Queens, harlequins and admirals

The last mild, sunny days of autumn are bringing out scores of insects. Standing under a large flowering ivy today the sound of buzzing bees, bluebottles, droneflies and wasps was extraordinary, especially given that November is only a couple of days away. Yesterday, six red admirals sunnied and gorged themselves on the ivy blossom. They are charging batteries before their migration to South Europe and North Africa.

Red Admiral and passing droneflies on ivy

 A green shieldbug, Palomena prasina, climbing a tree.

 Today, a queen Bombus hypnorum fed on lavender flowers. 

 A female Araneus diadematus spider sat proudly on her silky egg cocoon. 

Honeybees on ivy flowers

Dozens of harlequins and 7 spot ladybirds flew about landing on a sunny wall and leaving again.

Ready for winter

Only a couple of weeks ago, 7 spot ladybirds were mating. Today we found this little cluster, with a harlequin trying to merge in, nestled on a wall, ready for winter. More BugBlog ladybird posts here.

Mating 7 spots on 9/10/11.

The singing lacewings

Adult common green lacewings, Chrysoperla carnea, are starting to search of suitable hibernation places, and they often come inside buildings. This one was inside my office the other day and allowed me to take her portrait. C. carnea was once thought to be a single widespread species but it is now known to be a species complex, an aggregate of morphologically very similar species that often co-exist.  Courtship involves males and females drumming a song on the substrate where they are sitting with their abdomens. The vibrations are detected by organs in their legs. Males and females respond to each other's drumming in a complex duet and only when they sing the same song does the courtship ends in mating. The different species in the complex have different songs, with characteristic drumming frequencies. The figure below illustrates the differences between the six biological species within the C. carnea group that are recognised in Europe.

 

The drumming songs of European cryptic species of Chrysoperla carnea sensu lato (from Henry et al in

Lacewings in the crop environment By Peter K. McEwen, T. R. New & A.E. Whittington)

Both C. lucasina (probably the top photo) and C. c. 4 "motorboat" also known as C. c. "sensu stricto" have been found in the U.K. C. lucasina does not change colour in winter, has "pointy wings" and a dark membrane between the sternites and tergites in the abdomen. C. carnea "sensu stricto" has rounded wings, changes colour and does not have the dark membrane. However, individuals that do not fit either of the species are often found in the U.K.

As their distinctive songs are difficult to tell apart for the untrained eye (ear?), and the morphological characters that do differ between the cryptic species are sometimes not apparent or distinctive enough, identification to these lacewings on the field is tricky. 

 C. carnea 4 "motorboat" may change colour prior hibernation (photo from 10 October 2011).

Lacewing larvae, distinctive large jaws and covered on detritus, which often are the shrivelled skins of the aphids she feeds on.

Earwigs and the conundrum of cryptic species complexes

While collecting grapes, I came across a group of adult earwigs. Earwigs are insects of the order Dermaptera, characterised by the presence of  a pair of sexually dimorphic appendages at the end of the abdomen called forceps. Female forceps are more or less straight (above), while the male's (below, with two males of different sized forceps) are larger, curved and furnished with a pair of teeth. F. auricularia males are also dimorphic, with a large forceps form (macrolabic) and a small forceps form (brachylabic).

Earwig forceps are used for defence - they readily raise their forceps when disturbed - and are involved in reproduction, males fight using their forceps as weapond and display them to females during courtship. Males with larger forceps seem to be preferred by females, so they appear to have evolved through sexual selection. Earwigs are also unusual amongst insects in their level of maternal care. Females build a nest chamber, and stay with their eggs after oviposition, they continuously groom their eggs keeping them fee from fungi and sit atop them, occasionally moving them within the nest to areas of optimal temperature and humidity conditions. They also provide their larvae with food and defence for several instars. In 1998 Thiery Wirth and colleagues, while examining the inheritance of brood number variation in the common European earwig Forficula auricularia through laboratory crosses, found that single brooded and two-brooded forms did only rarely produce offspring. Further genetic analyses confirmed that F. auricularia is made of two cryptic species. Cryptic or sibling species are species that cannot be distinguished easily by their morphology, although they are reproductively isolated and might differ in song or pheromones so, despite their similarity to our eyes, males and females do not recognise each other as mates. Cryptic species are very common among many invertebrate groups and are a nightmare for the biologist trying to understand the behaviour or ecology of a species, as it is often impossible to be sure that one is dealing with a single species without using genetic tools. In F. auricularia, the two cryptic species have not been formally described, but one, referred to as species A, prefers colder climates or higher altitudes, females are single brooded, and tend their clutch for longer and the larvae disperse later; while species B typically lives in more temperate areas, females produces two broods, tends its brood fo r a short time and has an earlier larvae dispersal. In his PhD thesis, Gordon Brown concludes that a single species inhabits the UK, and this is the single brooded species A. At this time of the year, males and females are found above ground and they will be mating. Although males stay with the female and may help with nest building, they are unlikely to make it through the winter and are excluded from the nest once oviposition takes place, while females will overwinter in the nest, where they will lay their eggs early in the year and tend the next generation of earwigs.

References
Guillet, S., Guiller, A., Deunff, J. & Vancassel, M. (2000). Analysis of a contact zone in the Forficula auricularia L. (Dermaptera: Forficulidae) species complex in the Pyrenean Mountains. Heredity, 85 (5), 444-449 DOI: 10.1046/j.1365-2540.2000.00775.x
Thierry Wirth, René Le Guellec, Michel Vancassel & Michel Veuille (1998). Molecular and reproductive characterisation of sibling species in the European earwig (Forficula auricularia) Evolution, 52 (1), 260-265.
Gordon Brown (2007) Sperm competition and male forceps dimorphism in the European earwig Forficula auricularia (Dermaptera: Forficulina). PhD Thesis University of St. Andrews.

Spider beetle

I found this tiny spider beetle, Ptinus sexpunctatus in the bath today. The second time I see this species, both times found in the bathroom. The name spider beetle comes from the long legs and antennae of the beetle and its tucked-in head, which makes them resemble a spider superficially. They feed on decaying insects and are often found in bee nests, presumably feeding on the pollen/larvae.

Late bumblebee collecting pollen

It is not unusual to see bumblebees in Autumn. Queens are still about, storing up some reserves before hibernation. What I found unusual is a worker of a Bombus pascuorum collecting pollen in my patch of Lamium maculatum today. The bumblebee visited each flower inserted its head deep into it and as exiting, wiped its furry back with its rear legs collecting the pollen on its corbicula or pollen basket. I understand that bumblebees collect pollen for their larvae, so there must be still be B. pascuorum active nests this late in the year.

The curious Autumn spider mating tactics

Female spiders tend to be larger than males. Large females are thought to be selected for as they can produce more eggs. The relative size differences between males and females depend on the type of competition between males, that is, on the importance of intra-sexual selection. When males do not compete much with one another they are smaller than females, whereas when there are male-male contests for females, then large males are selected for, and size differences with females become smaller. The spider, Metellina segmentata, is an orb spider common during September and October, when most mature individuals are found. Males are more powerfully built and have longer legs than females, suggesting that male-male contests occur in this spider. When young, males build their own webs to hunt insects, but upon reaching their final moult, they mature and start searching for female webs. Once they encounter a receptive female web - likely through detecting a pheromone - they adopt a curious sit and wait strategy. They have to wait, often days, until a large fly falls in the web. Only when the female starts eating the fly does he starts his courtship, taking advantage of the diminished cannibalistic tendencies of sated females. Of course, during this wait, other suitors might arrive to the female's web and when two males encounter each other fights follow. Males are often injured or killed in these fights, where the larger male has an advantage and this is what provides the selective pressure for powerfully built males.
 In addition, males are able to monitor several female webs when they are nearby and this results on males guarding webs becoming larger as the season progresses, and a pool of smaller wandering males.
 The mature female Metellina on the top photo has hung her web on a tomato plant since at least mid september. I haven't noticed any males but I shall keep an eye for these in the next days.

Reference
Prenter, J., Elwood, R., & Montgomery, I. (2003). Mate guarding, competition and variation in size in male orb-web spiders, Metellina segmentata: a field experiment Animal Behaviour, 66 (6), 1053-1058 DOI: 10.1006/anbe.2003.2266

BugBooks: Chinery's Insects

Given that the oncoming months will, by necessity, subdued at BugBlog, I have decided to start a new section. I will present and review my favourite books on British bugs, books that I routinely use to find information or to identify the bugs that feature in BugBlog. Please feel free to comment with your own favourites. My first choice has to be undoubtedly Michael Chinery's Insects of Britain and Western Europe, a very informative, superbly illustrated field guide. An additional advantage is its size, soft bound and small. Its 320 pages are absolutely packed with information, including distribution pattern in Western Europe and in Britain, time of the year where they are found, behaviour and habitat. The colour illustrations are superb, detailed and accurate. Many species are illustrated with adult and caterpillar or larvae and the illustrations often shows common behaviour. A key at the beginning of the book will help you identify what group an unidentified insect belongs to. At the end of the book, there is a section with a selection of species of non-insect arthropod groups such as Spiders, Woodlice, Millipedes, Centipedes Scorpions and Harvestmen, which comes in handy.
My copy from the reprinted first edition in 1986, is getting dated. Since it was put together, many new species have arrived to the British Isles and have become now common and are not described (e.g., the ubiquitous Harlequin or the Horse Chestnut Miner). In addition, the distribution of many other species has significantly shifted northwards (e.g Speckled Wood, Comma) or they have moved to the U.K. from the continent (Tree bumblebee, Ivy Bee). But those are minor quibbles, I couldn't do without this book. There is a more recent revised edition (2007), which is a bit pricey. A proviso, this book does not include all species of European insects (there are over 100,000 described), but a selection of the most common or noticeable. Once you become familiar with an insect group - be butterflies, hoverflies or dragonflies - you will require a specialist guide.
 Overall, a must for the bug lover.

Two white plate orb spiders

The garden is scattered with orb spiders, including the ubiquitous garden spider Araneus diadematus (above) sat in the middle of their webs during the day, and females, now laden with eggs, are very obvious. But there is a smaller species of orb spider can easily pass unnoticed despite being common in gardens, its the beautifully named, more delicate Metellina segmentata, also known as autumn spider (below). It has longer front legs, and there is a round empty space in the middle of her web. But days are shorter and the sun not as strong, and I miss natural light when taking photos. The orb spiders pose a challenge for my usual white bowl spider portrait technique: they are not walking spiders, and they are at their most comfortable hanging from their webs. So, for these shots of spiders in the garden I replaced my usual white bowl by a large white plate, which I carefully held behind each web while I took their portraits.

Knowledge is power for the sun spot owners

Even as the butterfly season comes to an end, Speckled Wood butterflies, Pararge aegeria, are still going strong in my local overgrown cemetery. The hundred year old trees, shade the ground and sunny clearings are highly prized by Speckled Wood males. Yesterday, I watched them squabbling incessantly in a patch of grassy area amongst the trees. At some point, the resident male chased two other individuals, the three butterflies flying around in tight circles away from the prized spot. Another individual comes by oblivious to the ownership contest and takes possession of a sunny dock leaf in prime position (above). By the time the initial "owner" comes back victorious from the skirmish, the newly arrived one believes this is his spot and the subsequent squabble ensues. It is really never ending in this warm autumnal morning with the sunspot owners.
 What determines how is the fight settled? In the late 1970s Davies work suggested that prior ownership is a very strong predictor of success in a fight: residents always won. Later work by Christer Wiklund and collaborators have expanded and refined Davies' findings, indicating that although a good predictor, ownership is not the only factor involved in territorial fights. Age and size are factors that are known to be predictors of fight outcome, but in the Speckled Wood these have little importance. Martin Bergman, Martin Olofsson and Christer Wiklund investigated the effect of motivation on territorial fight outcome. Residents might be more motivated to fight because they have more information on the value of the resource they are fighting for: the resident male might have prior mating experience in that spot, or knows how prized the spot is for other males. The intruder, most of the time lacks such information. This creates an asymmetry in which the resident is more determined to fight than an intruder.
 To test this hypothesis, the researchers set up experiments in large outdoor cages with a prime large sun-spot, and smaller, suboptimal sunspots. They released two males in each cage and waited until there was a clear dominant male that took possession of the large sunspot. They they removed the dominant male and divided the subordinate males in two groups, half of the males repeatedly encountered a female during a 30 min residency period (female encounter group), while the other half (the control group) did not have any female encounters. Then they tested the effect of this prior experience - motivated vs unmotivated males - on contest outcome when they introduced the original dominant individual back in the cage. The results were very clear.

Outcome of contests between Speckled Wood males during the second contest period when the original winner had been reintroduced, and after the original losers had either interacted with a female during 30 min (female encounter group, n = 30) or been alone for 30 min (control group, n = 30); ‘reversal’ (open bars) denotes that the male that lost the contest during the first contest period reversed the outcome and won the contest against the original winner in the second contest period, and ‘no reversal’ (filled bars) denotes that the same male won in both contest periods (from Bergman et al 2010).

Half of the originally subordinate males won their fight with the original dominant in the "female encounter group". In contrast, most of the dominant males won their fight for the prime sunspot when no females had been present. Also, the fights in the treatment group were more intense and took longer to resolve, while the control group the fights were settled quickly. In conclusion, these experiments showed that male experience in a sun spot increase his persistence in a fight, and therefore increase the chances of winning it, even if he was initially a subordinate male, indicating that motivation is an important factor for contest resolution in the Speckled Wood.

References

Bergman, M., Olofsson, M. & Wiklund, C. (2010). Contest outcome in a territorial butterfly: the role of motivation Proceedings of the Royal Society B: Biological Sciences, 277 (1696), 3027-3033 DOI: 10.1098/rspb.2010.0646
Davies, N. (1978). Territorial defence in the speckled wood butterfly (Pararge aegeria): The resident always wins Animal Behaviour, 26, 138-147 DOI: 10.1016/0003-3472(78)90013-1

On the Western Conifer Seed Bug and Christmas trees

This large, striking bug entered the house at night through an opened window. It is the alien species Leptoglossus occidentalis, the Western Conifer Seed Bug, a native from western North America, where is a minor pest of conifers. This species has long antennae and large rear legs, a pale zig-zag mark on the wings, and distinctly flattened and enlarged tibia, which gives the name to its group, the leaf-footed bugs. During last century, this species spread across North America and during the last decade has also been introduced in Europe, where it has quickly spread from the initial introduction point in Italy. It was accidentally transported in timber, and its spread could also possibly been aided by Christmas tree shipments. Nymphs and adults feed on the sap of cone seeds and buds, and therefore the damage is restricted to seed production. In continental Europe, where there are established populations, it does not appear to cause much damage. Every now and then, there are migratory influxes to the U.K. from the continent, as occurred in 2008. The bug often falls in moth traps, and is a good flyer. It is most obvious in the autumn, when it moves about looking for suitable hibernation sites, often entering buildings and sometimes forming large aggregations, attracted by pheromones produced by males. Nymphs have been found in a few sites in the U.K., so it appears to be establishing.
 If you have seen this bug, you can report it here.

References
Lis, Jerzy A., Barbara Lis & Jerzy Gubernator (2008). Will the invasive western conifer seed bug Leptoglossus occidentalis Heidemann (Hemiptera: Heteroptera: Coreidae) seize all of Europe? Zootaxa, 1740, 68-68
Taylor, S.J., G. Tescari & M. Villa (2001). A nearctic pest of Pinaceae accidentally introduced into Europe: Leptoglossus occidentalis (Heteroptera: Coreidae) in Northern Italy. Entomological News, 112, 101-103.
Blatt, S. & Borden, J. (1996). Evidence for a male-produced aggregation pheromone in the Western Conifer Seed Bug, Leptoglossus occidentalis Heidemann (Hemiptera: Coreidae) The Canadian Entomologist, 128 (4), 777-778 DOI: 10.4039/Ent128777-4