How Safe Is It to Rely on Macrolophus pygmaeus (Hemiptera: Miridae) as a Biocontrol Agent in Tomato Crops?

Abstract

Omnivorous mirids (Hemiptera: Miridae) are unusual as biocontrol agents, as they feed on both plants and pests. Therefore, extensive knowledge of their ecological behavior is required to maximize their predatory side and to minimize crop damage. Macrolophus pygmaeus is a known predator of small arthropods, used in European tomato crops for more than 20 years. This mirid is currently considered harmless to tomato, although some controversy remains in relation to the status of the species. The aim of this work was to investigate the benefits that M. pygmaeus provides as a predator and the likely damage as a plant feeder. The experiment was carried out in 6 experimental greenhouses in southern Spain. Two treatments, low and high M. pygmaeus populations, were assayed in a complete factorial randomized design with three replicates. Low and high M. pygmaeus populations were achieved by direct and pre-plant release methods, respectively. Tomato plants with a lower number of M. pygmaeus had a significantly higher number of whiteflies and Tuta absoluta galleries than those with a higher number of the mirid, and vice versa. A significantly higher proportion of aborted flowers and fruits was registered in greenhouses with higher M. pygmaeus numbers. Yield was also lower in greenhouses with higher mirid populations. The number of fruits harvested did not differ between treatments, but average fruit weight was significantly lower in the greenhouses with higher mirid numbers. The number of punctures attributed to M. pygmaeus on fruits were low in general and slightly higher in the treatment with more mirids. This work shows that M. pygmaeus provides both "services," as an efficient biocontrol agent of key pests in tomato crops, and "disservices," as it feeds on the reproductive organs of tomato plants, reducing yield. A deeper understanding of the factors that modulate the zoophytophagous response of this economically important species is needed.

Biological Control Potential and Drawbacks of Three Zoophytophagous Mirid Predators against Bemisia tabaci in the United States

“…In contrast, Macrolophus species used in biocontrol programs are widely considered harmless [ 1 ]. However, M. caliginosus Wagner can damage tomatoes and cause economic loss through flower and fruit drop [ 48 ] and high densities of M. pygmaeus can cause significant tomato fruit damage, particularly when the plant was infected with Pepino mosaic virus [ 49 , 50 ]. As found with other Macrolophus biocontrol agents, careful management of M. praeclarus numbers may be necessary and further studies should be conducted.…”

Beneficial Insects Deliver Plant Growth-Promoting Bacterial Endophytes between Tomato Plants

“…Migration from stems to roots has already been demonstrated for 32A in grapevine [31]. In the case of increased predator density [5], mirid feeding on plants could lead to slight yield losses [16,17]. Mirids were provided with either mock-inoculated or bacterium-inoculated tomato plants as only food source and differences in tomato shoot length after M. pygmaeus-mediated transmission were greater in PsJN-inoculated plants compared to mock-and 32A-inoculated plants.…”

“…Macrolophus pygmaeus and N. tenuis have piercing and sucking mouthparts that contain two channels: one to pump salivary fluid into plant tissues and the other to suck sap fluids from the host [13]. These two species frequently complement their carnivore diet with plant sap feeding [14,15], which could also lead to slight yield losses [16,17]. For example, M. pygmaeus feeds mainly on the mesophyll of leaves, stems and fruits, and high population densities caused fruit damage when plants are infected with pepino mosaic virus (PepMV) [18].…”

The Role of Host Plants, Alternative Food Resources and Herbivore Induced Volatiles in Choice Behavior of an Omnivorous Predator

“…However, Moerkens et al (2016) reported that M. pygmaeus, can cause economic damage in tomato crops regardless the presence or absence of prey. In addition, Sanchez et al (2018), reported that high populations of this mirid may lead to a yield reduction due to increased plant feeding. Yet, further research is necessary regarding other species of host plants.…”