The resting position of Tetragnatha on a leaf.
Saturday, 25 June 2016
Friday, 24 June 2016
Yellow-barred Long-horn moth, Nemophora degeerella. Long-horn moths are truly spectacular micromoths. Males are not only beautifully marked with metallic golden, chestnut and blue metallic stripes and a broad diagnostic yellow band across the wings, but their antennae are extremely long, several times their body length. It is astounding they can actually fly! Not only they can fly, but they perform a dancing flight, males bobbing up and down in a small area in shady wooded glades where they gather forming mating swarms or leks. These swarms, and possibly pheromones the males emit presumably serve to attract females and mate. Do females prefer males with longer antennae? These are day flying moths and I've watched the swarms in the morning or afternoon in warm sunny days in May and June. The antennae are white and so stand out as the moths fly. Although I've never seen a female, they are similar to males, but with short antennae. The caterpillars feed on leaf litter.
This is a short video of one of the moths appearing to sip honeydew from a leaf.
Monday, 6 June 2016
The abdominal spines of male Wool carder bees
Most female bees mate once shortly after emergence, so males only had a chance of mating successfully early in the season. Females store the sperm of this early mating and use it to fertilise their eggs throughout the nesting season. Females will repel or avoid courting males vigorously once they've been mated. In contrast, Wool-carder bees are unusual in that females both mate multiple times and accept matings throughout their flight season. Witnessing solitary bees mating is quite rare, but with Wool carder bees, matings are quite frequent. Many females visiting a defended flower patch will mate with the resident male. The male defending a good flower patch will likely gain many matings with several visiting females, but, given what we know about sperm usage in solitary bees, will he benefit from fathering the female's offspring?
Mating Wool carder bees
In a recent study, Kathrin Lampert and colleagues from Ruhr-University Bochum carried out some experiments to investigate why Wool Carder bee mating behaviour is so different from other bees. They in particular were interested in testing the hypothesis that Wool-carder bees might show what is known as 'late male sperm preference' in which the last male mating with a female has a disproportionally higher chance of fathering the females offspring.
To find out 'who is the daddy' they used genetic testing in a similar way to how paternity is tested in humans, using genetic markers that have many variants, and therefore are likely to be different between individuals. In order to be able to capture the likely mothers and fathers of particular nests they constructed large flight cages containing Betony plants (for pollen and nectar) and Stachys byzantina (for plant wool, which the females collect to line their nest cells). Wool carder bees nest readily in sections of bamboo sticks, and they fixed artificial nesting sites inside the flight cages. Offspring of a female are found in a linear nest in consecutive order, the deeper cells in the bamboo stick contain the earlier laid eggs, while the cells closer to the entrance contain the later brood, which is likely to be male offspring. They carried out three experiments, in the first one, to test the feasibility of these experiments wild males and females (likely to have mated before) were captured, individually labelled with a dot of paint in the thorax, and released in the flight cage. In the second experiment, males in the cage were swapped to test if males with later access to females would father offspring. In the third experiment males were removed after a few days and females left to nest with no males, to investigate if females are able to store sperm. After the females had completed their nests in all the experiments, DNA samples were taken from the males and females, and them and the offspring found in the artificial nests screened for genetic paternity analyses.
A problem with their experiment were cleptoparasitic wasps, which destroyed the bee larvae and prevented genotyping. Another problem, which stems from bee's sex determination system, is that only female offspring have a dad: males develop from unfertilised eggs, so they only have a mum. They could only find out if offspring were male or female after genetic screening. Despite this, they obtained a number of female offspring from many females.
The results revealed that the males flying with females at the time the females were provisioning a cell, where they are close to laying the egg, were the most likely fathers of the offspring (84% of the time), whereas most of the remaining fathers were males present in the cage in previous days, supporting the hypothesis of late male sperm preference. Males that were dominant, that is, chased away other males from flowers, tended to father more offspring, as most matings happened on flowers.
The male removal experiment showed that females were able to store sperm for at least 11 days, and possibly much longer.
This research suggests that a predisposition for late male sperm precedence in the ancestors of wool carder bees might have been what favoured the aggressive territorial behaviour seen in males, as they can benefit from monopolising floral resources visited by females.
Lampert, K. P., Pasternak, V., Brand, P., Tollrian, R., Leese, F., & Eltz, T. (2014). ‘Late’male sperm precedence in polyandrous wool-carder bees and the evolution of male resource defence in Hymenoptera. Animal Behaviour, 90, 211-217.
Tuesday, 31 May 2016
Although males and females sharp-tailed bees can be found nectaring at flower sources, they are cuckoo bees. The females do not collect pollen, instead, they are cleptoparasites, looking for ready made cells already provisioned with a pollen load. Their usual hosts are leaf-cutter bees, and their common name derives from their tapered abdomen of females, ending in a fine point, which is able to slice through the leaf wrappers of leaf-cutter bees, laying one egg either under the pollen load, or in between layers of the leaf wrapping of the cell before the cell is sealed. The cuckoo bee will also match the sex of her eggs to the host eggs sex, with the male eggs positioned in the outer cells of a nest. Once the larva hatches, they use their large mandibles to kill the host larvae or any other competitors. The cuckoos larvae complete their development and emerge at the same time as their hosts.
I find the male abdominal spines very intriguing. What is their function? Coelioxys belong to the same family - Megachilidae - than Anthidium manicatum, the wool-carder bee, whose males are armed with formidable abdominal spines with a similar disposition. Male wool carder bees use these spines as weapons to defend their flower territory from other males and also other bees. They can fearlessly attack honeybees and large bumblebees, and are capable of killing them. It is unlikely that sharp-tailed bees use their spines in a similar way, as females do not collect pollen and there is no flower resources to defend. In the monograph Bees of the World, by Charles Michener, he hints at the spines being involved in dealing with the modified female's abdominal tip during copulation.
There are eight species of sharp tailed bees in the UK, but in general they are very hard to identify without a specimen, so I will have to content myself with not having a definite identification for now.
I have gone through my records of this genus in the wildlife garden, just five of them in June and July and here I show some record shots.
A male Coelioxys feeding on sage (12/6/10)
Female Coelioxys on birds-foot trefoil (4/6/2011).
Male Coelioxys resting. Many bees hold on with their mandibles in their sleep (10/7/2009).
Female Coelioxys on marjoram (2/7/2011).
Male Coelioxys on meadow cranesbill (11/7/2011).
Cuckoo bees tend to be rare bees, and sharp-tailed bees are no exception. The presence of cleptoparasites indicates a healthy host population. Often cleptoparasites decline and get locally extinct when a host population declines. In a study on sharp-tailed bees, about 3% of over 14,000 host cells (Megachile inermis) contained Coelioxys funeraria and less than 10% of Megachile relativa were parasitised. So, what about the hosts in my garden? The bee posts and bee hotels are commonly used by leaf-cutter bees of at least two species in my garden: Megachile willughbiella and Megachile centuncularis, used as hosts by several British Coelioxys species. Some species of Coelioxys are thought to parasitise Anthophora furcata, which is also a regular bee foraging and possibly nesting in the garden log piles. The synchrony of the hosts is remarkable as both male leaf-cutters and A. furcata, appeared in in garden in the last couple of days too.
This was the first of the year A. furcata in the garden, a male yesterday.
Male M. willughbiella, 29th May.
Male Megachile, possibly centuncularis, yesterday.
Scott, V. L., Kelley, S. T., & Strickler, K. (2000). Reproductive biology of two Coelioxys cleptoparasites in relation to their Megachile hosts (Hymenoptera: Megachilidae). Annals of the Entomological Society of America, 93(4), 941-948.
Michener, Charles Duncan. The bees of the world. Vol. 1. JHU Press, 2000.
Falk, Steven and Richard Lewington 2015. Field guide to the Bees of Great Britain and Ireland. Bloomsbury, London. 432 pp.
Saturday, 16 April 2016
Lowe, Christopher N., and Kevin R. Butt. Life cycle traits of the parthenogenetic earthworm Octolasion cyaneum (Savigny, 1826). European Journal of Soil Biology 44.5 (2008): 541-544.