A Loveliness of Ladybirds*

A Loveliness of Seven-Spot Ladybirds, Coccinella septempunctata

The Seven-spot Ladybird (Coccinella septempunctata) is the most common species of ladybird present in Ireland, often quite abundant in areas. Adults are emerging, or have emerged, from hibernation at this time of year and will remain active until October (1). It is a species that is widespread throughout the palaearctic region, and its success is due to a high degree of ecological plasticity. It is a highly mobile beetle, and capable of thriving in a variety of different habitats (eurytophic). Its can also be considered polyphagous in its diet, with at least 24 species of aphid being counted as prey (2). Post emergence from hibernation, when aphid number are be quite low, C. septempunctata will feed on nectar and pollen from a variety of plants. Females can also suspend oviposition in the presence of already hatched larvae, which avoids any problems of cannibalism. When eggs are layed, an excess of offspring for the carrying capacity of local food resources often results, which allows C. septempunctata to take advantage of unpredicatably occuring aphid populations (2).
 

Evidence of eurytophy in Coccinella septempunctata: larvae on a sand-dune

While numbers of C. septempunctata remain high in Ireland, they may soon be under threat from the invasive Harlequin Ladybird (Harmonia axyridis) which can not only out-compete, but also feeds on C. septempunctata larvae. The breeding site for H. axyridis reported on this blog last year (but sighted in 2012) along with another from Co. Carlow are worrying developments.

*The title of this post comes from the collective noun for a group of ladybirds, a loveliness.

References:

1. Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 150
2. Hodek and Michaud, 2008. European Journal of Entomology p. 1-12

A Floral Attraction

A Drone Fly, Eristalis tenax

One of the first large insects to be conspicuous at this time of year is the family of hoverflies known as Drone Flies (Eristalis spp.). The availability of pollen and nectar from the newly emerged catkins of willow provide a bountiful supply of food for the flies, and as the number of plants in flower increases, so will their numbers. Their common name, Drone Flies, comes from their resemblance to bees, a form of Batesian mimicry that no doubt gives them some degree of predators. Their larvae employ no such disguise and are quite distinctive, possessing a long respiratory tube attached to their anal gills that enables respiration as they are buried in the mud and earning them the name 'Rat-Tailed Maggots' (1).

Eristalis tenax covered in Willow pollen after feeding

Yet, watching one of the most common of the Drone Flies currently in flight, Eristalis tenax, flit from flower to flower in search of food does beg the question how do they know where the food is. How do they know that a flower is a flower? The answer is a variety of olfactory and visual signalling structures used by plants to attract insects. E. tenax in particular is attracted to yellow flowers, or yellow spots on flowers, with light in the colour range of 510-600 nm (green/yellow light) releasing the extension of the proboscis (2). Flowers use guide lines to attract the flies from a distance, which are also most effective when yellow (3). Attraction to the yellow colour is due to the fact that this is the colour of pollen, food for E. tenax. This explains it eliciting a feeding reaction.

Identification of Eristalis spp. is notoriously difficult, so I was very grateful to Stuart Dunlop at the Donegal Wildlife blog for his tips on identifying E. tenax.

References:

1. Robinson, 2005. Handbook of Urban Insects and Arachnids p. 188
2. Lunau, 1995. Plant Systematic and Evolution 198 pp.  235–252
3. Dinkel and Lunau, 2001. Journal of Insect Physiology 47 pp. 1111–1118

Triumph in Shade

Opposite-Leaved Golden-Saxifrage, Chrysosplenium oppositifolium

Flowering at this time of the year locally along shady stream banks and woodland flushes, the Opposite-Leaved Golden-Saxifrage (Chrysosplenium oppositifolium) is a wonderful, almost ephemeral plant. Its delicate yellow-green flowers that lack petals are found on stems that will root to form often dense patches, rarely rising over 10 cm high (1). Thriving as it does in such wet but moreover shady conditions, C. oppositifolium is remarkably adapted to the problems associated with living in low levels of light. As a shade adapted plant, C. oppositifolium has developed thinner leaves than its light loving close relatives (other members of the Saxifragaceae, eg. Saxifraga spathularis). Thin leaves are prone to sugar leakage, which can lead to fatal fungal infections. C. oppositifolium counteracts this threat by using sedoheptulose as its principal soluble sugar (2). This, being a 7-carbon sugar, is not readily metabolised by fungi giving C. oppositifolium a distinct advantage.

References:

1. Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 208
2. Crawford, 2008. Plants at the Margin: Ecological Limits and Climate Change p. 256

A Model Plant

Thale Cress, Arabidopsis thaliana

An inconspicuous weed of waste ground and walls throughout Ireland, and indeed much of the northern hemisphere, Arabidopsis thaliana (Thale Cress) doesn't look much. With tiny white flowers on a long stem arising from a neat rosette of leaves, the whole plant rarely grows over 40 cm high (1). Yet its small size belies its enormous stature as a model plant in genetics. Research on Arabidopsis has resulted in priceless information a variety of plant mechanisms such as how flowers develop and how plants control their circidarian rhythms (2). In terms of publication in the scientific literature, Arabidopsis is by far and away the most thoroughly studied plant in the world: in 2008, for example, 3500 papers were published on the plant (3).

Thale Cress, Arabidopsis thaliana

But why is it such an important plant? Economically it has no value, either as a food stuff or as a raw material. Crucially, Arabidopsis possess features that make it very suitable for genetic research, namely a short generation time, a small physical size that limits the need for growth facilities and prolific seed production through self pollination. It has a small genome, just 157 megabase pairs in length with just 5 chromosomes making it ideal for gene mapping (3).

Thale Cress, Arabidopsis thaliana

Such seemingly suitability is really only part of the story however when explaining its enduring  popularity as a model organism. Tireless work by a number of individuals in experimentation and analysis of Arabidopsis has also help elevate it to the plant par excellence in genetic research. The first research carried out on Arabidopsis was by Friedrich Laibach who determined the correct chromosome number during his PhD research in 1907 and published a compelling argument for its case as a model for genetic studies in 1943 (3). The Hungarian botanist George Rédei, working in the United States, continued to work on the plant in the 1950's and it was a review published by him in 1975 (4) that lead researchers such as Chris Somerville, Elliot Meyerowitz, Maarten Koornneef and David Meinke to realise its potential as a genetic model. Through collaboration and conferences they, among others, helped establish a vibrant network and a critical mass of information that lead to Arabidopsis' currently importance.

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife
2. Reeves and Coupland, 2000. Current Opinion in Plant Biology 3 pp 37–42
3. Koornneef and Meinke, 2010. The Plant Journal  61 pp. 909–921
4. Rédei, 1975. Annual Review of Genetics 9 pp 111-127