Insect fauna in nests of the Eurasian griffon vulture (Gyps fulvus) in Croatia

Qualitative, quantitative and trophic structure of insects found in Eurasian griffon vulture nests were analysed. A total of 249 insects belonging to six orders were found in 18 griffon vulture nests, collected in three colonies on the islands Cres and Plavnik (Adriatic Sea). Eudominant orders were beetles (64.26%) and ants (22.49%). Dermestid beetles were present in all examined nests and comprise the permanent nest fauna. Other groups of insects (cockroaches, web spinners, ants, flies, aphids) were found to occur occasionally in nests.     

Flexible social organization and high incidence of drifting in the sweat bee, Halictus scabiosae

The very diverse social systems of sweat bees make them interesting models to study social evolution. Here we focus on the dispersal behaviour and social organization of Halictus scabiosae , a common yet poorly known species of Europe. By combining field observations and genetic data, we show that females have multiple reproductive strategies, which generates a large diversity in the social structure of nests. A detailed microsatellite analysis of 60 nests revealed that 55% of the nests contained the offspring of a single female, whereas the rest had more complex social structures, with three clear cases of multiple females reproducing in the same nest and frequent occurrence of unrelated individuals. Drifting among nests was surprisingly common, as 16% of the 122 nests in the overall sample and 44% of the nests with complex social structure contained females that had genotypes consistent with being full-sisters of females sampled in other nests of the population. Drifters originated from nests with an above-average productivity and were unrelated to their nestmates, suggesting that drifting might be a strategy to avoid competition among related females. The sex-specific comparison of genetic differentiation indicated that dispersal was male-biased, which would reinforce local resource competition among females. The pattern of genetic differentiation among populations was consistent with a dynamic process of patch colonization and extinction, as expected from the unstable, anthropogenic habitat of this species. Overall, our data show that H. scabiosae varies greatly in dispersal behaviour and social organization. The surprisingly high frequency of drifters echoes recent findings in wasps and bees, calling for further investigation of the adaptive basis of drifting in the social insects.     

Population differences in host plant preference and the importance of yeast and plant substrate to volatile composition

Divergent selection between environments can result in changes to the behavior of an organism. In many insects, volatile compounds are a primary means by which host plants are recognized and shifts in plant availability can result in changes to host preference. Both the plant substrate and microorganisms can influence this behavior, and host plant choice can have an impact on the performance of the organism. In Drosophila mojavensis, four geographically isolated populations each use different cacti as feeding and oviposition substrates and identify those cacti by the composition of the volatile odorants emitted. Behavioral tests revealed D. mojavensis populations vary in their degree of preference for their natural host plant. Females from the Mojave population show a marked preference for their host plant, barrel cactus, relative to other cactus choices. When flies were given a choice between cacti that were not their host plant, the preference for barrel and organ pipe cactus relative to agria and prickly pear cactus was overall lower for all populations. Volatile headspace composition is influenced by the cactus substrate, microbial community, and substrate‐by‐microorganism interactions. Differences in viability, developmental time, thorax length, and dry body weight exist among populations and depend on cactus substrate and population‐by‐cactus interactions. However, no clear association between behavioral preference and performance was observed. This study highlights a complex interplay between the insect, host plant, and microbial community and the factors mediating insect host plant preference behavior.     

Interaction of diffuse competition and insect herbivory in limiting brittle prickly pear cactus,Opuntia fragilis (Cactaceae)

We tested the effects of above- and belowground competition and evaluated insect herbivory on the growth of a common cactus (Opuntia fragilis) in Sandhills prairie. Our purpose was to determine the independent and joint contribution of these factors to the variation observed in cactus size and local abundance. We manipulated ambient prairie vegetation and surface water availability in a full factorial design. When Opuntia fragilis was released from competition with surrounding vegetation, it grew significantly larger in the second growing season, both in terms of number and size of new cladodes. Ramets grown within live prairie vegetation averaged no net growth. These ramets were also more frequently fed upon by the larvae of two internally feeding cactus insects. As a result, insect herbivory reinforced the competitive suppression of the cactus by grasses. Water supplementation had no significant effect, either on cactus growth or on insect herbivory. We conclude that the mechanism by which dense prairie vegetation influenced net growth of O. fragilis was both direct, through competition for nonwater resources such as light, and indirect, through its mediation of feeding by specialized insect herbivores. Furthermore, since the direct growth response to treatment did not precede the indirect effect of habitat-mediated variation in feeding by insects, our results contradict the current expectation that indirect effects require more time to be expressed than do direct effects.     

The nesting biology of Archbold's Bowerbird Archboldia papuensis and a review of that of other bowerbirds (Ptilonorhynchidae)

Thirteen active and 14 old Archbold's Bowerbird Archboldia papuensis nests were studied in Tari Gap, Southern Highlands, Papua New Guinea. Clutch size was one egg. At two nests, only one-parent nest attendance was observed. Incubation and nestling periods were considerably longer and nestling growth slower than in other bowerbird species, possibly reflecting adaptation to a colder environment depauperate in insects. Of 382 identified nestling meals, 71% were exclusively fruit (14 spp. identified) and 29% were animal. Of 112 animal meals, 30% were skinks (Reptilia), 28% were small arthropods, 17% were beetles and the remainder (25%) were larger insects, pieces of nestling birds and unidentified items. Most active nests were built adjacent to older nests and the significance of this is discussed.     

Nest-site competition between bumblebees (Bombidae), social wasps (Vespidae) and cavity-nesting birds in Britain and the Western Palearctic

Capsule There is no evidence of widespread significant nest-site competition in Britain or the Western Palearctic between cavity-nesting birds and bumblebees or social wasps.

Aims To investigate competition between cavity-nesting birds and bumblebees and wasps, particularly the range-expanding Tree Bumblebee, Saxon Wasp and European Hornet in Britain, and review evidence throughout the Western Palearctic.

Methods We compared field data from English and Polish studies of tits and woodpeckers breeding in nest-boxes and/or tree holes to assess nest-site competition with bumblebees and wasps. We reviewed the literature quantifying nest-site competition between birds and these insects in the Western Palearctic.

Results Bumblebees and wasps are capable of usurping small passerines from nests. In England, these insects commandeered a mean annual 4.1% of tit nests initiated in nest-boxes; occurrence of hornets showed a long-term increase, but not other wasps or bumblebees. Across the Western Palearctic, insect occupation of nest-boxes was generally low, and was lower in England than in Poland. No insects were discovered in tree cavities, including those created by woodpeckers (Picidae).

Conclusion Nest-site competition between cavity-nesting birds and bumblebees and wasps appears to be a ‘nest-box phenomenon’, which may occasionally interfere with nest-box studies, but appears negligible in natural nest-sites.     

Bacterial succession in necrotic tissue of agria cactus (Stenocereus gummosus).

The bacterial communities associated with the development of necroses in injured agria cactus tissue were examined in the field by using both human-induced injuries and cactus tissue inoculated with cactophilic bacteria. Whole-cell bacterial fatty acids were used to determine when and where each of 23 detected species occurred. This information was then used to describe successional patterns of bacterial colonization. Although the number of bacterial species in human-induced injuries reached a maximum on day 16, the Shannon-Weaver diversity index increased to a plateau, which reflects a stable bacterial community. The potential of the bacterial community to macerate the injured cactus tissue was also examined, and the results indicate that the bacteria initially colonizing the newly injured cactus tissue were more likely to contain pectinolytic, proteolytic, and lipolytic enzymes than were the bacteria entering the injuries once tissue maceration had already begun. The cactophilic fruit fly Drosophila mojavensis has been previously shown to carry bacteria to newly injured cactus tissue. In these studies, exclusion of these insects did not significantly affect bacterial succession or community structure. This supports our contention that bacteria colonize injured tissue primarily by passive transport, e.g., on wind-blown particles.     

Biology of the solitary wasp Trypoxylon (Trypargilum) agamemnon Richards 1934 (Hymenoptera: Crabronidae) in trap‐nests

Buschini, M.L.T. and Fajardo, S. 2009. Biology of the solitary wasp Trypoxylon (Trypargilum) agamemnon Richards 1934 (Hymenoptera: Crabronidae) in trap‐nests. —Acta Zoologica (Stockholm) 91 : 426–432. Some Trypoxylon species build their nests in preexisting tubular cavities like hollow stems and beetle borings in branches. Study of the biology of these insects is relatively easy because the females of these wasps nest with enormous success in trap‐nests. The aim of this study was to investigate the abundance, seasonality and life‐history of Trypoxylon agamemnon. For capture of these insects, trap‐nests were installed in the Parque Municipal das Araucárias in araucaria forest, grassland and swamp, from December, 2001 to December, 2005. Two hundred and ninety seven nests were obtained. They were constructed more often during the summer (from December to April). The nests were built only in araucaria forest and consisted of a linear series of cells, divided by mud partitions, whose number varied from 1 to 7. Normally they have only one vestibular cell. The inner cells had been provisioned, usually with spiders of Anyphaenidae family. Sex‐ratio was strongly female biased. Its main natural enemies included Chrysididae, Ichneumonidae and Tachinidae.     

巢居蚂蚁更倾向于在人造光源附近定居繁殖

光污染被认为是“环境陷阱”, 可以聚集周围的昆虫。而昆虫的聚集和光源本身可能会吸引捕食性昆虫在光源附近定居繁殖, 从而改变昆虫群落的结构, 威胁昆虫多样性和生态系统服务功能。蚂蚁(膜翅目)是昆虫中的优势类群, 能提供多种生态系统服务功能, 其中有许多巢居型蚂蚁利用中空的树枝或者竹子筑巢繁殖, 是森林中非常重要的捕食者和分解者。然而, 光污染对巢居蚂蚁群落的影响尚不清楚。本研究以巢居蚂蚁为研究对象, 探究在雨季和干季3种不同生境(原始林、次生林、橡胶林)中发光二极管(LED灯)在空间距离上对巢居蚂蚁筑巢模式以及群落组成的影响。我们在3种生境中共安装了15个LED灯, 并在距离光源0 m、10 m、50 m和100 m处设置不同入口大小的人工竹巢, 7周后回收。竹巢中共发现蚂蚁40种形态种, 隶属于12个属, 其中弓背蚁属(Camponotus)是优势属。接近光源处的竹巢占用率最高, 且在干季最明显; 在远离光源处(10-100 m)占用率较低, 并且在3种不同的生境呈现相同的模式。竹巢入口大小对竹巢占用率没有显著影响。雨季和干季的蚂蚁群落组成差异显著; 干季原始林和次生林、次生林和橡胶林蚂蚁群落组成有弱显著差异; 在3种生境中不同灯距下蚂蚁群落组成没有显著差异。我们的研究表明, 光污染增加了巢居蚂蚁在光源处的筑巢密度, 影响蚂蚁群落组成和空间分布。     

Behavioral evolution accompanying host shifts in cactophilic Drosophila larvae

For plant utilizing insects, the shift to a novel host is generally accompanied by a complex set of phenotypic adaptations. Many such adaptations arise in response to differences in plant chemistry, competitive environment, or abiotic conditions. One less well‐understood factor in the evolution of phytophagous insects is the selective environment provided by plant shape and volume. Does the physical structure of a new plant host favor certain phenotypes? Here, we use cactophilic Drosophila, which have colonized the necrotic tissues of cacti with dramatically different shapes and volumes, to examine this question. Specifically, we analyzed two behavioral traits in larvae, pupation height, and activity that we predicted might be related to the ability to utilize variably shaped hosts. We found that populations of D. mojavensis living on lengthy columnar or barrel cactus hosts have greater activity and pupate higher in a laboratory environment than populations living on small and flat prickly pear cactus cladodes. Crosses between the most phenotypically extreme populations suggest that the genetic architectures of these behaviors are distinct. A comparison of activity in additional cactophilic species that are specialized on small and large cactus hosts shows a consistent trend. Thus, we suggest that greater motility and an associated tendency to pupate higher in the laboratory are potential larval adaptations for life on a large plant where space is more abundant and resources may be more sparsely distributed.     

Comparative and population genomics approaches reveal the basis of adaptation to deserts in a small rodent

Organisms that live in deserts offer the opportunity to investigate how species adapt to environmental conditions that are lethal to most plants and animals. In the hot deserts of North America, high temperatures and lack of water are conspicuous challenges for organisms living there. The cactus mouse (Peromyscus eremicus) displays several adaptations to these conditions, including low metabolic rate, heat tolerance, and the ability to maintain homeostasis under extreme dehydration. To investigate the genomic basis of desert adaptation in cactus mice, we built a chromosome‐level genome assembly and resequenced 26 additional cactus mouse genomes from two locations in southern California (USA). Using these data, we integrated comparative, population, and functional genomic approaches. We identified 16 gene families exhibiting significant contractions or expansions in the cactus mouse compared to 17 other Myodontine rodent genomes, and found 232 sites across the genome associated with selective sweeps. Functional annotations of candidate gene families and selective sweeps revealed a pervasive signature of selection at genes involved in the synthesis and degradation of proteins, consistent with the evolution of cellular mechanisms to cope with protein denaturation caused by thermal and hyperosmotic stress. Other strong candidate genes included receptors for bitter taste, suggesting a dietary shift towards chemically defended desert plants and insects, and a growth factor involved in lipid metabolism, potentially involved in prevention of dehydration. Understanding how species adapted to deserts will provide an important foundation for predicting future evolutionary responses to increasing temperatures, droughts and desertification in the cactus mouse and other species.     

Specialised placement of morphs within the gall of the social aphid <Emphasis Type="Italic">Pemphigus spyrothecae</Emphasis>

Background  

The strategic placement and aggregation of certain castes within the nests of eusocial insects such as bees and ants results in complex colonies that enjoy increased fitness through improved efficiency of social tasks. To examine if this advanced social phenomenon might apply to social aphids, the location of the numerous morphs within the nests (plant galls) of the aphid species Pemphigus spyrothecae was examined.     

日本弓背蚁亲系识别的研究

亲系识别在社会昆虫活动中具有重要作用 ,为当前社会昆虫学研究中的五大热点之一。本文对采自西安地区 4巢日本弓背蚁 Camponotusjaponicus Mayr进行了进攻性行为测试 ,并结合酯酶、苹果酸脱氢酶同工酶电泳对亲系识别进行了综合研究。结果显示行为识别与同工酶电泳反应出的亲缘关系有一定相关性。     

Demographic models reveal the shape of density dependence for a specialist insect herbivore on variable host plants

1. It is widely accepted that density-dependent processes play an important role in most natural populations. However, persistent challenges in our understanding of density-dependent population dynamics include evaluating the shape of the relationship between density and demographic rates (linear, concave, convex), and identifying extrinsic factors that can mediate this relationship. 2. I studied the population dynamics of the cactus bug Narnia pallidicornis on host plants (Opuntia imbricata) that varied naturally in relative reproductive effort (RRE, the proportion of meristems allocated to reproduction), an important plant quality trait. I manipulated per-plant cactus bug densities, quantified subsequent dynamics, and fit stage-structured models to the experimental data to ask if and how density influences demographic parameters. 3. In the field experiment, I found that populations with variable starting densities quickly converged upon similar growth trajectories. In the model-fitting analyses, the data strongly supported a model that defined the juvenile cactus bug retention parameter (joint probability of surviving and not dispersing) as a nonlinear decreasing function of density. The estimated shape of this relationship shifted from concave to convex with increasing host-plant RRE. 4. The results demonstrate that host-plant traits are critical sources of variation in the strength and shape of density dependence in insects, and highlight the utility of integrated experimental-theoretical approaches for identifying processes underlying patterns of change in natural populations.     

BIRD-INSECT NESTING ASSOCIATIONS IN AUSTRALIA.

Australian records, beginning in 1866, of birds associating with aggressive insects for nesting purposes are assembled. Five species of the genus Gerygone are known to associate with wasps, more or less consistently, in tropical areas, and another species is reported as associating with wasps in the tropics and ants in temperate areas. Such birds deliberately seek the society of the insects, by which they are recognized and tolerated.
If protection is the motive, it would seem to be aimed against reptiles rather than against other birds or mammals. Other possible reasons for the practice ate suggested.
Australian records of insects frequenting birds' nests also are summarized; these include parasites such as the blood-sucking larvae of a fly, together with moth, beetle and fly larvae that serve a beneficial purpose as scavengers, and, in addition, wasps and beetles parasitic on the other insects. On the question of how the insects find the nests at appropriate times, it is suggested that some are guided by odour and others by some undetermined influence.     

Colony structure and spatial distribution of food resources in the polydomous meat ant <Emphasis Type="Italic">Iridomyrmex purpureus</Emphasis>

Polydomous social insects may reduce the costs of foraging by the strategic distribution of nests throughout their territory or home-range. This efficiency may most likely be achieved if the resources are relatively stable in place and time, and the colonies and nests are distributed in response to the location of the resources. However, no study has investigated how the distribution of food sources influences the spatial patterns of nests within polydomous colonies under natural conditions. Our two year study of 140 colonies of the Australian ant Iridomyrmex purpureus revealed that the decentralization of nests within colonies is associated with the distribution of trees containing honey-dew producing hemiptera. We show there is a positive correlation between the maximum distance between trees containing hemiptera and the maximum distance between nests within a colony. In addition, we demonstrate the mechanism by which this pattern may arise; new nests are built nearer to trees containing hemiptera than existing nests. Further, the distance between trees containing hemiptera and the nearest nests was negatively correlated with the length of exploitation of that tree. Finally, we show that most food is delivered to the nearest nest after which other ants redistribute it between the nests. Combined, these data suggest that foraging efficiency may be an important selection pressure favouring polydomy in I. purpureus. Received 6 April 2006; revised 29 September; accepted 4 October 2006.     

Mating frequency and mating system of the polygynous ant, Leptothorax acervorum

Multiple mating by queens (polyandry) and the occurrence of multiple queens in the same colony (polygyny) alter patterns of relatedness within societies of eusocial insects. This is predicted to influence kin-selected conflicts over reproduction. We investigated the mating system of a facultatively polygynous UK population of the ant Leptothorax acervorum using up to six microsatellite loci. We estimated mating frequency by genotyping 79 dealate (colony) queens and the contents of their sperm receptacles and by detailed genetic analysis of 11 monogynous (single-queen) and nine polygynous colonies. Results indicated that 95% of queens were singly mated and 5% of queens were doubly mated. The corrected population mean mating frequency was 1.06. Parentage analysis of adults and brood in 17 colonies (10 monogynous, 7 polygynous) showed that female offspring attributable to each of 31 queens were full sisters, confirming that queens typically mate once. Inbreeding coefficients, queen-mate relatedness of zero and the low incidence of diploid males provided evidence that L. acervorum sexuals mate entirely or almost entirely at random. Males mated to queens in the same polygynous colony were not related to one another. Our data also confirmed that polygynous colonies contain queens that are related on average and that their workers had a mixed maternity. We conclude that the mating system of L. acervorum involves queens that mate near nests with unrelated males and then seek readoption by those nests, and queens that mate in mating aggregations away from nests, also with unrelated males.     

Bacteria associated with Copestylum (Diptera, Syrphidae) larvae and their cactus host Isolatocereus dumortieri

We describe the gut bacterial diversity inhabiting two saprophagous syrphids and their breeding substrate (decayed tissues of the columnar cactus Isolatocereus dumortieri). We analyzed the gut microbiota of Copestylum latum (scooping larvae that feed on decayed cactus tissues) and Copestylum limbipenne (whose larvae can also feed on semiliquid tissues) using molecular techniques. DNA was extracted from larval guts and cactus tissues. The V1-V3 region of the 16S rRNA genes was amplified and sequenced. A total of 31,079 sequences were obtained. The main findings are: C. limbipenne is dominated by several Enterobacteriaceae, including putative nitrogen-fixing genera and pectinolitic species and some denitrifying species, whereas in C. latum unclassified Gammaproteobacteria predominate. Decayed tissues have a dominant lactic acid bacterial community. The bacterial communities were more similar between larval species than between each larva and its breeding substrate. The results suggest that the gut bacterial community in these insects is not strongly affected by diet and must be dependent on other factors, such as vertical transmission, evolutionary history and host innate immunity.     

NOTES ON SOME ANTS IN NORTHERN SOMALIA

The paper describes observations made over a period of two years on the feeding habits, general ecology and distribution of five species of ants (harvester-, stink-, soldier-, tree-, and sugar-ants) in Northern Somalia, p-incipally in the plains and bushland of the Haud.
Harvester and stink ants are discussed in some detail, and some dimensions of excavated nests and runways are given. The occurrence of associated insects is noted and the ecological roles of seed-eating and predatory ants (particularly in relation to termites) are discussed.
There are notes on the climate and topography of the region, and a glossary of vernacular names is appended.     

Indirect versus direct effects of grasses on growth of a cactus (Opuntia fragilis): insect herbivory versus competition

Variation in plant performance between microhabitats is usually attributed to direct mechanisms, such as plant physiological tolerances or competitive interactions. However, indirect mechanisms, such as differences in herbivore pressure mediated by microhabitat differences, could create the same pattern of variation. In this study, we investigated the effect of insect herbivore pressure on the growth of the grassland cactus Opuntia fragilis under different regimes of grassland canopy cover. Our purpose was to establish the extent to which canopy cover plays a direct, competitive role versus an indirect, mediatory role in cactus growth. We manipulated aboveground microhabitat, specifically the cover of adjacent grasses. The three treatments were: (1) open canopy, with grass pinned down away from the cactus; (2) shaded canopy, with a partial mesh cage staked over the cactus; and (3) ambient grass canopy. We measured seasonal plant growth and recorded changes in insect herbivore occurrence and damage in relation to cover. Cactus growth, defined as the change in number of live cladodes, was higher in the open than under either treatment where the plant was more shaded (P<0.05). However, allocation to new growth, measured as the proportion of new segments (cladodes) in a patch, did not differ among cover treatments. Thus, the hypothesis that physiological constraints, or competition for light, limited cactus performance in grass is rejected. Instead, we found that both cladode mortality, caused by the larvae of a cactus moth borer (Melitara dentata), and occurrence of the moth were lower in the open microhabitat than in either shaded microhabitat. Thus, higher net growth in the open, unshaded treatment, rather than representing a release from competition for light with grasses, was better explained as an indirect effect of grass cover on the activity and impact of the cactus moth. These results show that indirect effects can lead to a misinterpretation of experimental data on direct effects. These data also contribute to an improved understanding of mixed results in the biological control of weedy cacti. Clearly, future evaluations of the relative importance of physiology, competition, and insect herbivory in plant performance must be environmentally explicit.