Ladybird invasion Print E-mail
News - Ons Omgewing
Tuesday, 22 January 2008 02:00
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It’s like an Alfred Hitchcock movie. Or maybe like the Biblical plagues of Egypt. And it happens every year around the end of December or beginning of January. Swarms of alien ladybirds reach high-lying homes in Zwavelpoort and Mooikloof.

These ‘goggas’ can by no means be described as ‘ladies’. They push through cracks in windows and creep through crevices and air vents just to get inside. Once inside they form tight clusters in corners, behind ornaments, books and furniture and try their best to hibernate there for the rest of the season. When disturbed, they cause smelly yellow stains that are difficult to get rid of.


Ladybirds annually invade high-lying homes in Zwavelpoort and Mooikloof

Why on earth they try to hibernate in mid-summer, and where they come from, nobody seems to know. How long they’ve been doing this in our area is also not clear – people estimate it to be about a decade.

Reports indicate infestations in houses on the Bronberg ridge and those on hilltops in Mooikloof, but high-lying houses in Olympus apparently don’t fall prey to these invasions. The orange ladybirds seem to migrate in a narrow band and always fly north from a southerly direction.

Those attempting to identify these ladybirds have come to the conclusion that they cannot be indigenous because they seem to have no natural enemies here. Available information has led us to suspect that we are dealing with the Asian ladybird.

Entomologists are welcome to disagree with us and are invited to send us more information. We’ve determined that other ladybird species, such as Hippodamia convergens, also gather into groups and move to higher land, such as a mountain, to hibernate. However, this species has a black head, a
feature lacking in our local home invader.


Swarms of ladybirds reach Zwavelpoort?s Bronberg ridge each year

These ladybirds force blood out through their joints, resulting in a yellow stain that is difficult to get rid of

Pest
Our leading suspect, the Asian ladybird, Harmonia axyridis, was introduced to the rest of the world as a biological control agent against aphid and cale infestations in greenhouses, crops and gardens. They can quickly disperse over long distances and so have the potential for rapid geographic expansion. These ladybirds are increasing internationally to the detriment of indigenous species. They have a voracious appetite which enables them to out-compete and even eat other ladybirds and larvae. Native ladybird species have experienced dramatic declines in areas invaded by these foreigners.

In Britain, 46 native ladybird species are under threat. Introduced from Asia into North America to control plant pests, they have spread across all states, becoming by far the most common ladybird in less than 20 years. In Europe they got the name‘harlequin’ because of the species’ tendency to vary in colour from a deep orange to yellow. The harlequin measures between 5-8 mm, but can be difficult to identify because of the variations in colour,
spot size, and spot count.

Bleed
Harlequin ladybirds cause stains because they can force blood out through joints and other weak areas in their exoskeleton, an adaptation called ‘reflex bleeding’. Like other ladybirds, their blood contains isopropyl methoxy pyrazine which they use as a defensive chemical to deter predation. But these invaders contain this chemical in its haemolymph at much higher concentrations than many other ladybird species. That is why the reflex bleeding has such a foul odour.

It is believed that some people have allergic reactions when repeatedly exposed to these ladybirds which, apparently, can also bite. Harlequin ladybirds hibernate in cooler months, although they will wake up and move around whenever the temperature reaches about 10°C. Because they use crevices and other cool, dry, confined spaces to hibernate, significant numbers may congregate inside homes. These large populations can be problematic because they form swarms and linger in an area for a long time.

Luck
Before the invasion of the harlequin, ladybirds and their larvae have always been considered as a bonus to any garden. Some people consider seeing them or having them land on one’s body to be a sign of good luck, and that killing them foreshadows bad luck.

In parts of northern Europe, tradition says that your wish will be granted if a ladybird lands on you. In Italy, it is considered good luck if a ladybird flies into your bedroom. In central Europe, a ladybird crawling across a girl’s hand is thought to mean she will get married within the year.

In Russia, there is a popular children’s rhyme where a ladybird is asked to fly to the sky and bring back bread. Similarly, in Denmark children ask a ladybird to fly to“our Lord in heaven and ask for fairer weather in the morning”. In Irish, the insect is called “God’s little cow”.

The esteem with which these insects are regarded has roots in ancient beliefs. Despite the fact that their blood contains toxic alkaloids - or perhaps because of it – ladybirds have been used for medicinal purposes. People in pre- Industrial Europe used ladybirds as a cure for measles and colic. They
were also mashed and stuffed in cavities to cure toothaches.


A closer view of the intruders

Family
Ladybirds’ family name comes from their type genus, Coccinella. Coccinellids are found worldwide, with over 5 000 species. Most ladybirds mate in spring or summer and the female lays a cluster of eggs, numbering from a few to a few hundred, depending on the species, as near as possible to an aphid colony.

They also lay extra infertile eggs to provide a backup food source for the larvae when they hatch. The ratio of infertile to fertile eggs increases with scarcity of food at the time of egg laying.

Ladybirds develop rapidly. The larva emerges from the egg five to ten days after being laid and reaches maturity within two weeks. Pupation takes place on the plant where the larva fed and the adult emerges from the pupa after four to ten days. There are eight indigenous Coccinelidae subfamilies in southern Africa.

Ladybirds are often brightly coloured to ward away potential predators. This defence works because most predators associate bright colours (especially range and black or yellow and black) with poison and other unpleasant properties. This phenomenon is called aposematism.

In fact, most Coccinellids are indeed poisonous to smaller predators, such as lizards and small birds. A human would have to eat several hundred Coccinellids before feeling any effects.

 

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