Category Archives: Ecology

5 Fascinating Facts about Ladybirds.

Ladybirds are members of the beetle family Coccinellidae, and are predatory insects that control populations of aphids in gardens and in fields. Ladybirds, or ladybeetles/ladybugs, are well recognizable insects that are adored for their beautifully spotted bodies, but there are several things about ladybirds that one should know…

1. Ladybirds practice cannibalism

When food is scarce, ladybirds may resort to eating whatever soft-bodied organism is nearby, including other adults, pupa, larvae and even eggs of other ladybirds. Even the ladybird larvae which are the first to emerge eat their future siblings (unhatched eggs), but some of these have not even been fertilised by the adult, presumable for the purpose of giving the first hatching young more of a chance of survival.

2. Ladybirds bleed from their knees when threatened.

Ladybirds signal their toxicity using aposematic coloration (black spots upon red, white spots upon orange…), but they have another defence. When startled, ladybirds will seep toxic and foul-smelling hemolymph (rich in alkaloids) from its leg joints, leaving yellow stains on the surface below it. Predators are deterred by the prospect of eating such a rank smelling and bad looking prey item, and are repulsed enough to search elsewhere.

3. Ladybirds are highly promiscuous

Ladybirds are so promiscuous that in 2-spot ladybirds clutches often contain eggs fertilised by more than 3 different males. Because of this, ladybirds can transmit mites that feed on blood below the elytra to one another during mating- an STD! A mite-infested ladybird can reduce the size and viability of clutches. And as expected the higher the number of mating partners, the more mites a female ladybird will catch- sometimes up to 81 mites!

4. Ladybirds aggregate in the winter to hibernate

When temperatures fall and days become shorter, ladybirds seek shelter in protected locations- under leaves, behind bark and even in houses. Thousands of ladybirds may gather in one location to take advantage of the collective heat for energy conservation.

5. A ladybird may eat as many as 5000 aphids in its lifetime

Aphids are beneficial predators that control populations of pest aphids, whitefly, scale insects and mealybugs. An extremely hungry ladybird can consume 50 aphids per day. To ensure that ladybird larvae have access to plenty of aphid prey, their eggs are laid among a young aphid colony.

MYTHS:

“You can tell a ladybird’s age by the number of spots” Spots actually indicate species. (Two-spotted ladybird, 10-spotted ladybird..)

“Those big white spots are the ladybird’s eyes”. Those white spots are there to scare predators.

Further Reading:

Majerus, M. E. (1994). Ladybirds. HarperCollins Academic.

Roy, H., Brown, P., Frost, R., & Poland, R. (2011). Ladybirds (Coccinellidae) of Britain and Ireland. Natural Environment Research Council (NERC).

Featured image from www.alexanderwild.com.

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How else do pollinators benefit from plants?

bees

Plants primarily attract pollinators by offering nectar rewards (as a source of sugar for energy) and pollen (as a protein source for developing young). In return, the pollinator will pass on the plant’s genetic material for sexual reproduction. Using this animal vector is much more efficient than relying on wind pollination, but how does the pollinator benefit from this interaction? Besides nectar and pollen, what other rewards can flowers offer? How can plants sometimes ‘deceive’ pollinators by providing a false reward?

Some neotropical plants, including orchids, produce scent which is collected by the males of Euglossine bees to use as pheromones for courtship. The bees secrete saliva full of lipids onto the floral surface, which absorbs the scent compounds and is then collected by the bee’s ‘corbicula’, a modified pollen basket. Whilst the bees are collecting these female-attracting scents, the orchid’s specialized anthers deposit a ‘pollonium’ onto the back of the bee.

Pollinators have also been found to consume floral tissues (the plant itself!) as a reward for assisting with reproduction. Beetle species often consume floral tissues but also act as pollinators. For example cycads are often pollinated by specialized weevils that eat the cycad ‘flowers’ called cones. To limit the damage done, the plants often produce low concentrations of secondary metabolite (toxins) that accumulate in the insect and this limits the amount of floral tissue the pollinator can eat.

Other specialized plant-pollinator mutualisms has the plant producing oils which are used by bees to build nests and feed larvae. In many cases these fatty acid secretions are made rather than nectar, which means a more specialized pollinator can co-evolve with the plant. This leads to more efficient pollination as the insect is limited to only travelling and distributing pollen between a few plant species.

Sometimes pollination occurs by deceit. The dead horse arum produces chemical compounds that mimic those produced by carcasses. This attracts carrion flies and traps them in the flower overnight, covering them with pollen. Orchids of the genus Ophrys emit compounds which mimic female wasp pheromones and have visual displays that look similar to female wasps. The male wasp visits and attempts to mate with the flower, but inadvertetly pollinates it if fooled twice! Neither of these plants reward the pollinator with food (or otherwise) for pollinating it- this one sided ecological interaction is known as ‘commensalism’.

Many different incentives to attract insect pollinators to specialise on a particular species (or genus) of plant exist. The bizarre strategy of the fig tree has a chalcid wasp insert its long ovipositor to lay its eggs inside the fig fruits. The fig tree grows it’s flowers inside the fig fruits so the wasp actually pollinates it in return for the plant providing a habitat and food source for the developing larvae. Other plants have been shown to ‘cheat’ and deceive their pollinators into accepting a non-existent reward (like the wild orchid wasp mimic). However recent research has found that bumblebees have a preference for plant scent compounds that give an honest indication of reward quality. Plant resources put towards reward quality is limiting however, so an equilibrium exists between the evolution of cheaters and ‘honest’ signallers.

 

Irwin, R. E., Adler, L. S., & Brody, A. K. (2004). The dual role of floral traits: pollinator attraction and plant defense. Ecology, 85(6), 1503-1511.

Knauer, A. C., Schiestl, F. P. (2014), Bees use honest floral signals as indicators of reward when visiting flowers. Ecology Letters. doi: 10.1111/ele.12386

Simpson, B. B., & Neff, J. L. (1981). Floral rewards: alternatives to pollen and nectar. Annals of the Missouri Botanical Garden, 301-322.

Can green roofs enhance conservation of biodiversity in cities?

A-computer-generated-image-of-city-buildings-with-green-roofs-copy

Important pollinator populations grow more quickly in areas with urban and sub-urban gardens than flower-rich farmland. Allotment gardens have a greater diversity of nectar flowers compared with monocultures of crops in farmland, therefore support more populations of (for example) the buff-tailed bumblebee, Bombus terrestris terrestris. The close proximities of gardens in these urban parks allow pollinators to forage in a ‘matrix’ of gardens, each with a different floral make-up. But can roofs with built-in wild vegetation (green roofs) enhance biodiversity?

Green roofs are becoming increasingly common in cities as they absorb rainwater, regulate building temperatures (insulation), lower urban air temperatures and reduce the heat-island effect. These novel ecosystems also support generalist insect species, and scientists propose that they may also help conserve rare taxa, even vertebrates if connected to ground level habitats.

Williams and colleagues evaluated 6 hypotheses to test their effectiveness. They found that green roofs could aid rare species conservation if specific populations of species are targeted. For example, the Bay Checkerspot is an endangered species and only persists in a few fragmented populations, so populations would have to be relocated to an area within the butterfly’s range first before making use of the green roofs.

The study concluded that green roofs overall do provide important ecological and environmental benefits in the urban environment. It is also clear that green roofs support greater diversity than non-green roofs. However a policy shift towards replacing lost or declining habitats with poor-quality ones must be avoided. More research on the biodiversity of green roofs and the ecological interactions is required before policy action can maximise biodiversity gains.

Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R. R., Doshi, H., Dunnett, N., … & Rowe, B. (2007). Green roofs as urban ecosystems: ecological structures, functions, and services. BioScience, 57(10), 823-833.
Williams, N. S., Lundholm, J., & MacIvor, J. S. (2014) Do green roofs help urban biodiversity conservation?. Journal of Applied Ecology. DOI: 10.1111/1365-2664.12333