Life-history variation in a seed beetle: adult egg-laying vs. larval competitive ability

Summary Populations of the seed beetle Callosobruchus maculatus differ genetically in several traits that mediate intraspecific competition. This study examined competitive interactions between larvae from two strains that differed in their propensity to oviposit on occupied hosts. In a strain (S) where females avoided laying >1 egg/seed, larvae were highly competitive; if two larvae entered a small host simultaneously, only one adult emerged. In a strain (I) whose females were sloppier in their egg-laying decisions, more than half of the seeds bearing two larvae yielded two adults. If seeds contained one larva from each strain, only one adult emerged per seed, and 70% of these adults belonged to the more competitive S strain. A larva's probability of emergence could be increased if it entered the seed before its competitor. A two-day headstart was needed merely for I larvae to compete equally with S larvae. Competition also affected development time and adult weight, but its effect was highly strain- and sex-specific. Adult life-history traits also differed substantially between strains. Compared to I beetles, S beetles exhibited decreased longevity, lower fecundity, a truncated period of oviposition, and larger egg and body size. Fecundity was linearly related to body size in the I strain, but was largely independent of size in the S strain. When faced with a shortage of hosts, S females (whose progeny are highly competitive) withheld eggs and died without depositing 40% of their lifetime supply. In contrast, the fecundity of I females was independent of seed availability. Comparisons with previous studies suggest that both highly uniform egg-laying and strong interference among larvae may be a consequence of chronic association with a relatively small host. Results from the larval competition experiments were used as parameter estimates for a simple, game-theoretic model that postulates interference vs. exploitative strategies. Fitness comparisons suggest that a strategy employing interference competition cannot be invaded by a more exploitative form of competition in a small host.     

Host-associated fitness variation in a seed beetle (Coleoptera: Bruchidae): evidence for local adaptation to a poor quality host

The geographic distributions of many generalist herbivores differ from those of their host plants, such that they experience coarse-grained spatial variation in natural selection on characters influencing adaptation to host plants. Thus, populations differing in host use are expected to differ in their ability to survive and grow on these host plants. We examine host-associated variation in larval performance (survivorship, development time, and adult body weight) and oviposition preference, within and between two populations ofStator limbatus (Coleoptera: Bruchidae) that differ in the hosts available to them in nature. In one population,Acacia greggii (Fabaceae: Mimosoideae) andCercidium microphyllum (Fabaceae: Caesalpininoideae) are each abundant, while in the second population onlyC. floridum andC. microphyllum are present. In both populations, egg-to-adult survivorship was less than 50% onC. floridum, while survivorship was greater than 90% onA. greggii. Most of the mortality onC. floridum occurred as larvae were burrowing through the seed coat; very low mortality occurred during penetration of the seed coat ofA. greggii. Significant variation was present between populations, and among families (within populations), in survivorship and egg-to-adult development time onC. floridum; beetles restricted toCercidium in nature, without access toC. floridum, survived better and developed faster onC. floridum than beetles that had access toA. greggii. Large host effects on body size were detected for female offspring: females reared onA. greggii were larger than those reared onC. floridum, whereas male offspring wee approximately the same size regardless of rearing host. Trade-offs between performance onC. floridum andC. floridum were not detected in this experiment. Instead, our data indicate that development time and survivorship onC. floridum may be largely independent of development time and survivorship onA. greggii. Patterns of oviposition preference corresponded to the observed patterns of host suitability: in laboratory preference tests, beetles with access toA. greggii in nature tended to prefer this host more than beetles without access to this host in nature.     

Influence of cowpea pod maturity on the oviposition choices and larval survival of a bruchid beetle Callosobruchus maculatus

The active or dispersing morph of Callosobruchus maculatus, a pest of stored cowpeas, is presumed to infest cowpea plants in the field prior to harvest. In oviposition choice tests, both normal and active females preferred pods that were full-size but still green over younger, smaller pods or older, mature pods. Exposed seeds were usually preferred over intact pods of all stages, although females laid more eggs on green pods than on the rough-coated seeds of one cowpea variety. Egg-to-adult survivorship was highest for eggs laid directly on seeds. On both green and mature pods high mortality occurred because newly hatched larvae failed to penetrate a seed after they drilled through the pod wall. However, since 20–50% of eggs laid on green pods do develop into adults, cowpea plants are susceptible to C. maculatus well before pods dehisce to expose the seeds. The oviposition preferences of C. maculatus may be strongly influenced by the surface texture of potential oviposition sites.

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Résumé La forme active de Callosobruchus maculatus, ennemi de Vigna unguiculata stocké, est suspectée d'infester les gousses dans les champs avant la récolte. Lors d'essais sur le choix du lieu de ponte, toutes les femelles, normales et actives, ont préféré les gousses encore vertes mais ayant atteint leur taille définitive aux gousses plus jeunes ou aux gousses plus âgées (jaunes) ou mûres. Les graines étaient presque toujours préférées aux gousses à tous les stades, mais quand les graines étaient rugueuses, elles pondaient de préférence sur les gousses vertes.Le pourcentage le plus élevé d'adultes a été obtenu à partir des oeufs pondus sur les graines. Avec les pontes sur gousses vertes ou mûres, la mortalité élevée se produisait lors de la pénétration dans la gousse. Néanmoins, comme 20 à 50% des oeufs pondus sur des gousses vertes donnent des adultes, V. unguiculata est susceptible d'être attaqué par C. maculatus bien avant la déhiscence des gousses et l'exposition des graines. L'évolution temporelle des propriétés physiques des gousses paraît à l'origine de la relation complexe entre l'âge et l'attractivité des gousses.

     

Causal mechanisms underlying host specificity in bat ectoparasites

In parasites, host specificity may result either from restricted dispersal capacity or from fixed coevolutionary host-parasite adaptations. Knowledge of those proximal mechanisms leading to particular host specificity is fundamental to understand host-parasite interactions and potential coevolution of parasites and hosts. The relative importance of these two mechanisms was quantified through infection and cross-infection experiments using mites and bats as a model. Monospecific pools of parasitic mites (Spinturnix myoti and S. andegavinus) were subjected either to individual bats belonging to their traditional, native bat host species, or to another substitute host species within the same bat genus (Myotis). The two parasite species reacted differently to these treatments. S. myoti exhibited a clear preference for, and had a higher fitness on, its native host, Myotis myotis. In contrast, S. andegavinus showed no host choice, although its fitness was higher on its native host M. daubentoni. The causal mechanisms mediating host specificity can apparently differ within closely related host-parasite systems.     

Female's preference for oviposition site and larval performance in the water-lily beetle,Galerucella nymphaeae (Coleoptera: Chrysomelidae)

Water-lily beetles prefer younger rather than older water-lily leaves as oviposition sites. By the time of hatching, however, young leaves have aged consieerably. Larval performance of the water-lily beetle was measured on different types of leaves of the yellow water-lily and compared with oviposition preference of females. The leaf types used in the experiments were categorized as (i) young, (ii) natal (medium-aged) and (iii) old. The natal leaves were the ones on which larvae from a particular egg-batch had hatched. There were two sets of experiments. First, larvae were raised from eggs to pupae on young and on old leaves. Second, the growth of the 1st-instar larvae was measured on young, natal, and old leaves. The development time from egg to pupa did not differ between young and old leaves, but larvae growing on young leaves attained a higher pupal weight. In the second experiment the 1st-instar larvae grew fastest on their natal leaves, but there was also variation in the growth rate of progeny from different egg-batches. Larval growth on young and old leaves did not differ significantly. Larvae tried to emigrate much less from natal than other types of leaves. Females tended to lay eggs on leaves where larval growth was fastest. It seems that medium-aged leaves are best for larval growth, but the leaf characteristics responsible for this remain unresolved.     

Genetic architecture of population differences in oviposition behaviour of the seed beetle Callosobruchus maculatus

Few studies have examined the genetic architecture of population differences in behaviour and its implications for population differentiation and adaptation. Even fewer have examined whether differences in genetic architecture depend on the environment in which organisms are reared or tested. We examined the genetic basis of differences in oviposition preference and egg dispersion between Asian (SI) and African (BF) populations of the seed beetle, Callosobruchus maculatus. We reared and tested females on each of two host legumes (cowpea and mung bean). The two populations differed in mean oviposition preference (BF females preferred cowpea seeds more strongly than did SI females) and egg dispersion (SI females distributed eggs more uniformly among seeds than did BF females). Observations of hybrid and backcross individuals indicated that only the population difference in oviposition preference could be explained by complete additivity, whereas substantial dominance and epistasis contributed to the differences in egg dispersion. Both rearing host and test host affected the relative magnitude of population differences in egg dispersion and the composite genetic effects. Our results thus demonstrate that the relative influence of epistasis and dominance on the behaviour of hybrids depends on the behaviour measured and that different aspects of insect oviposition are under different genetic control. In addition, the observed effect of rearing host and oviposition host on the relative importance of dominance and epistasis indicates that the genetic basis of population differences depends on the environment in which genes are expressed.     

Genetic variability in the egg-laying behaviour ofTrichogramma maidis

SomeTrichogramma maidis females [Hymenoptera: Trichogrammatidae] aggregate their eggs in adjacent hosts whereas others scatter them amongst distant host eggs. The individual variability of aggregated-attack behaviour in matedTrichogramma maidis females was studied by isolating them with a uniform patch of about 500Ephestia kuehniella [Lepidoptera: Pyralidae] UV killed eggs. Genetic analysis demonstrated that similar behaviour exists between sisters and that the trait is transmissible and relatively stable over 2 successive generations. The ethological basis and the ecological significance of this variability are discussed.      

Horizontal transmission of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), to three coccinellid species of Nova Scotia

Convergent lady beetles, Hippodamia convergens Guérin-Méneville, are a popular choice for aphid control in North America. An unidentified microsporidium was found in H. convergens adults that were purchased from a commercial insectary in 2004. This study examined egg cannibalism and egg predation as a means of horizontal transmission of the unidentified microsporidium among H. convergens larvae and three coccinellid species found in Nova Scotia: Coccinella septempunctata (seven-spotted lady beetle), C. trifasciata perplexa (three-banded lady beetle), and Harmonia axyridis (multicolored Asian lady beetle). The microsporidium was transmitted with 100% efficiency when first instars fed on microsporidia-infected eggs. Mean spore count data from smear preparations of infected beetles suggest that the infection was as heavy in C. trifasciata perplexa (a native coccinellid) (11.2 ± 0.96 spores/100 μm²) as it was in H. convergens (the natural host) (12.8 ± 1.16) but lighter in the introduced species C. septempunctata (7.5 ± 0.65) and H. axyridis (0.8 ± 0.11). For all of the beetle species examined, larval development was significantly longer for microsporidia-infected individuals than for their uninfected cohorts. The microsporidium had no effect on larval mortality. Based on the results of this study, field-collected H. convergens should be examined for microsporidia and uninfected individuals should be used to rear individuals for release in biological control programs. However, this is unlikely to happen because H. convergens are relatively easy and inexpensive to collect from their overwintering sites for redistribution.     

Relationships of the MadagascarBignoniaceae: A striking case of convergent evolution

Most MadagascarBignoniaceae have indehiscent fruits and have been assigned to the tribeCrescentieae. As thus constituted, theCrescentieae are remarkably disjunct between Central America (and the West Indies) and Madagascar with a single monotypic genus also on continental Africa. This paper analyzes the evolutionary relationships of the MadagascarCrescentieae and concludes that they are descended from a different ancestral stock than the New WorldCrescentieae. A revised tribal taxonomy is proposed to reflect phylogenetic relationships withCrescentieae restricted to the neotropic species andColeeae resurrected for the indehiscent-fruited Madagascar species.     

Genetic architecture of a heterotic cross between two populations of maize

Summary The nature and magnitude of variability in the interpopulation cross of Mezcla Amarillo Selection (MAS), an introduction from CIMMYT, Mexico, and J607, a population developed in India using indigenous, American, and Yugoslavian germplasm, were studied. Interpopulation progenies developed by following the North Carolina Design I were evaluated at two locations. The additive genetic variance component in interpopulation cross, _A(12) ² , and in one population assuming the other population as tester, _A12 ² and _A21 ² were significant for all the traits evaluated, namely ear length, ear girth, kernel rows and days to silk, with one exception. For kernel rows, the dominance variance component, _A(12) ² , was also significant but it was smaller than _A(12) ² . The variance component due to dominance X location interaction, _DL(12) ² , was significant for all traits except kernel rows. In the case of ear length and ear girth, _DL(12) ² was greater than the other components. _AL(12) ² , _AL12 ² and _AL21 ² were not significant for any trait. Expected genetic advance indicated a superiority of half-sib reciprocal recurrent selection over full-sib reciprocal recurrent selection.     

Prior encounters modulate subsequent choices in host acceptance behavior by the bark beetle Ips pini

Laboratory bioassays indicate that the bark beetle Ips pini employs flexible, rather than absolute, responses to phytochemicals in its host acceptance behavior. Each beetle's decision to enter substrate was influenced by the types and concentrations of monoterpenes present. However, previous rejection of a simulated host containing a moderate concentration of monoterpenes increased the likelihood that the same concentration would be accepted upon a second or third encounter. This flexibility more than offsets any loss of vigor due to starvation and age that accompanies a process of trial and error. Starvation decreased beetles' total lipid content, but beetles can recover some energetic losses by a small amount of feeding during each trial. In addition to its adaptive value, a flexible host acceptance strategy may yield population level consequences. That is, bark beetles preferentially enter trees having low concentrations of monoterpenes, but may modify their acceptance thresholds when cues associated with stressed trees are not available. This could partially explain how some tree-killing bark beetles colonize a broader physiological range of trees during outbreaks. The adaptive value of relating individual decisions to population density may arise from two ecological relationships: first, as populations rise, the pool of stressed trees is rapidly depleted; secondly, healthy trees are attainable through pheromone – mediated mass attacks when adequate numbers of beetles are present. Flexible host acceptance behaviors may also reduce the advantage of relying exclusively on pre-landing cues to distinguish between susceptible and non-susceptible trees.     

Host selection in insects: reproductive interference shapes behavior of ovipositing females

In nature, closely related species often utilize different host species, but it is still unclear what factors contribute to the evolution and maintenance of such diversified host selection. In this review, I describe how negative interspecific mating interactions (reproductive interference) can shape host selection by animals, focusing mainly on phytophagous and predatory insects. First, I explain an important premise of this hypothesis, which is that the adult reproductive site is the same as the feeding site for the offspring. Next, I describe several mathematical models and well-studied empirical systems to show that reproductive interference can sufficiently drive and maintain different host selection between phylogenetically related species. Then, I argue for the first time that reproductive interference can cause an oviposition preference in insects that is not optimal for the survival and development of the offspring, as a result of maternal adaptive behavior that maximizes the mother's own fitness. Furthermore, I argue that in insects, reproductive interference probably shapes oviposition behavior before the female alights on the host (e.g., habitat preference), without affecting post-alighting decision making. I would like to emphasize that these two arguments represent the novel approach to clarify the unrevealed pattern of complex insect oviposition behavior.     

Genetic parameters for growth, wood density and pulp yield in Eucalyptus globulus

Genetic variation and co-variation among the key pulpwood selection traits for Eucalyptus globulus were estimated for a range of sites in Portugal, with the aim of improving genetic parameters used to predict breeding values and correlated response to selection. The trials comprised clonally replicated full-sib families (eight trials) and unrelated clones (17 trials), and exhibited varying levels of pedigree connectivity. The traits studied were stem diameter at breast height, Pilodyn penetration (an indirect measure of wood basic density) and near infrared reflectance predicted pulp yield. Univariate and multivariate linear mixed models were fitted within and across sites, and estimates of additive genetic, total genetic, environmental and phenotypic variances and covariances were obtained. All traits studied exhibited significant levels of additive genetic variation. The average estimated within-site narrow-sense heritability was 0.19 ± 0.03 for diameter and 0.29 ± 0.03 for Pilodyn penetration, and the pooled estimate for predicted pulp yield was 0.42 ± 0.14. When they could be tested, dominance and epistatic effects were generally not statistically significant, although broad-sense heritability estimates were slightly higher than narrow-sense heritability estimates. Averaged across trials, positive additive (0.64 ± 0.08), total genetic (0.58 ± 0.04), environmental (0.38 ± 0.03) and phenotypic (0.43 ± 0.02) correlation estimates were consistently obtained between diameter and Pilodyn penetration. This data argues for at least some form of pleiotropic relationship between these two traits and that selection for fast growth will adversely affect wood density in this population. Estimates of the across-site genetic correlations for diameter and Pilodyn penetration were high, indicating that the genotype by environment interaction is low across the range of sites tested. This result supports the use of single aggregated selection criteria for growth and wood density across planting environments in Portugal, as opposed to having to select for performance in different environments.     

Reciprocal latitudinal clines in oviposition behavior ofPapilio glaucus andP. canadensis across the Great Lakes hybrid zone: possible sex-linkage of oviposition preferences

Summary The eastern tiger swallowtail butterfly,Papilio glaucus, is the most polyphagous of all Papilionidae species. While diverse larval detoxication abilities are known for bothPapilio glaucus and the closely relatedP. canadensis, the factors affecting oviposition preferences in adult females are unknown. These congeneric species were studied to determine the extent of oviposition mistakes on toxic plants. We were also interested in comparing the geographic patterns of variation in oviposition preferences and the genetic basis of these differences. We conducted oviposition three-choice studies with the Canadian tiger swallowtail butterfly,Papilio canadensis, and the Eastern tiger swallowtail,Papilio glaucus, giving them the choice of (1) tuliptree,Liriodendron tulipifera, which is toxic to virtually all populations (P. canadensis) north of the Great Lakes Region of North America, (2) quaking aspen,Populus tremuloides, which is toxic to essentially all populations (P. glaucus) south of the Great Lakes, and (3) black cherry,Prunus serotina, which is an excellent foodplant for all members of thePapilio glaucus group, but which does not occur at latitudinal extremes of North America (in Alaska and most of Canada or the southern half of Florida). Handpaired interspecific hybrids were tested under the same experimental design to evaluate the possibility of sexlinked oviposition behavior. There was considerable variability in the choice of plants by individual butterflies, but a general trend suggesting that the females of each species had a lower preference for the plant toxic to their larvae. More than 6000 oviposition bouts were counted from 37 differentp. canadensis and 54p. glaucus females along a latitudinal transect of approximately 5000 km from Alaska south through the Great Lakes hybrid zone region to southern Florida. While not exceptionally high anywhere, the preference for aspen (Salicaceae) declined precipitously in central Michigan (45° N latitude) and remained very low (5–12%) in all locations southward to Florida, whereas we observed a reciprocal trend in preference for tuliptree (Magnoliaceae) which was greatest in Florida (87% of all eggs) and steadily declined northward across the Great Lakes region. Cherry was selected in these 3-choice tests at a relatively consistent and low frequency at all latitudes. Fixed allele differences in sex-linked (LDH and PGD) and autosomal (HK) electromorphs are known forP. glaucus andP. canadensis. Our electrophoretic data suggest that the preference of an individual female for aspen is not simply a characteristic of the northern species (P. canadensis) but can occur inP. glaucus females. The reciprocal situation is also evident in Northern Michigan and Wisconsin females (scored electrophoretically and morphologically asP. canadensis) which sometimes exhibit a clear preference for the toxic tuliptree. In fact, Alaskan populations ofP. canadensis chose tuliptree for about 52% of their eggs, even though none of their offspring has ever survived on this plant species in laboratory studies. We conclude that even with distinctive latitudinal trends, a considerable amount of local variation in relative oviposition preference exists among individuals of these polyphagous species. BothP. glaucus andP. canadensis will lay eggs on toxic plants. It appears that factors selecting against oviposition on toxic tuliptrees have been minimal (relative to other factors) in Alaska and somewhat stronger in the Great Lakes hybrid zone. It is in this zone of contact with tuliptree where selection against theP. canadensis populations ovipositing on tuliptree may be strong due to high larval mortality when such natural mistakes are made. We do not know whether behavioral preference changes evolutionarily preceded or followed the development of specific physiological detoxication abilities for tuliptree or quaking aspen. However, for bothP. canadensis andP. glaucus the occurrence of oviposition mistakes on toxic plants by adults extends geographically well beyond the larval detoxication abilities of their offspring. Hybrid female offspring of pairings with Michigancanadensis females andglaucus males show distinct preferences for tuliptree, suggesting that oviposition may be controlled by a factor (or factors) on the sex chromosome. Unfortunately we were unable to obtain reciprocal hybrids to evaluate the possibility of sex-linked aspen preference.     

Quantitative genetics of speciation: additive and non-additive genetic differentiation between <Emphasis Type="Italic">Drosophila madeirensis</Emphasis> and <Emphasis Type="Italic">Drosophila subobscura</Emphasis>

The role of dominance and epistasis in population divergence has been an issue of much debate ever since the neoDarwinian synthesis. One of the best ways to dissect the several genetic components affecting the genetic architecture of populations is line cross analysis. Here we present a study comparing generation means of several life history-traits in two closely related Drosophila species: Drosophila subobscura, D. madeirensis as well as their F ₁ and F ₂ hybrids. This study aims to determine the relative contributions of additive and non-additive genetic parameters to the differentiation of life-history traits between these two species. The results indicate that both negative dominance and epistatic effects are very important in the differentiation of most traits. We end with considerations about the relevance of these findings for the understanding of the role of non-additive effects in speciation.     

Hybridization leads to host-use divergence in a polyphagous butterfly sibling species pair

Climate warming has lead to increased genetic introgression across a narrow hybrid zone separating the eastern and Canadian tiger swallowtails (Papilio glaucus and Papilio canadensis). This situation has led to the formation of an allochronically separated hybrid population with a delayed emerging phenotype or “late flight”. Here, we assess how the recombination of the parental genomes that lead to this phenotype may have facilitated another major ecological shift, host-use divergence. We first contrast the ovipositional profiles of the late flight population to that of the parental species P. glaucus and P. canadensis. Subsequently we contrast the larval survival and growth of the late flight, a P. canadensis and a P. glaucus population, and a population from the northern edge of the hybrid zone on five hosts. Our results indicate that the ovipositional preference of this hybrid swarm is identical to that of the introgressing parental species, P. glaucus. Due to the absence of the preferred hosts of P. glaucus (Liriodendron tulipifera L. and Ptelea trifoliata L.) where the late flight occurs, this ovipositional pattern implies a functional specialization onto a secondary host of both parental species, Fraxinus americana L. In contrast, the larval host-use abilities represent a mixture of P. glaucus and P. canadensis, indicating divergence in larval host-use abilities has not taken place. However, high genetic variability (genetic coefficient of variation) is present for growth on F. americana in the late flight hybrid swarm and tradeoffs for larval performance on the preferred hosts of the parental species are evident; indicating a strong potential for future specialization in larval host-use abilities. This current scenario represents an instance where a shift in a major ecological trait, host use, is likely occurring as a byproduct of a shift in an unrelated trait (delayed emergence) leading to partial reproductive isolation.     

Epistatic,additive and dominance variation in a triple test cross of bread wheat (Triticum aestivum L.)

Summary Triple test cross progenies resulting from the crossing of three testers (Kloka, UP 368 and an f₁ intermediate between them) and 24 varieties of bread wheat have been studied for plant height (cm), peduncle length (cm), ear length (cm), number of spikelets per spike and harvest index (ratio between economic and total yield). Epistasis was not significant for any of the characters studied. The testers were inadequate for plant height and for peduncle length although the testers varied considerably for these traits. Additive variance played a significant role in the inheritance of all the characters except number of spikelets per spike. The dominance variance was important for plant height, ear length and harvest index. The degree of dominance was in the over-dominance range for plant height. Complete dominance was operative for ear length, number of spikelets per spike and harvest index whereas for peduncle length only partial dominance was observed. The possibility of the isolation of the recombinants with high harvest index has been stressed.     

Comments on flower evolution and beetle pollination in the generaAnnona andRollinia (Annonaceae)

Dynastid scarab beetle pollination appears basic within the genusAnnona. Those species ofAnnona which are more morphologically derived, as well as allRollinia spp. possess reduced floral chambers and attract small beetles likeNitidulidae orStaphylinidae. Pollination of the primitive species ofAnnona byDynastinae would imply that the genus had not evolved before the Tertiary. The fossil record is in congruence with this hypothesis. Once again it is stressed that the cantharophilous syndrome, as it is found in theAnnonaceae, Magnoliaceae, Eupomatiaceae andCalycanthaceae, with beetles being exclusive pollinators, is a secondary and derived condition and obviously different from the expected basic entomophily of the original angiosperms.     

Dynamic interaction between a leaf beetle, Galerucella nipponensis, and an aquatic plant, Trapa japonica. II. Dispersal behavior of larvae

The dispersal behavior of the larvae of a leaf beetle, Galerucella nipponensis, was investigated to analyze the dynamic interaction between the leaf beetle and its aquatic host plant, Trapa japonica. The hatchlings dispersed from the hatched leaf to other leaves in a rosette within 12 h. Some larvae even dispersed on the water surface. As a result, the hatchlings distributed uniformly within the rosette. This larval dispersal appeared to be adaptive behavior responding to a rapid turnover of T. japonica leaves. The female adults preferred young or middle-aged leaves to old leaves as oviposition sites. Received: June 14, 2001 / Accepted: December 17, 2001