Farmers of the settlement of Regaderos (Province of Valle del Cauca) have the remedy in their crops to attack the greenhouse whitefly (Trialeurodes vaporariorum). Amitus fuscipennis is the wasp which roam plants around vegetable crops and suck its extrafloral nectar.

This yellow-green colored fly under 2mm long has an effect on approximately 16% of the vegetable crops of the area of the Province of Valle del Cauca. In fact this small fly is one of the most important vegetable crop pests around the world.

Whitefly females lay between 80 and 300 eggs, live between 5 and 28 days, and feed on young leaf undersides. There is sucks the sap of plants and impacts plant yields. Furthermore it releases honeydew which favors the appearance of the sooty mold which interferes with photosynthesis.

The wasp parasitoid potential lies when it lays its eggs on whitefly nymphs causing its death and fulfilling its parasitic or controlling action.

“When the wasp detects the presence of the thick substance excreted by whitefly nymph when feeding, it searches the nymph and introduces an egg into its body. This egg hatches and develops into a larvae. After 38 days and at 19 °C (66.2 °F) the wasp emerges and the whitefly nymph dies,” said María del Rosario Manzano PhD, Entomology Professor and Director of the Universidad Nacional de Colombia (UNal) in Palmira Tritrophic Interactions Research Group.

After extracting the honeydew from the wasp digestive tract and using a regent which detects this substance known as antana and then comparing it to adjoining plants, researchers determined that to improve the habitat of wasps for biological control it is recommendable to establish adjoining plants, wrongfully called ‘weeds’, which produce nutritious substances (sugar in form of extrafloral nectar) which favor insect populations thus providing shelter to the insect,” said UNal-Palmira Professor Joel Tupac Otero Ospina who has also supported the project.

Research has determined that the wasp is present in approximately 30% of the plants close to the crops or within them. Furthermore 20% of these insects are in adult stage; therefore identifying the plants and its features is an essential task for implementing this natural controlling strategy.

Therefor they proved that plants such as the common morning-glory (Ipomoea purpurea), chayote (Sechium edule), squash (Cucurbita maxima) and citronella (Critoniella acuminata) are good company for wasps.

“One of the most relevant results of the research project was to report the presence, for the first time, of extrafloral nectars from Phaseolus vulgaris beans. In other words, developmentally the crop indirectly helps the parasite (wasp) providing honeydew as a source of energy required for search and parasitization of the whitefly, but for this to happen plants must be at least 12 meters (39 ft.) from the crop,” said Manzano.

Wasp airport

Another aspect is determining wasp dispersion distance with respect to the crop. Therefore during two days they released 24,000 individuals on 12 occasions at a height between 30 and 50 cms. (11.8 and 19.6 in.) and at a wind speed of 1.37 meters per second (m/s). The wasps dispersed up to 12 meters (39.3 ft.) mainly towards the east, an interesting information taking into account that this is the bearing of the wind in the Andes Mountains at a latitude less than 15 degrees.

"This confirms the importance of wind direction in dispersing of a parasite as small as A. fuscipennis, with the purpose of reaching the desired crop,” said Manzano.

To establish the dispersion distance of wasps after 48 hours after their release, they placed traps with glue on 50 cms. wooden planks, sustained by wooden rods at three different heights.

The results of this research project will help provide suggestions to farmers on the places they should maintain adjoining plants. Furthermore this is proof that biological control effectively works and is useful both on diminishing production costs as well as decreasing damages caused by herbicide action to the environment.

Agencia de Noticias UNAL