The Mediterranean predatory bug Nesidiocoris tenuis (also called Nesi) is increasingly infesting tomato crops in Dutch greenhouses. These predators are useful for the control of whiteflies and the tomato leaf miner moth Tuta absoluta, but at the same time they cause serious crop damage, making this predator in fact a pest. At Wageningen University & Research, BU Greenhouse H we studied whether crop infestations could be reduced by pre-establishment of plants by other related predatory bugs. Three new species of mirid bugs strongly reduced the establishment and population growth of Nesi in tomato.
Populations of the commonly released predator Macrolophus pygmaeus are often outcompeted by an unintended infestation of the Mediterranean N. tenuis (Nesi). This predator has a shorter generation developmental time than Macrolophus and develops extremely fast at high temperatures. The damage they cause can be serious by feeding on the fruit and stems resulting in growth deformation. Feeding on stems causes typical necrotic rings which can result in stem breaking after crop handling practices. Controlling this predator with pesticides is impossible without affecting the Macrolophus. The result is often that controlling Nesi totally disrupts the biological control system of pests.
Setup greenhouse trial
The question whether establishment and population growth of Nesi in tomato can be reduced by pre-establishment of related predatory bugs was studied in a long running greenhouse trial at Wageningen University & Research in Bleiswijk. Establishment by Nesi was compared in treatments with and without other predators. The other way around, whether Nesi affects the other predators, was also tested by including treatments of new predators without Nesi. Three new species of predators were tested, which resulted in seven treatments in total. The experimental unit was a large walk-in cage with one single plant cv Brioso, grafted and with two stems. Populations of predators were followed during summer for 14 weeks with biweekly assessments.
De predator Nesi was able to establish in all treatments, but densities were considerably lower in treatments where other predators were released prior to the Nesi introductions. The final population densities of Nesi in the three treatments with other predators were on average 85, 92 and 95 percent lower compared to the control treatment without other predators. Laboratory studies showed that all adults of these new predator species predate on the nymphal stages of Nesi. In the greenhouse trials we did not observe opposite effects: Nesi introductions did not significantly affect the population densities of the other species of predatory bugs. Observations in practice often show that Macrolophus is outcompeted by Nesi, whereas the new tested species show the opposite, which can be a major benefit compared to Macrolophus. However, before switching to the use of new predators, it needs to be clear how effective they control the major pests in tomato. Upcoming year we will study the effects of the new predators on greenhouse and tobacco whiteflies in tomato.
This study is part of the project “Pest control by omnivorous predatory bugs”, which started in 2016. This public private partnership has 50% funding from the ministry of economics and 50% funding from private companies and foundations. The private partners in our project are the cooperatives for tomato, gerbera and rose crops, the foundation for research in greenhouse crops and Koppert Biological Systems. The project is leaded by Wageningen UR Greenhouse Horticulture and coordinated by LTO Glaskracht. Besides tomato, we also study the potential of new predatory bugs for pest control in gerbera and rose crops.