Insect Diapause: a Review
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Journal of Agricultural Science and Technology A 7 (2017) 454-473 doi: 10.17265/2161-6256/2017.07.002 D DAVID PUBLISHING Insect Diapause: A Review Harsimran Kaur Gill1, Gaurav Goyal2 and Gurminder Chahil3 1. Department of Entomology, University of Florida, Gainesville, FL 32611, USA 2. Technical Agronomist, Monsanto, St. Louis, MO 63167, USA 3. Agriculture Extension Coordinator, Manitoba Agriculture, Swan River, MB R0L 0Z0, Canada Abstract: Diapause is defined as a period of suspended development in insects and other invertebrates during unfavorable environmental conditions. Diapause is commonly confused with term “quiescence” as both are dormant development stages. Here this paper aimed to review the research work done on different aspects of diapause. Attempt was made to explain definitions of diapause, incidence, stages and termination of diapause, genetic control, factors affecting diapauses, including temperature, photoperiod, moisture and food, etc.. Key words: Diapause, quiescence, diapauses theory, stages of diapauses, genetic control, biotic and abiotic factors, insects. 1. Introduction embryonic, larval, pupal or adult stages. For example, silkworm moth (Bombyx mori) overwinters in embryo Diapause is an important adaptation in many insect stage, just before segmentation. The gypsy moth species enabling them to sustain in regions which (Lymantia dispar) enters diapause as a fully formed would otherwise be unfavorable for permanent larva with hatching occurring immediately after habitation, and to maintain high numbers in an diapause ends. Obligate diapause is often universal, environment which might otherwise support only a resulting in strictly univoltine life cycle with every low population [1]. The term “diapause” was applied individual in every generation experiencing diapause, by Wheeler [2] to egg stage of grasshopper, irrespective of any possible environmental variations. Conocephalus ensiferum at which its development On the other hand, facultative diapause occurs due to was ceased. Later the scope of diapause widened into environmental variations and results in a multivoltine various stages of insects as “periods of arrest in life cycle. In this life cycle, one or more generations in ontogenetic (origin and development of organisms) which few individuals enter diapause alternate with a development” by Henneguy [3]. Diapause process is a generation in which all or nearly all the individuals splendid chance for insects to survive a great deal of enter diapause. But in a particular environment seasonal changes in the environment. (usually near the limit of geographic distribution of a Diapause can be categorized according to seasonal species), facultative diapause may result in a virtual variations as aestivation (summer diapause) or univoltine life cycle in which most individuals in hibernation (winter diapause); or according to life every generation enter diapause. stages as an egg (embryonic), larval, nymphal or adult According to physiological and ecological (imaginal, reproductive) diapause; or according to the mechanisms of its incidence and termination, diapause influence of environmental factors as obligatory and can be classified into three types: parapause (an facultative diapause. Depending on the species, obligatory hereditary arrest of development or activity diapause can occur at different stages, such as arising in every generation at a species specific instar), oligopause (an arrest of development or activity with Corresponding author: Harsimran Kaur Gill, Ph.D., control of its induction, maintenance and termination, research field: entomology. Insect Diapause: A Review 455 similar for all these periods) and eudiapause (a in various ways from the basic ideas of processes facultative arrest of development or activity with including delayed response to growth, interference different controlling mechanisms of induction and with development indirectly due to environmental termination, e.g., through photoperiod and chilling, factors and prolonged arrest of development, growth respectively) [4]. or reproduction, etc.. Diapause is not a physiological process; rather it is 3. Incidence of Diapause brought about by token stimuli that presage a change in the environment. It is highly important in temperate Diapause may occur in any stage of the life cycle of zone insects that overwinter. Most of the insects enter insects, such as eggs, larvae, pupae or adults. The diapause at a single species-specific stage in their life stage at which diapause occurs is highly characteristic cycle. Usually, diapause occurs in that stage of the life for each species. Moreover, there is no case known in cycle which is highly adapted to resist the hardness of which diapause occurs in more than one stage in the the climate. Below the definitions, intensity and same life cycle. At the egg stage, it may begin when incidence of diapause along with different phases of the embryo is still very young (e.g., Gryllulus, diapauses, theories of diapause, factors affecting Austroicetes); when embryo is half-grown (e.g., diapause, diapause termination and genetic control of differential grasshopper, Melanoplus diflerentialis); or diapause have been detailed. when embryo is fully grown and apparently almost ready to hatch (e.g., red-legged grasshopper, forest 2. Definitions of Diapause tent caterpillar). In nymphs and larvae, diapause may Many definitions of diapause have been proposed occur more often in the last instar than other instars. by scientists and some of them are given below: “a The incidence of diapause may be quite variable, not stage in the development of certain animals, during only from species to species, but also between which morphological growth and development are different populations of the same species. suspended or greatly decelerated” [1]. According to 4. Intensity of Diapause Beck [5], “state of arrested development in which the arrest is enforced by a physiological mechanism rather Diapause is also immensely variable in its intensity; than by concurrently unfavorable environmental duration of diapause can be taken as a measure of conditions”. Although diapause is not maintained intensity. Diapause lasts for 9-10 months in the directly by environmental factors, but it is induced, temperate zones, and may persist for a year or more in and also terminated in many species, in response to less common cases. During diapause, most insects do environmental stimuli. Tauber et al. [6] mentioned not feed at all or, in the case of some larvae and adults, that “diapause is hormonally mediated state of low feed very little. This indicates that the insect must metabolic activity associated with reduced sequester sufficient food reserves in the pre-diapause morphogenesis, increased resistance to environmental phase to meet its metabolic needs during diapause and extremes and altered or reduced behavioral activity”. still have sufficient reserves remaining at the end of Tauber [7], again defined this term as “diapause is a diapause to complete development and resume activity neurohormonally mediated, dynamic state of low [8]. activity that occurs during a genetically determined Diapause lasting more than a year is known as stage(s) of metamorphosis, usually in response to prolonged or extended diapause [9], and has been environmental stimuli that precede unfavorable documented in 64 insect species. For example, yucca conditions”. Definitions of diapause have been framed moth (Prodoxus y-inversus) adults emerge after 19 456 Insect Diapause: A Review years of diapause as prepupae [10]. Another example, during this phase are food storage, behavioral changes where larvae had been in soil up to three years and some changes in rate of development. followed by emergence of wheat-blossom midges 5.2 Diapause Phase (Cantarinia tritici Kirby), whereas larvae of wheat blossom midge (Sitodiplosis mosellana) overwintered 5.2.1 Initiation Phase for 12 years in the soil before adult emergence [11]. In “Direct development (morphogenesis) ceases, some sawflies, diapause stage lasts for 3-4 years. which is usually followed by regulated metabolic Extra-long diapause may be achieved either by suppression. Mobile diapause stages may continue entering diapause exceptionally early (premature accepting food, building of energy reserves and diapause) or by completing diapause exceptionally seeking suitable microhabitat. Physiological late (prolonged diapause). In both the cases, induction preparations for the period of adversity may take place of diapause may be density-dependent or and intensity of diapause may increase.” density-independent [12]. The physiological 5.2.2 Maintenance Phase mechanisms of prolonged diapause are still “Endogenous developmental arrest persists while incompetently understood [7]. the environmental conditions are favorable for direct development. Specific token stimuli may help to 5. Phases/Stages of Diapause maintain diapause (prevent its termination). Metabolic Insect diapause is a dynamic process consisting of rate is relatively low and constant. Unknown several successive phases. In the literature, the physiological process leads to more or less gradual conception and naming of diapause phases are decrease of diapause intensity and increase of ambiguous and unsettled. The phases of diapause were sensitivity to diapause terminating conditions.” distinguished by Koštál [13]. The definitions of 5.2.3 Termination Phase different phases are given below as suggested by “Specific changes in environmental conditions Koštál