We provide a synthesis of the literature describing biochemical interactions between microorganisms and insects by way of microbial volatile organic compound (MVOC) production. We evaluated the functionality and ecological context of MVOC signals, and explored important metabolic pathways involved in MVOC production. The cosmopolitan distribution of microorganisms creates a context for frequent, and frequently overlooked, insect responses to microbial emissions. There are numerous instances of MVOCs being closely associated with insect feeding behaviors, but some MVOCs are also powerful repellants. Emissions from microorganisms in situ may signal aspects of habitat suitability or potential exposure to entomopathogens. In some ecosystems, bacterial or fungal volatiles can also incite insect aggregations, or MVOCs can resemble sexual pheromones that elicit mating and oviposition behaviors from responding insects. A single microorganism or MVOC can have different effects on insect behaviors, especially across species, ontogenies, and habitats. There appears to be a multipartite basis for insect responses to MVOCs, and complex tritrophic interactions can result from the production of MVOCs. Many biochemical pathways for behaviorally active volatile production by microbial species are conserved across large taxonomic groupings of microorganisms. In addition, there is substantial functional redundancy in MVOCs: fungal tissues commonly produce polyketides and short-chain alcohols, whereas bacterial tissues tend to be more commonly associated with amines and pyrazines. We hypothesize that insect olfactory responses to emissions from microorganisms inhabiting their sensory environment are much more common than currently recognized, and that these signals represent evolutionarily reliable infochemicals. Insect chemoreception of microbial volatiles may contribute to the formation of neutral, beneficial, or even harmful symbioses and provide considerable insight into the evolution of insect behavioral responses to volatile compounds.

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Summary1. Traditional species diversity measures do not make distinctions among species. Faith's phylogenetic diversity (PD), which is defined as the sum of the branch lengths of a phylogenetic tree connecting all species, takes into account phylogenetic differences among species and has found many applications in various research fields. In this paper, we extend Faith's PD to represent the total length of a phylogenetic tree from any fixed point on its main trunk. 2. Like species richness, Faith's PD tends to be an increasing function of sampling effort and thus tends to increase with sample completeness. We develop in this paper the 'PD accumulation curve' (an extension of the species accumulation curve) to depict how PD increases with sampling size and sample completeness. 3. To make fair comparisons of Faith's PD among several assemblages based on sampling data from each assemblage, we derive both theoretical formulae and analytic estimators for seamless rarefaction (interpolation) and extrapolation (prediction). We develop a lower bound of the undetected PD for an incomplete sample to guide the extrapolation; the PD estimator for an extrapolated sample is generally reliable up to twice the size of the empirical sample. 4. We propose an integrated curve that smoothly links rarefaction and extrapolation to standardize samples on the basis of sample size or sample completeness. A bootstrap method is used to obtain the unconditional variances of PD estimators and to construct the confidence interval of the expected PD for a fixed sample size or fixed degree of sample completeness. This facilitates comparison of multiple assemblages of both rarefied and extrapolated samples. 5. We illustrate our formulae and estimators using empirical data sets from Australian birds in two sites. We discuss the extension of our approach to the case of multiple incidence data and to incorporate species abundances.

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We report here a first survey of insect orientation to fungal cultures and fungal volatiles from a community ecology perspective. We tested whether volatiles from a ubiquitous yeast-like fungus (Aureobasidium pullulans) are broadly attractive to insects in an agricultural landscape. We evaluated insect attraction to fungal cultures and synthetic compounds identified in fungal headspace (2-methyl-1-butanol, 3-methyl-1-butanol, 2-phenylethanol) in a spearmint (Mentha spicata L.) plantation. Three findings emerged: (1) 1,315 insects representing seven orders and 39 species oriented to traps, but 65 % of trapped insects were Dipterans, of which 80 % were hoverflies (Diptera: Syrphidae); (2) traps baited with A. pullulans caught 481 % more insects than unbaited control traps on average, and contained more diverse (Shannon's H index) and species rich assemblages than control traps, traps baited with Penicillium expansum, or uninoculated media; and (3) insects oriented in greatest abundance to a 1:1:1 blend of A. pullulans volatiles, but mean diversity scores were highest for traps baited with only 2-phenylethanol or 2-methyl-1-butanol. Our results show that individual components of fungal headspace are not equivalent in terms of the abundance and diversity of insects that orient to them. The low abundance of insects captured with P. expansum suggests that insect assemblages do not haphazardly orient to fungal volatiles. We conclude that volatiles from a common fungal species (A. pullulans) are attractive to a variety of insect taxa in an agricultural system, and that insect orientation to fungal volatiles may be a common ecological phenomenon.

The cost of plant reproduction or defense at the expense of other fitness traits is a central component of life history theory. Yet the three central resource allocation pathways of growth, reproduction, and defense have rarely been assessed simultaneously nor across individual to landscape scales. This information is critical towards identifying the physiological, environmental, and genetic mechanisms underpinning resource allocation. This study assessed trade-offs in resource allocation between tree growth, defense, and reproduction across scales among piñon pine (Pinusedulis), a widespread mast-seeding conifer of the southwestern USA. Time series (2004-2016) of tree growth (radial and primary shoot growth), defense (resin duct production; a key constitutive defense for this species), and cone production among individual trees from populations across a broad environmental gradient were used to investigate these trade-offs in resource allocation across three scales: individual, population, and landscape. We found evidence for a defense-reproduction trade-off among individuals whereby total resin duct area in annual xylem rings was lower during years of above average cone production. Despite variability in cone and resin duct production across trees within a population and across populations, there was no association between these fitness traits at either of those scales. There was no evidence of trade-offs between cone production and growth at any scales measured, whereas resin duct production and growth were positively related at all scales. Our study suggests that a strategic trade-off occurs whereby investment into defense is temporarily curtailed to favor reproduction, despite increased risk of exposure to natural enemies and the ability of piñon pine to simultaneously allocate carbon to growth and defense. Our study provides new insights into physiological expressions of growth, defense, and reproduction over time in this long-lived masting conifer and indicates the presence of trade-offs with direct importance for individual fitness and population dynamics under global change.

Research to discover and develop attractants for the codling moth, Cydia pomonella L., has involved identification of the chemicals eliciting moth orientation to conspecific female moths, host fruits, fermented baits, and species of microbes. Pear ester, acetic acid, and N-butyl sulfide are among those chemicals reported to attract or enhance attractiveness to codling moth. We evaluated the trapping of codling moth with N-butyl sulfide alone and in combination with acetic acid and pear ester in apple orchards. Acetic acid was attractive in two tests and N-butyl sulfide was attractive in one of two tests. N-Butyl sulfide increased catches of codling moth when used with acetic acid to bait traps. N-Butyl sulfide also increased catches of codling moth when added to traps baited with the combination of acetic acid and pear ester. Male and female codling moth both responded to these chemicals and chemical combinations. These results provide a new three-component lure comprising N-butyl sulfide, acetic acid, and pear ester that is stronger for luring codling moth females than other attractants tested.

Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human-induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land-use change. Conversely, the suppression of natural disturbances threatens disturbance-dependent biota. Using a meta-analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α-diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively.