Life history and biological parameters of two Orius predators on flower and leaf-inhabiting thrips, with notes on the reproductive biology of Thrips setosus Moulton

Tese de mestrado, Biologia Humana e Ambiente, Universidade de Lisboa, Faculdade de Ciências, 2020The flower thrips Frankliniella occidentalis (Pergande), the leaf-dwelling thrips Echinothrips americanus Morgan and the most recent thrips invader Thrips setosus Moulton are currently amongst the most concerning pests in Dutch greenhouses. Although F. occidentalis is now successfully controlled by generalist predators of the genus Orius in vegetable crops, E. americanus and T. setosus still lack an efficient biological control agent, especially in ornamental crops where these pests are particularly problematic. In the first part of this study, we evaluated the predation capacity, predation behaviour, prey preference and life history traits of the two commercial anthocorid predators, Orius laevigatus (Fieber) and Orius majusculus (Reuter) on these key pests, in laboratory trials at 25 °C. Female adults of O. laevigatus and O. majusculus fed on 18 and 20 F. occidentalis adults, 30 and 42 E. americanus adults and 36 and 38 T. setosus adults per day, respectively. Complementarily, we observed that F. occidentalis showed a very agile behaviour in contrast to the low mobility levels observed for T. setosus and E. americanus. This suggests that prey’s mobility was one of the factors influencing the predation capacity of Orius. All development and reproductive parameters were more favourable on the prey E. americanus, including intrinsic rates of increase, averaging 0.1662 and 0.1538 females/female/day for O. laevigatus and O. majusculus, respectively. Additionally, slightly superior fecundities and longevities were scored by O. laevigatus in comparison to O. majusculus. Overall O. laevigatus reared on E. americanus had the best performance with values of fecundity (169 eggs/female), longevity (23.6 days for females) and intrinsic rate of increase, approaching what has previously been reported on the high-quality prey Ephestia kuehniella Zeller eggs. Contrastingly, O. majusculus reared on F. occidentalis registered an inferior performance with the lowest intrinsic rate of increase (0.1320). Regarding the second part of the study, we investigated the effects of supplemental foods on life history traits of T. setosus. This species has been recently introduced in Europe and little is known about its biology. We found that the addition of E. kuehniella eggs, Artemia franciscana Kellogg cysts, pollen or honey to a bean leaf did not influence the oviposition rate or longevity of T. setosus females. We thus conclude that these common commercial foods can be used to benefit populations of natural enemies without the risk of at the same time increasing densities of T. setosus. So far, this species have not shown omnivorous habits. Additionally, based on progeny production of unmated adult females we conclude that T. setosus reproduces through haplodiploid arrhenotoky (unfertilized eggs produce haploid males and fertilized eggs produce diploid females). Altogether our findings add to the understanding of the reproductive biology and feeding habits of this unstudied species. Furthermore, we show evidence of the potential of O. laevigatus and O. majusculus as biological control agents of F. occidentalis, E. americanus and T. setosus. Particularly, we discuss E. americanus as a high-quality prey for Orius