Monthly Archives: September 2014

How do Social Insects make Decisions?

beesmed

Using information passed on by others can greatly improve individual fitness, and has been the fundamental mechanism underlying the evolution of social insects such as bees, wasps, ants and termites. However in some situations it is better to ignore social information and for an individual to use its own prior knowledge and experience. So how do these colony-forming insects tailor their reliance on social information for the benefit of the ‘superorganism’? Scientists have recently reviewed the literature and made theories as to the nature of decision making in insects.

Social information is relatively ‘cheap’ to obtain for hymenopteran foragers, because they can bypass the costs associated with exploration and food sources obtained socially are likely to be better quality. In the truly eusocial western honeybee, Apis mellifera, generations overlap so information passed on by the ‘waggle dance’ (movements conveying location and quality of food sources) increases the fitness of that colony. Foraging choice are further refined by chemical cues (pheromone trails) and simply presence of other foragers.

Relying on social information may also incur costs and may not lend an evolutionary advantage. In the case of the ant forager, if she ignores social information she may find a novel food source that will benefit the colony as a whole, whilst a well-used food source is depleted (I.e. exploration produces more up-to-date information). Honeybees that rely on dance information may take time to find a dancer and may need multiple viewing and excursions to find the communicated food source.

A trade-off between these advantages and disadvantages will adjust how often (and what proportion of) social insects rely on social information. All animals tend to display the most profitable information they know, so relying on social information may be more profitable than exploration. For example honeybees only communicate their dance after finding high quality food sources. ‘Social learning strategies’ in animals are genetically determined in response to environmental and social cues. One such approach is the ‘copy if dissatisfied’ strategy, where animals will use social information if their current information is below a fitness ‘threshold’. These optimum social learning strategies can also be acquired (ironically) through social learning.

Grüter, C., & Leadbeater, E. (2014). Insights from insects about adaptive social information use. Trends in ecology & evolution, 29(3), 177-184.

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Acoustic Defence in Bush Crickets: Sex Differences

bush crickets

Many insects produce sounds for mating, territory defence and to communicate with other conspecifics. However only insects in the order orthoptera stridulate their body parts (usually a leg and a wing) to produce sounds for defence. Insects usually protect themselves from predators using distastefulness, odours, colouration (cryptic and aposematic) or by startle and escape behaviour. Sound production has evolved in orthoptera in multiple species  (convergent evolution), and in many tettigoniid species the female has also evolved a ‘response song’.

In most tettigoniid only males have the sound-producing apparatus on their wings, which are rubbed together with a modified toothed vein on the left wing (the file) which is moved against the strong edge of the right wing (the plectrum). However both male and female bush crickets are capable of this defensive behaviour, although they evolved the stridulatory structures independently from one another. Scientists therefore wanted to discover whether there is a difference between the sexes, using the bush cricket (or katydid), Poecilimon ornatus, as a model.

It was found that females had a more varied syllable duration in their defence sound. The male sound last for significantly longer and contains more impulses, which is balanced by their increased tendency to regurgitate gut contents to repulse small predators such as ants and spiders.

It is thought that bush crickets rely on this method to defend themselves because their shorter wings (used for sound production) leave them unable to fly (escape) from predators. Another theory is that both male and female Poecilimon ornatus produce sounds to “evenly distribute” the increased predation risk among the sexes. The different exposure risk to the sexes may explain the differences in acoustic defence between the two sexes.

Kowalski, K. N., Lakes-Harlan, R., Lehmann, G. U., & Strauß, J. (2014). Acoustic defence in an insect: Characteristics of defensive stridulation and differences between the sexes in the tettigoniid< i> Poecilimon ornatus</i>(Schmidt1850). Zoology.

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

Release of GM Mosquitoes to fight Dengue Fever in Brazil

aedes_aegypti04

In Rio de Janeiro, scientists have released thousands of mosquitoes infected with a bacteria that will hopefully suppress dengue fever. The theory is that the genetically modified yellow fever mosquitos (Aedes aegypti) will breed with the existing population and become the dominant type, thus eliminating the disease spreading variants.

Dengue is one of the most widespread and rapidly spreading mosquito-borne diseases in the world, with a 30-fold increase in global incidence over the past 50 years. So far Aedes aegypti have proved difficult to control with insecticides and more traditional methods. However it was discovered that A. aegypti transinfected with the wMel strain of Wolbachia showed limited dengue virus (DENV) replication. Virus-blocking persists in Wolbachia-infected mosquitoes after their release and establishment (like a vaccine). This, coupled with the ability of Wolbachia to both induce pathogen interferences and spread into mosquito vector population (i.e. become dominant) makes them ideal bio-control agents.

To achieve population suppression of Aedes aegypti using the RIDL system (Release of Insects carrying a Dominant Lethal), a large number of male mosquitos need to be released. This requires mass rearing techniques to obtain the highest quality males. RIDL is effective and an environmentally safe method of controlling mosquitoes, with no knock on effect to non-target organisms such as natural enemies.

Brazil leads the world in the number of dengue cases, with 3.2 million cases and 800 deaths reported in the 2009-14 period. Brazil has released around 11 million males in the 2012 programme, and part of the programme is also taking place in Australia, Vietnam and Indonesia.

Bian, G., Zhou, G., Lu, P., & Xi, Z. (2013). Replacing a native Wolbachia with a novel strain results in an increase in endosymbiont load and resistance to dengue virus in a mosquito vector. PLoS neglected tropical diseases, 7(6), e2250.
Carvalho, D. O., Nimmo, D., Naish, N., McKemey, A. R., Gray, P., Wilke, A. B., … & Capurro, M. L. (2014). Mass production of genetically modified Aedes aegypti for field releases in Brazil. JoVE (Journal of Visualized Experiments), (83), e3579-e3579.
Frentiu, F. D., Zakir, T., Walker, T., Popovici, J., Pyke, A. T., van den Hurk, A., … & O’Neill, S. L. (2014). Limited Dengue Virus Replication in Field-Collected Aedes aegypti Mosquitoes Infected with Wolbachia. PLoS neglected tropical diseases, 8(2), e2688.
Peter, R., & Scott, O. N. (2014, September). Using Wolbachia infections to control dengue transmission. In 8th Cuban Congress on Microbiology and Parasitology, 5th National Congress on Tropical Medicine and 5th International Symposium on HIV/aids infection in Cuba.

Detecting invasive species: the case of the wood-boring beetle

wood boring beetle

Invasive species are mostly likely to invade an area through a port. We need a better understanding of the factors affecting their arrival and establishment if we are to detect them. Davide Rassati and colleagues from the university of of Padua in Legnaro, Italy, looked at how the port size and surrounding landscape (i.e. forests) influenced the occurrence of the wood-boring beetle, Cordylomera spinicornis.

At 15 Italian international ports, the surrounding forests and ports themselves were monitored using multi-funnel traps with bait. Both alien and native bark beetles (subfamily Scolytinae), longhorn beetles (family Cerambycidae) and jewel beetles (family Buprestidae) were found. Overall 14 alien species were found, 4 of which are new to Italy.

Alien species richness was positively correlated with imported commodities. However total forest cover near ports was positively correlated with the occurrence of native but not alien species. The alien and native species richness was higher in surrounding forests than the ports themselves.

Early detection of the invasive wood-boring beetles can be improved by identifying sites where the arrival and establishment of aliens is more probable, combined with an efficient trapping protocol. Ways to detect these insects include pheromone traps and encounter rate models (forecasts).

Byers, J. A., & Naranjo, S. E. (2014). Detection and monitoring of pink bollworm moths and invasive insects using pheromone traps and encounter rate models. Journal of Applied Ecology.
Rassati, D., Faccoli, M., Toffolo, E. P., Battisti, A., & Marini, L. (2014). Improving the early detection of alien wood‐boring beetles in ports and surrounding forests. Journal of Applied Ecology.