Fauna of phloemo-xylophagous insects,their parasitoids and predators on <Emphasis Type="Italic">Ulmus minor</Emphasis> in Serbia

The fauna of phloemo-xylophagous insects, their parasitoids and predators was studied on Ulmus minor in Serbia. Sixty insect species were recorded, of which 22 species were phloemo-xylophagous insects, 33 species were their parasitoids and 5 species were their predators. Among phloemo-xylophagous insects, the most common and most abundant species were Scolytus pygmaeus (59.93%), Magdalis armigera (11.79%), S. multistriatus (9.24%), Exocentrus punctipennis (8.68%), S. ensifer (5.48%) and S. kirschii (1.28%). The most frequent and most abundant parasitoid was the species Ecphylus silesiacus (65.95%). Also, the parasitoids Dendrosoter protuberans (7.46%), Rhaphitelus maculatus (6.25%), Cheiropachus quadrum (5.49%), Acrocormus semifasciatus (3.68%), Entedon ergias (1.65%), Spathius rubidus (1.53%), Eubazus augustinus (1.46%) and Eurytoma morio (1.37%), were of major importance.     

Significance of parasitoids in the reduction of oak bark beetle Scolytus intricatus Ratzeburg (Col., Scolytidae) in Serbia

Abstract:  As the vector of vascular fungi of the genus Ophiostoma the oak bark beetle, Scolytus intricatus , is one of the significant links in the chain of agents of oak forest decline in Serbia. It is known that the adults of this bark beetle, which develop under the bark of the trees infected by fungi of the genus Ophiostoma , transport the spores of these fungi. During the maturation feeding, the spores are transmitted to healthy tree crowns, where they germinate and cause infection. In period 1992–96 at 27 localities in Serbia, the significance of parasitoids in the reduction of this bark beetle was examined, as the intensity of spore transmission depends upon the number of oak bark beetle adults in nature. In the research of parasitoids of S. intricatus 20 species were identified in five families of Hymenoptera: Braconidae (six species), Eurytomidae (one), Pteromalidae (10), Eupelmidae (one) and Eulophidae (two). Among these parasitoids the greatest influence on the abundance of oak bark beetle was the species Ecphylus silesiacus . It was identified in 90.91% of study samples, its domination was 39.15% and the percentage of oak bark beetle parasitism was 5.66%. In addition, the species Entendon ergias , Dendrosoter protuberans and Cheiropachus quadrum were significant in reduction of S. intricatus . The average percentage of parasitism of oak bark beetle by E. ergias was 2.74%, by D. protuberans it was 2.63% and by Ch. quadrum 1.63%. The significance of other parasitoids in the reduction of oak bark beetles was low. In the study period the total parasitism of oak bark beetle varied between a minimum of 8.64% in 1992 and a maximum of 19.64% in 1996. The average for the whole study period was 14.49%.     

Laboratory validation of rubidium marking of herbivorous insects and their predators

A simple and effective marking technique is an invaluable tool for tracking the movement of invertebrates in the field. In order to do this, the technique must be validated in a controlled setting. In the first study, two soft bodied herbivores with different feeding strategies and two of their insect predators, also with different feeding strategies, were marked with rubidium (Rb), an elemental marker previously shown to be effective in marking herbivorous invertebrates. The naturally occurring concentration of Rb was determined for both the herbivores and their predators. Rb concentrations were determined in (1) the herbivore species over several days of feeding on rubidium chloride (RbCl) marked plants; (2) in the predatory species immediately after consuming prey marked at different rates with Rb; and (3) in the predatory species for several days after consuming a single meal of Rb marked prey. The concentration of Rb within the marked herbivores was found to be significantly higher than the naturally occurring concentration after eating RbCl marked plants for to up 8 days. A significantly higher concentration of Rb was found in both predators when fed prey that had been on the RbCl sprayed plants for 2 or 8 days compared with naturally occurring concentrations. There was also a significant difference between the Rb concentrations in the controls and each of days 5, 10 and 15 since feeding in both predators. A second smaller study was carried out to examine the effect of feeding Rb marked prey to spiders. The concentration of Rb in the spiders fed marked prey was significantly higher than that of the controls. This suggests that Rb is an effective way of marking both herbivores and their insect and arachnid predators enabling them to be tracked in the field and to determine their movements across habitats.     

Effects of neem-treated aphids as food/hosts on their predators and parasitoids

Abstract:  Experiments were conducted in the laboratory and in greenhouses. Of three neem preparations sprayed upon eggs, only neem oil (NO) exerted a negative impact on the hatching rate of Coccinella septempunctata and Chrysoperla carnea . First instar larvae of Episyrphus balteatus proved to be highly susceptible, when feeding 24 h on aphids sprayed with neem kernel water extract (NKWE). First instar larvae of C. septempunctata showed a very high mortality when feeding on aphids sprayed with different neem preparations. Aphid feeding and live span was reduced. When NKWE had been applied to the soil, the mortality of larvae of E. balteatus and C. septempunctata were lower, when feeding on aphids. Second instar larvae of C. septempunctata were far less susceptible when feeding 48 h on neem-sprayed aphids than first instars; the time of their development was prolonged, and aphid consumption reduced. Larvae of C. carnea proved to be less susceptible, when feeding on neem-sprayed aphids, than E. balteatus and C. septempunctata . In C. carnea , however, significant influences were also observed in aphid consumption, time of development, mortality, longevity, and rate of deformity. NO, containing a very low concentration of azadirachtin A, had stronger negative effects than NeemAzal-T/S^®, in all observations. In the parasitoid Diaeretiella rapae , NKWE application to the soil induced negative reactions, when aphids on these plants were parasitized: low percentage parasitization, lowered mummy weight, low emergence rate of adults of F1 and even of F2. Foliar sprays of NKWE had less severe effects in this parasitoid species. The results are discussed with regard to their theoretical and practical significance.     

Patterns of intra- and interspecific association in leaf-mining insects on three oak host species

Abstract. 1. We determined mortality and distributional patterns of leaf miners on three oak host species (Quercus falcata, Q.nigra and Q.hemisphaerica) in northern Florida, U.S.A.
2. Patterns of intra- and interspecific occurrence within leaves, and mortality of five most abundant leaf miner species were analysed as a test of competition.
3. Miners co-occurred on leaves more often that expected by chance (P<0.05) in six of ten possible species combinations and log-linear model analysis showed no negative higher-order interactions.
4. All five miner species had highly clumped distributions between leaves (P<0.01).
5. Leaf miner survival was less than expected for four of five species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone (P<0.05).
6. We conclude that interspecific competition is unapparent within this leaf miner guild and that intraspecific competition occurs in four of the five major leaf miner species. We discuss leaf miner selection of common leaves, perhaps based on chemical/physical leaf characters, as a cause of intra- and interspecific aggregation.     

Wolbachia infection in six species of gall wasps and their parasitoids

Wolbachia are endosymbiotic bacteria that are widely present in nematodes and arthropods and sometimes have a significant impact on the evolution, ecology, and biology of their hosts. The co-occurrence of Wolbachia within both Cynipid gall wasps and their parasitoids has rarely been studied. In this study, we report the occurrence of six species of gall wasps and 10 species of their parasitoids in central China. Wolbachia detection using the wsp gene showed that Wolbachia infected two species of gall wasps as well as their parasitoids, indicating that horizontal transmission of Wolbachia occurs between gall wasps and their parasitoids. Given that parasitoids will kill their hosts, Wolbachia may be horizontally transferred from gall wasps to their parasitoids. Using multilocus sequence typing (MLST) analysis, five new strains of Wolbachia were identified, all of which belonged to supergroup A. The strains of Wolbachia that infected gall wasps were not the same as those that infected their parasitoids. This result indicated that Wolbachia may evolve independently in parasitoids after they have been transferred from the host gall wasps.     

Guild structures of seed insects in relation to acorn development in two oak species

We investigated patterns of acorn growth in Quercus variabilis Blume and Quercus serrata Thunb., seasonal trends in emergence of seed insects found in the acorns, oviposition periods of the insects and falling periods of insect-infested acorns. In Q. variabilis, two insect guilds were associated with acorn development: (i) the immature acorn feeding (IAF) guild [Curculionidae sp., Poecilips cardamomi (Schaufuss), and Characoma ruficirra (Hampson)]; and (ii) the mature acorn feeding (MAF) guild [Curculio robustus (Roelofs), Curculio sikkimensis (Heller), and Cydia glandicolana (Danilevsky)]. In Q. serrata, there were three guilds: (i) the pistillate flower feeding (PFF) guild (cynipid wasp); (ii) the IAF guild [sap absorption by Mechoris ursulus (Roelofs)]; and (iii) the MAF guild (M. ursulus, C. sikkimensis, Cydia danilevskyi (Kuznetzov), C. glandicolana and Autostichidae sp.). The succession of guilds during acorn development may be a consequence of the use by different species of the limited food resource. The lack of a PFF guild in Q. variabilis that was found in our field site would have a positive effect on IAF guilds in utilizing the acorns.     

Seasonal occurrence of postharvest dried fruit insects and their parasitoids in a culled fig warehouse

Parasitoids of dried-fruit insects were surveyed at a culled fig warehouse in Fresno, CA. Three parasitoids of pyralid larvae were found: Habrobracon hebetor (Say), Venturia canescens (Gravenhorst), and at least one species in the genus Goniozus F?rster. Two parasitoids of pyralid pupae also were noted: Mesostenus gracilis (Cresson) and a new species of Psilochalcis Keifer. The latter is a new host association. Several beetle parasitoids were present, including Anisopteromalus calandrae (Howard), three species of Cephalonomia Westwood, Laelius centratus (Say), and Cerchysiella utilis Noyes. C. utilis, a parasitoid of driedfruit beetle, Carpophilus hemipterus (L.), is a new record for California. Most activity by parasitoids (detected by yellow flight traps) occurred directly above the fig mass. Pyralid parasitoids exhibited two peaks of seasonal activity; one in late summer through early fall, shortly after new figs were brought into the warehouse, and one in the spring. H. hebetor generally attacked older host larvae, whereas V. canescens equally attacked older and younger larvae, indicating that these two parasitoids may coexist by exploiting different portions of the host population. H. hebetor was active throughout the winter, suggesting that winter release of H. hebetor could be used to control diapausing pyralid populations in dried fruit and nut storage areas.     

Alien arthropod predators and parasitoids: interactions with the environment

Many species of entomophagous arthropods have been introduced either intentionally (through the practice of biological control) or unintentionally to new regions. We examine interactions of these aliens with their new environments in the context of rapid global change linked to human activity. We consider effects of such interactions on establishment and spread of the alien species and effects on indigenous biota and ecosystems. Major elements of global change that affect alien-environment interactions include landscape modifications by humans (e.g., cultivation, habitat loss and fragmentation) and increases in atmospheric CO₂ and other gases resulting in climate change and other effects (e.g., changes in food quality for herbivores that affect higher trophic levels as well). Alien arthropod predators can alter landscapes for their benefit, to the detriment of indigenous species. A brief review also of blood-feeding alien arthropods makes clear that interactions with the environment critically influence invasions of zoophagous arthropods in general.     

Non-native and translocated fish species in Serbia and their impact on the native ichthyofauna

A total of 22 fish species have been introduced into the inland waters of Serbia, either intentionally or accidentally. This paper provides a summary of data concerning time and reason of introduction, mode of expansion, degree of acclimatization, impact on native fish and estimated area of recent distribution. Four of the non-native fish species currently occupy more than 51% of Serbian territory while 5 of them occupy between 21–50% of territory. This paper reviews impacts of introduced freshwater fish in Serbia based on collected data.     

Survey traps for parasitoids, and coccinellid predators of the citrus blackfly, Aleurocanthus woglumi

The attractiveness of sticky traps of eight colors for two parasitoids Amitus hesperidum Silverstri and Prospaltella opulenta Silvestri, and seven species of coccinellid predators of the citrus blackfly, Aleurocanthus woglumi Ashby (Homoptera: Aleyrodidae) was evaluated in insectory and field tests.Yellow traps captured significantly more parasitoids and coccinellids than other colors tested; captures were greatest in traps placed in the lower half of citrus trees. These traps can be used to survey for and monitor the population trends of the citrus blackfly and its natural enemies.

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Résumé Nous avons évalué l'attraction de Amitus hesperidum Silvestri et Prospaltella opulenta Silvestri, parasitoïdes d'Aleurocanthus woglumi Ashby et de 7 espèces de Coccinellides prédatrices de cette espèce, par des pièges à glu de 8 couleurs différentes (jaune, orange, rouge, bleu, vert, noir, blanc et transparent).Les pièges jaunes capturent significativement plus de parasitoïdes et de coccinelles que les autres couleurs; les captures sont plus importantes avec des pièges placés dans la moitié inférieure des citronniers. Ces pièges peuvent être utilisés pour suivre et contrôler l'évolution des populations d'A. woglumi et de ses parasitoïdes et coccinelles prédatrices.

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Fla. Agr. Exp. Stn. J. Ser. No. 2271     

Tri-trophic interactions among congeneric sympatric host plants of Chamaecrista, seed predators and parasitoids

The defensive role against seed predation of a set of plant traits in 13 congeneric sympatric taxa (Chamaecrista: Leguminosae), and the influence of the third trophic level on seed predators’ performance and host range were investigated. Taxa co-occur in rupestrian grasslands in Serra do Cipó, Brazil, and belong to three taxonomic sections. Fruit production, fruit pubescence, and seed size were analyzed. Measures of these traits in the 13 taxa were regressed separately against seed predation rates by endophagous and ectophagous insects. Time of seed production and fruit pubescence showed no influence on seed predation rates by either predator type. Seed size was positively correlated to bruchid seed predation, but negatively related to ectophagous seed predation. There was a negative correlation between glandular fruit trichome length and parasitism rates of bruchids, suggesting that seed predation pressure may have produced evolutionary responses from plants (fruit trichome reduction), which should facilitate parasitoid action.     

麦蚜寄生蜂和捕食性天敌种群对景观复杂性的响应

农业景观结构影响昆虫的物种组成与多样性,本文选择复杂景观和简单景观的麦田景观为研究对象,研究了不同麦田景观结构对麦蚜天敌种群的影响。在简单与复杂两种景观下,分析了麦蚜寄生蜂和捕食性天敌的迁入时间、迁入量、种群增长率及种群密度之间的差异。结果表明:复杂景观中麦蚜寄生蜂和捕食性天敌的物种多样性较高,复杂景观下寄生蜂的迁入量高于简单景观下寄生蜂的迁入量。景观复杂性同样影响捕食性天敌的迁入时间,且捕食性天敌在复杂景观下迁入量均高于简单景观,而且存在显著性差异。两种景观中寄生蜂和捕食性天敌种群增长速率与最大种群密度均存在显著性差异。     

Reactions of various predators to insects storing heart poisons (cardiac glycosides) in their tissues

Notes are given of experiments in which mammals and birds were fed with insects which sequester and store cardiac glycosides, and the insensi-tivity of the quail (Coturnix japonicus Tern.) to these substances is recorded. The variation in predators' reactions to toxic insects is discussed.     

Genetic diversity, structure, and demographic change in tanoak, Lithocarpus densiflorus (Fagaceae), the most susceptible species to sudden oak death in California

Knowledge of population genetic structure of tanoak (Lithocarpus densiflorus) is of interest to pathologists seeking natural variation in resistance to sudden oak death disease, to resource managers who need indications of conservation priorities in this species now threatened by the introduced pathogen (Phytophthora ramorum), and to biologists with interests in demographic processes that have shaped plant populations. We investigated population genetic structure using nuclear and chloroplast DNA (cpDNA) and inferred the effects of past population demographic processes and contemporary gene flow. Our cpDNA results revealed a strong pattern of differentiation of four regional groups (coastal California, southern Oregon, Klamath mountains, and Sierra Nevada). The chloroplast haplotype phylogeny suggests relatively deep divergence of Sierra Nevada and Klamath populations from those of coastal California and southern Oregon. A widespread coastal California haplotype may have resulted from multiple refugial sites during the Last Glacial Maximum or from rapid recolonization from few refugia. Analysis of nuclear microsatellites suggests two major groups: (1) central coastal California and (2) Sierra Nevada/Klamath/southern Oregon and an area of admixture in north coastal California. The low level of nuclear differentiation is likely to be due to pollen gene flow among populations during postglacial range expansion.     

Host range in phytophagous insects: the potential role of generalist predators

Summary The potential role of generalist natural enemies is presented as one of the important ecological pressures that select for narrow host range in phytophagous insects, and dominant relative to physiological bases for specialization. Experiments are described in three completely different systems indicating that generalist herbivores are more vulnerable to predation than specialist herbivores. The three predators were (a) the vespid waspMischocyttarus flavitarsus, (b) the Argentine antIridomyrmex humilis and (c) the coccinellid beetleHippodamia convergens. It is concluded the predators may provide strong selection pressure for maintenance and perhaps evolution of narrow host range in insect herbivores.     

15N-enrichment of plant tissue to mark phytophagous insects, associated parasitoids, and flower-visiting entomophaga

New techniques are presented on the use of ¹⁵N to mark insects. ¹⁵N, a stable isotope of nitrogen, was enriched above natural abundance in plant and insect tissues. Two laboratory studies demonstrated that enriched ¹⁵N-concentrations could be tracked from plant to insect using mass spectrometry. In the first study, adult Cotesia plutellae (Kurdjimov) (Hymenoptera: Braconidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were allowed to feed at the flowers of rapid-cycling Chinese cabbage plants that had been fertilized with ¹⁵N-enriched potassium nitrate (KNO₃-¹⁵NO₃). Both insect groups were found to have significantly elevated ¹⁵N levels after visiting the flowers of the ¹⁵N-enriched plants for 48 hours. In the second study, ¹⁵N-enriched bean plant (Phaseolus vulgaris L.) tissue was incorporated into an insect diet and fed to navel orangeworms, Amyelois transitella (Walker) (Lepidoptera: Pyralidae). When the navel orangeworm larvae were 4th instars, they were removed from the diet and exposed to the parasitoid, Goniozus legneri Gordh (Hymenoptera: Bethylidae). Results indicated that the enriched ¹⁵N-concentration of the bean plants was transferred to the navel orangeworms and, subsequently, to the parasitoids. This work may provide useful techniques to help establish whether agriculturally important entomophaga visiting ¹⁵N-enriched flowers or parasitizing enriched sentinel larvae in the field can be effectively marked with ¹⁵N.     

Discordance of species trees with their most likely gene trees

Because of the stochastic way in which lineages sort during speciation, gene trees may differ in topology from each other and from species trees. Surprisingly, assuming that genetic lineages follow a coalescent model of within-species evolution, we find that for any species tree topology with five or more species, there exist branch lengths for which gene tree discordance is so common that the most likely gene tree topology to evolve along the branches of a species tree differs from the species phylogeny. This counterintuitive result implies that in combining data on multiple loci, the straightforward procedure of using the most frequently observed gene tree topology as an estimate of the species tree topology can be asymptotically guaranteed to produce an incorrect estimate. We conclude with suggestions that can aid in overcoming this new obstacle to accurate genomic inference of species phylogenies.