KNOW THE MOST COMMON PESTS IN OUR CROPS

KNOW THE MOST COMMON PESTS IN OUR CROPS

do you know the most common pests in our crops? We understand agricultural pests as a minimum group of individuals that feed on plants (phytophagous animals) and as a result reduce the quality and final production of the crop. Pests can also be understood as diseases that affect crops and are caused by fungi, bacteria and viruses; and invasive species, weeds, that compete directly with the cultivar with which they coexist. In the latter two cases, there is also a reduction in crop quality and quantity. All these pests represent what is known as biotic stress in cultivated plants.

In this and subsequent blog posts we will focus on arthropods and nematodes that cause significant economic losses for the agricultural sector. Usually, the period of greatest incidence of these types of organisms is between spring and autumn due to the weather conditions that favour their development and emergence.

Arthropods, including insects and arachnids, can be classified according to the way they feed on crops (suckers, leafminers, chewers and borers) causing weakening of the plant, galleries inside the tissues and damage to all vegetative organs.

CHAPTER I: PRAYS

We will start with Prays Oleae, the olive moth or prays, which belongs to the order of Lepidoptera, commonly known as butterflies. It is a monophagous species, i.e. it feeds exclusively on one crop, in this case the olive tree. It is widespread throughout the Mediterranean basin.

Morphology

Adult: butterfly 6-6.5 mm long with a wingspan of 13-16 mm. It has a greyish colour with silvery highlights. The edges of the wings are fringed with hairs and the forewings have one or two characteristic spots in the central area.

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Egg: about 0.5 mm in diameter, lenticular in shape with an elliptical rim and a whitish colour that turns yellowish as hatching approaches.

Larva: it has between < 1 to 8 mm throughout its development, the colouring is variable according to its feeding, although it is characteristically hazel with the presence of two longitudinal green bands along the dorsum, and two lighter ones laterally. The front of the head is brownish and has two mandibles. It has fine hairs of varying lengths all over the body.

Chrysalis: 5 to 6 mm long, with no specific morphology. It wraps itself in silk and organic plant debris both on the ground and above ground, depending on the generation stage it is in.

Life cycle

It has a biological cycle with 3 annual generations perfectly synchronised with the phenological development of the olive tree, affecting all plant organs.

The first generation, philophagous, comes from the previous autumn’s laying (October-November). It establishes itself on leaves and buds from late winter to early spring. The emerged larvae penetrate into the leaf near the midrib, digging galleries between the two epidermal layers, where they settle during the winter (leafminers).

The second generation, which is anophagous, moves between April and June, in the adult stage, to the flowers, making a hole at their base through which they penetrate inside to feed. The female lays eggs in the flowers, from which larvae hatch and feed and complete their development in all the floral organs.

The third generation, carpophagous, occurs from June to October. On the one hand, the adults of the previous generation lay their eggs in the freshly set olives, and on the other, the larvae penetrate the stalk insertion of the olives, moving towards the centre of the fruit, which they feed on, causing it to fall prematurely when the prays enters and/or leaves.

Symptoms and damage

In the phyllophagous generation, some leaf galleries can be observed, but damage is difficult to assess.

During the anophagous generation, desiccation and flower drop may occur. Quantification can also be complicated, but if we take into account that the olive tree itself discards more than 95% of its flowers, this damage should not have a major impact. In addition, the moth needs the olives to complete their development in order to make room for the next generation. It is the carpophagous generation that causes the greatest loss of production. The olives, which have almost finished forming, fall to the ground at the same time as the prays.

goes to the outside. Depending on the year, it can increase more or less, and sensitive olive varieties can lose around 15% of their olives.

Treatments

Non-conventional treatments authorised for control are kaolin and Bacillus thuringiensis kurstaki. During the carpophagous generation, it is profitable to treat when there are more than 20% of olives with eggs present. The application is carried out when half of the clutch has already hatched, and it is recommended to treat the anophagous generation in order to reduce the subsequent fruit drop by 30-40%.