New species of plants and animals are recorded regularly in the Maltese islands. Some arrive naturally while others are brought in either intentionally or accidentally. In most cases, new species do not manage to establish themselves permanently but some manage to do so and sometimes they can do untold damage.
In a well-balanced environment, species are controlled by several factors such as stiff competition, predators, herbivores and parasites. Very often species arriving in a new zone do not have to face other controlling species and increase in number to such an extent that they become serious pests.
One such species, the Mediterranean vine-leaf beetle, was first recorded in Malta in 2010. It has since established itself in vine fields but has not yet spread to all parts of the Maltese islands.
The vine-leaf beetle is indigenous to the Mediterranean region, including Sicily. It can also be found further north in Switzerland and Germany.
The adult beetle has a metallic green colour. The larvae grow between eight and nine-and-a-half millimetres long but adults are much smaller varying in size between 3.3 and 5.2 millimetres. The larvae feed on the underside of vine leaves. The adults feed on the whole leave piercing them, making them look like a sieve.
Before resorting to insecticides, other methods of control should be investigated and tried
If the area of leaf damaged by these insects is large, the vine tree is unable to absorb enough light energy to photosynthesise sufficiently which results in a poorer crop. The first reaction when seeing damaged leaves is to control these insects by using insecticides.
Insecticides do not just harm this beetle but most insects in the area, including ones that play an important role in controlling other invertebrate species.
Before resorting to insecticides, other methods of control should be investigated and tried.
The Mediterranean vine-leaf beetle is controlled by the blue shieldbug, a predatory insect found throughout Europe but which is not found in Malta. This species should be introduced under controlled conditions and its impact on the vine-leaf beetle and other species investigated. If the results are positive it should be released in areas where the vine-leaf beetle is present.
Such biological pest control has been used in Malta in the past and can be used again as long as chemical insecticides, which would also kill beneficial predators, are not used concurrently.
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