Implementing and assessing the efficacy of Calendula officinalis L. (marigold) as banker plant for Macrolophus pygmaeus (Rambur) in protected vegetable production

Abstract: The generalist predatory mirid bug Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) is a biocontrol agent widely used in protected tomato crops for pest control. If its efficacy is well recognized, the costs of M. pygmaeus releases and the potential delay and variability for good crop colonization are still highlighted as an impediment. Moreover, these beneficials tend to disappear at the tomato uprooting. Two experiments were implemented at the INRA station of Alénya (Pyrénées Orientales, France) in 2016 and 2017 to test whether Calendula officinalis L. (pot marigold called Calendula in the present article) can be used as winter shelter to maintain M. pygmaeus until the next tomato crop. In the first trial, bug populations were monitored during the overwintering period on sown, planted and potted Calendula placed in the previous commercial tomato crop under plastic tunnels in soil. In the second trial, Calendula pots full of M. pygmaeus were introduced at early spring into two 400 m² tomato tunnels with 10 and 40 pots per tunnel compared to a control treatment. M. pygmaeus and whiteflies [Trialeurodes vaporariorum (Westwood)] populations on tomato were monitored. Planted and potted Calendula use confirmed its potential as winter shelter for M. pygmaeus conservation between two summer host crops. The introduction of Calendula pots in tomato tunnels significantly improved M. pygmaeus set up and T. vaporariorum regulation compared to the control treatment. Such practices here tested in commercial-size tunnels offer promising results to reduce farms’ pesticides dependency and to improve the resilience of agroecological crop protection strategies.