The larva of the Palaearctic Renocera pallida (Fallén, 1820) is confirmed as a predator of small species of bivalve molluscs of the family Sphaeriidae. To date only the larvae of three Nearctic Renocera species (and larvae of two other species of Sciomyzidae in two genera) are known to have the same food preference. The life cycle, biology, larval feeding and behaviour are described for the first time and compared with that of the Nearctic Renocera. The systematic position and biology of Renocera in general are discussed. Descriptions of the egg, second and third larval instars and the puparium of R. pallida are presented, the main features of the egg and larvae are illustrated by scanning electron micrographs.
Climate features that influence life cycles, notably severity, seasonality, unpredictability and variability, are summarized for different polar zones. The zones differ widely in these factors and how they are combined. For example, seasonality is markedly reduced by oceanic influences in the Subantarctic. Information about the life cycles of Arctic and Antarctic arthropods is reviewed to assess the relative contributions of flexibility and programming to life cycles in polar regions. A wide range of life cycles occurs in polar arthropods and, when whole life cycles are considered, fixed or programmed elements are well represented, in contrast to some recent opinions that emphasize the prevalence of flexible or opportunistic responses. Programmed responses ale especially common for controlling the appearance of stages that are sensitive to adverse conditions, such as the reproductive adult. The relative contribution of flexibility and programming to different life cycles is correlated with taxonomic affinity (which establishes the general lifecycle framework for a species), and with climatic zone, the habitats of immature and adult stages, and food., Hugh V. Danks, and Lit
The gypsy moth oophagous predator guild in the Mamora forest is an assemblage of many species whose succession in egg masses enhances the exploitation of this food source. Life history, biological Features and trophic capacities of predator species are described from field observations and laboratory rearing. Extreme diversity of diets, capacity to resist prolonged fasting and extended larval development with extra-instars enable them to survive on the cork oak when gypsy moth egg masses are absent. The 1986-1990 gypsy moth outbreak occurred in a forest part where unhealthy cork oaks are common. by providing abundant shelter for numerous arthropods these trees are beneficial to the oophagous predators which find there various and abundant food sources. This probably explains why egg predator activity in the infested area rapidly increased so that the pest outbreak collapsed.
Insect dormancy responses, in the broad sense of modifications of development, are examined from a general perspective. The range of responses is extraordinarily wide because environments are diverse, different taxa have different evolutionary histories, adaptations are needed for both seasonal timing and resistance to adversity, and not only development but also many other aspects of the life-cycle must be coordinated. Developmental options are illustrated by examining the wide range of ways in which development can be modified, the fact that each individual response consists of several components, and the different potential durations of the life-cycle. The concepts of alternative life-cycle pathways (chosen according to current and likely future environmental conditions) and of active and passive default responses are treated. Also introduced are aspects of variation and trade-offs.
Some general conclusions that help in understanding dormancy responses emerge from such an examination. Many options are available (cf. Table 1). The nature of the habitat, especially its predictability, determines the potential effectiveness of many of the developmental options. Any particular set of responses reflects evolutionary history and hence depends on past as well as current environments. It is not necessarily obvious what kinds of selection, especially requirements for timing versus resistance to adversity, explain a particular life cycle. Life-cycle pathways have multiple components, so that components cannot be analyzed in isolation. A given feature, such as delayed development, can have multiple roles. Default responses can be either active (development continues unless signalled otherwise) or passive (development stops unless signalled otherwise), making necessary a broad approach to understanding the action of environmental cues. Even relatively minor effects that fine-tune dormancy responses enhance survival, but may be difficult to detect or measure. Trade-offs are not inevitable, not only when certain resources are surplus, but also because resources in very short supply (constraints) cannot be traded off. Life-cycle components are widely, but not universally, coordinated. These conclusions confirm that the range of dormancy responses is wider, more complex and more integrated than has often been recognized.