Bo G. Svensson

Habitat preferences of nest-seeking bumble bees (Hymenoptera: Apidae) in an agricultural landscape.

The aim of this study was to find out where bumble bee queens place their nests in the agricultural landscape. Nest-seeking behaviour was used to indicate nesting site preferences. Four types of agricultural landscape were investigated near Uppsala, Sweden: open, relatively open, relatively wooded and wooded. Twelve 500-metre-long transects, each including several intermingled habitats (e.g., field boundaries, pastures, clearings), were inspected repeatedly over a two-month period, from April to June 1991. In total, 147 observations of bumble bee queens (Bombus spp.) of eight species were recorded. Nest-seeking queens were observed most frequently along forest boundaries and field boundaries, in open uncultivated areas and in the relatively open landscape, whereas they were least frequent in forest and in clearings. Fields, pastures and road boundaries had intermediate frequencies. Differences among species were found in terms of both landscape type and habitat preferences: B. terrestris, B. lapidarius, B. sylvarum and B. subterranius preferred open terrain, whereas B. lucorum and B. pascuorum preferred forest boundaries. Withered grass and tussocks were the preferred nest-seeking patches among all species.

Nuptial gift size prolongs copulation duration in the dance fly Empis borealis

Abstract. 1. The time that pairs of the dance fly Empis borealis (L.) (Diptera: Empididae) spent in copula was positively correlated with the volume of the nuptial gift.

Why do males of the dance fly Empis borealis refuse to mate? the importance of female age and size

Empis borealisfemales form swarms, and males carrying a nuptial gift come to swarms to mate. Males either mated with one of the females (accepted swarms) or left swarms without mating (refused swarms). Males mated with the younger (low wing-wear) and relatively larger females in accepted swarms. They seemed to be able to judge the relative size of the females but to ignore their absolute size. Visiting males stayed shorter in accepted swarms as female size variation increased. This probably reflects their greater ease in choosing a mate among females of relatively different sizes. Females in accepted swarms tended to be larger and to have less worn wings than females in rejected swarms.

Why insects swarm: testing the models for lek mating systems on swarming Empis borealis females

SummaryFemale dance-flies, Empis borealis L., gather to swarm, and males carrying nuptial gifts visit swarms for mating. Field observations and experiments were performed on this behaviorally sex-role reversed species to test models of lekking behavior. The key predictions were: (1) female preference model: male visiting rate and mating rate should increase with the number of females in swarm (swarm size), (2) hotspot model: male visiting rate should be independent of swarm size, and (3) hotshot model: swarm size should be positively correlated with the body size of the largest female in swarm. We found that male visiting rate and mating rate increased with swarm size, and that mating rate per female increased with swarm size. Males also mated more often in larger swarms than in smaller ones. Both males and females visited swarm sites even in the absence of other individuals. When females were successively removed from swarm sites more males than females on average arrived at these sites: 2.25 males per female. When no individuals were present at the swarm site, arriving males moved on to another site, whereas arriving females generally stayed. Larger experimental swarm-markers attracted both more males and more females and even more males when swarming females were present. There was no correlation between mean or median female size in swarms and the number of females in swarms. Thus, the female preference model and the hotspot model were corroborated, while other models were judged unlikely to explain swarming behavior in E. borealis.

Marking pheromones ofAlpinobombus males

The male marking pheromone blends which emanate from the cephalic part of the labial gland, have been analyzed in four species of the bumble bee genusAlpinobombus, viz.,A. alpinus,A. balteatus, A. hyperboreus, andA. polaris, by combined capillary gas chromatography, mass spectrometry, and thin-layer chromatography. In all, 36 specimens were analyzed.A. alpinus andA. polaris, which are similar morphologically, both showed an acetogenic composition of the pheromone blend. The dominant compound inA. alpinus proved to be a hexadecenol, whereasA. polaris had a hexadecadienol and a hexadecenol in the proportions 5∶2 as major components.A. balteatus andA. hyperboreus, another species pair as regards their morphology, differed more in their chemical makeup. Both mevalogenins and acetogenins were found in their marking secretions.A. balteatus is unique among all other male bumble bee species analyzed, 29 in total, by having C12- and C14-butyrates in the secretion, which dominated together with tetradecyl acetate and geranylcitronellol. InA. hyperboreus the main marking compounds are an octadecenol and 2,3-dihydro-6-trans-farnesol. This species also contains citronellol and geranylcitronellol.

Systematic relationship of halictinae bees based on the pattern of macrocyclic lactones in the Dufour gland secretion

Abstract The volatile Dufour gland secretion from 16 species within the subfamily Halictinae has been studied by gas chromatography and mass spectrometry. Isolation and identification was performed on single individuals. From 1 to 15 individuals of each species were collected and chemically analyzed over a period of 1 to 5 yr. The secretions of each species were found to be built up by characteristic combinations of saturated and mono-unsaturated macrocyclic C16-, C18-, C20-, C22- and C24-lactones, together with some straight chain hydrocarbons. Individuals of each species did not vary appreciably in the set-up of their secretions. Of the species studied five represent the genus Halictus and 11 represent the genus Lasioglossum. H. eurygnathus and H. rubicundus, which belong to the subgenus Halictus, have 24-tetracosanolide and 22-docosanolide as the main volatile constituents, whereas L. albipes and L. calceatus, which belong to the subgenus Evylaeus, have 16-hexadecanolide as the dominating volatile component. Based on the pattern of compounds in the secretions of the species, the systematical relationships between these species are discussed.

Swarming Behavior, Sexual Dimorphism, and Female Reproductive Status in the Sex Role-Reversed Dance Fly Species Rhamphomyia marginata

Dance flies are predaceous insects which often form male mating swarms. In many species males prior to swarming catch an insect prey, which is presented to the female at mating. In Rhamphomyia marginata, females in contrast to males gather to swarm, while males carrying a prey visit swarms for mating. Here I describe the swarming and courtship behavior in R. marginata and provide data on sexual dimorphism and swarming female reproductive status. Females swarm in small clearings in the forests. There was no specific swarm-maker. The swarming period lasted for 2–3 h and peaked around sunset. Identical swarm sites were used each evening and for several years. The mean number of females in swarms (swarm sites with at least one female) was 9.9 ± 9.1 (range, 1–40; n = 107) in 1993 and 7.1 ± 7.0 (range, 1–35; n = 68) in 1994. No obvious competition between females in swarms was observed. The operational sex ratio in swarms was extremely female biased (all swarms, 0.04). Less than one-third of male visits to swarms resulted in mating and males were found more often in larger swarms. Nuptial prey consisted of male midges. Females seem to mate more than once. Swarming females had undeveloped eggs, whereas mated females in swarms had further developed eggs than unmated females. Amount of sperm in the spermatheca was correlated with egg size. Amount of sperm and egg size did not correlate with wet weight, wing length, or wing load, except for egg size and weight. The wing coloration pattern and shape in R. marginata females are unique among dance flies, being greatly enlarged (1.6 times larger than that of males) and bicolored (gray part, 60% of wing area). When females, instead of males, possess extravagant secondary sexual characters, it is predicted from sexual selection theory that females should compete for males and that males should be selective in their choice of partner. A sex-role reversal will evolve when assess to males limit female reproductive success. The dance fly species R. marginata, like Empis borealis, another dance fly species studied earlier and discussed here, seems to fit these predictions.

Pyrobombus lapponicus auct., in Europe recognized as two species: P. lapponicus (Fabricius, 1793) and P. monticola (Smith, 1849) (Hymenoptera, Apoidea, Bombinae)

Pyrobombus (Pyrobombus) lapponicus (Fabricius, 1793) and P. (P.) monticola (Smith, 1849) are described from type material. The male and worker are described of the former; the lectotype and a paralectotype (worker) are designated and in addition the male of P. monticola is described. Type studies of rondoui Vogt, 1909 and scandinavicus Friese, 1911, previously regarded as subspecies of P. lapponicus, revealed conspecificity with P. monticola. Furthermore, the subspecies hypsophilus Skorikov, 1912 and konradini Reinig, 1965 are also regarded as forms of P. monticola. The status of glacialis Schneider, 1902 is uncertain. P. lapponicus is distributed in northern Europe: Fennoscandia - eastwards in the northern parts of the USSR, while P. monticola exhibits a boreo-alpine distribution: Fennoscandia, eastwards on the Kola peninsula, the British Isles, Italy, the Pyrenees, the Alps and the Balkan mountains. In Fennoscandia P. lapponicus is found both in alpine/subalpine habitats and in adjacent coniferous forests, whereas P. monticola is restricted to alpine/subalpine areas. A comparative diagnosis of the two species, reinforced by drawings, is given. Metric studies of male abdominal sternite 7, hind basitarsus and position of ocelli on the vertex of queens were made to establish their diagnostic value. Some remarks on the biology of both species are also provided. The status of the Nearctic forms allied to P. lapponicus are discussed.

Flagellar Sensilla of Sphecodes Bees (Hymenoptera, Halictidae)

The antenna of Sphecodes bees were investigated as regards the type and distribution of the sensilla. Eleven species originating from Sweden were used. Totally 325 specimens were studied. The distribution of sensilla placodea and sensilla trichodea on the antennal segments were studied in the light stereomicroscope. One to three antennae per species were also examined by SEM. The following types of sensilla were found: s. placodea; pit organs; s. campaniformia; s. basiconica; s. trichodea A, B and CD; and setae. The distribution of sensilla, especially s. placodea and s. trichodea A, was found to be species‐specific in the male sex and their diagnostic value in taxonomy is stressed. In the female sex no specific characteristics were found, although two groups could be distinguished.

Habitat heterogeneity, coexistence and habitat utilization in five backswimmer species (Notonecta spp.; Hemiptera, Notonectidae)

In this study, we present data on life history, distribution and coexistence among five backswimmer species, Notonecta glauca, N. lutea, N. maculata, N. obliqua and N. reuteri, from 72 waters in a study area on the Swedish west coast. Two temporal life history patterns were found; species reproducing in the autumn (N. reuteri and N. lutea) and those reproducing in the spring (N. glauca N. obliqua and N. maculata). Female backswimmers were generally larger than conspecific males, except for N. lutea, in which the sexes were similar in size. The sex ratio of N. glauca, N. lutea and N. reuteri did not differ from 1/1. The most abundant species was N. glauca (49% of the waters inhabited by backswimmers) and then N. obliqua (19%), N. maculata (14%), N. lutea (10%) and N. reuteri (8%). In all, 972 individuals were recorded. The species were sequenced, with reference to their habitat use (from species occurring in temporal habitats to more stable and complex ones), as follows; N. maculata – N. glauca – N. obliqua – N. reuteri – N. lutea. N. glauca had the widest habitat distribution pattern. Two species combinations in pools were most commonly found and the five species were never found together. Possible competition among adults, according to their habitat distribution, may occur for: N. glauca with all species; N. obliqua mainly with N. glauca; N. lutea mainly with N. reuteri; N. reuteri mainly with N. lutea and N. glauca; N. maculata mainly with N. glauca. If body size is an important factor in the competitive ability between individuals, not merely species but also sex and temporal aspects have to be considered. The most intense competition should then exist between N. lutea and N. reuteri females.