Seasonal Development of Plant Bugs (Heteroptera, Miridae): Subfamily Mirinae, Tribe Mirini

Abstract

The available data on seasonal development of plant bugs (Mirinae: Mirini) are reviewed, and the level of understanding of their seasonal adaptations is evaluated. The ecological responses involved in control of seasonal development of 14 species from 5 genera (Adelphocoris, Apolygus, Lygus, Lygocoris, and Stenotus) are analyzed in detail. All the studied species are broadly polyphagous and produce a varying number of annual generations in different climatic zones. The studied members of four genera, namely Adelphocoris, Apolygus, Lygocoris, and Stenotus, hibernate at the embryonic stage while bugs of the genus Lygus do so at the adult stage. Some species of the genera Adelphocoris and Lygus, in particular Lygus pratensis, have acquired a pronounced ability to fly over long distances, facilitating the search for flowering vegetation. However, unlike many insects that make distant migrations in the state of adult diapause, females of plant bugs of the genus Adelphocoris migrate with mature eggs in their oviducts. This feature allows Adelphocoris females to successfully colonize new areas even in the absence of males, since females do not need additional mating in the colonized area. For the majority of Mirini species experimentally studied in the laboratory, the temperature parameters of development and the sum of effective temperatures needed to complete the full generation were calculated. When combined with observations done under natural conditions, these data allowed us to determine the exact number of annual generations produced by the species or population. The role of day length in the control of seasonal development was analyzed in detail in three species of the genus Adelphocoris: A. triannulatus, A. suturalis, and A. lineolatus. The conditions inducing and terminating adult diapause were studied in detail in Lygus hesperus in the southern United States. The seasonal development of Lygocoris pabulinus is an unusual example of an obligate host plant change during the year. The diapausing eggs of this species overwinter in the tissues of woody plants but the nymphs then migrate onto herbaceous plants on which the summer generations develop. Such a seasonal strategy is more characteristic of aphids (Homoptera) than of true bugs (Heteroptera). On the whole, our analysis of the available data indicates that the control of seasonal development of plant bugs of the subfamily Mirinae is still poorly understood despite their high economic importance. Most reports deal with a small number of experimentally studied species and are limited to the data on temperature parameters of development. The important role of photoperiodic adaptations in the control of seasonal development has been demonstrated only for a few well-studied species (e.g., Adelphocoris triannulatus); such data are crucial for analysis and prediction of seasonal development and spread of harmful and beneficial insects, since the seasonal cycle of each population of a given species is strictly synchronized with the local conditions.