Morphometry and molecular markers to discriminate betweenMacrolophus pygmaeus and Macrolophus melanotoma

Abstract: Macrolophus melanotoma (= M. caliginosus) and Macrolophus pygmaeus have beenreferred to as important predators of pests in vegetable crops in the Palaearctic region. Due totheir high morphological similarity, these two mirid species have been confused, with importantconsequences for their use in inoculative and/or conservative biological control programmes. Inthis study we review the taxonomic characters that proved reliable to separate the two species, asthe profiles of cuticular hydrocarbons, a discriminant function of four morphometric ratios ofmales, and specific primers to distinguish both species through conventional PCR. We alsodiscuss the correct assignation of Macrolophus species in historical records. All the testedMacrolophus samples from the IRTA’s old lab colonies were identified as M. pygmaeus, showingthat the articles we have previously published on “M. caliginosus” using laboratory coloniesshould have referred to M. pygmaeus. When samples from comercial companies were analyzedusing the previously mentioned specific primers , in all cases, the species was identified asM. pygmaeus. This result shows that in most cases the species being commercially released isM. pygmaeus. We can therefore hypothesize that most of the field work done on ‘M. caliginosus’in the Mediterranean Basin, and presumably also in the rest of Europe, which has mainly focusedon tomato crops, could probably have referred to M. pygmaeus. The identification of native plantsthat are sources of the predator that colonises the tomato crop is a key element in the implementationof conservation biological control programmes for this crop. However, most of the host plants forboth species still remain largely unknown.