The cottony scale insect

The cottony cushion scale is native to Australia. It was identified in New Zealand in 1878 but spread to every place around the world where citrus trees are cultivated. In Malta it was found in a garden at St Georges near San Giljan in 1907. Immediate action was taken to slow its spread to other parts of the Maltese islands until a system to control it biologically which was giving successful results in other countries could be used in Malta. The action taken might have slowed down its spread but did not stop this insect from reaching the central parts of Malta, including Lija, Attard and Balzan which at the time were well known for the cultivation of orange trees.
Last summer a small numbers of scale insects decided to set up home on some of my aubergine plants. I allowed them to grow so that I would be able to photograph them and follow their life cycle. This species of scale insects has an oval shape and can grow up to half a centimeter long. Mature insects attach themselves to a host plant by means of waxy secretions and remain stationary. In summer they produce a white egg sac on grooves on their back in which they deposit hundreds of red eggs. A few days ago I photographed minute nymphs coming out of the egg sac. These nymphs are the dispersal stage of the insect. They crawl from one plant to another but they are so are so light that they are often lifted up by the wind and carried to other areas to establish new populations.
The nymphs damage the host plant as they suck fluids from the veins of leaves and small twigs. As they grow they break out of their skin (exoskeleton) and move to another spot leaving behind their telltale skin and waxy secretions. When they become larger they move to larger twigs and eventually to the branches or tree trunk.
Most cottony cushion scales are hermaphrodites. They fertilise themselves and produce hermaphrodite insects. Males do exist. When a male fertilises a female both hermaphrodites and males are produced.
This insect is of interest because it was one of the first pests to be successfully controlled biologically. Between 1888 and 1889 a species of ladybird, the vedalia beetle, was imported into the United States from Australia to control this pest which was threatening California’s citrus trees. The experiment was a success and farmers in other countries started to use the beetle to control the scale insect wherever it appeared. In 1911 the vedalia beetle, which is known in Maltese as nannakola tas-salib, was imported into Malta by the Department of Agriculture to control the spread of the cottony scale insect which by that time was infesting citrus trees in most parts of Malta. (This article was published in The Times on 22.12.10)

Grasshoppers

As autumn turns to winter one starts seeing less insects in the countryside. Last Sunday while taking pictures at Selmun the only insects I saw in any number were grasshoppers. Several jumped into the large spaces between the stones of an old wall and walked slowly on the white limestone dust into the inner part of the wall until they disappeared from view. 

Grasshoppers overwinter as eggs, nymphs or adults so the ones I was observing could be looking for a suitable place to lay eggs or to hibernate.

Grasshoppers are familiar insects with short antennae and large hind legs. Sometimes the hind legs have short projections that are rubbed against the lower edges of the forewing to make a noise during the day. The legs are hard and can exert a lot of force and this gave rise to the idea in Malta that grasshoppers are armed with a knife which they use for self defense.

It is estimated that there are about 11,000 species of grasshopper in the world. Most live in tropical areas especially in rain forests. About 25 species are found in the Maltese islands. Some species are very common and you will see them jumping away from you wherever you walk in the countryside. Most are greyish brown and blend perfectly well with their surroundings. 

Some species have brightly coloured hind wings which are normally kept hidden under the forewings. They are uncovered only when they are flying. Te bright colours have an important function. 

When danger approaches these insects rely on their excellent camouflage for protection but if a predator approaches too closely they fly away startling their enemy with their bright colour for long enough to be able to fly away. They do not fly very far away but as soon as they land they disappear again.

Grasshoppers eat mostly vegetation and some species can become pests.

They have an incomplete metamorphoses as when they hatch the young look like small wingless adults which grow progressively larger as they break out of one exoskeleton after the other until they reach adulthood.

In Africa and in other parts of the world where they occur in large numbers, grasshoppers can be an important source of proteins, minerals and vitamins especially in times of food shortage. 

This article was pubished in The Times on 8.12.10

The rosemary leaf beetle lives on herbs

Rosemary leaf beetle (Chrysolina americana)

The rosemary leaf beetle is a common beetle that lives on rosemary and other herbs. Its scientific name is Chrysolina americana. Despite its scientific name, it is a native of southern Europe. In the early 1990s it appeared in Britain and during the last decade it has become an established pest on rosemary, lavender and related plants.

It is an attractive beetle with metallic green and purple stripes down its back. . In the sunlight these stripes reflect all the colours of the rainbow - rather like oil on water. This effect is very beautiful to see but difficult to capture on camera.

It is usually found in groups on stems or feeding on the new growth of plants. The larvae are small slug-like grubs which are usually found on the underside of leaves. They are light grey with horizontal dark stripes running the length of their body.

Their favourite food plant, the rosemary is a medium-sized bush of the Mediterranean, recognised by its narrow fleshy leaves, small pale blue flowers and more than anything else by its typical aromatic smell. The bush is usually about one metre high but when hanging down from a vertical rock face it can grow up to two metres. It flowers throughout the year.

The rosemary leaf beetle, known in Maltese as żabbella tal-klin, belongs to the Chrysomelidae family, a group of beetles known as the leaf beetles. This is a family of over 35,000 species, one of the largest and most commonly-encountered of all beetle families. About 60 of these species are found in the Maltese islands. Another common member of this large family is the red leaf beetle, żabbella ħamra in Maltese, which is found in vegetation in the countryside. Adult and larval leaf beetles feed on all sorts of plant tissue. Many are economically important pests of agriculture. 

This article was published in The Times on 05.01.2010

The invasive cockroaches

I do not think that there is any household in the Maltese islands that at some time or the other has not had cockroaches visiting the kitchen. These insect pests are scavengers that eat any food and manage to find something edible even in the cleanest of homes.

There are about 4,500 species of cockroach, of which about seven species are found in the Maltese islands. Four can be found in houses and unless controlled can become pests.

The large brown cockroach one sometimes sees scurrying in the street is the American cockroach which did not originate in America but came from Africa. It was introduced in America around 1625 and is now common in most tropical countries thanks to international shipping and commerce. It feeds on decaying organic matter and a variety of other foods and is particularly fond of fermenting foods. It is known in Maltese as wirdiena ħamra.

Another common species is the brown banded cockroach which is known as kokroċ in Maltese. The preferred habitat of this species is houses especially kitchens. It is much smaller but can reach large numbers if it finds the right conditions.

Some species such as the field cockroach which is known in Maltese as wirdiena ta’ l-għelieqi, live in the countryside and do not visit buildings.

Cockroaches are mainly warmth-loving insects. Some species thrive in buildings because these provide warmth and food throughout most of the year. They are known to transport microbes on their body surfaces including those that are potentially dangerous to humans. They also produce chemicals which can trigger allergic reactions and have been linked to asthma

Cockroaches are tough creatures that can survive in the most difficult conditions. They can live without food or water for a very long time. Some species can survive without air for up to 45 minutes and have been submerged in water for half an hour and survived to live another day. It is also said that if man had to destroy himself with a nuclear war the cockroaches would survive and take over the earth. 

This article was published in The Times on 04.08.2010