by Enric Vila, AGROBIO, F. Madeira, UDL

 

More than 50% of the total surface of tomatoes produced in the greenhouses of the South of Spain, aprox. 10,200 ha, are produced using biological control. The control of the main pests is provided by a cheap preventive strategy based mainly on releases of the predatory bug Nesidiocoris tenuis in the nursery, prior to transplanting the tomato plants in the greenhouses (fig. 1). This predatory bug offers a good control of the pests but also can damage the plants (fig. 2), and chemical treatments are needed to keep the populations at low levels when prey are scarce.

 

serra pomodoro bug
Fig. 1. Releases of N. tenuis in the nursery, one week prior to transplanting. Fig. 2. Damages on tomatoes produced by N. tenuis.                                          Fig. 3. Nymph of Dicyphus spp. emerged on tomato plants after adult release on seedlings.

 

In order to provide an alternative predator as effective against the pests, but less harmful for the plants, the company Agrobío, in collaboration with IRTA and the University of Lleida, has set up a rearing system for the predatory bug Dicyphus spp. (fig. 3). A trial was set up in the spring of 2016 in an experimental greenhouse to evaluate the option of releasing this predatory bug in the nursery. Two treatments were set up: (1) releases of N. tenuis and (2) releases of Dicyphus spp., using in both cases a ratio of 0.5 individuals per plant. First results showed that this predatory bug can be established in the crop after releases on seedlings, but a major challenge must be addressed, the easy colonization of N. tenuis of the plants where Dicyphus has been released, which may be due to its high abundance in the landscape. Then, N. tenuis displaces this alternative predator and becomes the dominant species.