Latex Metabolome of Euphorbia Species: Geographical and Inter-Species Variation and its Proposed Role in Plant Defense against Herbivores and Pathogens

Based on the hypothesis that the variation of the metabolomes of latex is a response to selective pressure and should thus be affected differently from other organs, their variation could provide an insight into the defensive chemical selection of plants. Metabolic profiling was used to compare tissues of three Euphorbia species collected in diverse regions. The metabolic variation of latexes was much more limited than that of other organs. In all the species, the levels of polyisoprenes and terpenes were found to be much higher in latexes than in leaves and roots of the corresponding plants. Polyisoprenes were observed to physically delay the contact of pathogens with plant tissues and their growth. A secondary barrier composed of terpenes in latex and in particular, 24-methylenecycloartanol, exhibited antifungal activity. These results added to the well-known role of enzymes also present in latexes, show that these are part of a cooperative defense system comprising biochemical and physical elements.

A Bombardier Beetle Pheropsophus aequinoctialis (L.) (Insecta: Coleoptera: Carabidae)

Pheropsophus aequinoctialis (L.) is a ground beetle in the tribe, Brachinini, native to parts of South and Central America. Ground beetles of this tribe are commonly referred to as bombardier beetles due to their ability to produce a powerful and hot defensive chemical spray directed at would-be predators. This spray is capable of harming humans, resulting in discomfort, physical burns (due to the spray temperature), and possibly contact dermatitis. The adults of this species are nocturnal and believed to be generalist predators and scavengers. However, larval stages appear to depend on an exclusive diet of mole cricket eggs. As such, Pheropsophus aequinoctialis may have potential use as a biological control agent against certain invasive mole cricket pests in North America. This article describes this insects biology, development, and behavior. Also published on the Featured Creatures website at http://entnemdept.ufl.edu/Creatures/BeneFICIAL/beetles/Pheropsophus_aequinoctialis.html

Aphid Species Specializing on Milkweed Have Distinct Bacterial Symbiont Communities

Host plant range is arguably one of the most important factors shaping microbial communities associated with insect herbivores. However, it is unclear whether host plant specialization limits microbial community diversity or to what extent herbivores sharing a common host plant evolve distinct microbiomes. To investigate whether variation in host plant specialization influences the composition of herbivore symbiont populations we compared bacterial diversity across three milkweed aphid species (Aphis nerii, Aphis asclepiadis, Myzocallis asclepiadis) feeding on a common host plant (Asclepias syriaca) using 16S rRNA metabarcoding. Overall, bacterial species richness did not vary with degree of host plant specialization. However, aphid species harbored distinct bacterial communities that varied in composition and relative abundance of key symbionts. Differences in aphid microbiomes were primarily due to strain variation in the obligate symbiont Buchnera and facultative symbiont Arsenophonus, as most of the low-abundant taxa were found in all three species. Interestingly, A. asclepiadis harbored a greater diversity of unique strains of Buchnera and significantly higher Arsenophonus relative abundances compared to the other two aphid species. Although many low abundance microbes were shared across all milkweed aphids, key differences exist in symbiotic partnerships that could influence additional ecological variation, including variation in ant tending observed across milkweed aphid species via microbial induced changes to honeydew or defensive chemical profiles. This study suggests generalist and specialist herbivore microbiomes are similar when feeding on a common host plant and highlights an intriguing potential role for strain level variation of key aphid symbionts in host-plant interactions.

Allelopathic Effects of Three Herb Species on Phytophthora cinnamomi, a Pathogen Causing Severe Oak Decline in Mediterranean Wood Pastures

The ability of three herbaceous plants (Diplotaxis tenuifolia (L.) DC., Eruca vesicaria L. and Raphanus raphanistrum L.) from Iberian wood pastures to reduce Phytophthora cinnamomi Rands pathogen populations through allelopathic relationships is studied. The inhibitory capacity of their aqueous root extracts (AREs) on mycelial growth and production of P. cinnamomi reproductive structures is analysed in vitro. In addition, Quercus seedlings were grown in infested by P. cinnamomi-soils and with the presence or absence of allelopathic and susceptible herb species to the pathogen to assess the defensive chemical response of Quercus seedlings through their leaf phenolic compounds. Results show a strong inhibitory capacity of AREs on P. cinnamomi activity in vitro and a protective effect of these herb species on Quercus plants against P. cinnamomi in vivo. D. tenuifolia would be especially suited for biological control in the pathogen suppression.

Persistence of the ground beetle (Coleoptera: Carabidae) microbiome to diet manipulation

ABSTRACTHost-associated microbiomes can play important roles in the ecology and evolution of their insect hosts, but bacterial diversity in many insect groups remains poorly understood. Here we examine the relationship between host environment, host traits, and microbial diversity in three species in the ground beetle family (Coleoptera: Carabidae), a group of roughly 40,000 species that synthesize a wide diversity of defensive compounds. This study found that the ground beetle microbiome is consistent across different host food sources. We used 16S amplicon sequencing to profile three species that are phylogenetically distantly related, trophically distinct, and whose defensive chemical secretions differ: Anisodactylus similis LeConte, 1851, Pterostichus serripes (LeConte, 1875), and Brachinus elongatulus Chaudoir, 1876. Wild-caught beetles were compared to individuals maintained in the lab for two weeks on carnivorous, herbivorous, or starvation diets. Soil environment but not diet had a significant effect on bacterial diversity and composition. The three carabid species have patterns of microbial diversity similar to those previously found in other insect hosts. Metagenomic samples from two highly active tissue types — guts, and pygidial gland secretory cells (which produce defensive compounds) — were processed and sequenced separately from those of the remaining body. The observed similarity of the pygidial gland secretory cell microbiome across hosts suggests the possibility that it may be a conserved community, possibly due to functional interactions related to defensive chemistry. These results provide a baseline for future studies of the role of microbes in the diversification of defensive chemical biosynthesis in carabids.

The instantaneous multi-pronged defense system of latex against general plant enemies

Based on the hypothesis that variation of the metabolomes of latex is a response to selective pressure and should thus be affected differently from other organs, their variation could provide insight into the defensive chemical selection of plants. Metabolic profiling was utilized to compare tissues of Euphorbia species collected in various regions. The metabolic variation of latexes was much more limited than that of other organs. In all of the species, the levels of polyisoprenes and terpenoids were found to be much higher in latexes than in leaves and roots. Polyisoprenes were also observed to physically delay the contact and growth of pathogens with plant tissues. A secondary barrier composed of terpenes and, in particular, 24-methylenecycloartanol, exhibited antifungal activity. These results, together with the known roles of the enzymes also present in latexes, demonstrate that they are part of a cooperative defense system that comprises both biochemical and physical elements.

Foraging behavior across paths that vary in risk cues and frequency of occurrence

Cooperatively foraging species often adjust their search strategies in complex environments to efficiently find and exploit food sources. These strategies become more complicated when food and risk can be simultaneously present and when they differ in predictability. For example, there may be multiple paths to reach a foraging site that vary in risk. This study examines how colonies of Argentine ants (Linepithema humile) respond to such a situation where identical-length paths differ in how they present risk. The risk cues are either a live competitor (velvety tree ants, Liometopum occidentale (LO)) or formic acid (FA), a defensive chemical commonly associated with formicine ant species. Across four paths to food, the presence of cues also varied from always to never present. Although the non-risky path was used more often, in no case did colonies completely avoid the paths with risk. Overall, more L. humile workers explored paths associated with LO than with FA. This had a significant impact on foraging ability where LO colonies were faster at finding food than FA colonies. Further, L. humile workers’ response to FA was similar over time while declined for LO, suggesting a ‘dear enemy’ habituation and reduction in aggression over time. Thus, it appears that L. humile foragers categorize risk cues and will vary their responses in potentially effective ways.