Biological studies of the Australian predatory mite Typhlodromalus lailae (Schicha) (Acari: Phytoseiidae)

Abstract The biology of the Australian phytoseiid mite Typhlodromalus lailae is described from material collected in Western Australia and New South Wales in 1994. At 25°C, when fed on cumbungi ( Typha sp.) pollen, the life cycle is completed in approximately 6 days, with an intrinsic rate of natural increase ( r _m ), of 0.38. Female−male pairs produced a mean total of 44.6 eggs within 22 days of oviposition, with 39% of these females living in excess of 29 days. Females that were deprived of males after first mating stopped laying eggs after 4−9 days, but if another male was added they resumed egg laying and produced close to a full complement of eggs (mean 42 eggs). At 25°C, fecundity on a diet of cumbungi pollen or thrips larvae (first-instar Frankliniella schutzei Trybom) was high, averaging 3.71 and 3.33 eggs per day, respectively, over a 3-day period. The sex ratio was approximately 1.5 females to 1 male. Consumption rate of thrips was also high, with an average of approximately seven first-instar or two second-instar F. schultzei larvae eaten per day. The species was also observed to feed on broad mite, Polyphagotarsonemus latus (Banks), and tomato russet mite, Aculops lycopersici (Massee). No diapause was observed under conditions of 25°C 8 h light and 10°C 16 h dark. Eggs were sensitive to low humidity, with 50% failing to hatch below 71.1% relative humidity. This species is of interest as a candidate biological control agent for thrips, broad mite and tomato russet mite in protected crops.     

Effects of photoperiod and temperature on the development and diapause of the bark beetle Ips typographus

Abstract:  Diapause was induced in a Central European population of Ips typographus grown at 20°C when the day length decreased below 16 h [50% diapause incidence occurred in the 14.7:9.3 h L:D (light:dark) regime]. The non-diapausing adults fed on days 2–6 and 10–14 after the ecdysis and swarmed after the second feeding bout with chorionated eggs in the ovaries and sperm in the spermiducts. Neither gonads nor the flight muscles matured and no swarming occurred in the diapausing adults. The development from egg to adult took about 34 days in both 18:6 h (no diapause) and 12:12 h L:D (diapause) regimes, but it was extended by up to 30% without diapause induction when only larvae or pupae were exposed to L:D 12:12 h. Diapause was induced in insects reared at L:D 12:12 h through the last larval and the pupal instars and/or in the adult stage. Temperature ≥ 23°C prevented diapause induction at L:D 12:12 h but diapause occurred at L:D 14:10 h associated with 26:6°C thermoperiod. The effect of thermoperiods on the developmental rate requires further research. Exposure of the non-diapausing adults to 5°C for several days blocked feeding and evoked a diapause-like state, whereas diapausing adults fed and their gonads slowly developed at this temperature. Diapausing adults exposed in forest to low night temperatures and transferred in October to 20°C readily reproduced at 18:6, but not 12:12 h L:D photoperiods. After 2-months at 5°C and darkness, they became insensitive to the photoperiod, matured and most of them also swarmed at 20°C in the 12:12 h L:D regime. In a Scandinavian population, diapause occurred at 18:6 h L:D and was terminated either by exposure to 5°C or by very long photoperiod (L:D 20:4 h) combined with high temperature (23°C).     

Effects of delayed mating and male mating history on longevity and reproductive performance of the rice stem borer, Chilo suppressalis (Walker) (Lep., Pyralidae)

Abstract:  The mating potential, effects of delayed mating and male mating history on longevity and reproductive performance of female rice stem borer (RSB), Chilo suppressalis , were investigated under laboratory conditions. Given the opportunity, RSB males copulated an average of 2.7 times, while females generally mated only once. Females were more severely affected by mating delay than males in terms of female longevity and reproductive performance. With increasing age at mating, females' longevity increased, while oviposition period, fecundity and egg fertility decreased. Mean fecundity and egg fertility of females mated 1 and 7 days after emergence were 251.3% and 99.2%, and 96.2% and 75.5% respectively. Both were reduced significantly when female mating was delayed beyond 4 days after emergence. However, irrespective of the first mating age and different mating history of the males, the results indicated that both did not result in a significant difference in the quality of their contributions to female longevity and reproductive performance. The results obtained in this study are discussed in relation to the potential effect on pheromone control of RSB.     

Biological studies of the Australian predatory mite Typhlodromips montdorensis (Schicha) (Acari: Phytoseiidae), a potential biocontrol agent for western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)

Abstract The biology of the Australian phytoseiid mite Typhlodromips montdorensis is described from material collected in Queensland and South Australia in 1994−1996. At 25°C, when fed on cumbungi ( Typha sp.) pollen, the life cycle was completed in approximately 7 days, with an intrinsic rate of natural increase ( r _m ) of 0.32. Female−male pairs produced a mean total of 52.7 eggs within 28 days of oviposition. Females that were deprived of males after first mating stopped laying eggs after 7−19 days; however, if another male was added, they resumed egg laying and produced, on average, a total of 49.4 eggs. The sex ratio was 2.24 females to one male. At 25°C, fecundity on a diet of thrips larvae (first-instar Frankliniella schultzei Trybom) was high, ranging from 2.72 to 3.58 eggs per day on the third day, depending on previous diet. Consumption rate of thrips was also high, with an average of 7.23−14.44 first-instar larvae eaten per day on the third day, depending again on previous diet and also on number of thrips larvae made available. The species was also observed to feed on: (i) broad mite, Polyphago­tarsonemus latus (Banks); (ii) tomato russet mite, Aculops lycopersici (Massee); and (iii) two-spotted mite, Tetranychus urticae Koch. No diapause was observed under conditions of 25°C, 8 h light and 10°C, 16 h dark. Eggs were sensitive to low humidity, with 50% failing to hatch below 70.8% relative humidity. This species is of interest as a candidate biological control agent for thrips, broad mite and tomato russet mite in protected crops.     

Sexual reproduction and diapause of Hexarthra sp. (Rotifera) in short-lived ponds in the Chihuahuan Desert

1. In the life cycle of monogonont rotifers it is generally assumed that diapausing eggs invariably hatch into amictic stem females which produce female offspring parthenogenetically. Diapausing eggs are only produced by later generations after sexual reproduction has been induced by environmental cues. 2. We show that populations of an undescribed Hexarthra species inhabiting small temporary ponds in the Chihuahuan Desert deviate from this life cycle pattern. These ponds may dry within days and up to 85% of females were mictic. Females producing male offspring and diapausing eggs were observed 1 or 2 days, respectively, after ponds had filled with water. 3. Under laboratory conditions, 7–46% of females hatching from re‐hydrated sediments were sexual. Male offspring of these females can fertilise other mictic stem females leading to diapausing egg formation. In laboratory experiments, females produced fully developed diapausing eggs within 1.9 days at 20 °C and 1.2 days at 30 °C. 4. In addition, embryonic development time (1.1–0.3 days at temperatures between 12 and 30 °C) and juvenile period (2.1–0.5 days for the same temperature range) are shorter than those of other rotifer species. In short‐lived habitats, the potential for rapid population development and production of new diapausing eggs may be crucial in the long‐term survival of populations.     

Fecundity,nymphal development and longevity of field‐collected tropical bedbugs,Cimex hemipterus

This study examined the fecundity, oviposition, nymphal development and longevity of field‐collected samples of the tropical bedbug, Cimex hemipterus (Fabricius) (Hemiptera: Cimicidae). Under environmental conditions of 26±2°C, 70 ± 5% relative humidity and a 12‐h photoperiod, with bloodmeals provided by a human host, six strains of tropical bedbug had a fecundity of up to 50 eggs per lifetime, over 11–14 oviposition cycles. Increased feeding frequency improved fecundity. After feeding and mating, adult females normally took 2–3 days to produce a first batch of eggs. The oviposition period lasted 2–7 days before cessation of the oviposition cycle. The egg incubation period usually lasted 5–7 days before the emergence of first instars. The nymphs underwent five stadia (the first four of which each took 3–4 days, whereas the last took 4–5 days) before becoming adults at a sex ratio of 1 : 1. More than five bloodmeals were required by the nymphs to ensure a successful moult. Unmated adults lived significantly longer than mated adults (P < 0.05). Unmated females lived up to almost 7 months, but the longevity of mated males and females did not differ significantly (P > 0.05).     

Post‐mating enhancement of fecundity in female Lygus hesperus

Although mated females of the western tarnished plant bug Lygus hesperus Knight are known to produce more eggs than virgins, the nature of the inducing stimuli and the specific changes occurring in the female require additional elucidation. Compared with virgin females isolated from males, those exposed to male precopulatory behaviours produce similar numbers of eggs, whereas inseminated females produce 50% more during the observation period. Although the quantity of seminal fluids received by a female does not influence egg number, mating twice within a 10‐day span causes a 16% increase in fecundity, on average. Females mating more than twice during the same period do not exhibit additional increases in egg number. Because virgin females contain more chorionated eggs than are laid, mating appears to enhance the rate of oviposition. However, to achieve a sustained increase in fecundity, an augmented rate of oocyte maturation would also be required. Male‐derived spermatophores lack substantive quantities of nutrients that might otherwise have enhanced female fecundity. The total amounts of carbohydrate, protein and lipid, as well as eight essential minerals transferred by the male, are insufficient for producing even a single egg, and the female has already produced a large number of chorionated oocytes before she mates. Collectively, the data suggest that seminal fluid contains one or more activational molecules, such as a peptide, which triggers an increase in egg deposition. A prolonged increase in oviposition rate may be achieved through multiple matings to ensure a supply of sperm or to offset the degradation of the putative activational factor.     

A Single Hot Event Stimulates Adult Performance but Reduces Egg Survival in the Oriental Fruit Moth,Grapholitha molesta

Climate warming is expected to increase the exposure of insects to hot events (involving a few hours at extreme high temperatures). These events are unlikely to cause widespread mortality but may modify population dynamics via impacting life history traits such as adult fecundity and egg hatching. These effects and their potential impact on population predictions are still largely unknown. In this study, we simulated a single hot event (maximum of 38°C lasting for 4 h) of a magnitude increasingly found under field conditions and examined its effect in the oriental fruit moth, Grapholitha molesta. This hot event had no impact on the survival of G. molesta adults, copulation periods or male longevity. However, the event increased female lifespan and the length of the oviposition period, leading to a potential increase in lifetime fecundity and suggesting hormesis. In contrast, exposure of males to this event markedly reduced the net reproductive value. Male heat treatment delayed the onset of oviposition in the females they mated with, as well as causing a decrease in the duration of oviposition period and lifetime fecundity. Both male and female stress also reduced egg hatch. Our findings of hormetic effects on female performance but concurrent detrimental effects on egg hatch suggest that hot events have unpredictable consequences on the population dynamics of this pest species with implications for likely effects associated with climate warming.     

An interval timer controls the production of sexual morphs in Myzus persicae (Homoptera: Aphididae)

Abstract The interval timer mechanism was examined in two clones of Myzus persicae (Sulzer) originating from peach in Naousa, North Greece. Overwintering eggs were collected in April 1997 and after egg hatch the morphs of progeny were recorded at LD 10 : 14 h and 17 °C until the appearance of sexuals. In one clone, observations were continued until the 21st generation after egg hatch. In addition, the production of sexual morphs was examined in two other clones originating from Lehonia, Central Greece, when apterae (wingless females) were transferred from long to short days and 17 °C in the second and eighth generation of parthenogenetic rearing after their collection from peach trees. In clones from Naousa, the first gynoparae appear and comprise 10% of alate (winged) females in the second half of the third generation after egg hatch. The percentage of gynoparae increased in each consecutive generation, reaching 100% in fifth and seventh generations in clones Nb and Na, respectively. First males appeared later than gynoparae, in fifth and sixth generation in clones Nb and Na, respectively. In clone Nb, the number of males, after their appearance in fifth generation, was relatively constant from the sixth to the ninth generation (10.8–12.3). Then a significant increase was observed in the 10th generation, thereafter remaining relatively constant until the 21st generation (18.1–19.8). A similar trend in the number of males produced was observed in clones deriving from Lehonia.     

Importance of multiple mating to female reproductive output in Diaphorina citri

Abstract The importance of multiple mating to female reproductive output in Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is evaluated by grouping individual females with one or three males for 24 h (short duration) or 2 weeks (long duration) and examining oviposition over 18–19 days. For the short‐duration treatments, females lay more eggs per day when grouped with multiple males, whereas females in the long‐duration treatments lay more eggs when paired with one male. When held for 24 h with one or three males, females show a decline in fecundity beginning 10 and 15 days after mating, respectively. Total fecundity is relatively high for females paired with one male for 2 weeks, but fecundity is low and mortality high when females are held with three males for 2 weeks. In treatments in which females are held with males for 2 weeks, oviposition increases dramatically in the days after removal of males. For females paired with a male for 24 h and re‐paired for 24 h, 9 days later, fecundity remains high throughout the 18–19‐day observation period. Egg fertility does not differ among treatments, but varies over time in a manner that is similar among treatments. The present study demonstrates that, in D. citri, females require multiple matings over time to achieve high reproductive output, but oviposition is constrained by the presence of males.     

Long-term egg retention and parasitization in Trichogramma principum (Hym., Trichogrammatidae)

Laboratory experiments with Trichogramma principium Sug. et Sor. females that were offered Sitotroga cerealella Oliv. eggs demonstrated that less than half of the ovipositing females started oviposition during the first 2 days of the experiment, whereas the rest of the ovipositing females showed a delay in parasitization ranging from 2 to 10 days after contact with the host. Almost 10% of the wasps refused to parasitize the grain moth eggs over 12 days. The delay in parasitization may be as long as 6–8 days without any significant decrease in the number of mature ovarial eggs, in the number of eggs laid during the first 48 h of oviposition, and in the total lifetime fecundity. This egg retention is responsible for the fact that in spite of a relatively short mean duration of the oviposition period in each individual female (approximately 4 days), host parasitization by a group of simultaneously emerged wasps was almost uniformly distributed over 8–10 days. When induced, the parasitization state (i.e. the tendency to parasitize sequentially offered portions of host eggs) was stable both in the presence of a host and under host deprivation extended up to 8 days. These data provide further evidence for our hypotheses that the stability of the parasitization state in Trichogramma is based on endocrine mechanisms.     

The influence of temperature and photoperiod on the reproductive diapause and cold tolerance of spotted‐wing drosophila,Drosophila suzukii

Knowledge regarding the reproductive status of spotted‐wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is of critical importance in predicting potential infestations of this invasive pest, as eggs are laid in ripe or ripening fruit of several commercially important small‐fruit crops. Token environmental stimuli for the induction of reproductive diapause and improved cold tolerance were identified for D. suzukii. Diapause induction was evaluated by assessing, via dissection, the number of mature eggs carried by field‐captured D. suzukii and laboratory‐reared D. suzukii held under various temperature and photoperiod regimes. Egg load decreased over time in females trapped from July to December at sites in Benton County, OR, and Ontario County, NY, both USA, and reached zero eggs by December at all sites. Photoperiods below 14 h of day length led to reduced egg maturation in laboratory‐reared flies held at moderate temperatures (15 or 20 °C). Whereas very few mature eggs were found in females held at 10 °C under short‐ or long‐day photoperiods for several weeks after eclosion, a spontaneous return to ovarian maturity was observed in short‐day‐entrained females after 7 weeks. Diapause termination was investigated by evaluating fecundity in diapausing females returned to optimal environmental conditions. Whereas long‐day‐entrained flies began producing offspring immediately upon return to optimal conditions, short‐day‐entrained flies returned after 1 and 6 weeks at 10 °C were slower to produce offspring than colony flies or short‐day‐entrained flies returned after 7 weeks. Cold tolerance was evaluated by observing chill coma recovery rates after 24 h exposure to ?1 °C. Cold‐acclimated (diapausing) females recovered from chill coma faster than cold‐hardened or unacclimated females.     

Life table and biological studies of Harmonia axyridis Pallas (Col., Coccinellidae) reared on the grain moth eggs of Sitotroga cerealella Olivier (Lep., Gelechiidae)

The developmental period of immature stages, survival per cent, longevity, fecundity and life table parameters of Harmonia axyridis by feeding on fresh and frozen grain moth eggs (GME) of Sitotroga cerealella were studied under laboratory conditions. The effect of crowding adults on fecundity of females was also determined. The total developmental time from egg hatching to adult eclosion ranged from 18.89 ± 0.32 to 22.5 ± 0.21 days on fresh and frozen GME, respectively. Survival per cent from egg hatching to adult emergence differed significantly when the predator fed on the two diets of GME. Also, pupal and adult weights were affected by feeding on fresh and frozen GME. There were no significant differences in longevity of females, while there were significant variations in fecundity of females and longevity of males. The calculated values of T , DT , R_o , r_m , and e^rm were high by feeding on fresh GME. Morever, rates of survivorship ( Lx ), and maximum oviposition per female per day ( Mx ) were higher when the predator was reared on fresh than on frozen GME. Crowding conditions of predator adults affected the fecundity of females due to egg cannibalism by both males and females of the predator.     

Effects of forced egg-retention in Aedes albopictus on adult survival and reproduction following application of DEET as an oviposition deterrent.

The insect repellent DEET (0.1% concentration), used as a mosquito oviposition deterrent in the laboratory, influenced the retention and maintenance of mature eggs by caged gravid female Aedes albopictus Skuse. This egg-retention mechanism could benefit survival because the gravid females were ultimately able to lay maintained eggs upon availability of water, but the length of forced egg-retention time reduced the number of eggs laid per female. Gravid females with retained eggs also laid a higher percentage of eggs that failed to tan, and this percentage increased with time duration of egg-retention. Percent egg hatch was not significantly affected by DEET when used as an oviposition deterrent; however, percent hatch was affected by time duration of egg-retention in both treated (exposed to DEET) and untreated (control) gravid females. The rate of egg hatch was considerably reduced after three weeks of retention; this reduction declined to zero for treated and control females at six and four weeks post-treatment, respectively. The fecundity and fertility of gravid female Ae. albopictus were affected by the time duration of forced egg-retention.     

DIETARY LUFENURON REDUCES EGG HATCH AND INFLUENCES PROTEIN EXPRESSION IN THE FRUIT FLY Bactrocera latifrons (HENDEL)

Lufenuron (LFN), a chitin synthase inhibitor, impacts the fertility of Ceratitis capitata, Bactrocera dorsalis, B. cucurbitae, and B. latifrons. We posed the hypothesis that LFN curtails egg hatch in the solanaceous fruit fly, B. latifrons. In this study, newly emerged virgin adults were sexed and fed for 12 days with varying concentrations of LFN‐laced agar diets until sexual maturation. Eggs were collected from 12‐d‐old adults and the egg hatch was assessed. Egg hatch decreased in adults reared on LFN‐treated diets. LFN‐treated media did not influence fertility after one gender was reared on experimental and the other on control media before mating. Exposure to LFN‐treated medium after mating led to reduced egg hatch. We infer that LFN is not a permanent sterilant, and reduced egg hatch depends on continuous exposure to dietary LFN after mating. Proteomic analysis identified two differentially expressed proteins, a pheromone binding protein and a chitin binding protein, between adults maintained on LFN‐treated and control diets. Expression of two genes encoding chitin synthase 2, and chitin binding protein, was altered in adults exposed to dietary LFN. LFN treatments also led to increased expression of two odorant binding proteins one in females and one in males. We surmise these data support our hypothesis and provide insight into LFN actions.     

Delayed mating reduces fecundity of blackheaded fireworm, Rhopobota naevana, on cranberry

This study examines the effects of delayed mating on two successive generations of blackheaded fireworm, Rhopobota naevana Hübner (Lepidoptera: Tortricidae), a pest of cranberry, Vaccinium macrocarpon Aiton (Ericaceae). The first (spring) generation produces eggs that hatch soon after oviposition, whereas the second (summer) generation produces mostly diapause eggs. Unmated female and male moths were placed together on the first, second, fourth, sixth, or eighth day after emergence. In the first generation, incidence of mating was greatest in the 1-, 2-, and 4-day treatments then declined as female survival decreased. In the second generation, incidence of mating was lowest in the 1-day treatment and greatest in the 2-, 4-, and 6-day treatments. Most second generation females in the 6- and 8-day treatments survived to mate. The mean oviposition period was 2.6 days for first generation females and 4.1 days for second generation females. Fecundity of singly mated females in both generations declined as age at mating advanced, but the pattern of decline differed between generations. First generation females that were mated on the first or second day laid more eggs than those mated on the fourth, sixth, or eighth day, and the number of infertile eggs increased as age at mating advanced. Fecundity of second generation females declined more gradually and the number of infertile eggs was greatest for females mated on the first, sixth, or eighth day. A consequence of the marked decline in fecundity due to mating delays in the first generation was that mean fecundity of the entire group of first generation females was ca. 13% less than that of the group of second generation females. On cranberry farms, pheromone-mediated mating disruption can prevent or delay mating of blackheaded fireworm. If the frequency of disrupted (prevented and delayed) matings is similar in the two generations, fewer eggs will be laid in the first generation than in the second.     

多次交配对小菜蛾精包形成与生殖力的影响

【目的】小菜蛾Plutella xylostella是主要为害十字花科作物的一种世界性害虫,强大的生殖能力是其成为田间最难防治的害虫的主要原因之一。交配是营两性生殖昆虫繁衍后代必要的一个生理过程,明确小菜蛾雌雄成虫的交配行为及交配后的生理响应,对于小菜蛾种群监测和综合防治具有重要意义。【方法】解剖观察小菜蛾成虫生殖腺及精包形成;利用行为学与生物学实验,测定和分析小菜蛾成虫交配与再交配能力、精包形成与消化,以及交配次数对精包形成以及雌虫生殖力的影响。【结果】小菜蛾雄成虫在交配过程中精液以精包的形式传递给雌成虫,在交配囊中精包呈白色、不透明、气球状结构,交配结束后精包可被充分消化和吸收。成虫交配能力观测结果显示,小菜蛾雌雄成虫均具有多次交配行为。首次交配后,雄成虫表现出短暂的再交配延迟,20 min内其交配成功率为54.6%,显著低于首次交配。虽然交配次数不会影响雄成虫的交配时长,但雄成虫交配史对其自身的精包大小以及雌成虫的生殖力均具有显著的抑制作用。雌成虫表现出明显的再交配抑制性,交配过的雌成虫在12 h内的交配率显著低于未交配雌成虫的,这可能取决于首次交配后精包的消化和吸收速率。雌成虫多次交配后,其产卵量和卵孵化率与单次交配的相比没有显著差异。【结论】多次交配会使小菜蛾雄成虫再交配延迟,雌成虫再交配受到抑制;多次交配产生的雄成虫精包显著减小,雌成虫产卵量与卵孵化率并没有从多次交配中获得收益。本研究为解析小菜蛾雌雄成虫生殖调控机制奠定理论基础。     

A shift toward early reproduction in an introduced herbivorous ladybird

1. In May 1971, fifteen male and thirty female overwintering adults of a thistle-feeding ladybird Epilachna niponica were taken from the Asiu Experimental Forest of Kyoto University and introduced into the Botanical Garden of Kyoto University, 30 km south of Asiu and 10 km south of the southern limits of its distribution. The introduced population established successfully and thereafter maintained densities sufficiently high to defoliate their host plants.
2. Reproductive parameters (reproductive lifespan of females, overall fecundity, and oviposition schedules) of the introduced population were compared with those of the source population 10 years after the introduction. Comparisons were made in the laboratory under five temperature regimes.
3. The lifespan of females differed significantly with temperature, decreasing linearly with increasing temperature. Temperature also had a significant effect on overall fecundity for both populations; overall fecundity at 15 and 30 °C was significantly lower than that at the 20–25 °C regimes.
4. The oviposition activity of the introduced population was significantly higher than that of the source population at 23 and 25 °C. The lifespan of females of the introduced population was also significantly shorter than those of the source population at 20 and 25 °C.
5. The reduced lifespan and higher oviposition activity of introduced females indicate that they directed greater reproductive efforts early in their reproductive lifetime than those of the source population.     

Does time until mating affect progeny sex ratio? A manipulative experiment with the parasitoid wasp Aphelinus asychis

In haplodiploid organisms, unmated or sperm depleted females are “constrained” to produce only male progeny. If such constrained females reproduce, the population sex ratio will shift toward males and unconstrained females will be selected to produce more females. Assuming that a female's own time spent constrained is an index of the population-wide level of constrained oviposition, and that constrained and unconstrained females reproduce at the same rate, the proportion of sons that females produce when unconstrained should decrease with increasing time spent constrained. Alternatively, if females cannot measure time spent constrained or if time spent constrained is not an index to the level of constrained oviposition in the population, the proportion of sons among progeny produced when unconstrained should not depend upon time spent constrained and should be female biased to an extent depending upon the average time spent constrained over evolutionary time. To test these predictions, we manipulated the amount of time spent virgin in the parasitoid wasp Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and measured the number of males and females among progeny produced before and after mating. First, we found no interaction between age and age at mating in their effect on fecundity, which suggests that mating does not change fecundity. Second, we found that females mated at 8 days and 15 days produced equal sex ratios after mating but these were slightly more female biased than the sex ratios of females mated at 1 day. This observed “step response” suggests that females may perceive time from emergence to mating as a discrete rather than a continuous variable (i.e., short versus long), or that females do not perceive time per se but assess their age class (i.e., young versus old) at the time of mating.     

Adaptive strategies of overwintering adults: Reproductive diapause and mating behavior in a grasshopper,Stenocatantops splendens (Orthoptera: Catantopidae)

Abstract To understand the adaptive strategies of the overwintering adults of Stenocatantops splendens, the mechanism of maintenance and termination of the reproductive diapause, the variation in mortality between overwintering females and males, and the mating strategy of the males were investigated. The results indicated that the adult reproductive diapause in natural conditions was mainly regulated by photoperiod in the fall – long photoperiods promoted reproductive development and short photoperiods maintained reproductive diapause, and the sensitivity of the overwintering adults to photoperiod was over before the end of the winter. When transferred from natural conditions to controlled laboratory conditions on dates from September through February, pre‐oviposition became increasingly shorter with increasingly deferred transfer dates regardless of photoperiod conditions. The adults treated with low temperature for 30 days in September through November had significantly shorter pre‐oviposition, suggesting that low temperatures in winter had an important role in the termination of reproductive diapause. The female had a significantly lower supercooling point than the male, which was related to their lower mortality after winter. In addition, observations of wild populations of the species indicated that mating behavior prior to winter and the duration of pre‐mating period were not affected by photoperiod; mating and sperm transfer were mostly completed by November. Compared with females only mating before winter, females mating in the spring had shorter life span, longer pre‐oviposition, lower hatching rate and laid fewer egg pods while showing no significant difference with regard to ovipositional interval, per pod number of eggs and nymph dry weight.