Apple Orchard Challenges – Defending Against the Silent Threat of Biotic Factors

Author: Dr. Miloš Petrović, Assistant Professor at Faculty of Agriculture, University of Novi Sad

Apple, the most prominent, financially potent but besides that the most beautiful fruit species. It is grown all over the world, and Europe, Asia and North Africa are famous for apple production. From the very beginning of the vegetation cycle, apples are under attack by some of the biotic factors. Fungi from the genus Venturia and Podosphaera can infect leaves so small, that you did not know they are present on apple trees. Later, during the vegetation, besides fungi, other problems occur and most of them belong to the class Insecta.

Apple Codling Moth

Insect pests of apples are far more numerous when we talk about entomology in fruit production. The representatives from all insect orders are present in some numbers as more or less economically important pests. When you take a quick glance at the number of pesticides in general registered in all of Europe, one insect species always stands out. Apple codling moth, species from the order Lepidoptera, also known as butterflies, is the species responsible for more than 80% of registered insecticides in apple production.

And why is that the case? Why do Chemical and Biological companies invest so much time and money in the development of new chemical or biological agents to “fight” against such a small insect?

This species is called apple codling moth, and its scientific name is Cydia pomonella. The length of the adult ranges from 10 to 16mm. On the wings, they have distinctive ellipsoid markings, often referred to as the mirror. The adults are active during the noon and early night hours, and during the day they tend to relax, hidden in the leaves or bark of the apple trees. After the mating, females lay eggs, choosing the right spot for the next generations of the caterpillars.

And what is the right spot for an apple codling moth?

The places where the fruits join, or the fruits and leaves join, are the perfect places for females to lay eggs. The embryogenesis – or the length of the development of the caterpillar inside the egg horion is strongly affected by the outside temperature.

The species have two to three generations per year, and the first one which occurs during April or early May is the longest one to develop mainly because of the lower temperatures. The second generation which starts to fly and mate during late June or early July is one to develop faster when embryogenesis takes from 5 to 7 days, contrary to 10 to 12 days for the first generation on average.

After hatching, caterpillars have one distinctive move, and that is eating their own horion as a first meal rich in protein. And then, the trouble for apple producers starts, because this is the point when larvae start to eat fruit skin, and consequently burrow inside the fruit making the corridors filled with pelletized feces. On the outside, symptoms of the damage, looks like a small bump made of dark red to brown pellet, which is in reality digested fruit, expelled as excrement.

These described symptoms are the main reason why this species is so special when it comes to potent damage status. Lack of monitoring, low-quality pesticide spraying, and lack of knowledge when it comes to proper pesticide management in mixture with the plasticity of biology and ecology of this species makes it so economically important. Damaged fruits are often unusable, mainly because their appearance is unappetizing for human consumers, and bitter in taste for animals. Moreover, damaged fruits pose a threat to healthy fruits, because the openings on the skin serve as an entry point for many beneficial but also phytopathogenic microorganisms, which act as live decomposers of apple fruit tissue.

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