Andrea Liliana Clavijo McCormick

The specificity of herbivore-induced plant volatiles in attracting herbivore enemies

Plants respond to herbivore attack by emitting complex mixtures of volatile compounds that attract herbivore enemies, both predators and parasitoids. Here, we explore whether these mixtures provide significant value as information cues in herbivore enemy attraction. Our survey indicates that blends of volatiles released from damaged plants are frequently specific depending on the type of herbivore and its age, abundance and feeding guild. The sensory perception of plant volatiles by herbivore enemies is also specific, according to the latest evidence from studies of insect olfaction. Thus, enemies do exploit the detailed information provided by plant volatile mixtures in searching for their prey or hosts, but this varies with the diet breadth of the enemy.

Herbivore-induced volatile emission in black poplar: regulation and role in attracting herbivore enemies

After herbivory, plants release volatile organic compounds from damaged foliage as well as from nearby undamaged leaves that attract herbivore enemies. Little is known about what controls the volatile emission differences between damaged and undamaged tissues and how these affect the orientation of herbivore enemies. We investigated volatile emission from damaged and adjacent undamaged foliage of black poplar (Populus nigra) after herbivory by gypsy moth (Lymantria dispar) caterpillars and determined the compounds mediating the attraction of the gypsy moth parasitoid Glyptapanteles liparidis (Braconidae). Female parasitoids were more attracted to gypsy moth-damaged leaves than to adjacent non-damaged leaves. The most characteristic volatiles of damaged versus neighbouring undamaged leaves included terpenes, green leaf volatiles and nitrogen-containing compounds, such as aldoximes and nitriles. Electrophysiological recordings and olfactometer bioassays demonstrated the importance of nitrogenous volatiles. Under field conditions, parasitic Hymenoptera were more attracted to traps baited with these substances than most other compounds. The differences in volatile emission profiles between damaged and undamaged foliage appear to be regulated by jasmonate signalling and the local activation of volatile biosynthesis. We conclude that characteristic volatiles from damaged black poplar foliage are essential cues enabling parasitoids to find their hosts.

Little peaks with big effects: establishing the role of minor plant volatiles in plant–insect interactions

Plants emit complex mixtures of volatile organic compounds from floral and vegetative tissue, especially after herbivore damage, so it is difficult to associate individual compounds with activity towards pollinators, herbivores or herbivore enemies. Attention has usually focused upon the biological activity of the most abundant compounds; but here, we detail a number of reports implicating minor volatiles in attractant or deterrent roles. This is not surprising given the exquisite sensitivity of insect olfactory systems for certain substances. In this context, it is worth reconsidering the methods involved in sampling volatile compounds from plants, measuring their abundance and determining their biological activity to ensure that minor compounds are not overlooked. Here, we describe various experimental approaches and chemical and statistical methods that should increase the chance of detecting minor compounds with major biological activities.

Two herbivore-induced cytochrome P450 enzymes CYP79D6 and CYP79D7 catalyze the formation of volatile aldoximes involved in poplar defense

Aldoximes are precursors of several classes of direct plant defense compounds. This study characterizes two cytochrome P450 monooxygenase enzymes, CYP79D6/7, which are involved in gypsy moth–induced aldoxime formation in western balsam poplar. Volatile formation mediated by CYP79s may be a general phenomenon in the plant kingdom. Aldoximes are known as floral and vegetative plant volatiles but also as biosynthetic intermediates for other plant defense compounds. While the cytochrome P450 monooxygenases (CYP) from the CYP79 family forming aldoximes as biosynthetic intermediates have been intensively studied, little is known about the enzymology of volatile aldoxime formation. We characterized two P450 enzymes, CYP79D6v3 and CYP79D7v2, which are involved in herbivore-induced aldoxime formation in western balsam poplar (Populus trichocarpa). Heterologous expression in Saccharomyces cerevisiae revealed that both enzymes produce a mixture of different aldoximes. Knockdown lines of CYP79D6/7 in gray poplar (Populus × canescens) exhibited a decreased emission of aldoximes, nitriles, and alcohols, emphasizing that the CYP79s catalyze the first step in the formation of a complex volatile blend. Aldoxime emission was found to be restricted to herbivore-damaged leaves and is closely correlated with CYP79D6 and CYP79D7 gene expression. The semi-volatile phenylacetaldoxime decreased survival and weight gain of gypsy moth (Lymantria dispar) caterpillars, suggesting that aldoximes may be involved in direct defense. The wide distribution of volatile aldoximes throughout the plant kingdom and the presence of CYP79 genes in all sequenced genomes of angiosperms suggest that volatile formation mediated by CYP79s is a general phenomenon in the plant kingdom.

The timing of herbivore-induced volatile emission in black poplar (Populus nigra) and the influence of herbivore age and identity affect the value of individual volatiles as cues for herbivore enemies

BackgroundThe role of herbivore-induced plant volatiles as signals mediating the attraction of herbivore enemies is a well-known phenomenon. Studies with short-lived herbaceous plant species have shown that various biotic and abiotic factors can strongly affect the quantity, composition and timing of volatile emission dynamics. However, there is little knowledge on how these factors influence the volatile emission of long-lived woody perennials.The aim of this study was to investigate the temporal dynamics of herbivore-induced volatile emission of black poplar (Populus nigra) through several day-night cycles following the onset of herbivory. We also determined the influence of different herbivore species, caterpillars of the gypsy moth (Lymantria dispar) and poplar hawkmoth (Laothoe populi), and different herbivore developmental stages on emission.ResultsThe emission dynamics of major groups of volatile compounds differed strikingly in response to the timing of herbivory and the day-night cycle. The emission of aldoximes, salicyl aldehyde, and to a lesser extent, green leaf volatiles began shortly after herbivore attack and ceased quickly after herbivore removal, irrespective of the day-night cycle. However, the emission of most terpenes showed a more delayed reaction to the start and end of herbivory, and emission was significantly greater during the day compared to the night. The identity of the caterpillar species caused only slight changes in emission, but variation in developmental stage had a strong impact on volatile emission with early instar L. dispar inducing more nitrogenous volatiles and terpenoids than late instar caterpillars of the same species.ConclusionsThe results indicate that only a few of the many herbivore-induced black poplar volatiles are released in tight correlation with the timing of herbivory. These may represent the most reliable cues for herbivore enemies and, interestingly, have been shown in a recent study to be the best attractants for an herbivore enemy that parasitizes gypsy moth larvae feeding on black poplar.

Carcass and meat quality of finished and non-finished Limousin heifers from alpine livestock systems differing in altitudinal origin of the forage.

ABSTRACT Effects of the alpine origin of the forage and of finishing on carcass and beef quality were quantified by modelling different alpine livestock system alternatives. Thirty-five Limousin heifers, initially weighing 383 ± 45 kg, were fed fresh grass at 400 or 2000 m above sea level, or a 1:1 mixture of alpine grass and lowland grass hay at 2000 m. After 9 weeks, the six heaviest and oldest animals per group were slaughtered. The remaining animals were finished for 8 weeks on a silage-concentrate diet in the lowlands to similar age and body weight as the first slaughtered group. Carcass and meat quality (M. longissimus thoracis) were assessed in various respects. The average daily gains achieved were of about 600 g/d and similar between forage-type groups. Dressing percentage was 53.5% in the alpine and 57.2% in the lowland group. Carcass conformation and fat cover scores did not differ between forage-type groups. The meat from the alpine groups had greater ultimate pH and smaller redness, yellowness and protein contents. Still, these differences were of minor practical relevance. There was no forage-type effect on water-holding capacity and shear force of the meat. The alpine systems enhanced the proportion of α-linolenic acid in intramuscular fat and decreased the levels of some volatile compounds in perirenal fat. Finishing resulted in compensatory growth, especially in the animals previously fed lowland grass. There was a trend for the finished compared with the non-finished groups towards greater carcass fat cover and intramuscular fat content. Additionally, ultimate pH was smaller and cooking loss was greater with than without finishing. Meat colour differences were also observed. Shear force was not affected by finishing. The finished animals had a smaller α-linolenic acid proportion in the intramuscular fat. In conclusion, the forage type had small effects on carcass and meat quality. Finishing did not substantially improve carcass and meat quality. The (alpine) grass-specific differences in fatty acid profile found in the unfinished cattle were not present in the finished animals.

Exploring the Effects of Plant Odors, from Tree Species of Differing Host Quality, on the Response of Lymantria dispar Males to Female Sex Pheromones

A widely accepted hypothesis for host-plant selection in herbivorous insects is that ovipositing females select host-plants that maximize the survival and performance of their offspring. However, numerous studies indicate that this is not always the case for polyphagous species. Lymantria dispar is a highly polyphagous forest defoliator and has flightless females in some subspecies, resulting in a limited capacity to make host-choices. Males of other Lepidopteran species utilize a combination of sexual pheromones and plant volatiles in their mating choices and exhibit preferences among plant species. We explored the behavior of L. dispar males towards sexual pheromone in the presence and absence of plant volatiles and their ability to discriminate between two plant species with different degrees of suitability for their offspring: a suboptimal host (Pinus sylvestris), and an optimal host (Quercus robur). In no-choice wind tunnel assays, we found that rates of male success in locating a pheromone source were not altered by the presence of plant odors; however, the time spent by males searching for the pheromone source after reaching the full length of the tunnel was reduced by more than 50% in the presence of plant volatiles. In dual choice assays, males exhibited a clear preference for a combination of pheromones and plant volatiles over the pheromone alone. However, we did not find evidence of an innate ability to discriminate between the odors of optimal and suboptimal host plants. We discuss possible ecological and evolutionary explanations for these observations.

Comparing the Expression of Olfaction-Related Genes in Gypsy Moth (Lymantria dispar) Adult Females and Larvae from One Flightless and Two Flight-Capable Populations

In insects, flight and sophisticated olfactory systems go hand in hand and are essential to survival and evolutionary success. Females of many Lepidopteran species have secondarily lost their flight ability, which may lead to changes in the olfactory capabilities of both larval and adult stages. The gypsy moth, Lymantria dispar, an important forest pest worldwide, is currently undergoing a diversification process with three recognized subspecies: the Asian gypsy moth (AGM) L. dispar asiatica, the Japanese gypsy moth L. dispar japonica (JGM) and the European gypsy moth (EGM) L. dispar dispar. Females of EGM populations from North America have lost their flight capacity whereas the JGM and AGM females are flight capable, making this an ideal system to investigate the relationship between flight and olfaction. We used next-generation sequencing to obtain female antennal and larval head capsule transcriptomes in order to (i) investigate the differences in expression of olfaction-related genes among populations; (ii) identify the most similar protein sequences reported for other organisms through a BLAST search, and (iii) establish the phylogenetic relationships of these sequences with respect to other insect species. Using this approach, we identified 115 putative chemosensory genes belonging to five families of olfaction-related genes. A principal component analysis revealed that the gene expression patterns of female antennal transcriptomes from different subspecies were more similar among them than to the larval head capsules of their respective subspecies supporting strong chemosensory differences between the two developmental stages. An analysis of the shared and exclusively expressed genes for three populations shows no evidence that loss of flight affects the number or type of genes being expressed. These results indicate either that (a) loss of flight does not impact the olfactory gene repertoire or that (b) the secondary loss of flight in the American EGM populations may be too recent to have caused major changes in the genes being expressed. However, we found higher expression values for IRs, OBPs GRs and ORs in EGM females, suggesting that differences in transcription rates could be an adaptation of flightless females to their chemical environment. Differences in olfactory genes and their expression in the