The South American leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) was firstly reported outside its native range in Eastern Spain in 2006 and, in 2007, dispersed to Africa via Algeria, Morocco and Tunisia (Desneux et al., 2011; Desneux et al., 2022). Now, it is widely distributed in more than 100 countries (EPPO 2023). The primary host of this pest seems to be Solanum lycopersicum L., although it can feed and develop on other plants within Solanaceae and Convolvulaceae, such as the bittersweet nightshade (Solanum dulcamara L.), black nightshade (Solanum nigrum L.), cape gooseberry (Physalis peruviana L.), common thorn (Datura stramonium L.), eggplant (Solanum melongena L.), pepper (Capsicum annuum L.), potato (Solanum tuberosum L.), sweet potato (Ipomea batatas (L.) Lam.), tobacco (Nicotiana tabacum L.) and wild tomato (Lycopersicon hirsutum Dunal) (Veira, 2016). Tuta absoluta is a key pest of tomato crops, causing devastating economic impacts to growers (Biondi et al., 2018), sometimes reaching 100% of economics losses fruits (Rostami et al., 2020). Foliage damages are the primary cause of the economic losses, especially when populations are abundant. The damages result predominantly from feeding activity of larvae on leaf tissues where they produce mines. When attacks are extreme, mines may merge causing destruction of the leaves. The reduction of leaf tissues induces dispersion to new organs, including the fruits. The larvae penetrate fruits, often below the calyx, facilitating fruit infection by pathogens (Chermiti et al., 2009; Balzan & Moonen, 2012; Guedes & Picanço, 2012).
The zoophytophagous Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) is recognized as one of the most promising biological control agents against T. absoluta (Arnó et al., 2021). This mirid has been successfully mass reared for commercial purposes (van Lenteren, 2012) and used in the biological control of different arthropod pests, such as aphids, thrips, whiteflies, and spider mites (Fauvel et al., 1987; Alvarado et al., 1997; Barnadas et al., 1998; Riudavets & Castañé, 1998; Margaritopoulos et al., 2003; Perdikis et al., 2008; Arnó et al., 2009; Calvo et al., 2009; Urbaneja et al., 2009; Castañé et al., 2011; Urbaneja et al., 2012). Macrolophus pygmaeus is widely distributed across the Mediterranean area, including Portugal. It was firstly referred to the Azores, in 2012 (Kerzhner & Josifov, 1999), but no information is available on the origin and date of colonization. Most likely, the Azorean populations have originated from Portugal mainland. Although Dicyphini mirids are zoophytophagous, the level of damage they can originate in host plants is variable, depending on the species. Macrolophus pygmaeus has been seen as a candidate to replace Nesidiocoris tenuis (Reuter), in biological control in tomato crops, because the damage inflicted on plants is much less. Nevertheless, we should take in consideration that plant feeding allows mirids being present in the field, when prey is scarce, which is a critical aspect in biological control, due to a faster build-up of their populations. Thus, mirid zoophytophagy can be seen as an advantage in biological control tactics if the originated crop damage is tolerable (Abraços-Duarte et al., 2021; Perez-Hedo et al., 2021; Coppel & Mertins, 1977).
Biological and ecological traits of the pests and their natural enemies should be accessed to predict how successful a biocontrol agent can be for augmentative biological control (Coppel & Mertins, 1977). The effectiveness of pest control is largely determined by the relationship between biocontrol agent voracity and pest population growth (Coppel & Mertins, 1977), especially the females that, in general, are the most voracious developmental stage and, depending on the availability of prey, biomass consumption may translate in a positive reproductive numerical response. That is, changes in the number of predators on prey colonies may result from two different mechanisms: attraction of predators to prey aggregations (aggregational response) and increased rate of predator reproduction when prey is abundant (reproductive numerical response). Predation or parasitism rate must be higher than the growth rate of prey/host (Coppel & Mertins, 1977). In insect pests with fast population growth, such as aphids, it is essential that biocontrol agents must have a high voracity (Borges et al., 2011; 2013). However, prey may differ in their suitability driving alterations on predator’s survival and development rate. The consumption of different prey species can have consequences for predator’s reproductive numerical responses changing, by this way, the success of biological control. Predator egg production also requires nutritional intake beyond a maintenance level, and thus high-quality food sources are mandatory for supporting predator reproduction (Seagraves, 2009; Sebastião et al., 2015; Hodek, 1962; Hodek & Honěk, 1996; Hodek & Evans, 2012).
Recently, Borges et al. (2023) provided experimental evidence that T. absoluta eggs can be considered essential food for M. pygmaeus. That is, when fed only with T. absoluta eggs, nymphs of M. pygmaeus can complete development and the originated adults are able to reproduce. From an applied point of view, the assessment of the number of eaten (killed) eggs of T. absoluta is an important predictor of a predator’s potential as a biological control agent. Prey consumed by insects can vary greatly in quality. Prey quality affects growth, development and reproduction. The percentage of consumed prey biomass converted into predator biomass (the so-called efficiency of conversion of ingested material or relative growth rate) is a useful proxy to test food quality (Waldbauer, 1968). Expressing predator voracity as the amount of biomass intake, allows i) to compare similar biological traits among different prey, given that species do not have the same body weight and ii) to estimate some physiological parameters, as the conversion efficiency. Following biomass consumption, weight increases and conversion efficiency are good predictors of energy intake and associated costs (Waldbauer, 1968; Odum, 1956). According to the universal model of energy flow (Odum, 1956), conversion efficiency corresponds to the proportion of biomass consumed allocated to growth.
In the present study, we assessed the voracity, the weight gain and conversion efficiency of M. pygmaeus females when fed on T. absoluta eggs. We compared two feral populations of M. pygmaeus, i.e., one from Portugal mainland and one from Azores archipelago. We intended to estimate the predatory activity of M. pygmaeus, assessing to what extent will it be possible to mass-reared under laboratory conditions, using a factitious prey, for later use in IPM of T. absoluta, as well as investigating if its predatory performance may vary among populations of different geographical origin.