in terms of physiology, behavior, phenology, distribution, and species interactions, as well as the effect of increased frequency and duration of extreme events such as hot and cold spells, fires, droughts, and floods on these parameters. We warn that, if no action is taken to better understand and reduce the action of climate change on insects, we will drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems. We discuss perspectives on relevant ways to conserve insects in the face of climate change, and we offer several key recommendations on management approaches that can be adopted, on policies that should be pursued, and on the involvement of the general public in the protection effort.

Tremendous strides have been made regarding our understanding of how host plant chemistry influences the interactions between herbivores and their natural enemies. While most work has focused on plant chemistry effects on host location and acceptance by natural enemies, an increasing number of studies examine negative effects. The tritrophic role of plant chemistry is central to several aspects of trophic phenomena including top-down versus bottom-up control of herbivores, enemy-free space and host choice, and theories of plant defense. Furthermore, tritrophic effects of plant chemistry are important in assessing the degree of compatibility between biological control and plant resistance approaches to pest control. Additional research is needed to understand the physiological effects of plant chemistry on parasitoids. Explicit tests are required to determine whether natural enemies can act as selective forces on plant defense. Finally, further studies of natural systems are crucial to understanding the evolution of multitrophic relationships.

1. The reproductive biology of the polyembryonic encyrtid wasp Copidosoma floridanum was examined in a series of laboratory experiments and related to observations from field collections. Females laid one or two eggs per host, producing broods comprised of all males, all females, or both sexes (mixed). Each egg produced multiple embryos that developed into either precocious larvae that never became adult or reproductive larvae that developed into reproductive adults. 2. The age of the host-egg when it was parasitized was found to have a substantial effect on offspring clutch sizes and sex ratios. (i) The clutch sizes and overall survivorship of female and mixed broods decreased with increasing host-egg age, whereas male clutch sizes and survivorship were relatively unaffected by host-egg age. (ii) Offspring sex ratios (proportion males) of mixed broods were higher in older hosteggs. (iii) Body sizes of males and females were negatively correlated with clutch size. Larger females had higher fecundities and larger males had greater mating abilities. 3. Host-egg age also affected competitive asymmetries between males and females. In young host-eggs, female precocious larvae were much more abundant than males and were instrumental in reducing the number of males in mixed broods. In older host-eggs, the numbers of male and female precocious larvae were much lower, and were approximately equal. As a result, sex ratios of mixed broods in older host eggs were closer to equality. 4. Ovipositing females responded to host-egg age and host encounter rates when making oviposition decisions. Females laid more female eggs in younger hosts and more mixed broods in older hosts. Females laid more mixed broods when encounter rates were low and more female broods when encounter rates were high