Aphidius colemani

Aphidius colemani

Aphidius colemani (Aphidius colemani Viereck, 1912) is a small Hymenopteran belonging to the Braconidae family.

Systematics –
From a systematic point of view, it belongs to the Eukaryota Domain, Animalia Kingdom, Subgenus Eumetazoa, Superphylum Protostomia, Phylum Arthropoda, Subphylum Tracheata, Superclass Hexapoda, Class Insecta, Subclass Pterygota, Cohort Endopterygota, Superorder Oligoneoptera, Hymenopteroid Section, Section Hymenoptera, Subordinate Section, Hymenoptera Section Terebrantia, Superfamiglia Ichneumonoidea, Family Braconidae and therefore to the genus Aphidius and to the species A. colemani.

Geographical Distribution and Habitat –
Aphidius colemani is a small hymenoptera, a solitary parasitoid; it is a cosmopolitan species that parasitizes over 41 host aphid species and that carries out the larval cycle within the body of these and that it can control in various environments such as: gardens, agricultural crops, urban landscapes, etc.

Morphology –
The adults of the Aphidius colemani measure 2-3 mm, of slender structure, with blackish body, brown legs and with the long antennae typical of the braconids.

Attitude and biological cycle –
Aphidius colemani is a solitary parasitoid, which develops the larval cycle within the body of some aphids. The biological cycle of this insect takes place with the phases of egg, larva, pupa, adult.
The females, who are endowed with a high research capacity, frequent the sites of aphid settlement and once identified the aphid lay an egg inside. The female that lays its egg inside the body of the aphid can parasitize both nymphs and adults. The parasitized aphid does not die immediately.
In fact, the parasitized aphid continues to feed normally for 3 days (the time the egg hatches inside it); at this point the small larva of the A. colemani begins to feed on non-viable internal organs. After 7 days from the parasitization (with average temperatures of 21 ° C) the parasitoid fixes the host on the leaf and forms a pupa which causes the attached aphid to swell which, at this point, takes on a golden-brown color with a paper aspect ( mummy). Four days later (with temperatures of 21 ° C) the adult of A. colemani flickers through a round hole. The pre-imaginal development period lasts approx. 14 days (at 21 ° C), which is longer than that of aphids in optimal circumstances (6-9 days). However this is largely compensated by the hundreds of eggs laid by the Braconide for the most part in the first 4 days from the flicker.
An adult of A. colemani can live for 2-3 weeks. The parasitoid identifies the plant attacked by aphids through the chemical signals emitted by the plant itself. At shorter distances it is the honeydew that leads him to his victim. The adults of A. colemani feed on honeydew. With the presence of parasitoids inside a colony of aphids, they begin to emit pheromones of alarm. Alerted, aphids get agitated and often fall to the ground where they usually die.

Ecological Role –
The parasitoid Aphidius colemani is an Hymenopteran Braconide able to act effectively against M. persicae and A. gossypii and, in general, of large aphids, while with regard to small aphids like Macrosiphum euphorbiae and the like it is very little effective. It is the larval state of Aphidius colemani that determines biological control, while adults feed on honeydew.
This parasitoid performs the best action at temperatures around 20 ° C and is used both in organic farming and in integrated pest control on various vegetable, flower and ornamental crops.
The good level of parasitization and the specificity towards the host make the use of Aphidius colemani very valid in biological-integrated control programs, implementing a distribution of the insect through more throws, from 0.5-2 individuals / sqm, so as to immediately obtain a good balance between the aphid and its antagonist.
Since aphids reproduce very quickly it is necessary that the launches are carried out very soon. In many crops it is advisable to start throws in susceptible periods (or even after transplanting) at a dosage of 0.5 to 10 A. colemani / m2, continuing the throws for 3-4 weeks.
Aphidius colemani behaves well even at temperatures below 20 °, so it can be very preventive in throws. Sometimes the launch of A. colemani can be affected by hyperparasites that live at the expense of auxiliary larvae and pupae. From the mummy, with a certain delay, does not flutter a Braconide, but an adult of hyperparasite. The easiest method for recognition is to control the flicker hole; when a hyperparasit has come out the hole is lateral and serrated (not round and central).
The use techniques of the ide pest vary according to the crop to be protected, the species of aphid to be controlled and the environment in which it operates.
In protected cultivation the most common strategies are:
– repeated introductions to the appearance of the first aphids;
– preventive launches in the most risky situations;
– use of “banker plants” (ie grass plants on peat and on rock wool on which there are aphids that live and reproduce only on these plants without there being the danger that they attack the crop).
In summer, due to persistent high temperatures, the species is less effective so:
– the quantities to be introduced are increased;
– A. colemani is used together with other entomophages;
– or you decide to use another entomophagus.
In general, some indications are given for the main cultures.
Cucurbitaceae (melon, watermelon, cucumber, courgette):
– 6-10 individuals / m2 divided into 4-6 launches every week since the first attack is identified; in case of “preventive” defense, in periods usually at risk of infestation, throw 0.5 individuals / m2 weekly for 4-6 times; to the appearance of aphids increase the unit launch quantity.
peppers:
– 4-8 individuals / m2 distributed in 4-6 throws on a weekly basis with the appearance of the first aphids.
Eggplant:
– 6-10 individuals / m2 distributed in 4-6 throws on a weekly basis with the appearance of the first aphids.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.- Russo G., 1976. Agrarian Entomology. Special Part. Liguori Editore, Naples.- Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.