Galerucella Nymphaeae Research Articles

Underwater Attachment of the Water-Lily Leaf Beetle Galerucella nymphaeae (Coleoptera, Chrysomelidae).

While the reversible attachment of artificial structures underwater has moved into the focus of many recent publications, the ability of organisms to walk on and attach to surfaces underwater remains almost unstudied. Here, we describe the behaviour of the water-lily leaf beetle Galerucella nymphaeae when it adheres to surfaces underwater and compare its attachment properties on hydrophilic and hydrophobic surfaces underwater and in the air. The beetles remained attached to horizontal leaves underwater for a few minutes and then detached. When the leaf was inclined, the beetles started to move upward immediately. There was no difference in the size of the tarsal air bubble visible beneath the beetles’ tarsi underwater, between a hydrophilic (54° contact angle of water) and a hydrophobic (99°) surface. The beetles gained the highest traction forces on a hydrophilic surface in the air, the lowest on a hydrophobic surface in air, and intermediate traction on both surfaces underwater. The forces measured on both surfaces underwater did not differ significantly. We discuss factors responsible for the observed effects and conclude that capillary forces on the tarsal air bubble might play a major role in the adhesion to the studied surfaces.

Catalogue of Iranian subfamily Galerucinae s. str. (Coleoptera: Chrysomelidae)

The first comprehensive catalogue of leaf beetles (subfamily Galerucinae s. str.) from Iran is reviewed and several field trips were conducted from 2012 to 2015. In total, 44 species belonging to 18 genera of three tribes (Galerucini, Hylaspini and Luperini) are listed. Iranian Galerucinae is characterized by 11 endemic species. For every species provincial distributions is given based on available literature records and additional province records were examined. All species that deposited in Jalal Afshar Zoological Museum (University of Tehran) are reported. Moreover, Luperus perlucidus Iablokoff-Khnzorian, 1956 is reported as a new record for Iranian Chrysomelidae. Theone octocostata afghanistanica Mandl, 1968, Galerucella nymphaeae (Linnaeus, 1758), Galeruca pomonae (Scopoli, 1763), Exosoma thoracicum (Redtenbacher, 1843) and Luperus kiesenwetteri Joannis, 1865 which were omitted in the catalogue of Palaearctic Coleoptera added again to the leaf beetle fauna of Iran. In addition, 13 new records for the administrative provinces of Iran are provided.

Water-skiing beetles get a bumpy ride

![Figure][1] Time-lapse image of Galerucella nymphaeae flying on the water surface. Photo credit: Haripriya Mukundarajan. Blink and you've missed it: Manu Prakash from Stanford University, USA, describes how one moment a waterlily beetle ( Galerucella nymphaeae ) is sat on the surface of a

Surface tension dominates insect flight on fluid interfaces

Flight on the 2D air-water interface, with body weight supported by surface tension, is a unique locomotion strategy well adapted for the environmental niche on the surface of water. Although previously described in aquatic insects like stoneflies, the biomechanics of interfacial flight has never been analysed. Here, we report interfacial flight as an adapted behaviour in waterlily beetles (Galerucella nymphaeae) which are also dexterous airborne fliers. We present the first quantitative biomechanical model of interfacial flight in insects, uncovering an intricate interplay of capillary, aerodynamic and neuromuscular forces. We show that waterlily beetles use their tarsal claws to attach themselves to the interface, via a fluid contact line pinned at the claw. We investigate the kinematics of interfacial flight trajectories using high-speed imaging and construct a mathematical model describing the flight dynamics. Our results show that non-linear surface tension forces make interfacial flight energetically expensive compared with airborne flight at the relatively high speeds characteristic of waterlily beetles, and cause chaotic dynamics to arise naturally in these regimes. We identify the crucial roles of capillary-gravity wave drag and oscillatory surface tension forces which dominate interfacial flight, showing that the air-water interface presents a radically modified force landscape for flapping wing flight compared with air.

Ecological separation versus geographical isolation: population genetics of the water-lily leaf beetleGalerucella nymphaeae(Coleoptera: Chrysomelidae)

Many sedentary species with specific habitat demands occur in isolated populations and thus show strong intraspecific genetic differentiation, shaped either by geographical isolation or by local ecological adaptation to specific environmental conditions. The water-lily leaf beetle Galerucella nymphaeae has two ecotypes: one only found feeding as a specialist on just a few host plant species of the family Polygonaceae, and the other on various representatives of the family Nymphaeaceae as a generalist. To test whether the differentiation in ecotypes is also reflected in the population genetic structure, we combined amplified fragment length polymorhism data (> 500 polymorphic fragments; four sampling sites, 27–31 individuals each) with ex-situ feeding experiments (ten individuals from each site). We found that both ecotypes are genetically well differentiated. Furthermore, the genetic divergence between the two studied generalist Nymphaeaceae ecotype populations was also high. In contrast, the two specialist Polygonaceae ecotype populations clustered closely together (thus not depending on geographical isolation), indicating an ecology-driven genetic structuring. Our ex-situ reciprocal feeding experiment revealed that only individuals of the Polygonaceae ecotype are strictly dependent on their host plant family: individuals from populations feeding Polygonaceae are less likely to feed on species from the family Nymphaeaceae than the reverse. Our data show that host preference may drive genetic differentiation even more strongly than simple geographical distance.

Attachment of Galerucella nymphaeae (Coleoptera, Chrysomelidae) to surfaces with different surface energy.

Numerous studies deal with insect attachment onto surfaces with different roughness; however, little is known about insect attachment onto surfaces that have different chemistry. In the present study, we describe the attachment structures of the water-lily leaf beetle Galerucella nymphaeae and test the hypothesis that the larval and adult stages generate the strongest attachment on surfaces with contact angles that are similar to those of leaves of their host plants. The larvae bear a smooth attachment system with arolium-like structures at their legs and a pygopodium at the abdomen tip. Adults have pointed setae on the ventral side of the two proximal tarsomeres and densely arranged spatula-shaped ones on their third tarsomere. In a centrifugal force tester, larvae and adults attained the highest friction forces and safety factors on surfaces with a water contact angle of 83 deg compared to those of 6, 26 and 109 deg. This comes close to the contact angle of their host plant Nuphar lutea (86 deg). The similarity in larval and adult performances might be a result of the similar chemical composition of their attachment fluid. We compare our findings with previous studies on the forces that insects generate on surfaces with different surface energies.

Anthophagy in the leaf beetles (Coleoptera, Chrysomelidae)

Laboratory experiments were performed on leaf beetles collected on flowers. Flower consumption (anthophagy) was demonstrated for adults of Donacia bicolora, D. brevitarsis, D. obscura, D. thalassina, Plateumaris discolor, Cryptocephalus laetus, C. sericeus, C. solivagus, Labidostomis longimana, Hydrothassa marginella, Phaedon concinnus, Galerucella nymphaeae, Neocrepidodera femorata, Altica oleracea, Aphthona lutescens, Longitarsus pellucidus, and larvae of Entomoscelis adonidis, H. marginella, and G. nymphaeae for the first time for all the species except for P. discolor, L. longimana, and C. sericeus. The feeding behavior was described, and the mouthparts of adults were studied. The mandibles and maxillae of the Donacia, Plateumaris, and Orsodacne species mentioned are adapted to consuming pollen. Some questions of ecology and evolution of anthophagy are discussed. An overview of literature on anthophagy in the leaf beetles is presented.

Differences in Preference and Performance of the Water Lily Leaf Beetle,Galerucella nymphaeaePopulations on Native and Introduced Aquatic Plants

Plant invasions represent ecological opportunities for herbivorous insects able to exploit novel host plants. The availability of new hosts and rapid adaptations may lead to host race formation and ultimately speciation. We studied potential host race formation in the water lily leaf beetle, Galerucella nymphaeae, in response to invasion by water chestnut, Trapa natans, in eastern North America. This leaf beetle is well suited for such studies because previous work showed that different herbivore populations follow different "evolutionary pathways" and specialize locally in response to differences in habitat preferences and host plant availability. We compared host preference and performance of G. nymphaeae offspring originating from T. natans and offspring of individuals originating from an ancestral host Nuphar lutea, yellow water lily, on T. natans and three native hosts (N. lutea, Nympheae odorata, and Brasenia schreberi). Regardless of origin (Trapa or Nuphar), adults strongly preferred their native host, N. lutea, over T. natans. Although laboratory survival rates (larva to pupa) were extremely high (80%) regardless of origin or host offered, survival rates in a common garden were greatly reduced, particularly for T. natans (24%) and to a lesser extent on N. lutea (54%), regardless of beetle origin. Larval drowning during more frequent leaf changes when developing on small Trapa leaves seems to be responsible for this difference. Preference of females for N. lutea is beneficial considering the much higher larval survival on the ancestral host. Abundant T. natans where the plant is invasive provides an alternative food source that beetles can use after egg/larval loads on their preferred host reach carrying capacity, but this utilization comes at a cost of high larval mortality.

Phylogenetic analyses of the leaf beetle genus Galerucella: Evidence for host switching at speciation?

It is still the subject of lively debate whether sympatric speciation is a general mode of speciation as opposed to allopatric speciation. In herbivorous insects, host switching, i.e. colonization of, and adaptation to, a new host by a herbivore, has been proposed as one of the driving mechanisms of sympatric speciation. Evidence for host switching as a speciation driving mechanism can be inferred from phylogenies of herbivores and host plants: if the host plant phylogeny is randomly distributed over the herbivore phylogeny, this indicates host switching. The Chrysomelid beetle genus Galerucella is a good taxon to study for evidence of host switching, because several closely related Galerucella species form sympatric species complexes associated with various unrelated plant species. Here we present the phylogenetic relationships of 10 species in the genus Galerucella, based on the mitochondrial gene fragments of the NADH-2 (410 bp) and CO-I (659 bp) genes, and analyzed with Bayesian, Maximum Likelihood and Maximum Parsimony methods. The resulting molecular phylogenetic tree proved to be largely congruent with morphologically based taxonomy. The host-associated taxa of the Galerucella nymphaeae species complex are not defined as distinct gene pools under the phylogenetic species concept (PSC), however, the species complex as a whole is. Two results indicate the contribution of host switching to the speciation of Galerucella: (1) the host-associated taxa of the G. nymphaeae species complex have diverged very recently and (2) constrained ML analyses showed that host use constraints led to a significantly different Galerucella tree compared to unconstrained analyses. This evidence for host switching, together with the observation that several sister taxa using unrelated host plants live in sympatry, suggests that sympatric speciation by host race formation can be an important mode of speciation in this genus.

Annotated List of the Leaf Beetles (Coleoptera: Chrysomelidae) of Kentucky: Subfamily Galerucinae, Tribes Galerucini and Luperini

Abstract An examination of leaf beetle specimens (Coleoptera: Chrysomelidae) in the largest beetle collections in Kentucky, recent inventory work in state nature preserves and other protected areas, and a review of the literature revealed thirty species of the tribes Galerucini and Luperini (Subfamily Galerucinae) present in Kentucky, thirteen of which are previously unreported for the state. Distribution maps and label data are presented for the thirty Kentucky species including spatial (state and Kentucky county records), temporal (years and months of collection in Kentucky), and plant association information. The following species are reported from Kentucky for the first time: Derospidea brevicollis (LeConte), Monocesta coryli (Say), Trirhabda canadensis (Kirby), Galerucella nymphaeae (L.), Ophraella americana (F.), Ophraella cribrata (LeConte), Acalymma gouldi Barber, Acalymma vinctum (LeConte), Phyllecthris dorsalis (Olivier), Phyllecthris gentilis LeConte, Phyllobrotica limbata (F.), Phyllobrotica s...

Ecological modulation of environmental stress: interactions between ultraviolet radiation, epibiotic snail embryos, plants and herbivores

1. The distribution of egg masses of the freshwater snails Lymnaea stagnalis and Planorbarius corneus on the undersides of water lily leaves (e.g. Nuphar lutea) is related to the prevalence of the leaf-mining beetle Galerucella nymphaeae. 2. When given the choice, Planorbarius significantly avoids leaves that were infested by the mining beetle. Conversely, Lymnaea did not discriminate against mined leaves. 3. Intact Nuphar leaves block over 95% of incident ultraviolet radiation. Yet, ultraviolet transmission reaches almost 100% under beetle mining scars. These are several times wider than snail embryos. 4. When exposed to natural sunlight, Lymnaea embryos proved to be resistant to ambient ultraviolet, while Planorbarius embryos were rapidly killed. Thus, one selective advantage of Planorbarius discrimination against mined leaves when depositing its eggs could be the avoidance of ultraviolet radiation passing through mining scars. 5. Other mining-related modifications of the leaves, reduced area, decreased longevity, altered aufwuchs (i.e. biofilm and epibionts) are discussed but seem less relevant for the oviposition preference of Planorbarius. 6. The discriminatory behaviour of this snail species was triggered by water-borne cues emitted by the damaged leaf, not by the eggs or larvae of the beetle. 7. This study illustrates how environmental stress on a given species, ultraviolet radiation in this case, can be ecologically buffered (shading by Nuphar) or enhanced (reduction of Nuphar shading through beetle mining) by associated species. It highlights how the impact of a given stress depends on the identity of the target species as well as on the identity and role of other species in the community.

Invertebrate predation on the water lily beetle, Galerucella nymphaeae (Coleoptera: Chrysomelidae), and its implications for potential biological control of water chestnut, Trapa natans

Abstract Classical biological weed control attempts to reduce abundance of invasive plants through introduction of specialized herbivores. Biocontrol programs emphasize introduction of organisms free of parasitoids and diseases from their native range. Unfortunately, a significant number of programs fail due to interference by resident natural enemies. Ecologically similar native herbivores in release areas offer an opportunity to assess presence and magnitude of biotic interference. We evaluated whether water strider Gerris insperatus , ladybird beetle Coleomegilla maculata , and backswimmer Notonecta spp., are important predators of a native leaf beetle, Galerucella nymphaeae which feeds on both the native water lily Nuphar lutea and introduced water chestnut, Trapa natans . Galerucella numphaeae is morphologically and ecologically similar to Galerucella birmanica , an Asian leaf beetle being investigated as potential biocontrol agent of T. natans . Notonecta always rejected G. nymphaeae larvae while G. insperatus and C. maculata predation significantly reduced larval and pupal survival. Identity of G. nymphaeae larval host plant ( T. natans or native N. lutea ) did not affect experimental outcomes, demonstrating that predation by G. insperatus and C. maculata could interfere with establishment and population build-up of G. birmanica . Various release methods, including cages, mass releases, habitat variables, timing of releases, and releases of different developmental stages should be evaluated for their ability to overcome potential biotic resistance from resident predators. Monitoring of associated plant, herbivore, and predator populations, including the development of food web models using stable isotopes may represent useful approaches to assess the overall ecological impact (including potential non-target effects) of a potential biocontrol agent release targeting T. natans .

Impact of the Native Water Lily Leaf Beetle,Galerucella nymphaeae(Coleoptera: Chrysomelidae), Attacking Introduced Water Chestnut,Trapa natans, in the Northeastern United States

Water chestnut (Trapa natans) is an annual soating aquatic plant native to Asia but invasive throughout northeastern North America. Information about the range of T. natans in Asia suggests that the plant has not reached its potential range in North America. We studied whether herbivory by the water lily leaf beetle, Galerucella nymphaeae, which has adopted T. natans as a new host in North America, can contribute to reductions in plant performance. We released 0, 10, 20, and 50G. nymphaeae Þrst-instar larvae on developingT.natans rosettes and measured larval survival, larval development time, plant growth, plant biomass, and reproductive output. The larval densities we chose in our experiment represent the range of densities we frequently observe in the Þeld, with the highest density exceeding Þeld attack rates. Larval mortality was particularly high for Þrst instars (50% within 1 wk) and not associated with treatment or lack of food. Overall, larval survival was extremely low, with survival rates of 5.1% in the highest (50 larvae) to 11.3% in the lowest (10 larvae) herbivore treatment after 4 wk. We found no signiÞcant differences among plants exposed to different herbivore treatments for the number of leaves, rosette diameter, biomass, or reproductive output. In central New York, it seems thatG. nymphaeae has no impact on water chestnut performance at the herbivore levels we see in the Þeld and chose in our experiments. Water chestnut is a poor (but abundant) food plant forG.nymphaeae in the northeastern United States, but it is unlikely that the leaf beetle can contribute to local or regional control of water chestnut or reduce its spread.

Midsummer spatial variation in methane efflux from stands of littoral vegetation in a boreal meso‐eutrophic lake

Summary1. Spatial variation of methane (CH4) efflux from the littoral zone of a meso‐eutrophic boreal lake was studied with a closed‐chamber technique for three summer days in 22 vegetation stands, consisting of three emergent and three floating‐leaved species.2. Between‐species differences in CH4 emission were significant. The highest emissions were measured from the emergent Phragmites australis stands (0.5–1.7 mmol m−2 h−1), followed by Schoenoplectus lacustris > Equisetum fluviatile > Nuphar lutea > Sparganium gramineum > Potamogeton natans. Within‐species differences between stands were not significant.3. In P. australis stands, the stand‐specific mean CH4 emission was significantly correlated with solar radiation, probably indicating the role of effective pressurised ventilation on CH4 fluxes. The proportion of net primary production emitted as CH4 was significantly higher in P. australis stands (7.4%) than in stands of S. lacustris and E. fluviatile (both 0.5%).4. In N. lutea stands, CH4 efflux was negatively correlated with the mean fetch and positively with the percentage cover of leaves on the water surface. There were no differences in CH4 efflux between intact N. lutea leaves and those grazed by coleopteran Galerucella nymphaeae. In S. graminaeum and P. natans stands, CH4 effluxes were not related to any of the measured environmental variables.5. For all vegetation stands, the biomass above water level explained about 60% of the observed spatial variation in CH4 emission, indicating the important role of plants as gas conduits and producers of substrates for methanogens in the anoxic sediment.

Genetically based polymorphisms in morphology and life history associated with putative host races of the water lily leaf beetle, Galerucella nymphaeae.

A host race is a population that is partially reproductively isolated from other conspecific populations as a direct consequence of adaptation to a specific host. The initial step in host race formation is the establishment of genetically based polymorphisms in, for example, morphology, preference, or performance. In this study we investigated whether polymorphisms observed in Galerucella nymphaeae have a genetic component. Galerucella nymphaeae, the water lily leaf beetle, is a herbivore which feeds and oviposits on the plant hosts Nuphar lutea and Nymphaea alba (both Nymphaeaceae) and Rumex hydrolapathum and Polygonum amphibium (both Polygonaceae). A full reciprocal crossing scheme (16 crosses, each replicated 10 times) and subsequent transplantation of 1,001 egg clutches revealed a genetic basis for differences in body length and mandibular width. The heritability value of these traits, based on midparent-offspring regression, ranged between 0.53 and 0.83 for the different diets. Offspring from Nymphaeaceae parents were on average 12% larger and had on average 18% larger mandibles than offspring from Polygonaceae parents. Furthermore, highly significant correlations were found between feeding preference of the offspring and the feeding preference of their parents. Finally, two fitness components were measured: development time and survival. Development time was influenced by diet, survival both by cross type and diet, the latter of which suggest adaptation of the beetles. This suggestion is strengthened by a highly significant cross x diet interaction effect for development time as well as for survival, which is generally believed to indicate local adaptation. Although no absolute genetic incompatibility among putative host races was observed, survival of the between-host family offspring, on each diet separately, was lower than the survival of the within-host family offspring on that particular host. Survival of offspring of two Nymphaeaceae parents was about two times higher on Nymphaeaceae than on Polygonaceae, whereas survival of offspring of two Polygonaceae parents was 11 times higher on Polygonaceae than on Nymphaeaceae (based on untransformed data). Based on these results, we conclude that genetically determined polymorphisms in morphology and feeding preference exist in G. nymphaeae, resulting in differential performance. Furthermore, in each diet separately, offspring of between-host family crosses were less fit than offspring of within-host family crosses. These results support the hypothesis that within this species two host races can be distinguished.

Host preference and larval performance suggest host race formation in Galerucella nymphaeae.

In this study we investigated the possibilities for host race formation in Galerucella nymphaeae. This is a chrysomelid beetle feeding on four different hosts, belonging to two different plant families, the Nymphaeaceae and Polygonaceae. Previous results showed that beetles living on the two different host families differ in morphology, i.e., body length, mandibular width, and color of the elytra. In the current study, the preference of G. nymphaeae for four hosts was investigated, together with larval performance on these hosts. In a multichoice experiment, both parents and offspring showed a strong feeding preference for their natal host plant family: between 88-98% of the total consumption consisted of the natal host plant family. Females preferred to lay eggs on their natal host family: 81-100% of the egg clutches were laid on the natal host family. Host preference was accompanied by differences in offspring performance. Offspring survival was 1.2-25 times as high on the host family from which their parents originated than on the hosts of the other plant family. Furthermore, larval development tended to progress faster on the natal than on the other host family. Since the beetles use their host plant as a mating place, positive assortative mating is a likely consequence of the beetles' host preference. Together, these results suggest that there are two host races of G. nymphaeae: one living on Nymphaeaceae and the other on Polygonaceae.

Interaction between coot ( Fulica atra) and waterlily ( Nymphaea alba) in a lake: the indirect impact of foraging

A previously unrecorded indirect impact is described of coot ( Fulica atra) on a floating-leaved species ( Nymphaea alba) during the plant growing season in a shallow eutrophic natural freshwater ecosystem, Lake Grand-Lieu, western France. The bird population was counted, the proportion of petioles cut by bird was estimated and the density of the four main invertebrate groups on the leaves was measured just after the breeding season, in July and then in September 1997 in the whole N. alba area (739 ha divided into 15 sections). Up to 6±1% of leaves were cut in July, with differences between sections (from 0.3±0.1 to 16±6%) when about 10,000 coots fed in this part of the lake. A positive relationship was recorded between the proportion of cut petioles and coot density during the first period (excluding sections where N. alba was mixed with another plant species, Trapa natans). In September, coot abundance fell to 5000 individuals and the impact decreased to 0.3±0.2% of leaves, new generations of leaves having meanwhile grown. The comparison of the mean density of invertebrates on cut and intact leaves showed a massive depletion of the beetle, Galerucella nymphaeae, present on the upper side of the leaves. The selection of this specific food item might explain this marked interaction, which was nevertheless insignificant in September because of high turn over rates of the plant.

Differences in morphology and reproductive traits of Galerucella nymphaeae from four host plant species

AbstractThe water lily beetle Galerucella nymphaeae L. (Coleoptera: Chrysomelidae) exploits different hosts, including Nuphar lutea Sm. and Nymphaea alba L. (both Nymphaeaceae), as well as Polygonum amphibium L. and Rumex hydrolapathum Hudson (both Polygonaceae). The present study investigates whether within‐species differences in morphological and reproductive traits are associated with differences in host species exploitation. A total of 1103 adult beetles were collected from 11 localities in The Netherlands, one of which contained all four hosts and three other localities contained hosts from both families (sympatric localities). Adults originating from Nuphar and Nymphaea were on average darker in colour and larger in size and had disproportionally bigger mandibles than beetles originating from Polygonum and Rumex across the 11 localities. Head capsules of first instar larvae from Nymphaeaceae hosts were between 17% and 28% larger than those of larvae from Polygonaceae hosts. Furthermore, beetles from Nuphar and Nymphaea laid larger sized eggs, but fewer eggs per clutch than beetles originating from Polygonum and Rumex. Although host related variation was less pronounced at the sympatric localities than in the allopatric localities, differences in larval and adult size were still highly significant at the sympatric localities. It is not clear whether the observed differences are genetically based, as opposed to host induced. However, leaf toughness varied among species in a way suggesting that leaf toughness may be partly responsible for host related differences in G. nymphaeae.

Intraspecific Variation in Feeding Preference and Performance of Galerucella nymphaeae (Chrysomelidae:Coleoptera) on Aquatic Macrophytes

The feeding preferences and performance of a freshwater macrophyte-feeding chrysomelid beetle (Galerucella nymphaeae) were assessed in laboratory experiments. Populations of Galerucella had a relatively narrow diet breadth, preferring species of Nuphar, Polygonum, and in 1 case Brasenia, while largely ignoring the remaining macrophytes offered in assays. However, because of interpopulation variation in host preferences, the species G. nymphaeae should be considered polyphagous. Distant populations from the Upper Peninsula of Michigan, Indiana, and North Carolina collected from Nuphar spp. all readily consumed Nuphar spp. and Polygonum spp., but beetles from a site in south Michigan collected from P. amphibium or from Brasenia schreberi treated Nuphar as a low-preference host. The performance of Galerucella in no-choice assays was clearly related to the behavioral preferences of the larvae: larvae performed well on 3 macrophyte species that they willingly consumed, but performed poorly when they refused to consume alternative host plants and presumably starved to death. It is unknown if the starved beetles could have performed well physiologically if they had eaten alternative hosts. Performance was also related to the quality of host plant, given that beetles collected from Nuphar luteum or N. advena reached a larger adult mass on N. luteum than on N. advena. The feeding preferences of Galerucella were largely non-plastic within a single generation, although there were sometimes behavioral differences among clutchmates raised on different host plants. Morphometric and preliminary allozyme data suggest the North American populations used in this paper are conspecific, but they probably represent a different species than European G. nymphaeae. The intraspecific variation of our North American G. nymphaeae in host preferences and performance suggests that at least 2 different ecotypes occur in North America.

A field test of inducible resistance to specialist and generalist herbivores using the water lily Nuphar luteum

We tested whether grazing by the specialist beetle Galerucella nymphaeae (Coleoptera: Chrysomelidae) induced resistance to herbivory in the water lily Nuphar luteum macrophyllum (Nymphaeaceae) using both the specialist beetle and the generalist crayfish Procambarus clarkii (Decapoda: Cambaridae). For 2 months, we allowed natural densities of beetles to develop on control plants of Nuphar, while removing beetles every 2-3 days from adjacent plants that were paired by location within our field site. By the end of the 2-month manipulation, beetle grazing had damaged twice as much leaf surface on control plants as on removal plants (30.6% vs. 14.2%, respectively). We then offered tissues from control and removal plants to adult and larval beetles and to crayfish in laboratory assays. Increased levels of previous attack by the specialist beetle either did not affect or increased water lily attractiveness to beetles, but significantly decreased attractiveness to the generalist crayfish. Beetle larvae did not feed preferentially on control vs. removal Nuphar in assays using either immature, undamaged leaves that had not yet reached the pond surface or intermediate aged leaves that had reached the surface and experienced some beetle grazing. Adult beetles consumed significantly more immature leaf tissue from the heavily grazed controls than from the less grazed removal plants but did not discriminate between control and removal leaves of intermediate age in either feeding or oviposition preference. In contrast, generalist crayfish consumed significantly more plant tissue from the less grazed treatment than from the more heavily grazed controls. Crude chemical extracts from Nuphar strongly deterred crayfish feeding, but neither phenolic content, protein content, nor differential effects of crude extracts from control vs. removal plants explained crayfish feeding on control versus removal leaves. Our assays suggest that induced resistance to crayfish may be chemically mediated, but the particular mechanisms producing this response remain unclear. Responses may be due to defensive metabolites that degrade rapidly following extraction.