Deceptive fruits reduce seed predation by insects inPistacia terebinthus L. (Anacardiaceae)

Summary The production of seedless fruits (parthenocarpy) is not yet understood from an evolutionary viewpoint, even though it is taxonomically widespread. Here I present a case in which parthenocarpy reduces the incidence of seed predation by insects. At least the first generation of chalcidoid wasps that oviposit in the fruits ofPistacia terebinthus L. (Anacardiaceae) cannot discriminate among viable and inviable fruits, allocating energy and time to oviposition on fruits that are not suitable for larval development.     

Weak interactions between avian and insect frugivores: the case of Pistacia terebinthus L. (Anacardiaceae)

Vertebrate frugivores often feed on fruits upon or within which insects also feed, yet little information exists on the potential magnitude of interactions between these consumers. The Mediterranean shrub Pistacia terebinthus, the birds that consume its fruits, and the wasps that feed upon its seeds are examined in this study. P. terebinthus produces a highly variable fraction of final-sized red fruits that never become mature (green-colored). Red fruits can be immature, parthenocarpic, aborted, or attacked by wasps, and their pulp is much less nutritious than that of mature fruits. A total of 20 bird species consumed the fruits in the study area. Legitimate dispersers accounted for 39% of the total fruit removal, while pulp eaters and seed predators accounted for the remainder. Birds strongly preferred the mature fruits (only 4% of the fruits consumed were red). The incidence of wasps in the seeds ranged from 0 to 42% of the crop in 1989 and from 0 to 24% in 1990. The influence of avian and insect frugivore guilds on each other appears to be quite low because of the narrow overlap in resource utilization by birds and wasps, and an overall low intensity of wasp seed predation. From an evolutionary perspective, the possible ability of wasps to preclude fruit maturation appears not to be attributable to the present interaction with avian frugivores.     

Influence of type of avian frugivory on the fitness ofPistacia terebinthus L.

Summary The fruits ofPistacia terebinthus, a circum-Mediterranean tree/shrub, are consumed by an array of bird species that differ in feeding methods and in relative frequencies of visits to plants. In this study I document interindividual variation in the proportion of fruits consumed by three types of frugivores: legitimate dispersers, pulp-consumers and seed predators. The results show that the relative frequencies of each kind of frugivore notably influence the final reproductive output (absolute number of viable seeds dispersed) and in fact prevail over the effects of pre-dispersal factors acting on plant fitness. Those relative frequencies are not associated with any of the plant traits related to fitness, such as fruit crop size and the number of viable seeds produced, suggesting that the type of avian frugivory exerts a negligible, if not null, selective pressure on such plant attributes. Plant specialization to attract the most effective seed dispersers seems to be precluded, given the small scale at which the high variation in seed dispersal success takes place.     

Effects of enhanced UVB on populations of the phloem feeding insect Strophingia ericae (Homoptera: Psylloidea) on heather (Calluna vulgaris)

Heather plants (Calluna vulgaris (L.) Hull) were grown for two years (April 1994–October 1996) under ambient or enhanced ultraviolet-B radiation (UVB: 280–315 nm), provided as a modulated treatment simulating a 15% ozone depletion (seasonally adjusted). Populations of the psyllid (Strophingia ericae (Curtis)) were measured before treatment and at yearly intervals thereafter. Before treatment there was no significant difference in the psyllid populations between treatments, or between the experimental and source populations. Enhanced UVB progressively produced a reduction in S. ericae populations compared with controls over 27 months. Analyses of C, N, total water soluble phenolics, total free amino acids and measurements of leaf angles and distances between leaflets demonstrated no effects of UVB treatment. However, concentrations of the amino acid isoleucine were lower (28%) in C. vulgaris exposed to the enhanced UVB treatment. Over the duration of the experiment the psyllid population structure at Lancaster changed from that typical of the upland site of origin (two-year cycle with overlapping cohorts) to a one-year life cycle typical of lowland sites, but this was independent of UVB treatments. Reduced isoleucine might explain the negative effects of elevated UVB on psyllid population numbers, but the precise effects of UVB on host chemistry and morphology are unknown. The problem of interpreting herbivore responses to enhanced UVB treatments in the field is discussed.     

The influence of ant attendance on larval parasitism in hawthorn psyllids (Homoptera: Psyllidae)

The influence of ant attendance on parasitization of the larvae of three hawthorn psyllid species [Cacopsylla peregrina Förster, C. melanoneura Förster, C. crataegi (Schrank)] was studied over 2 years. All three psyllid species had low parasitization rates. However, the ant-attended C. crataegi was almost exclusively parasitized by Prionomitus mitratus (Dalman) (Hymenoptera: Encyrtidae) while the unattended C. peregrina and C. melanoneura were predominantly attacked by P. tiliaris (Dalman). Additionally, C. peregrina and C. melanoneura has significantly higher hyperparasitization rates than the ant-attended C. crataegi, with Pachyneuron muscarum as the dominant hyperparasitoid of all three psyllids. The mummies of C. peregrina and C. melanoneura were also heavily attacked by anthocorids. Both Prionomitus tiliaris and P. mitratus were disturbed and jumped away when encountering foraging ants. However, ant exclusion experiments showed that the primary parasitoid P. mitratus benefitted from ant attendance of its host C. crataegi as honeydew-collecting ants provided it with protection from hyperparasitoids.     

Plant organ abscission and the green island effect caused by gallmidges (Cecidomyiidae) on tropical trees

Plants exhibit a wide array of inert and induced responses in defense against herbivore attack. Among these the abscission of organs has been argued to be a highly effective mechanism, depending, however, on the herbivore’s feeding mode. While consisting of plant tissues, insect induced galls are seen as the extended phenotype of the gall inducer which might circumvent many or most of the plant defenses. There is very little information whether and how far beyond the gall tissue gall inducers might affect plant tissues. A localized impact is likely to leave the abscission of galled organs as a viable defense although at a cost. Here, we report on an instance where the host plant, Neea madeirana (Nyctaginaceae) abscises leaves galled by two species of Bruggmannia (Diptera: Cecidomyiidae), more frequently than ungalled leaves in a rain forest in Amazonia, Brazil. Once on the forest floor the leaves decay quickly, while both gall types show signs of localized maintenance of healthy tissues for a while (the green island effect). However, on the forest floor galls are exposed to a new set of potential natural enemies. Both gall types show a minimum of a five-fold increase in mortality due to pathogens (fungi and bacteria) compared to galls that were retained on the host tree. We discuss the adaptive nature of plant organ abscission as a plant defense against gallers and as a gall inducer adaptive trait. Handling editor: Graham Stone.     

Petal herbivory by chrysomelid beetles (Phyllotreta sp.) is detrimental to pollination and seed production in Lepidium papilliferum (Brassicaceae)

Abstract.  1. Insect herbivory directed at flowers can decrease fruit and seed production by decreasing the attractiveness of a damaged flower to potential pollinators, by disrupting the transfer of pollen between pollinators and stigmas, or both.
2. Effects of petal herbivory by a chrysomelid beetle ( Phyllotreta sp.) on pollination and seed production in Lepidium papilliferum (Brassicaceae) were examined.
3. Under natural conditions, flowers with a hole chewed in a petal produced fruit and seed at a significantly lower rate than undamaged flowers (44% vs. 80% respectively). However, when damaged and undamaged flowers were hand pollinated, there was no significant difference in fruit or seed set (84% vs. 80% respectively).
4. Petal herbivory in L. papilliferum disrupts the effectiveness of insect-mediated pollination, but it does not physically inhibit pollination or seed production.     

The Origin of the Achiasmatic XY Sex Chromosome System in Cacopsylla peregrina (Frst.) (Psylloidea, Homoptera)

The status of an extra univalent, if it is a B chromosome or an achiasmatic Y chromosome, associating with the X chromosome in male meiosis of Cacopsylla peregrina (Frst.) (Homoptera, Psylloidea) was analysed. One extra univalent was present in all males collected from three geographically well separated populations, it was mitotically stable, and showed precise segregation from the X chromosome. These findings led us to propose that the univalent represents in fact a Y chromosome. The behaviour of the X and Y chromosomes during meiotic prophase suggested that their regular segregation was based on an achiasmatic segregation mechanism characterised by a 'touch and go' pairing of segregating chromosomes at metaphase I. To explain the formation of the achiasmatic Y within an insect group with X0 sex chromosome system, it was suggested that the Y chromosome has evolved from a mitotically stable B chromosome that was first integrated into an achiasmatic segregation system with the X chromosome, and has later become fixed in the karyotype as a Y chromosome.     

龙眼鸡Fulgora candelaria(L.)生物学特性的初步研究

龙眼鸡 F ulgora candelaria(L.)分布于东南亚 ,是中国南方龙眼树的一种重要害虫 ,年生一代 ,以成虫越冬。本文是作者等自七十年代末迄八十年代在福州金山以及福建南部的漳州、莆田等地 ,对这种害虫生物学特性进行初步研究的小结 ,并对分布、寄主以及天敌龙眼鸡寄蛾 Fulgoraecia bowringii Newman等有关问题进行了讨论     

The spermatodesm of Cloeon dipterum (L.): fine structure and sperm movement

Sperm bundles of the ephemeropteran Cloeon dipterum (L.) were found in the seminal vesicle. They are apically protected by cyst cells and sperm anterior regions are embedded in a secretion produced by these cells. Cyst cells further degenerate making sperm cells free. The sperm bundles are able to perform a forward progression only when sperm are stick together with their tail posterior tips. On the contrary, when sperm have their tail ends free, they beat but are unable to progress. The functional significance of the sperm bundles is discussed.     

Intra-crown variation in leaf herbivory and seed production in striped maple,Acer pensylvanicum L. (Aceraceae)

Summary Patterns of spatial variation in leaf herbivory and the effects of this variation on seed production and twig growth were studied in striped maple, Acer pensylvanicum (Aceraceae). Experimental removal of 25% of the leaf area from each of four leaves directly subtending a developing infructescence significantly reduced seed number in that infructescence. When leaf area was removed from leaves neighboring to, but not directly subtending developing infructescences, no reduction in seed production occurred. Together, these results suggest that only photosynthate from leaves directly subtending infructescences contributes to seed production in nearby infructescences. Effects of the experimental removal of leaf area did not persist the second year, suggesting that mobilization of storage products the following spring occurred independent of prior treatment. There was probably little negative impact of leaf herbivores on this plant species during the study year due to (1) low occurrence of localized damage within the crowns of censused trees and (2) delay of leaf area loss until completion of fruit development.     

The classification of adult colour forms of Philaenus spumarius (L.) (Homoptera: Insecta)

Philaenus spumarius is an insect of wide geographical distribution which has a number of colour morphs. This is a report of an attempt to provide an objective classification of the morphs by direct measurement of some visual characteristics. Distribution of these within the sample did not follow a normal curve but it was not possible to correlate the observed distribution with the subjectively sorted groups. This throws some doubt on the validity of the traditional subjective classification and on deductions based on this.     

A microtubule organizing centre (MTOC) is responsible for the production of the sperm flagellum in Matsucoccus feytaudi (Hemiptera: Coccoidea)

A microtubule organizing centre (MTOC) has been described in the spermatid of the hemipteran Matsucoccus feytaudi (Coccoidea). This structure, revealed as a fluorescent ring by treatment with γ-tubulin antibody, gives rise to a bundle of microtubules which surrounds the elongated cylindrical nucleus. This microtubule bundle has been considered an atypical sperm flagellum provided with sperm motility. A comparison of the M. feytaudi MTOC with the material associated with the centriole of Drosophila melanogaster spermatids confirms the great similarity between the two structures, both involved in the nucleation of microtubules. Like the D. melanogaster material associated with the centriole, the M. feytaudi MTOC is a transient structure which disappears or degenerates at the end of spermiogenesis and is no longer visible in the mature sperm.     

The effect of seed size on the development and yield ofVoandzeia subterranea (L.)Thouars. (Bambara groundnut)

Voandzeia subterranea (L.)Thouars (Bambara groundnut) is a drought and poor soil cultivated legume. The seeds vary both in colour and in size. The seed colour ranges from white, cream, ivory to dark brown red or black. The seed weight varies fromabout 0.15 g to 1.20 g. The effect of seed size on the development and yield of the cream coloured cultivar ofV. subterranea was investigated. The three size class of seeds used in the study are small (seeds weighing less than 0.40 g) medium (seeds weighing from 0.40–0.60g) and large (seeds weighing above 0.60g). The results of the investigation show that the number of leaves, pods and seeds, the leaf area, dry weight of plants and the seeds produced increased significantly with increase in the seed size.     

Feeding ecology and emergence production of annual cicadas (Homoptera: Cicadidae) in tallgrass prairie

The emergence phenology and feeding ecology of annual cicadas in tallgrass prairie are poorly documented. However, these large insects are abundant, and their annual emergence represents a potentially important flux of energy and nutrients from belowground to aboveground. We conducted a study at Konza Prairie Research Natural Area in eastern Kansas to characterize and quantify cicada emergence and associated energy and nutrient fluxes. We established emergence trap transects in three habitat types (upland prairie, lowland prairie, and riparian forest), and collected cicadas every 3 days from May to September. A subset of trapped cicadas was used for species- and sex-specific mass, nutrient, and stable isotope analyses. Five species were trapped during the study, of which three were dominant. Cicadetta calliope and Tibicen aurifera exhibited significantly higher emergence production in upland prairie than in lowland prairie, and were not captured in forested sites at all. T. dorsata emerged from all three habitat types, and though not significant, showed a trend of greater abundance in lowland grasslands. Two less abundant species, T. pruinosa and T. lyricen, emerged exclusively from forested habitats. Nitrogen fluxes associated with total cicada emergence were estimated to be ∼4 kg N ha^–1 year^–1 in both grassland habitats, and 1.01 kg N ha^–1 year^–1 in forested sites. Results of stable isotope analyses showed clear patterns of resource partitioning among dominant cicada species emerging from grassland sites. T. aurifera and C. calliope had δ¹³C and δ¹⁵N signatures indicative of feeding on shallowly rooted C₄ plants such as the warm-season grasses dominant in tallgrass prairie ecosystems, whereas T. dorsata signatures suggested preferential feeding on more deeply rooted C₃ plants. Received: 20 September 1999 / Accepted: 9 December 1999     

Hydroponic culture of Catharanthus roseus (L.) G. Don and studies on seed production

Under climatic conditions of Poland, Catharanthus roseus may be grown in the open field only as annual crop, using transplants raised in a greenhouse or in a plastic tunnel. An effective method of hydroponic culture has been elaborated and tested. Herbal material obtained in hydroponics showed considerable concentration of alkaloids in different plant parts. Seeds of C. roseus may also be produced under these conditions. Characteristics of seeds as well as the effect of different methods of their storage are presented. Seeds stored in paper bags at room temperature may retain germinability for 7 years and those stored in a refrigerator, at 5°C, up to 15 years. Storage in a freezer, at -10°C, resulted in a quick and sharp reduction of germination rate.     

The effect of deceptive fruits on predispersal seed predation by birds in Pistacia lentiscus

Deceptive fruits (fruits containing empty seeds and seedless fruits) inthe dioecious shrub Pistacia lentiscus L. (Anacardiaceae)remain attached to the plant throughout the dispersal season. This studyaddresses the hypothesis that deceptive fruits may contribute to parentalfitness by reducing predispersal seed predation by granivorous birds becausethese fruits represent handling costs to predators and they prefer to forageselectively on shrubs with filled fruits. This study was run in two populationsof P. lentiscus and finds that deceptive fruits reduceseedpredation by granivorous birds but only in the population that presented higherP. lentiscus female density, and a higher variability inthe percentage of deceptive fruits among P. lentiscusfemales. Under this scenario, the benefits of flying to another female might behigher than those of remaining in the same female searching filled seeds. Bycontrast, the costs of flying to other females, when they are scarce and have asimilar percentage of deceptive fruits may be higher than the benefits.     

Transmission of cotton seed and boll rotting bacteria by the southern green stink bug (Nezara viridula L.)

AIMS: To determine the ability of the southern green stink bug (SGSB) (Nezara viridula L.) to transmit Pantoea agglomerans into cotton (Gossypium hirsutum) bolls. METHODS AND RESULTS: An SGSB laboratory colony was kept on fresh green beans. A P. agglomerans variant resistant to rifampicin (Rif) (strain Sc 1-R) was used as the opportunistic cotton pathogen. Adult insects were individually provided green beans that were sterilized and then soaked in either sterile water or in a suspension of strain Sc 1-R. Insects were individually caged with an unopened greenhouse-grown cotton boll. After 2 days, live SGSB were collected, surfaced sterilized, ground, serially diluted, and then plated on nonselective media and media amended with Rif. Exterior and interior evidence of feeding on bolls was recorded 2 weeks after exposure to insects. Seed and lint tissue were harvested, ground, serially diluted, and then plated on media with and without Rif. Bacteria were recovered on nonselective media from all insects, and from seed and lint with signs of insect feeding at concentrations ranging from 10(2) to 10(9) CFU g(-1) tissue. The Sc 1-R strain was isolated only from insects exposed to the marked strain and from seed and lint of respective bolls showing signs of insect feeding. Evidence of insect feeding on the exterior wall of the carpel was not always apparent (47%), whereas feeding was always observed (100%) on the interior wall in association with bacterial infections of seed and lint. CONCLUSIONS: Nezara viridula readily ingested the opportunistic P. agglomerans strain Sc 1-R and transmitted it into unopened cotton bolls. Infections by the transmitted Sc 1-R strain caused rotting of the entire locule that masked internal carpel wounds incurred by insect feeding. Bacteria were recovered from penetration points by insects not exposed to the pathogen, but locule damage was limited to the area surrounding the feeding site (c. 3 mm). SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study that demonstrates the ability of SGSB to acquire and transmit plant pathogenic bacteria into cotton bolls.