Investigating alternative methods for enhancing the establishment of the zoophytophagous mirid Nesidiocoris tenuis (Reuter) in greenhouse tomato crops

The zoophytophagous mirid Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) is an effective natural enemy of some major pests of tomatoes in the Mediterranean region. In this area the colonization of protected tomato crops by this biocontrol agent may be hampered by the application of measures aimed at avoiding the transmission to tomato plants of insect-vectored diseases (e.g. TYLCD). Furthermore, various factors, such as the scarce availability of preys on crop plants and the severe deleafing of tomato plants, may affect the population build-up of artificially introduced predatory mirids. Since these natural antagonists have become commercially available in Europe, several methods have been explored to enhance their establishment on greenhouse tomatoes. This work reports the results of experiments carried out to investigate the effects of different release methods on the establishment of N. tenuis in commercial greenhouse tomato crops grown in southern Sardinia (Italy). The techniques tested can be summarized as follows: a) release of mirids before transplanting; b) introduction into release points covered by non-woven films; c) introduction into uncovered feeding points; d) traditional release method. N. tenuis was introduced at a rate of 0.8 individuals per stem grown (2.4-3.2 mirids plant^-1) in crops planted during late summer. All methods except the traditional one envisaged the distribution of 0.01 g plant^-1 of Ephestia kuehniella Zeller eggs, supplied three times at two-week intervals, as an alternative food source. Two months after planting, pre-plant release and the introduction into covered or uncovered release points allowed the predatory mirid to reach significantly higher densities in comparison with the traditional release method. Under the conditions tested, the anticipation of release and the supply of an artificial food source appear to be decisive factors for enhancing the establishment of N. tenuis in greenhouse tomato crops.