No-choice Trials Research Articles

Hydrocarbon divergence and reproductive isolation in Timema stick insects

BackgroundIndividuals commonly prefer certain trait values over others when choosing their mates. If such preferences diverge between populations, they can generate behavioral reproductive isolation and thereby contribute to speciation. Reproductive isolation in insects often involves chemical communication, and cuticular hydrocarbons, in particular, serve as mate recognition signals in many species. We combined data on female cuticular hydrocarbons, interspecific mating propensity, and phylogenetics to evaluate the role of cuticular hydrocarbons in diversification of Timema walking-sticks.ResultsHydrocarbon profiles differed substantially among the nine analyzed species, as well as between partially reproductively-isolated T. cristinae populations adapted to different host plants. In no-choice trials, mating was more likely between species with similar than divergent hydrocarbon profiles, even after correcting for genetic divergences. The macroevolution of hydrocarbon profiles, along a Timema species phylogeny, fits best with a punctuated model of phenotypic change concentrated around speciation events, consistent with change driven by selection during the evolution of reproductive isolation.ConclusionAltogether, our data indicate that cuticular hydrocarbon profiles vary among Timema species and populations, and that most evolutionary change in hydrocarbon profiles occurs in association with speciation events. Similarities in hydrocarbon profiles between species are correlated with interspecific mating propensities, suggesting a role for cuticular hydrocarbon profiles in mate choice and speciation in the genus Timema.

Sigma virus and male reproductive success in Drosophila melanogaster

The risk of disease transmission can affect female mating rate, and thus sexual conflict. Furthermore, the interests of a sexually transmitted organism may align or diverge with those of either sex, potentially making the disease agent a third participant in the sexual arms race. In Drosophila melanogaster, where sexual conflict over female mating rate is well established, we investigated how a common, non-lethal virus (sigma virus) might affect this conflict. We gave uninfected females the opportunity to copulate twice in no-choice trials: either with two uninfected males, or with one male infected with sigma virus followed by an uninfected male. We assessed whether females respond behaviorally to male infection, determined whether male infection affects either female or male reproductive success, and measured offspring infection rates. Male infection status did not influence time to copulation, or time to re-mating. However, male infection did affect male reproductive success: first males sired a significantly greater proportion of offspring, as well as more total offspring, when they were infected with sigma virus. Thus viral infection may provide males an advantage in sperm competition, or, possibly, females may preferentially use infected sperm. We found no clear costs of infection in terms of offspring survival. Viral reproductive success (the number of infected offspring) was strongly correlated with male reproductive success. Further studies are needed to demonstrate whether virus-induced changes in reproductive success affect male and female lifetime fitness, and whether virus-induced changes are under male, female, or viral control.

Grazer avoidance may explain the invasiveness of the red alga Gracilaria vermiculophylla in Scandinavian waters

The invasive red alga Gracilaria vermiculophylla has quickly spread across Europe, but it is unclear whether its success is based on a high tolerance to variations in environmental conditions or to the absence of native grazers that feed on this alga. We tested whether native invertebrate grazers prefer native algae to G. vermiculophylla. Feeding preferences of three common herbivores were quantified when offered G. vermiculophylla and native Fucus vesiculosus, Ceramium virgatum, and Ulva intestinalis in no-, two- and multiple-choice trials. Herbivore growth was measured when fed each of the algae separately. Grazers consumed G. vermiculophylla in no-choice trials, but avoided generally this alga when having a choice. U. intestinalis was always preferred over G. vermiculophylla, and grazers fed with U. intestinalis grew faster than those fed with G. vermiculophylla. We conclude that grazers avoid G. vermiculophylla to most native algae, which may benefit G. vermiculophylla in northern European estuaries.

Cognitive mechanisms of risky choice: Is there an evaluation cost?

We contrast two classes of choice processes, those assuming time-consuming comparisons and those where stimuli for each option act independently, competing for expression by cross censorship. The Sequential Choice Model (SCM) belongs in the latter category, and has received empirical support in several procedures involving deterministic alternatives. Here we test this model in risky choices. In two treatments, each with five conditions, European starlings (Sturnus vulgaris) faced choices between options with unpredictable outcomes and risk-free alternatives. In the delay treatment the five conditions involved choices between a variable option offering two equiprobable delays to reward and a fixed option with delay differing between conditions. The amount treatment was structurally similar, but amount of reward rather than delay was manipulated. As assumed (and required) by the SCM, latency to respond in no-choice trials reflected each option's richness with respect to the background alternatives, and, crucially, preferences in simultaneous choices were predictable from latencies to each option in forced trials. However, we did not detect reliable differences in response times between forced and choice trials, neither the lengthening expected from evaluation models nor the shortening expected from the SCM.

Life history and host range of Alagoasa extrema (Coleoptera: Chrysomelidae: Alticinae), a potential biological control agent of Lantana spp. (Verbenaceae) in Australia

The life history and host range of the lantana beetle, Alagoasa extrema, a potential biocontrol agent for Lantana spp. were investigated in a quarantine unit at the Alan Fletcher Research Station, Brisbane, Australia. Adults feed on leaves and females lay batches of about 17 eggs on the soil surface around the stems of plants. The eggs take 16 days to hatch and newly emerged larvae move up the stem to feed on young leaves. Larvae feed for about 23 days and there are three instars. There is a prepupal non-feeding stage that lasts about 12 days and the pupal stage, which occurs in a cocoon in the soil, lasts 16 days. Teneral adults remain in the cocoon for 3 days to harden prior to emergence. Males live for about 151 days while females live for about 127 days. The pre-oviposition period is 19 days. In no-choice larval feeding trials, nine plant species, representing three families, supported development to adult. Three species, Aloysia triphylla, Citharexylum spinosum and Pandorea pandorana were able to support at least two successive generations. These results confirm those reported in South Africa and suggest that A. extrema is not sufficiently specific for release in Australia. Furthermore, it is not recommended for release in any other country which is considering biological control of lantana.

Biology and host preference of the planthopper Taosa longula (Hemiptera: Dictyopharidae), a candidate for biocontrol of water hyacinth

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) is a planthopper from the South American tropics that feeds on water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae). The biology of T. longula was studied in the laboratory and field to evaluate it as a potential biological control agent for this widespread aquatic weed. The developmental time of nymphs was recorded at different temperatures (15, 19, 23, 25, 27 and 30 °C), and developmental threshold temperatures were obtained for the different instars. The host range was evaluated in terms of development and feeding preference. Development from instar I to adult was recorded in two no-choice trials, one with cut leaves of Pontederiaceae, and a second with growing whole plants. In the cut-leaf tests, adults were obtained from Pontederia cordata var. cordata, P. rotundifolia and water hyacinth. In the whole plant test, T. longula adults were obtained only from water hyacinth. Feeding preference was evaluated by means of a paired-choice test with 10 T. longula first instars on whole plants of P. c. cordata, P. rotundifolia and water hyacinth. The number of insects that fed on water hyacinth was significantly higher than on P. c. cordata and P. rotundifolia. Taosa longula showed a clear preference for water hyacinth and exhibited warm climate requirements, making it an attractive candidate for water hyacinth biological control in tropical and subtropical areas.

Place your bets: psychophysiological correlates of decision-making under risk

Emotions and their psychophysiological correlates are thought to play an important role in decision-making under risk. We used a novel gambling task to measure psychophysiological responses during selection of explicitly presented risky options and feedback processing. Active-choice trials, in which the participant had to select the size of bet, were compared to fixed-bet, no-choice trials. We further tested how the chances of winning and bet size affected choice behavior and psychophysiological arousal. Individual differences in impulsive and risk-taking traits were assessed. The behavioral results showed sensitivity to the choice requirement and to the chances of winning: Participants were faster to make a response on no-choice trials and when the chances of winning were high. In active-choice trials, electrodermal activity (EDA) increased with bet size during both selection and processing of losses. Cardiac responses were sensitive to choice uncertainty: Stronger selection-related heart rate (HR) decelerations were observed in trials with lower chances of winning, particularly on active-choice trials. Finally, betting behavior and psychophysiological responsiveness were moderately correlated with self-reported impulsivity-related traits. In conclusion, we demonstrate that psychophysiological arousal covaries with risk-sensitive decision-making outside of a learning context. Our results further highlight the differential sensitivities of EDA and HR to psychological features of the decision scenario.

Planarian (Dugesia polychroa) predation on freshwater gastropod eggs depends on prey species, clutch morphology, and egg size

Though triclad planarias could limit littoral snail recruitment by preying on eggs with their muscular ventral pharynx, planarian predation on eggs has never been quantified. Intact egg clutches encompassing eight snail species x three developmental stages were offered to Dugesia (= Schmidtea) polychroa (Paludicola: Dugesiidae) individuals (body length = 6-12 mm) in one-on-one, no-choice 24-h feeding trials to gain a first insight on snail egg palatability to dugesiid planarias. Predatory losses were quantified as differences in planaria-present trials v.s. parallel planaria-absent controls. D. polychroa predation on snail eggs was generally low. Eggs in monolayered, flat clutches of bithyniids (Bithynia leachii) and planorbids (Planorhis planorbis, Helisoma trivolvis, and Planorbarius corneus) were more susceptible to planarian predation than multilayered eggs in sausage-shaped clutches of physids (Physa acuta) and lymnaeids (Lymnaea stagnalis, Radix auricularia, and Stagnicola fuscus). Planarian predation also was higher on smaller eggs, and was not related to planarian body size. Vulnerability was also markedly species-specific, with appreciable losses recorded only for pre-hatching eggs of P. planorbis and, to a lesser extent, H. trivolvis. The results suggest that, with the possible exception for the soft-clutch, small eggs of P. planorbis, predation by D. polychroa on eggs does not impact gastropod recruitment appreciably.

Preference and performance of Aconophora compressa Walker (Hemiptera: Membracidae) on different lantana phenotypes in Australia

The plant phenotypic preference and performance of Aconophora compressa, a biocontrol agent for Lantana camara in Australia, were assessed. Overall, there were no significant trends of A. compressa favouring any one particular phenotype. However, there was a gradual decrease in performance through subsequent generations, with populations of A. compressa dying out on two phenotypes. Females did not show preference for any particular lantana phenotype, ovipositing similarly on all five phenotypes presented in choice trials and all 16 phenotypes in no-choice trials. Nymphs developed on all 16 phenotypes tested. Percent development and time to complete development were not significant in the first generation but were significant in the second generation. There was a general decrease in performance with generation. However, this was probably due to rising temperatures with season rather than an effect of phenotype. These results suggest that A. compressa should establish on all phenotypes within its geographic range.

Testing for mating isolation between ecotypes: laboratory experiments with lake, stream and hybrid stickleback

Mating isolation is a frequent contributor to ecological speciation - but how consistently does it evolve as a result of divergent selection? We tested for genetically based mating isolation between lake and stream threespine stickleback (Gasterosteus aculeatus L.) from the Misty watershed, Vancouver Island, British Columbia. We combined several design elements that are uncommon in the studies of stickleback mate choice: (i) we used second-generation laboratory-reared fish (to reduce environmental and maternal effects), (ii) we allowed for male-male competitive interactions (instead of the typical no-choice trials) and (iii) we included hybrids along with pure types. Males of different types (Lake, Inlet, hybrid) were paired in aquaria, allowed to build nests and then exposed sequentially to females of all three types. We found that Lake and Inlet males differed in behaviours thought to influence stickleback mate choice (inter- and intra-sexual aggression, display and nest activities), whereas hybrids were either intermediate or apparently 'inferior' in these behaviours. Despite these differences, Lake and Inlet fish did not mate assortatively and hybrid males did not have a mating disadvantage. Our study reinforces the noninevitability of mating isolation evolving in response to ecological differences and highlights the need to further investigate the factors promoting and constraining progress towards ecological speciation.

New Report ofChaetopsis massyla(Diptera: Ulidiidae) as a Primary Pest of Corn in Florida

The picture-winged fly Euxesta stigmatias Loew (Diptera: Ulidiidae) has been a serious pest of sweet corn in Florida since the 1930s and had been considered the only fly infesting Florida corn. In a sweet corn variety trial to evaluate E. stigmatias resistance in 2007, adult Chaetopsis massyla (Walker) (Diptera: Ulidiidae) was reared from the ears. Choice and no-choice trials were conducted in 2007 and 2008 to determine the pest nature of C. massyla on corn. In no choice tests, C. massyla pairs were caged on uninfested corn ears in green house and field trials. In choice tests, field collected corn ears were held for fly emergence. No choice tests showed that C. massyla could infest and complete development in ears that had no previous damage. Chaetopsis massyla emerged from corn ears with and without prior infestation by other insect species in choice tests. Subsequently, C. massyla were reared from corn ears collected from locations throughout the major sweet corn growing region of southern Florida. Therefore, we present what we believe to be the first report of C. massyla as a primary pest of corn ears in Florida and in the United States of America.

Laboratory and field evaluation for the resistance of commonly used woods against Coptotermes heimi (Wasmann).

AbstractThe current study was conducted to evaluate the resistance of four wood species (Azadirachta indica, Pinus roxberghii, Dalbergia sissoo and Populus deltoides) against subterranean termite species Coptotermes heimi by choice and no choice field and laboratory trials. Of these four wood species P. roxberghii and D. sissoo proved to be most resistant to termite attack. Taken together these results we can conclude that D. sissoo is the least preferred and P. deltoides is the most preferred wood by the C. heimi. The data obtained from the field choice and no-choice the woods are arranged in order of preference DS>PR>AI>PD whereas in laboratory choice and no-choice trials the order of preference was PD>AI>PR>DS.

Efficacy of anticoagulant‐free alternative bait products against house mice (Mus musculus) and brown rats (Rattus norvegicus)

The attractiveness and efficacy of four anonymous anticoagulant-free alternative rodenticides (active ingredients cellulose or plaster) were tested on wild strain groups of house mice (Mus musculus Linnaeus) and brown rats (Rattus norvegicus Berkenhout) in laboratory choice and no-choice experiments. In no-choice tests, the rodenticide product was offered ad libitum to the animals for 21 days (mice) and 10 days (rats), respectively. In choice tests, the rodenticide product and non-poisoned food were offered for 28 days (mice) and 14 days (rats). Two products with cellulose (C1 and C2) as the active ingredient were tested against both mice and rats. In two no-choice tests with mice, all animals died within 14 days (C1) and 21 days (C2); in a third no-choice test, 11% (2/18) of mice survived (C1: 21 days). In all three tests, numerous incidents of cannibalism were observed. The attractiveness of cellulose baits was tested for one product (C1) in three trials against normal food pellets. In all trials, bait consumption was low and all mice survived (15-34 days). Two no-choice trials with cellulose baits (C1) were conducted on groups of Rattus norvegicus; 11 of 12 rats survived the bait feeding period and no cannibalism or sign of aggression between conspecifics was observed. Two plaster-based (CaSO4 0.5H2O) products (P1 and P2) were tested against both mice and rats; in no-choice tests, only one mouse (n= 20) and no rats (n= 8) were killed, although the baits proved to be attractive for rats and mice in choice tests. The results of these experiments suggest that neither cellulose-based nor plaster-based rodenticides are suitable agents for the control of Mus musculus and Rattus norvegicus.

Potential impact and non-target effects of Gallerucida bifasciata (Coleoptera: Chrysomelidae), a candidate biological control agent for Fallopia japonica

A pre-release evaluation of a potential biological control agent is designed to estimate the impact the agent will have on the target in the introduced range, and whether the agent poses an acceptable level of risk to biodiversity. Here, we present an evaluation of the Asian leaf-beetle, Gallerucida bifasciata, a potential biological control agent for Japanese knotweed, Fallopia japonica. First we tested the impact of different larval and adult densities on the plant under laboratory conditions . After six weeks, the biomass of F. japonica was 15% or 28% that of control plants if larvae or adults were added, with levels of damage plateauing quickly with increasing insects densities. High fecundity and larval density dependence means that this agent could substantially and quickly suppress plant growth, although this damage only occurs early in the season, allowing F. japonica time to compensate. Second, following on from general host-specificity trials, we investigated potential non-target effects on the commercially important plant buckwheat, Fagopyrum esculentum, in more depth. The leaf-beetle showed some minor adult feeding on F. esculentum in choice trials, and in no-choice trials the leaf-beetle was able to complete its life cycle and sustain a population on F. esculentum, albeit causing lower levels of damage than on F. japonica. This suggests that if the beetle dispersed to areas where F. japonica is not present, it might colonise F. esculentum. Therefore, despite potentially being an effective agent, that the risk of non-target feeding is unacceptably high.

Pre-harvest infestation of beans ( Phaseolus vulgaris L.) by Acanthoscelides obtectus Say (Coleoptera: Bruchidae) in relation to bean pod maturity and pod aperture

Acanthoscelides obtectus is a bruchid beetle that oviposits into ripening bean pods in the field. More precise data are needed for developing management strategies for small-scale farmers in East Africa. In farmers' fields, an infestation rate of 6.9% infested bean seeds was recorded in dry pods, but in wilting yellow pods there was a lower infestation of 2.5%. No wilting green pod had been infested. After releasing 680 bruchids in an open field, the infestation rate in dry pods increased to 39 and 7% in wilting yellow pods, but again no wilting green pod was found to be infested. In no-choice laboratory trials, however, A. obtectus infests wilting pods; and pod aperture did not influence infestation rates. Stimulants for oviposition were evaluated in no-choice trials. Bean pods containing seeds were as attractive as bean seeds alone, and significantly more attractive as empty opened bean pods. Bean pods without seeds were more attractive than the empty control. The natural infestation rate in fields close to homesteads was higher than in fields more than 1 km away from any habitation. Farmers are advised to be aware of the infestation danger in the field, and to consider early harvest if they have infestation-free storage.

Visual Plant Differentiation by the Milfoil Weevil, Euhrychiopsis lecontei Dietz (Coleoptera: Curculionidae)

Euhrychiopsis lecontei Dietz (Coleoptera: Curculionidae) is an aquatic weevil native to the northern United States that specializes on plants in the genus Myriophyllum (milfoils). Euhrychiopsis lecontei is currently being used in the U.S. as a biological control agent for the invasive Eurasian watermilfoil (Myriophyllum spicatum L.: Haloragaceae; Newman 2004). The weevil has expanded its host range to include M. spicatum since the plant’s introduction from Eurasia in the 1940s. Field and laboratory studies have shown that E. lecontei reduces M. spicatum densities, and also prefers M. spicatum over other (native) milfoils (see Newman 2004 for summary of E. lecontei life history and use as a biological control agent). Euhrychiopsis lecontei can use visual cues for plant location (Reeves et al. 2009). However, during no-choice plant differentiation trials, weevils were attracted to both M. spicatum and coontail (Ceratophyllum demersum L.: Ceratophyllaceae; Reeves et al. 2009). Specifically, weevils swam equally quickly to sealed vials containing one or the other of these plants when one individual plant stem was the only visual stimulus in the behavioral arenas used. We present results here describing how the weevils responded to choice trials where both M. spicatum and C. demersum were placed side by side in the behavioral arenas. This short communication expands on the work presented by Reeves et al. (2009) which showed that weevils can use vision for at least initial host-plant detection, but may not be able to visually differentiate between plant species. Because Reeves et al. (2009) did not conclusively show in no-choice trials that weevils were unable to visually J Insect Behav (2009) 22:473–476 DOI 10.1007/s10905-009-9186-z

Courtship and mate discrimination within and between species of Timema walking-sticks

The evolution of premating isolation via divergence in mating behaviour has been strongly implicated in the process of speciation. Timema walking-sticks show weak to moderate reproductive isolation between populations of the same species on different host plants, and high levels of isolation between species. In this paper we conducted experimental studies of within-species and between-species mating behaviour in Timema to address two central issues pertaining to the influence of behaviour on speciation: (1) how divergence in courtship influences reproductive isolation within and between species, and (2) whether the same or different traits mediate premating isolation within and between species. Mating behaviour involves three phases: pairing (whereby the male climbs onto the female's dorsal surface), courtship (which involves leg and antenna waving), and copulation. We found that courtship was qualitatively similar across the genus, but there were statistically significant quantitative differences in leg and antenna waving frequencies between Timema species. However, no-choice trials within and between species showed that discrimination within species is a function of whether males will court females after pairing, while discrimination between species is a function of whether males and females will pair. Because in both cases mate discrimination occurs before courtship is performed, we infer that courtship does not directly influence reproductive isolation in Timema. Moreover, because within-species and between-species discrimination take place at different stages in the mating sequence, intraspecific mate discrimination and species recognition appear to represent distinct processes. These findings suggest that, at least in Timema, speciation may involve the accumulation or replacement of mate discrimination mechanisms used within species.

Male pheromone blend preference function measured in choice and no-choice wind tunnel trials with almond moths, Cadra cautella

An almost universal component of moth reproduction is the long-range attraction of males by female-produced sex pheromones. Males are hypothesized to discriminate against incomplete and aberrant blend ratios. Male moth preference functions would then be unimodal with a single optimum coincident with the mean female sex pheromone blend. The resulting variation in female mating success would impose stabilizing selection on the ratio of components in the female sex pheromone. Stabilizing male preference functions would tend to constrain pheromone evolution, reduce phenotypic variation, and eliminate heritable variation. Despite the fact that these predictions are implicit to some models of pheromone evolution, there are few studies that have examined the shape of male moth preference functions over the range of pheromone blends produced by female moths. The shape of the male almond moth preference function was estimated using choice and no-choice wind tunnel trials to a range of naturally occurring ratios of pheromone components. Choice trials documented the predicted unimodal (stabilizing selection) preference function, whereas in the no-choice trials a flat (no selection) male preference function was documented. The no-choice trials are likely to be more representative of mating opportunities under natural conditions than the choice trials, as the opportunity to choose among equally receptive and available females may be rare in the field. If choice does not occur, this may reflect historical stabilizing selection, and male mating preferences may not be stabilizing over the range of currently produced female blend ratios.

Differential effects of flower feeding in an insect host–parasitoid system

Abstract In many insect host–parasitoid systems, both the host and its parasitoids forage on shared floral resources. As a result of insect behaviour, morphology and physiology, flower species may act selectively at different levels of such systems, e.g., between the trophic levels of hosts and parasitoids, between species within a guild, between sexes or individuals within a species or between life history traits within an individual. We asked if effects of selectivity are consistent across levels in the horse chestnut leafminer, Cameraria ohridella , and its parasitoid complex. Insects were exposed singly in no-choice feeding trials to twelve common flower species and their survival and reproduction were recorded. Only one of twelve flower species ( Ranunculus acris ) tended to selectively favour the longevity of leafminers, but not of parasitoids. No flower species were found to favour parasitoids only. Both trophic levels profited from feeding on Anthriscus sylvestris , however, parasitoids benefited up to eight times more than their hosts. No differences were found among the species of the parasitoid guild, but females lived significantly longer than males, and single individuals within species were able to exploit generally unfavourable flower species. Out of the seven flower species that increased the longevity of leafminer females, only Chaerophyllum hirsutum significantly enhanced the number of eggs laid. Fecundity was generally positively correlated with longevity of leafminer females, but two flower species ( C. hirsutum , Taraxacum officinale ) had an additional positive effect on fecundity. In conclusion, we demonstrated that flowers act differently on life history traits in a host–parasitoid system at a multitude of biological levels and that these effects are not always consistent across levels. Selective plant-derived resources can therefore modify herbivore–natural enemy interactions in ways that are more complex than currently appreciated.

Effects of nickel hyperaccumulation in Alyssum pintodasilvae on model arthropods representatives of two trophic levels

An experimental assessment of the defence hypothesis of nickel (Ni) hyperaccumulation in Alyssum was lacking. Also, to date no study had investigated the effects of hyperaccumulator litter on a detritivore species. We performed several experiments with model arthropods representatives of two trophic levels: Tribolium castaneum (herbivore) and Porcellio dilatatus (detritivore). In no-choice trials using artificial food disks with different Ni concentrations, T. castaneum fed significantly less as Ni concentration increased and totally rejected disks with the highest Ni concentration. In choice tests, insects preferred disks without Ni. In the no-choice experiment, mortality was low and did not differ significantly among treatments. Hence, this suggested a deterrent effect of high Ni diet. Experiments with P. dilatatus showed that isopods fed A. pintodasilvae litter showed significantly greater mortality (83%) than isopods fed litter from the non-hyperaccumulator species Iberis procumbens (8%), Micromeria juliana (no mortality) or Alnus glutinosa (no mortality). Also, isopods consumed significantly greater amounts of litter from the non-hyperaccumulator plant species. The behaviour of isopods fed A. pintodasilvae litter suggested an antifeedant effect of Ni, possibly due to post-ingestive toxic effects. Our results support the view that Ni defends the Portuguese serpentine hyperaccumulator A. pintodasilvae against herbivores, indicating that Ni can account both for feeding deterrence and toxic effects. The effects of hyperaccumulator litter on the detritivore P. dilatatus suggest that the activity of these important organisms may be significantly impaired with potential consequences on the decomposition processes.