Major Host Plants Research Articles

Erysiphe monascogera sp. nov., an unusual powdery mildew fungus found on fruits of Styrax japonica

Morphological observations using light and scanning electron microscopes and molecular phylogenetic analysis revealed that the fungus growing on the surface of fruits or sepals of Styrax japonica collected at Nagano, Japan, is a new powdery mildew with an unusual morphology, described here as Erysiphe monascogera. This fungus has mainly a single ascus in a chasmothecium, but molecular phylogenetic analysis and the shape of the hyphal appressoria suggest that it is an Erysiphe species. Erysiphe monascogera is a sister-species to E. nomurae on Symplocos chinensis var. leucocarpa f. pilosa, although there are obvious morphological differences between the two species. This inconsistency between molecular phylogeny and morphology may be explained by the unique habitat of E. monascogera. Erysiphe monascogera and E. nomurae are included in a clade composed of the E. alphitoides complex, which suggests that these two species diverged by host jumping of the E. alphitoides complex, having oaks as major host plants.

<i>Erysiphe monascogera</i> sp. nov., an unusual powdery mildew fungus found on fruits of <i>Styrax japonica</i>

Morphological observations using light and scanning electron microscopes and molecular phylogenetic analysis revealed that the fungus growing on the surface of fruits or sepals of Styrax japonica collected at Nagano, Japan, is a new powdery mildew with an unusual morphology, described here as Erysiphe monascogera. This fungus has mainly a single ascus in a chasmothecium, but molecular phylogenetic analysis and the shape of the hyphal appressoria suggest that it is an Erysiphe species. Erysiphe monascogera is a sister-species to E. nomurae on Symplocos chinensis var. leucocarpa f. pilosa, although there are obvious morphological differences between the two species. This inconsistency between molecular phylogeny and morphology may be explained by the unique habitat of E. monascogera. Erysiphe monascogera and E. nomurae are included in a clade composed of the E. alphitoides complex, which suggests that these two species diverged by host jumping of the E. alphitoides complex, having oaks as major host plants.

Mother’s choice of the oviposition site: balancing risk of egg parasitism and need of food supply for the progeny with an infochemical shelter?

Oviposition site selection of herbivorous insects depends primarily on host plant presence which is essential for offspring survival. However, parasitoids can exploit host plant cues for host location. In this study, we hypothesised that herbivores can solve this dilemma by ovipositing within high plant diversity. A diverse plant species composition might represent an ‘infochemical shelter’, as a potentially complex volatile blend can negatively affect the host location ability of parasitoids. We examined this exemplarily for the egg-laying response of the generalist leaf beetle, Galeruca tanaceti, in relation to (1) host plant availability and (2) plant species diversity in the field. Further, we investigated the effect of odours from mixed plant species compositions on (3) leaf beetle oviposition site selection and on (4) the orientation of its specialised egg parasitoid, Oomyzus galerucivorus. In the field, egg clutch occurrence was positively related to the presence and quantity of two major host plants, Achillea millefolium (yarrow) and Centaurea jacea, and to the number of herbaceous plant species. In two-choice bioassays, female beetles oviposited more frequently on sites surrounded by an odour blend from a diverse plant species composition (including yarrow) than on sites with a pure grass odour blend. In the presence of yarrow odour and an odour blend from a diverse plant mixture (including yarrow) no difference in the oviposition response was recorded. Experienced parasitoid females were attracted to yarrow odours, but showed no response when yarrow odours were offered simultaneously with odours of a non-host plant. In conclusion, it could be shown in laboratory bioassays that the parasitoid responds only to pure host plant odours but not to complex odour blends. In contrast, the herbivore prefers to oviposit within diverse vegetation in the field and in the laboratory. However, the laboratory results also point to a priority of host plant availability over the selection of a potential ‘infochemical shelter’ for oviposition due to high plant diversity.

Morphometric differences between rice and water-oats population of the striped stem borer moth, Chilo suppressalis (Lepidoptera: Crambidae)

The striped stem borer moth, Chilo suppressalis, has two major host plants; rice, Oryza sativa, and the water-oats, Zizania latifolia. It has been suggested that there is reproductive isolation between the populations feeding on rice (rice population) and water-oats (water-oats population). We compared the morphological characteristics of the two populations using multi variate analyses based on eight genital and ten non-genital traits in male adults. Body size differed between the two populations as shown previously. However the results of a principal component analysis (PCA) based on genital traits showed a proportional difference between the two populations, but not on the non-genital traits. This shows the existence of a morphological difference in the genitalia of male adults between the populations. We also conducted a discriminant function analysis (DFA) based on seven genital and five non-genital traits. The discriminant function obtained could classify the two populations with 94.3% accuracy. Another discriminant function using only four genital traits also could distinguish the two populations with 88.6% accuracy. DFA would be of use in the practical forecasting of occurrence.

The origin of groundnut infestation by the seed beetle Caryedon serratus (Olivier) (Coleoptera: Bruchidae): Results from cytochrome B and ITS1 gene sequences

Caryedon serratus, the groundnut seed beetle, is a major pest of groundnut ( Arachis hypogaea), an introduced legume of the subfamily Papilionoideae. Native hosts of C. serratus in Senegal include Bauhinia rufescens, Cassia sieberiana, Piliostigma reticulatum and Tamarindus indica, all of which belong to the legume subfamily Caesalpinioideae. To determine the extent of isolation between native forms and forms feeding on groundnut, we analysed cytochrome B (Cyt. B) and ITS1 sequences within and among 24 Senegalese populations of C. serratus feeding on its five major host plants. Results show a strong differentiation of insects from different host trees, with specimens from C. sieberiana possibly representing a sibling species and insects from B. rufescens and T. indica a distinct host race. Groundnut and P. reticulatum populations are indistinguishable on the basis of sequence sets.

Butterfly response to severe ENSO‐induced forest fires in Borneo

Abstract. 1. Little is known about animal community response to severe El Niño Southern Oscillation (ENSO)‐induced fire events. Here the response of butterflies to the 1997/98 ENSO‐induced fire event in East Kalimantan (Indonesian Borneo) is assessed. In addition to the community‐wide study, a detailed assessment of the lycaenid Jamides celeno is made.2. Species richness declined significantly from 211 species pre‐ENSO to 39 species post‐ENSO and community composition changed significantly. Along with the decline in species richness there was a marked increase in dominance. Jamides celeno, for example, increased from 3% of the pre‐ENSO assemblage to 58% of the post‐ENSO assemblage. Like J. celeno, most of the species in the post‐ENSO assemblage were generalists; most of the specialist species having disappeared from pre‐ to post‐ENSO.3. The major host plant used by J. celeno was the abundant resprouting Fordia splendidissima. Furthermore, significantly more eggs were laid on plants with the crazy ant, Anoplolepis gracilipes, present than on plants with other ants or no ant attendance. Caterpillar presence was significantly higher on plants tended by ants than on untended plants.4. The median distance moved by J. celeno was 30 m with a maximum recorded distance of 290 m.5. The abundance of J. celeno and other generalists in the post‐ENSO assemblage at Wanariset was probably related to their ability to utilise the few available resources after the fire (e.g. F. splendidissima resprouts), their presence in degraded habitats surrounding the Wanariset forest, and their ability to disperse successfully by either being strong fliers (e.g. Euploea spp.) or being able to attain very high population sizes and thereby produce a surplus of dispersers (e.g. J. celeno).

Chemical basis for differential acceptance of two sympatric rutaceous plants by ovipositing females of a swallowtail butterfly, Papilio polytes (Lepidoptera, Papilionidae)

In the natural habitat of Papilio polytes, a Rutaceae feeder utilizing Toddalia asiatica as a major host plant, some other rutaceous plants such as Murraya paniculata (abundant) and Glycosmis citrifolia (relatively rare) occur sympatrically as potential hosts. Whereas G. citrifolia is occasionally infested in the field, M. paniculata remains entirely unexploited by the butterfly. We thus examined the phytochemical mechanisms that can explain the differential acceptance of the two plants by ovipositing females of P. polytes. The foliage of G. citrifolia was found to readily induce oviposition and females deposited eggs in response to a methanolic extract of the plant. Stimulatory activity-directed fractionation of the extract revealed the presence of two characteristic compounds, trans-4-hydroxy-N-methylproline and 2-C-methylerythronic acid, known to serve as oviposition stimulants for the butterfly. In addition, larvae performed as well or better onG. citrifolia as on T. asiatica. Similar examination of the inhibitory chemical constituents of M. paniculata led to the isolation of an oviposition deterrent. The compound, identified as trigonelline (N-methylpyridine- 3-carboxylic acid), exhibited moderate oviposition deterrency to females. These results combined with our previous data are in agreement with the observed differential utilization of the two plants by P. polytes in the field.

Geographic variation in oviposition choice of a leaf beetle: the relationship between host plant ranking, specificity, and motivation

AbstractThe degree of adaptation of herbivorous insects to their local flora is an important component of the evolutionary processes that lead to host plant specialization in insects. In this study we investigated geographic variations in the oviposition preference of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae: Chrysolini) in relation to differences in host plant specialization, in the field. We focused on the mechanisms of host choice and asked whether potential differences among populations are due to variations in host plant ranking and/or host plant specificity. We performed a combination of simultaneous choice and sequential no‐choice experiments with two of the major host plants of the beetle [Cirsium spinosissimum (L.) and Adenostyles alliariae (Gouan) (Asteraceae)]. The results suggested that spatial variation in host plant specialization has resulted in differences between populations in some aspects of the oviposition choice of O. elongata, while other aspects seem unaffected. We found no variation in host plant ranking among populations, as estimated in simultaneous choice tests. In contrast, the sequential no‐choice test indicated that host plant specificity was lower in a population that never encountered the highest ranked plant in the field. This finding agreed with our expectations, and we discuss our results in relation to the commonly used hierarchical threshold model. The results suggested that the mechanism for the differences in specificity is the variation among populations in the general motivation to oviposit, rather than quantitative differences in relative preference for the two hosts. We stress that it is essential to establish which of the two mechanisms is most important, as it will affect the probability of evolutionary change in host plant ranking.

Apple and peach fruit volatiles and the apple constituent butyl hexanoate attract female oriental fruit moth, Cydia molesta, in the laboratory

Abstract:Volatiles emitted from immature and mature peach and apple fruits were all attractive to mated female oriental fruit moth, Cydia molesta (Busck), in a dual choice arena. Females did not discriminate between odours emitted by these two major host plants. The same natural blends were behaviourally ineffective for virgin females. A major component of apple fruit volatiles, butyl hexanoate, also attracted female C. molesta. Mated females were attracted to two medium dosages, while virgin females responded positively to the lowest of the five dosages tested. The time course of the captures of the moths shows a diurnal activity cycle known from the field. The possible implications of a semiochemical which attracts females are discussed in the context of previous findings that gravid females may immigrate from peaches into apple orchards particularly in the later phase of the season.

Importance of Alternative Host Plants for the Annual Cycle of the Legume Pod Borer, Maruca vitrata Fabricius (Lepidoptera: Pyralidae) in Southern and Central Benin

The use pattern of alternative host plants by Maruca vitrata was investigated in southern and central Benin. Among the wild host plants, Pterocarpus santalinoides, Pueraria phaseoloides and Centrosema pubescens were found to be key relay hosts during the long dry season, Lonchocarpus sericeus and L. cyanescens were the most important hosts during the main rainy season, while Tephrosia platycarpa was an essential relay host during the short wet season in between. Cowpea was the major cultivated host plant and can sustain M. vitrata all year round, if available. However, this pest was able to maintain high population levels exclusively on wild hosts without needing to switch to cultivated crops. The relevance of these findings and their implications for the control of M. vitrata are discussed.

Lack of sequestration of host plant glucosinolates in Pieris rapae and P. grarricae

Sequestration of plant toxins in herbivores is often correlated with aposematic coloration and gregarious behaviour. Larvae of Pieris brassicae show these conspicuous morphological and behavioural characteristics and were thus suggested to sequester glucosinolates that are characteristic secondary metabolites of their host plants. P. rapaeare camouflaged and solitary, and are thus not expected to sequester. To test this hypothesis and to check the repeatabi-lity of a study that did report the presence of the glucosinolate sinigrin in P. brassicae, larvae were reared on three species of Brassicaceae (Sinapis alba, Brassica nigra and Barbarea stricta), and different leaf and insect samples were taken for glucosinolate analysis. The major host plant glucosinolates could only be found in traces or not at all in larval haemolymph, bled or starved larvae, faeces or pupae of both species or P. brassicae regurgitant. Haemolymph of both Pieris spp. was not rejected by the ant Myrmica rubra in dual-choice assays; the regurgitant of P. brassicae was rejected. This suggests the presence of compounds other than glucosinolates that might be sequestered in or produced by P. brassicae only. In faeces of both Pieris spp. a compound which yielded 4-hydroxybenzylcyanide (HBC) upon incubation with sulfatase was detected in high concentrations when larvae had been reared on S. alba. This compound may be derived from hydrolysis of sinalbin, the main glucosinolate of that plant. The unidentified HBC progenitor was apparently not sequestered in the two Pieris spp., and was not detected in faeces of larvae reared on B. nigra or B. stricta.

Chemical mediation of differential oviposition and larval survival on rutaceous plants in a swallowtail butterfly, Papilio polytes

Abstract Papilio polytes utilizes only a few plant species of Rutaceae as hosts in the field. We examined in detail the acceptability of Toddalia asiatica (a major host plant) and three other potential rutaceous hosts, Murraya paniculata, Melicope triphylla, and Phellodendron amurense, for ovipositing females of the butterfly. Female responses to the foliage, methanol extracts, and partitioned fractions from these plants were assayed for the presence of oviposition stimulants and/or deterrents. Larval survivorship on these plant species was also compared as an estimate of fitness. The foliage and a methanol extract of T. asiatica readily induced egg‐laying, while females responded moderately to the foliage and a methanol extract of P. amurense. By contrast, ovipositing females only marginally accepted Me. triphylla and completely rejected Mu. paniculata. Further experiments to test the biological activity of fractions derived from the respective plant species revealed that T. asiatica contains potent oviposition stimulant(s) and that weak stimulant(s) are present in P. amurense. Poor or negative oviposition responses to both Me. triphylla and Mu. paniculata proved to be attributable to strong deterrent(s) present in these plants. Larvae performed very well on T. asiatica and P. amurense, whereas larval mortality was much higher on Mu. paniculata and Me. triphylla, suggesting the involvement of antifeedant(s) or toxic substance(s) in these plants.

Will climate change have a different impact on different trophic levels? Phenological development of winter moth Operophtera brumata and its host plants

Will climate change have a different impact on different trophic levels? Phenological development of winter moth <i>Operophtera brumata</i> and its host plants

Diversity of birch sawfly responses to seasonally atypical diets

AbstractMost insect herbivores are specialised on a particular plant taxon. To have a better understanding of host shift functions and consequences for insect herbivores, it is essential to gather more information on the effects of variation in host quality on specialists across species and environments. We examined the effects of seasonally atypical food on mortality, developmental time, and final body mass of six sawfly species (Hymenoptera: Symphyta) feeding on the foliage of mountain birch (Betula pubescens ssp. czerepanovii), whose pooled larval feeding periods form a gradient and cover the growing season. Insect phenology was manipulated so that the larvae of early‐season species would feed on atypically mature leaves and mid‐ or late‐season species would feed on atypically young leaves of their major host plant. Mortality increased dramatically for all species when the larval feeding schedule was advanced or delayed. This indicates a high degree of specialisation not only on a particular host but also to its phenological phases. The main cause of mortality on novel food was a rejection of the diet by the young larvae and their subsequent starvation. An interesting observation was that late‐season species showed this response on nutritious young foliage. The effects of seasonally atypical diets on larval development and growth were species‐specific and milder than the effects on mortality. Interestingly, for those individuals that accepted it, atypical food seemed to be most beneficial for species appearing at both ends of the seasonal gradient, which might be related to a wider exposure to variable food quality in natural conditions compared with other species. The diversity of responses to atypical food among closely related herbivore species with overlapping feeding periods on the same host plant is the most crucial finding of this study.

Spatial Distribution of and Sampling Plans forMussidia nigrivenella(Lepidoptera: Pyralidae) on Cultivated and Wild Host Plants in Benin

The spatial distribution of Mussidia nigrivenella Ragonot was studied in maize fields and on four major wild host plants in the Republic of Benin, West Africa. Maize ears were sampled at harvest in 1994 and 1995, and fruits of the wild host plants were collected monthly from January 1996 to December 1997 during the fruiting periods of the respective host species. The spatial distribution was analyzed using the variance-to-mean ratio (s2/m), an index of departure from Poisson distribution, Iwao’s patchiness regression, and Taylor’s power law. The variance-to-mean ratio and the index of departure from Poisson gave similar results of nonrandom distribution of M. nigrivenella populations on the different host plants out of Gardenia sokotensis Hutch (Rubiaceae). On this specific host plant, the variance-to-mean ratio was not different from 1, whereas there was no overlap of the observed population and the Poisson distribution. Iwao’s patchiness regression was inappropriate for our data as shown by the nonhomogeneity of variance, whereas Taylor’s power law fitted the data well. Based on Taylor’s power law, M. nigrivenella was aggregated on all host plants out of G. sokotensis. The degree of aggregation of M. nigrivenella was positively correlated with the fruit size of the host plants. The optimal number of secondary sampling units needed to estimate M. nigrivenella densities on the respective host plants in Benin, varied from four fruits on G. sokotensis to 10 pods on P. biglobosa. These values were used to calculate the time expenditure needed to sample maize fields or wild host plant trees to achieve a predefined precision level of 25%.

Detecting decline in a formerly widespread species: how common is the common blue butterfly Polyommatus icarus?

Grid square distribution maps have been used widely to measure rates of decline and target conservation resources. However, common species that may have many populations per grid square can decline substantially from within squares without being lost from entire squares. In order to quantify this process, fine scale population and habitat data have been collected for the common blue butterfly Polyommatus icarus in a 35 km2 area of fragmented landscape in north Wales. Present day habitat associations, determined from over 2000 transect walks, combined with data on historical and present day habitat distributions reveal that the species has declined by about 74% since 1901. Similar data concerning the species major host plant Lotus corniculatus indicate a decline of 46%. Based on 1 km2 grid maps, neither species have been assessed as declining at all. These results suggest that apparently ‘common’ species may have declined just as much as many of Britain's rare species: using present methods of assessment these declines are undetected.

Fireblight (Erwinia amylovora) of pome fruits in Hungary: national phytosanitary measures and management of the disease

After the first detection of Erwinia amylovora in Hungary, as a result of an intensive survey started in spring 1996, it was concluded that the incidence of fireblight was highest in a zone 10–30 km wide and 200–250 km long near the southern and south‐eastern border. The disease was concentrated in the Békés, Bács‐Kiskun and Csongrád counties. Isolated infection foci were, however, also found in Baranya county. In 1997, further spread of the disease was recorded. Only three of the 19 counties could be considered as free from the disease. The disease attacked nine major host plants, but the majority of infected plants were quince and pear. During the eradication campaign in 1996, more than 60 000 trees were uprooted and destroyed across the country. Eradication was performed partly by special work teams and partly with the participation of growers. The pathogen most probably entered Hungary by aerial drift from Romania or Yugoslavia during the previous 2 or 3 years. In the interior of the country, introduction through nursery stock and possibly infested tools, as well as wind and insect movement, cannot be excluded. Major measures to control the disease are discussed.

Population dynamics of a phytophagous lady‐beetle, Epilachna vigintioctopunctata (Fabricius), living in spatio‐temporally heterogeneous habitats. III. Effects of habitat structure on population dynamics

Temporal changes in the population size of a phytophagous lady-beetle were analyzed to identify mechanisms affecting lady-beetle population dynamics at different spatial scales. The study area (15 ha) included 18 habitat patches. The major host plants were potato for first generation larvae and eggplant for second generation larvae. The habitat patches were classified into three groups according to the major host plants in each patch: P-E patches (both host plants available), P patches (potato only), and E patches (eggplant only). The winter disappearance of adults in the whole study area, and larval mortality in E patches were apparently the most important factors disturbing the overall population density. Density-dependent movement of females appeared to have the greatest stabilizing effect on the yearly fluctuation of population density. Rate of increase of female adults from the first to the second generation, R, was generally higher on eggplants in E patches than in P-E patches because the adult density of the first generation was much higher in P-E patches. The yearly fluctuation of adult density in each generation tended to be less in patches with all habitat components necessary for the full life cycle (P-E patches). However, such patches were not favorable for first generation females, as indicated by the lower rate of increase from the first to the second generation. The density and stability of lady-beetle populations is discussed in relation to habitat structure.

A flavonoid glucoside, phellamurin, regulates differential oviposition on a rutaceous plant,Phellodendron amurense, by two sympatric swallowtail butterflies,Papilio protenor andP. xuthus: The front line of a coevolutionary arms race?

We studied the chemical basis for the differential acceptance of a rutaceous plant.Phellodendron amurense, by ovipositing females of two sympatricPapilio butterflies,P. protenor andP. xuthus, that have a very similar host range.P. amurense, on which larvae of both species perform well, was rejected byP. protenor females but was marginally accepted byP. xuthus, even though water-soluble fraction of this plant elicited significant ovipositional responses from the two species. A prenylated dihydroflavonol glucoside, 3,5,7,4'-tetrahydroxy-8-(3-methylbut-2-enyl)flavanone-7-O-β-glucoside (phellamurin), was identified as a dominant active substance that deters oviposition.P. protenor responded highly sensitively to phellamurin, whereasP. xuthus was less susceptible and was affected conspicuously only at higher concentrations than that found in living plants, thereby accounting for their differential responses toP. amurense. InP. protenor, the deterrent effect of phellamurin was considered to outweigh the activity of coexisting stimulant(s) at the concentrations actually present in the foliage, resulting in avoidance of this plant. The phellamurin content in the foliage amounted to as much as 1.8% of the fresh weight, which is far higher than the average levels of flavonoids present in other major host plants ofPapilio. The dose-response experiments demonstrated that unacceptability ofP. amurense forP. protenor was attributable largely to such a high concentration of phellamurin. These results appear to provide information on possible coevolutionary interactions between herbivores and plants and also on the potential for shifts in host affiliation.

Factors associated with oligophagy in two species of sea hares (Mollusca: Anaspidea)

Unlike most marine invertebrate herbivores, many sea hares (Genus Aplysia) are relatively specialised feeders. In order to assess the factors associated with narrow diet breadth of Aplysia parvula (Guilding) Mörch and A. Juliana (Quoy & Gaimard) near Sydney N.S.W., occurrence of Aplysia spp. on host plants, algal abundance and nutritional quality, growth and consumption of different diets by Aplysia spp. and deterrence of predators by sequestered algal metabolites were measured. Both species only occurred on, and only ate, one ( A. Juliana) or a few ( A. parvula) species of algae. Aplysia Juliana only occurred on and only ate the green alga Ulva lactuca (Linnaeus), which was locally abundant and lacks secondary metabolites. The major host-plants for A. parvula, the red algae Delisea pulchra (Greville) and Laurencia obtusa (Hudson), were low in abundance, but were both rich in secondary chemistry. The nutritional value (% nitrogen content and % organic matter) of dietary algae for the sea hares was not higher than in co-occurring non-dietary algae. The growth and conversion efficiency of A. parvula varied strongly with diet and also varied depending on the host plant from which the animals were collected. Surprisingly, A. parvula did not grow when fed only D. pulchra-a main host plant-in the laboratory or field. Aplysia parvula sequesters secondary metabolites from D. pulchra, and the metabolite sequestered in highest concentrations by the animals significantly deterred feeding by fishes in field assays. In contrast, a second metabolite which is sequestered at low concentrations did not deter feeding by fishes. These experiments suggest that deterrence or avoidance of predators strongly affects food choice by A. parvula and further suggest that accumulation of D. pulchra metabolites by A. parvula has a significant cost to these animals. The factors affecting diet breadth for A. juliana are less clear. This species may gain a spatial escape from predation by specialising on the intertidal alga U. lactuca.