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With the invasion or local occurrence of Bemisia tabaci and Tuta absoluta in recent decades, they both have become two major insect pests of tomato crops in many countries. The biological control of these two pests through heteropteran predators, e.g., Nesidiocoris tenuis or Macrolophus pygmaeus, is a key pest management strategy. However, by contrast to M. pygmaeus, N. tenuis could usually cause plant damage and yield loss. The joint use of these two mirids for pest management has not been described yet, although it may be helpful in reducing the side effects of N. tenuis on crop (owing to competitive and/or agonistic interactions between the two species). In this study, we compared the abundance of predators and pests in treatments with N. tenuis and M. pygmaeus together versus N. tenuis alone and in the presence of B. tabaci only or B. tabaci and T. absoluta. We also measured necrotic rings and tomato flower production in these four treatments. We found that the joint use of both mirid predators together led to (1) a reduced overall mirid density and (2) a sustained biocontrol efficiency, when compared to the use of N. tenuis alone. In addition, plant feeding activities of mirids were significantly reduced when predators were used jointly (vs. N. tenuis alone). The applicability of zoophytophagous predators as biocontrol agents could be facilitated by simultaneously releasing two (or more) heteropteran predator species instead of a single one. [ABSTRACT FROM AUTHOR]

Macrolophus pygmaeus Rambur (Hemiptera: Miridae) is a generalist predatory mirid widely used in augmentative biological control of various insect pests in greenhouse tomato production in Europe, including the invasive tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera, Gelechiidae). However, its biocontrol efficacy often relies on the presence of alternative prey. The present study aimed at evaluating the effect of various prey foods (Ephestia kuehniella eggs, Bemisia tabaci nymphs, Tuta absoluta eggs and Macrosiphum euphorbiae nymphs) on some life history traits of M. pygmaeus. Both nymphal development and adult fertility of M. pygmaeus were significantly affected by prey food type, but not survival. Duration of nymphal stage was higher when M. pygmaeus fed on T. absoluta eggs compared to the other prey. Mean fertility of M. pygmaeus females was greatest when fed with B. tabaci nymphs, and was greater when offered M. euphorbiae aphids and E. kuehniella eggs than when offered T. absoluta eggs. Given the low quality of T. absoluta eggs, the efficacy of M. pygmaeus to control T. absoluta may be limited in the absence of other food sources. Experiments for assessing effectiveness of generalist predators should involve the possible impact of prey preference as well as a possible prey switching. [ABSTRACT FROM AUTHOR]

Increased pest control by generalist predators has been successfully achieved in several cases by promoting apparent competition, which is the reciprocal negative interactions between prey mediated by their shared predator. However, the presence of alternative prey does not always result in an improved control of the target pest species, due to the complexity and specificity of biotic interactions. To increase the effectiveness of IPM programs, a fine understanding of the interactions among co-occurring pest species and their biocontrol agents is necessary. We tested the occurrence of apparent competition between the major tomato pests Tuta absoluta and Bemisia tabaci when preyed on by a generalist mirid bug Macrolophus pygmaeus, by monitoring pest and predator population dynamics in a greenhouse experiment. We also measured the cascading effect of the shared predator on plant and fruit damage due to pests. We observed higher predator population growth and reduced population densities of both prey in treatments with two prey, as compared to treatments with one prey, showing that apparent competition occurred. Plant and fruit damage caused by B. tabaci was reduced in the presence of T. absoluta, but damage due to T. absoluta, which accounted for the major part, was not reduced in the presence of B. tabaci, resulting in similar levels of total damage when pests co-occurred. This study demonstrates that, even if promoting apparent competition leads to actual reduction in pest densities, yield loss may not be reduced when this strategy is applied to major pests such as T. absoluta. [ABSTRACT FROM AUTHOR]

Invasive species can strongly affect biotic interactions in ecosystems, interacting both directly and indirectly with local species. In European tomato greenhouses, the invasive alien pest Tuta absoluta may impact the population dynamics of other pests like whiteflies. Besides inducing damages to the host plant and competing for resources with local pests, this alien species may exert a predator-mediated interaction on local pests sharing common natural enemies. Biocontrol agents usually used against whiteflies may also prey upon T. absoluta and this could alter the dynamics of local pest populations. We evaluated possible resource competition and predator-mediated interactions in a system involving one mirid predator Macrolophus pygmaeus and two pests, T. absoluta and a local whitefly, Bemisia tabaci, on greenhouse tomatoes. Results showed that both resource competition and predator-mediated interactions occurred simultaneously. In the presence of the shared predator, there was a short-term positive effect of T. absoluta on B. tabaci [up to 5.9-fold increase of B. tabaci juveniles (egg + larvae) after four weeks]. However, in the long-term there was a negative predator-mediated interaction of T. absoluta on B. tabaci, i.e., after ten weeks the density of B. tabaci was 7.3-fold lower in the presence of the invasive pest. We emphasize the critical role of generalist predators in managing both local and invasive alien pest populations and that the strength and direction of predator-mediated indirect interactions can depend on the time scale considered. [ABSTRACT FROM AUTHOR]