With spring the flowers arrive and of course, the insects that eat them. We talked about thrips, insects that are difficult to love since they deform the fruits and eat the flowers of our precious crops. But, let’s make an effort to understand them.
We return with the plague of the month and this time we talk about a small insect, with precarious wings and that undergoes a metamorphosis halfway: the thrips. They do it very well is to eat flowers! And it is this diet that causes problems for farmers since the fruits grow ugly and unattractive. Therefore, I want to retrieve an article that was published in this magazine some time ago in defense of the consumption and trade of ugly fruits and vegetables. Beautiful people eat ugly fruit, remember?
Born, grows, reproduces … and eats flowers!
Tisanòpters are small insects, with little more than half a millimeter that we know as thrips. They are usually dark, brown or black and their name derives from the Greek: typos- , which means fringe and – pteron which means wing. Some species do not have wings and use the wind to travel taking advantage of the warm currents. They feed exclusively on vegetables thanks to their mouth appliance specialized in sucking plant sap. About 5,600 species are known, many of which are crop pests.
Since the order of the tisanòpters is so extensive, it would be a bit risky to explain a general life cycle, so we will use Pezothrips kellyanus as a model organism, among the thrips, the only one that attacks citrus flowers. The females lay the eggs in the tender parts of the plant, in the petals when there is a flower and in the young fruits and leaves when the flower has fallen. Nymphs live in flowers, between the petals and the fruits of which they feed. After the second stage, the nymphs are dropped to the ground and there, buried under the leaves pass the third and fourth stage, ending its development. The complete cycle lasts between 10 days (at 31-35 ° C) and 26 (at 15 ° C).
In incomplete metamorphosis (hemimetabolism) the individual goes through several molts to become an adult without going through a stage of inactivity and without ceasing to feed. The youth stages are the reduced version of the adult although without wings and immature sexually. They may also have fewer body segments. This type of metamorphosis occurs in some insects and also in annelids, echinoderms, mollusks, and crustaceans.
In this type of metamorphosis, the juvenile phases are called nymphs. In the last molt, they just developed the wings, the genitals, the thoracic musculature for the flight, the nervous system and some more specific systems.
On the other hand, in the holometábolo metamorphosis or complete metamorphosis, the following phases occur embryo, larva, pupa, and adult. The embryonic stage takes place within the egg from which the larva comes out, which has nothing to do, in terms of appearance and ecology, with the adult. The larva molts several times before reaching the state of the pupa in which drastic changes occur that include the differentiation of the tissues and organs of the adult and the destruction of those of the larva.
Agricultural importance and control
Since they feed on flowers or fruits, the damages in agriculture and horticulture are considerable since they cause deformities in the fruits. In addition, thrips are a vector of some of the most harmful viruses, such as the virus of canning tomatoes.
The scarification around the peduncle is a symptom of the presence of thrips, although sometimes these marks appear to the fruit rub against the branches. The most affected crops are lemons, navel oranges, and grapefruit in terms of citrus but there are more crops that are victims, we talk about almond cotton, cherry, plum, melon, tomato or grape.
If the attack of the trip on the flower occurs when the fruit is very young, it is aborted. But thrips have a kinder face and they have attributed a percentage of pollination, although there are no studies that provide concrete data.
Before moving on to chemical solutions, we must talk about prevention: to prevent our flowers from being forage of the thrips, we will have to eliminate the plants whose flowering explodes before that of our crop. Regarding the biological control with natural enemies, there are experiences that have demonstrated the effectiveness of the use of bedbugs as thrips predator in crops such as peppers.
On the other hand, the use of organophosphates must be minimized since the thrips become resistant very easily. If your crop is familiar, a good alternative is neem oil, available at any cooperative.