Category Archives: Biological Control

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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Release of GM Mosquitoes to fight Dengue Fever in Brazil

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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.