Cost of prolonged diapause and its relationship to body size in a seed predator

Abstract

Summary 1.Although metabolic resource losses are maintained at low rates during diapause, the accumulation of losses over a long period negatively affects organisms with prolonged diapause usually extending beyond 1 year. The seed-predatory weevil Exechesops leucopis (Jordan) (Coleoptera: Anthribidae) enters winter diapause at the final-instar larval stage within seeds of Styrax japonica Sieb. et Zucc. (Styracaceae) at a density of one larva per seed. After diapause, larvae pupate within the seeds and then emerge as adults. 2. The adult emergence pattern of a single cohort of E. leucopis was monitored for 5 years under seminatural conditions in the laboratory. The duration of diapause varied from 1 year (single winter) to 4 years (four winters). Adults that emerged after 1 year were smaller than those that emerged after 2 years or more. When temperature was not decreased experimentally in winter, no adults emerged in the following season. 3. Metabolic resource losses during diapause were examined by comparing adult body sizes between controls and groups in which emergence was delayed by 1 year under manipulated winter temperature regimes. Adults that emerged after an additional year in the larval stage were smaller than those in the control group. Moreover, the rates of reduction in body size as a consequence of diapause being extended experimentally were greater in smaller individuals. Thus smaller individuals have disadvantages in longer diapause, suggesting that weevils may vary the duration of diapause depending on individual body size. 4. Exechesops leucopis shows sexual dimorphism in the degree of eye protrusion. Eyestalk length affects male fitness through intrasexual selection. The duration of diapause affected the length of the eyestalks: when an additional year was spent in diapause, eyestalk length was nearly maintained in larger males but was greatly decreased in smaller males. In all females eyestalk length decreased according to the duration of diapause.

Pattern of Pink Bollworm Diapaused Larval Exit from the Last Season Cotton Bolls and Their Biological Parameters

“…Results of the present study indicated increasing in the mortality percentages of the exit diapused larvae, a lower fecundity and lower fertility. It has been recorded previously a lower post-diapause survival and reduced fecundity (Ellers and van Alphen, 2002;Williams et al, 2003;Munyiri et al, 2004;Matsuo, 2006). Finally, PBW is the key pest in the cotton-producing areas of the world which affects the cotton yield in several ways.…”

Relationship between the natural duration of diapause and post-diapause reproduction in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

“…In several insect species, diapause is longer in larger individuals (Bakke, 1971;Nesin, 1985;Powell, 1989;Danforth, 1999;Menu & Desouhant, 2002;Matsuo, 2006). For example, in the chestnut weevil Curculio elephas (Menu & Desouhant, 2002), the bee Perdita portalis (Danforth, 1999) and the seed-predatory weevil Exechesops leucopis (Matsuo, 2006), the probability of prolonged diapause increases with higher larval weight.…”

“…For example, in the chestnut weevil Curculio elephas (Menu & Desouhant, 2002), the bee Perdita portalis (Danforth, 1999) and the seed-predatory weevil Exechesops leucopis (Matsuo, 2006), the probability of prolonged diapause increases with higher larval weight. Such extra metabolic resources, associated with low energy consumption during prolonged diapause (Danks, 1987), could ensure higher fecundity of the long-cycle phenotype and consequently, could compensate for the cost of prolonged diapause.…”

“…However, diapause is generally believed to be costly. Costs of diapause are commonly reflected in lower post-diapause survival and reduced fecundity (Denlinger, 1981;Bradshaw et al, 1998;Han & Bauce, 1998;Kroon & Veendaal, 1998;Ellers & van Alphen, 2002;Williams et al, 2003;Munyiri et al, 2004;Matsuo, 2006;Ito, 2007). The two most likely physiological mechanisms underlying these costs are damage due to diapause-associated stresses, such as desiccation or cold shock, and the depletion of metabolic reserves that could contribute to a decrease in postdiapause fitness (Hahn & Denlinger, 2007).…”

Extremely Long-Closed Galls of a Social Aphid

“…Although aphids inside the galls perhaps may not enter "diapause" in its physiological sense, this phenomenon is akin to prolonged (or delayed) diapauses, which are known in various insect groups [38] such as weevils [39][40][41], gall midges [42], and carnid flies [43], and often are interpreted as a bet-hedging adaptation [39]. In the case of N. monzeni, it is also possible that gall inhabitants may avoid competition for nutrition within a yearly cohort that has formed galls on the same or nearby buds.…”