biocontrols: important definitions

Any living being that thrives at the expense of another living being is considered a predator. In agriculture, certain types of predation have been given specific names based on their feeding habits..

In general, living beings that thrive at the expense of plants and have an impact on crop yields and ornamental gardens, such as field mice, tomato blight caused by a fungus, and bean mosaic virus, are called pests. Among these, to cite a few examples, insect larvae that burrow into apples, snails that devour lettuce leaves, rodent mammals, butterfly caterpillars that devour leaves, etc., are called ravagers (or predators). Sucking insects, as their name suggests, include all insects that feed by extracting sap. Phytopathogenic agents refer to microscopic organisms (bacteria, viruses, fungi, etc.) that cause disease.

Many crop pests are a source of food for other living creatures, which are then referred to as beneficial insects. In agriculture, it is common to refer to all beneficial insects that feed directly on one or more pests as predators, followed by the name of their prey. For example, ladybugs are predators of aphids. This makes it easier to distinguish between pest insects and beneficial insects that are capable of controlling the proliferation of pest insects. An organism that thrives at the expense of a pest, either outside or inside its body, is called a parasitoid when it inevitably kills its host during or at the end of its development.

The word parasite is also used in some articles to refer to harmful insects, which is a misuse of language that can cause confusion with parasitoids, which are, of course, beneficial parasites. However, the word parasite is often used in agronomy studies to refer to chlorophyll-free plant organisms that grow at the expense of other plants. Dodder (a), or broomrape, endemic to the Mediterranean basin (but also very common in the Vendée region), are parasitic plants that feed on wild and cultivated plants. Broomrapes are formidable herbaceous plants, known to parasitize rapeseed, sunflowers, hemp, and melons in market gardening, for which there is no effective eradication treatment. Dodder parasites notably include tomatoes, carrots, melons, eggplants, onions, and potatoes.

All useful auxiliaries are grouped under the name “biological control agents” when they are used in biocontrol techniques

a) After germinating on the surface, the cuscute dodder plants appear as filamentous, spindly vines that wrap themselves around the stems of host plants and parasitise them with suckers. Some dodder plants resemble the rooted bindweed, whose stems also wrap around the stems of other plants..

Polyphagous and oligophagous insects

Polyphagia is a diet characterised by a choice of different plants that allows pests to survive if one of their preferred foods becomes scarce. Among the insects that are particularly polyphagous, it is useful to mention the following defoliating caterpillars:

• Corn borer (Heliothis armigera, Heliothis zea) also known as tomato borer, as it is also found on tomatoes and can also attack artichokes, cucurbits and legumes..
• The caterpillar of the bramble bombyx (Macrothylacia rubi) is sometimes called “the polyphagous”, for its ease of invading other plants including edible species for humans such as strawberry, raspberry, and others
• The Mediterranean moth (Spodoptera littoralis) originates from Africa and is present in France in the South-East. It thrives on cereal crops (maize, sorghum, etc.), alfalfa, potatoes, green beans, tomatoes, strawberries and other vegetable and ornamental crops. The caterpillars of this pest cause rapid and complete destruction of infested plants

In the list of polyphagous pests, migratory locusts are known for their catastrophic devastation in Africa, Australia and Asia.

There are many other polyphagous insects, some of which are endemic, such as the aphids described on this website by clicking ici

Some insects are restricted to one plant family or genus; their feeding behaviour is then referred to as oligophagy. Oligophagous insects are more numerous than polyphagous insects. One of the best known in vegetable production is the Colorado potato beetle and the aubergine beetle. Lacewings which include more than 35,000 species, are almost all oligophagous. In this large family, we can mention the famous golden beetle. Being more restrictive in their choice of food, oligophagous insects are more vulnerable to their natural predators and parasites, but some of them have developed defence systems to keep them away, notably by producing toxic or foul-smelling substances or both.