Identification of Volatiles That Are Used in Discrimination Between Plants Infested with Prey or Nonprey Herbivores by a Predatory Mite

Carnivorous arthropods can use herbivore-induced plant volatiles to locate their herbivorous prey. In the field, carnivores are confronted with information from plants infested with herbivores that may differ in their suitability as prey. Discrimination by the predatory mite Phytoseiulus persimilis between volatiles from lima bean plants infested with the prey herbivore Tetranychus urticae, or plants infested with the nonprey caterpillar Spodoptera exigua, depends on spider mite density. In this article, we analyzed the chemical composition of the volatile blends from T. urticae-infested lima bean plants at different densities of spider mites, and from S. exigua-infested plants. Based on the behavioral preferences of P. persimilis and the volatile profiles, we selected compounds that potentially enable the mite to discriminate between T. urticae-induced and S. exigua-induced volatiles. Subsequently, we demonstrated in Y-tube olfactometer assays that the relatively large amounts of methyl salicylate and (3E, 7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene emitted by T. urticae-infested bean plants compared to S. exigua-infested plants enable the predators to discriminate. Our data show that specific compounds from complex herbivore-induced volatile blends can play an important role in the selective foraging behavior of natural enemies of herbivorous arthropods.     

Impact of Herbivore-induced Plant Volatiles on Parasitoid Foraging Success: A Spatial Simulation of the <Emphasis Type="Italic">Cotesia rubecula,Pieris rapae,</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis> System

Many parasitoids are known to use herbivore-induced plant volatiles as cues to locate hosts. However, data are lacking on how much of an advantage a parasitoid can gain from following these plant cues and which factors can limit the value of these cues to the parasitoid. In this study, we simulate the Cotesia rubecula-Pieris rapae-Brassica oleracea system, and ask how many more hosts can a parasitoid attack in a single day of foraging by following plant signals versus randomly foraging. We vary herbivore density, plant response time, parasitoid flight distance, and available host stages to see under which conditions parasitoids benefit from herbivore-induced plant cues. In most of the parameter combinations studied, parasitoids that responded to cues attacked more hosts than those that foraged randomly. Parasitoids following plant cues attacked up to ten times more hosts when they were able to successfully attack herbivores older than first instar; however, if parasitoids were limited to first instar hosts, those following plant cues were at a disadvantage when plants took longer than a day to respond to herbivory. At low herbivore densities, only parasitoids with a larger foraging radius could take advantage of plant cues. Although preference for herbivore-induced volatiles was not always beneficial for a parasitoid, under the most likely natural conditions, the model predicts that C. rubecula gains fitness from following plant cues.     

Effects of Enhanced UV-B Radiation on Plant Chemistry: Nutritional Consequences for a Specialist and Generalist Lagomorph

Ultraviolet-B (UV-B) radiation has been increasing in temperate latitudes in recent decades and is expected to continue rising for some time. Enhanced UV-B radiation can change plant chemistry, yet the effects of these changes on mammalian herbivores are unknown. To examine the influence of enhanced UV-B radiation on nutrition of a specialist and generalist hindgut fermenter, we measured nutritional and chemical constituents of three common North American range plants, big sagebrush (Artemisia tridentata), yarrow (Achillea millefolium), and bluebunch wheatgrass (Pseudoregneria spicata), and how these changes influenced in vitro dry matter digestibility and in vivo digestibility by pygmy rabbits (Brachylagus idahoensis) and eastern cottontails (Sylvilagus floridanus). Forages were irradiated for 3 mo with ambient (1×) or supplemental (1.6×) UV-B radiation representing a 15% ozone depletion for Pullman, WA, USA. Enhanced UV-B radiation had minimal effects on the nutritional content and the tannin-binding capacity of forages. Similarly, the terpene concentration in sagebrush and yarrow was not affected by higher UV-B irradiances. Flavonoid compounds increased in sagebrush but decreased in yarrow. Rabbit preference and intake was not affected by treatment levels for any forage species and no differences were found between treatments for dry matter, fiber, protein digestibility, and apparent digestible energy.