Temperature Synchronized Development and Emergence

Many species of insects have highly synchronized larval development (all larvae are more or less at the same developmental stage) and/or synchronized eclosion, especially those that live in habitats where the climate is suitable for growth and reproduction for a limited period each year. Synchronized eclosion increases the chances of finding a mate. It may also increase the probability of finding suitable food or oviposition sites, or of escaping potential predators. Synchronized larval development also may be related to the availability of food, and in some situations it may be necessary in order to avoid interspecific competition for the same resource. For certain carnivorous species, such as Odonata, synchronized development may help reduce the incidence of cannibalism among larvae.

Perhaps not surprisingly in view of its effects on rate of development and activity, temperature is an important synchronizing factor in the life of insects. Its importance may be illustrated by reference to the life history of Coenagrion angulatum, which, along with several other species of damselflies (Odonata: Zygoptera), is found in or around shallow ponds on the Canadian prairies (Sawchyn and Gillott, 1975). For these insects the season for growth and reproduction lasts from about mid-May to mid-October. For the remaining 7 months of the year C. angulatum exists as more or less mature larvae, which, between about November and April, are encased in ice as the ponds freeze to the bottom. (The larvae themselves do not freeze, as the ice temperature seldom falls more than a few degrees Celsius below zero as a result of snow cover.) In C. angulatum both larval development and eclosion are synchronized by temperature. Synchronized development is achieved (1) by means of different temperature thresholds for development in different instars, that is, younger larvae can continue to grow in the fall after the growth of older larvae has been arrested by decreasing water temperatures, and (2) by a photoperiodically induced diapause. Thus, samples collected in mid-September include larvae of the last seven instars, whereas those from early October are composed almost entirely of larvae of the last three instars. Conversely, after the ice melts the following April, younger larvae can continue their development earlier than their more mature relatives, so that by mid-May more than 90% of the larvae are in the final instar. After their release from the ice larvae migrate into shallow water at the pond margin whose temperature parallels that of the air. Emergence occurs when the air temperature is 20oC to 21°C (and the water temperature is about 12°C). It begins normally during the last week of May and reaches a peak within 10 days. Emergence of C. angulatum follows that of various chironomids and chaoborids (Diptera), which form the main food of the adult damselflies during the period of sexual maturation. The development and emergence of other damselfly species that inhabit the same pond are also highly synchronized but occur at different times of the growing season. This enables the species to occupy the same pond and make use of the same resources, yet avoid interspecific competition. This is discussed further in Chapter 23 (Section 3.2.1).

Though unpredictable on a day-to-day basis, temperature does have a regular seasonal pattern that controls the onset and termination of diapause in some species. Temperature is the primary diapause-inducing stimulus for some subterranean species [e.g., some ground beetles (Carabidae)], wood- and bark-inhabiting species, and pests of stored products that live in darkness. It also is the major cue for diapause induction in some insects living near the equator where changes in photoperiod are too small to act as signals of seasonal change (Tauber et al., 1986; Denlinger, 1986). Temperature can also exert a strong influence on diapause and other photoperiodically controlled phenomena, as is discussed below (Section 3.2).

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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