Diapausing Females Research Articles

Seasonal changes in the reproductive and life‐history traits of Chrysomela populi L. (Coleoptera: Chrysomelidae)

AbstractSeasonal changes in the reproductive and life‐history traits of Chrysomela populi L. were investigated in Shobara (34°52′N, 133°01′E), Japan, in 2004 and 2005. Larvae were hatched and reared under natural photoperiod and temperature in 8 different periods between late April and early September in 2004. The incidence of adult diapause increased with progression of the season in 2004. The critical timing of diapause induction, as defined by 50% of females entering diapause, was estimated to occur between late July and early August. No effects of season on the survival rate from hatching to adult emergence, percentage ovipositing females and percentage females that deposited viable eggs were clearly detected. Adult weight at emergence fluctuated seasonally, which was probably caused by air temperature. No effect of season on the oviposition period was observed among females that averted diapause. Females that entered diapause in 2004 started oviposition from the first day of May in 2005. Reproductive output was significantly greater in diapause females than in non‐diapause females. This increase in the reproductive output of diapause females was caused by elongation of the oviposition period and consequently by enlargement of the number of egg clutches deposited. These results suggest that the seasonal timing of diapause induction in females of C. populi would be affected by various risks and benefits to reproduction and survival.

Phytochemicals as Population Sampling LureS

Most mosquito species have 2 hosts: vertebrate animals and vascular plants. The kairomones of vertebrates have been employed extensively as attractants in traps that are used for surveillance, either to assess adult density of mosquito populations or to detect pathogen activity. They also have been employed in basic field studies of mosquito physiology, behavior, and ecology. The semiochemicals that mosquitoes use to find plant hosts for their sugar, by contrast, have not been utilized at all. Currently we are characterizing attractive blends of volatile compounds produced by plant species visited by Aedes vexans, Culex pipiens, and Anopheles gambiae. These blends may be effective in attracting a unique subset of a mosquito population when deployed in surveillance traps. The principal advantages of phytochemical attractants are that they lure a) both sexes, b) all ages, including those that are newly emerged, c) females in all gonotrophic states, and d) both nondiapausing and reproductively diapausing females. Potential challenges to their successful use are the abundance of competing volatiles, narrow plant-host specificity, and a weaker behavioral response to phytochemical cues.

Diapause status of females affects attraction of male pear psylla, Cacopsylla pyricola, to volatiles from female‐infested pear shoots

AbstractA companion study showed that male pear psylla, Cacopsylla pyricola (Förster) (Homoptera: Psyllidae) were attracted to volatiles from pear shoots infested with post‐diapause females. The present study compared the behavioral response of males to diapause and post‐diapause females. Assays were done using a Y‐tube olfactometer. We collected male and female winterform psylla from pear orchards at regular intervals between late October (early diapause) and late February (post‐diapause). Female‐infested shoots were not attractive to males until the February samples, coinciding with ovarian maturation and onset of mating in the field. A second set of assays was done in which we manipulated diapause status in the laboratory either by exposing psylla to a long‐day photoperiod or by treating insects with an insect growth regulator, fenoxycarb. In the photoperiod experiments, both short‐day and long‐day males preferentially selected long‐day (post‐diapause) females over short‐day (diapause) females. Fenoxycarb‐treated males preferred fenoxycarb‐treated (post‐diapause) females over untreated (diapause) females; untreated males showed no preferences. Results support observations made elsewhere that male winterform pear psylla perceive and are attracted to volatile odors associated with pear shoots infested with post‐diapause females.

Suppression of water loss during adult diapause in the northern house mosquito,Culex pipiens

One of the major challenges of overwintering in the mosquito, Culex pipiens, is prevention of dehydration. In this study, we compare the water balance requirements of nondiapausing and diapausing adult females of C. pipiens. Although their percentage water content is lower, diapausing females contain both higher initial and dry masses than nondiapausing individuals. Both nondiapausing and diapausing females tolerate a loss of up to 40% of their water mass before dying, but diapausing female C. pipiens reach this point after a longer period due to their lower rate of water loss. Males, which do not overwinter in diapause, showed no differences in their water balance characteristics when reared under diapausing or nondiapausing conditions. Likewise, no changes were noted in the water balance of pupae, indicating that diapause-related changes do not occur prior to adult eclosion. This mosquito does not replenish internal water stores by generating metabolic water or by absorbing vapor from the atmosphere, but instead relies on drinking liquid water (or blood feeding in the case of nondiapausing females). The critical transition temperature, a point where water loss increases rapidly with temperature, was the highest for females, then males, then pupae, but was not influenced by the diapause program. Females in diapause did not utilize common polyols (glycerol, trehalose and sorbitol) to retain water, but instead the presence of twice the amount of cuticular hydrocarbons in diapausing compared with nondiapausing females suggests that the deposition of hydrocarbons contribute to the reduced rates of water loss. The laboratory results were also verified in field-collected specimens: mosquitoes in the late fall and winter had a lower percentage water content and water loss rate, higher initial mass, dry mass and more cuticular hydrocarbons than individuals collected during the summer. Thus, the major features of diapause that contribute to the suppression of water loss are the large size of diapausing females (reduction of surface area to volume ratio lowers cuticular water loss), their low metabolic rate and the deposition of extra cuticular hydrocarbons.

Factors terminating ovarian arrest in long-winged females of a flightless bug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

The aim of the present study was to determine the factors that are involved in termination of a non-diapause type of ovarian arrest in the adult macropterous females of a flightless bug, Pyrrhocoris apterus (L.), reared under a long-day (18L : 6D) photoperiod. Application of an active analogue of juvenile hormone, methoprene, to adult macropterous females kept under the above conditions induced precocious termination of ovarian arrest and shortened the length of the pre-oviposition period. The results indicate that a temporary ovarian arrest in spontaneously fasting long-day macropterous females results from a deficiency of juvenile hormone. The length of the pre-oviposition period was shortened and ovarian arrest terminated also by de-alation, high temperature and by a prolonged period of starvation. Mating of long-day macropterous females with reproductively active males had no effect on the length of the pre-oviposition period. There was a relationship between the length of the starvation period and the post-feeding pre-oviposition period. The longer the starvation period, the shorter the period from when food was supplied to first oviposition. The results indicate that depletion of the fat body reserves resulting from prolonged fasting, followed by resumption of food intake are pre-requisites for full activation of the corpus allatum and egg development, and play a role in completion and termination of non-diapause ovarian arrest in long-day macropterous females. This phenomenon was never observed in short-day brachypterous females in reproductive diapause.

Effect of Cold Exposure and Photoperiod on Diapause Termination of the Predatory MiteEuseius finlandicus(Acari: Phytoseiidae)

The effect of cold storage and photoperiod on diapause termination of the predatory mite Euseius finlandicus was studied under laboratory conditions. Females in diapause that developed under a short-day photoperiod of L:D 8:16 h and 20°C were exposed for 1–13 wk to 5°C and subsequently maintained under L:D 8:16 h and 20°C, after which the percentage of females terminating diapause was recorded. After 1–4 wk at 5°C, the number of days required for diapause termination in 50% of females (TA50) was similar to that of the control mites maintained continuously at L:D 8:16 h and 20°C. This indicates that cold is not a prerequisite for the completion of diapause development. Furthermore, when mites were maintained for longer periods (7, 10, or 13 wk) at 5°C, TA50 was significantly longer than in the control mites. This may indicate an adverse effect of cold storage on the completion of diapause development or on postdiapause development. However, the longer exposures to cold resulted in synchronous diapause termination. When diapause females were maintained under a series of different photoperiods and 20°C without previous cold exposure, diapause was terminated rapidly under the photoperiods of L:D 16:8, 14:10, and 13:11 h. In contrast, under the shorter-day photoperiods of LD 8:16, 10:14, and 12:12 h, diapause was maintained and eventually ended spontaneously after a long period of time. These results may be useful for the long-term storage of this predatory mite, which could be required for use in biological control programs.

Effect of Cold Exposure and Photoperiod on Diapause Termination of the Predatory Mite <I>Euseius finlandicus</I> (Acari: Phytoseiidae)

The effect of cold storage and photoperiod on diapause termination of the predatory mite Euseius finlandicus was studied under laboratory conditions. Females in diapause that developed under a short-day photoperiod of L:D 8:16 h and 20°C were exposed for 1–13 wk to 5°C and subsequently maintained under L:D 8:16 h and 20°C, after which the percentage of females terminating diapause was recorded. After 1–4 wk at 5°C, the number of days required for diapause termination in 50% of females (TA50) was similar to that of the control mites maintained continuously at L:D 8:16 h and 20°C. This indicates that cold is not a prerequisite for the completion of diapause development. Furthermore, when mites were maintained for longer periods (7, 10, or 13 wk) at 5°C, TA50 was significantly longer than in the control mites. This may indicate an adverse effect of cold storage on the completion of diapause development or on postdiapause development. However, the longer exposures to cold resulted in synchronous diapause termination. When diapause females were maintained under a series of different photoperiods and 20°C without previous cold exposure, diapause was terminated rapidly under the photoperiods of L:D 16:8, 14:10, and 13:11 h. In contrast, under the shorter-day photoperiods of LD 8:16, 10:14, and 12:12 h, diapause was maintained and eventually ended spontaneously after a long period of time. These results may be useful for the long-term storage of this predatory mite, which could be required for use in biological control programs.

Transcriptional Regulation of Uterine Vascular Endothelial Growth Factor during Early Gestation in a Carnivore Model, Mustela vison

Vascular endothelial growth factor (VEGF) is an essential angiogenic signaling element that acts through its two tyrosine kinase receptors, inducing both proliferation of endothelial cells and vascular permeability. Given the importance of vasculogenesis and angiogenesis to early pregnancy, it is of interest to understand the mechanisms regulating vascular development at this stage. We previously demonstrated that VEGF and receptors are up-regulated during embryo implantation in an unique animal model, the mink, a species displaying obligate embryonic diapause. Herein we examined the role of prostaglandin E2 (PGE(2)) as a regulator of VEGF during early pregnancy and established the mechanisms of this regulation. We demonstrate that activated embryos secrete PGE(2) and that expression of PGE synthase protein in the uterus is dependent upon direct contact with invading trophoblast cells during implantation. Using mink uterine stromal cells transfected with mink VEGF promoter driving the luciferase reporter gene, we show that PGE(2) induces promoter transactivation and that this response can be eliminated by blockade of protein kinase A. Treatment with antagonists to PGE(2) receptors EP2 and EP4 eliminated the PGE(2)-induced response in transfected cells. Deletional studies of the promoter revealed that a region of 99 bp upstream of the transcription start site is required for PGE(2)-induced transactivation. Mutation of an AP2/Sp1 cluster, found within the 99 bp, completely eliminated the PGE(2) response. Furthermore, chromatin immunoprecipitation assays confirmed binding of the AP2 and Sp1 transcription factors to the endogenous mink VEGF promoter in uterine cells. PGE(2) stimulated acetylation of histone H3 associated with the promoter region containing the AP2/Sp1 cluster. Taken together, these results demonstrate that PGE(2) plays an important role in regulating uterine and thus placental vascular development, acting through its receptors EP2 and EP4, provoking protein kinase A activation of AP2 and Sp1 as well as acetylation of histone H3 to transactivate the VEGF promoter.

Enhanced Cold and Desiccation Tolerance in Diapausing Adults of <I>Culex pipiens</I>, and a Role for <I>Hsp70</I> in Response to Cold Shock but Not as a Component of the Diapause Program

Culex pipiens L. reared under diapause-inducing conditions (short daylength; 18 degrees C) were more cold tolerant and desiccation resistant than their nondiapausing counterparts (long daylength; 18 degrees C). Upon cold exposure (-5 degrees C), diapausing mosquitoes reared at 18 degrees C survived nearly twice as long as nondiapausing mosquitoes reared at 18 degrees C and 10 times longer than nondiapausing mosquitoes reared at 25 degrees C. Thus, rearing temperature provided partial protection against low temperature injury in nondiapausing mosquitoes, but maximum resistance to cold was attained by the diapause state. In this species, the supercooling point is not a good indicator of cold tolerance. Both diapausing and nondiapausing females had supercooling points of approximately -16 degrees C, but diapausing as well as nondiapausing females died at temperatures well above the supercooling point, suggesting that low temperature mortality was due to indirect chilling injury. Diapause also conferred greater resistance to desiccation (1.6-2-fold increase in survival) compared with the nondiapause state. The gene encoding a 70-kDa heat shock protein, hsp70, was not up-regulated (i.e., more highly expressed) as a part of the diapause program, nor was it up-regulated by desiccation stress, but it was up-regulated during recovery from cold shock. Cx. pipiens thus differs from a number of other diapausing insect species that are known to developmentally up-regulate hsp70 during diapause.

Is period gene causally involved in the photoperiodic regulation of reproductive diapause in the linden bug, Pyrrhocoris apterus?

Earlier experiments demonstrated a strong up-regulation of per mRNA in wild-type (Wt) females of Pyrrhocoris apterus reared under diapause-inducing short days, while per mRNA levels were low in females of two non-diapause mutant strains (Nd), irrespective of photoperiod. In the present study, different sequences of per DNA in two strains of geographically different origin enabled us to analyse genetic linkage between the per gene and the Nd phenotype. Crosses between Wt females originating from C. Budejovice (Czech Republic) and Nd males originating from Lyon (France) resulted in F 2 progeny where 411 females entered diapause under short days and 120 females were reproducing. Thus, the segregation was very close to the 3:1 ratio in favour of diapause females, suggesting that the Nd trait behaves as a single autosomal recessive. Analysis of DNA in 20 females of the F 2 progeny revealed that their phenotype was not linked to the per genotype. We conclude that the per gene is not primarily responsible for the block to diapause photoresponsiveness in Nd mutants and its role, if any, is downstream from other gene(s) controlling diapause. This is the first attempt at genetic linkage analysis between a bona fide circadian clock gene and photoperiodism in a ‘non-drosophilid’ species.

Cold Hardiness of Neoseiulus californicus and N. womersleyi (Acari: Phytoseiidae)

Mites of the genus Neoseiulus are predatory mites that feed on pest species such as the two-spotted spider mite (Tetranychus urticae) and therefore act as biocontrol agents. Since the 1990s, the population of N. californicus in central and southwestern Japan has increased sharply, replacing the native N. womersleyi in many orchards in this area. However, in orchards of northern Japan, N. californicus is much less abundant than N. womersleyi. Here we tested the hypothesis that the lower abundance of N. californicus in the north is due to a lack of cold hardiness. The mean supercooling points of adult females of two strains of N. californicus (an indigenous strain and a commercial strain, neither of which enters diapause) and diapause and non-diapause N. womersleyi were all in the range −21.9 – 23.3°C and were not significantly different. However, more than 50% of diapause females of N. womersleyi survived for more than 7 days exposed to −5°C, while most females of the non-diapause N. womersleyi and the two N. californicus strains died after 3–5 days of exposure to −5°C. Exposure of adult females to −5°C for various periods did not significantly affect subsequent fecundity and egg viability. These results suggest that the lower cold hardiness of N. californicus might be one of the factors halting its northern advance, but it is probably not sufficient to be the only factor.

Diapause in Tarnished Plant Bug (Heteroptera: Miridae): Simulated Seasonal Occurrence in a Mississippi Population

The incidence of diapause was determined in adult tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), reared in environmental cabinets that simulated daily field photoperiods occurring at Starkville, MS, during every month of the year. Temperature was held constant at 26.7°C. Photoperiod played a major role in diapause induction. Most nymphs (77.6 to 100%) hatching between 15 September and 15 February, about half of nymphs hatching in early March or early September, and few nymphs hatching between 15 March and 15 August (1.8 to 10.3%) developed into diapausing adults. Thus, early March and early September are transitional periods during which about half of newly-hatched nymphs will develop into diapausing adults. Between those periods, almost all bugs were reproductive, and outside of them, almost all were in diapause. Hypertrophied fat body coupled with underdeveloped accessory glands were used to classify male diapause, and hypertrophied fat body coupled with lack of mature eggs were used to classify female diapause.

Ocorrência e diversidade de ácaros (Acari, Arachnida) associados a Tabebuia roseo-alba (Ridl.) Sand (Bignoniaceae), no município de São José do Rio Preto, São Paulo, Brasil

This study reports the mite fauna associated with Tabebuia roseo-alba, a native and ornamental tree, determining the abundance and seasonal occurrence of species and the diversity of the community. Twenty three species were found belonging to 11 families, 10 of predatory habits and five phytophagous. The food habits of the eight remaining species are not known. Besides the great richness, the diversity was small, as consequence of the dominance of Lorryia formosa Cooreman, 1958 and Aculus sp., the most abundant species. These species occurred in the same microhabitat but with seasonal segregation: L. formosa was the most abundant in the dry season, while Aculus sp. occurred only in the rainy season. In August, when the plant lost its leaves, the following species were found in the apical branch structures: Brevipalpus sp. (aff. phoenicis), Cheletogenes sp., Euseius citrifolius Denmark & Muma, 1970, Lorryia formosa, Pronematus sp., and diapause females of Tenuipalponychus tabebuiae Aguilar, Flechtmann & Ochoa, 1991. In September, with leaves growing again, Aceria sp. was the only species on the plant, and its abundance decreased accentuately in October. The richness and the abundance of the mite fauna were not correlated with the temperature or the precipitation. These data suggest that the plant phenology was more important than the climate in the occurrence of species.

Effects of endosymbioticWolbachiaon the diapause inTrichogrammahosts and effects of the diapause onWolbachia

AbstractUsed as an agent in biological control,Trichogrammawhich has been infected by endosymbiotic bacteria belonging to the genusWolbachiaand inducing the thelytokous mode of reproduction, increases rearing productivity in commercial insectaries. These insectaries can now make use ofTrichogrammadiapause to spread out and optimise their production. We therefore studied the effect ofWolbachiaon the diapause inTrichogramma evanescens. The symbionts show no beneficial or harmful effect on the proportion of emergence in diapausing individuals or on their fecundity. Therefore, infected strains can easily be used in crop protection. On the other hand, low temperatures exert a slightly negative effect onWolbachia,as detected from the proportion of females in the offspring of symbiotic diapausing females.

Preliminary observations of sperm storage in Adalia bipunctata (Coleoptera: Coccinellidae): sperm size and number

Sperm storage in Adalia bipunctata (L.) (Coleoptera, Coccinellidae) was examined and compared between diapausing and non-diapausing females. We observed that non-diapausing females store on average 13,688 (±722, S.E.) sperm in their spermatheca and that every female examined had sperm in storage (n=16). In contrast, most diapausing females had empty spermatheca and only two had sperm in storage (n=15). Mean sperm number in diapausing females was 250 (±112, S.E.). The mean length of the spermatozoa stored by non-diapausing females was 2,068.5 μm (±9.8, S.E.), ranging from 1,530.8 to 3,171.7 μm. Sperm length in diapausing females was only measurable in one female and was of 2,102.9 μm (±22.4, S.E.).

Developmental and diel changes of adipokinetic hormone in CNS and haemolymph of the flightless wing-polymorphic bug, Pyrrhocoris apterus (L.)

We have used an enzyme-linked immunoassay (ELISA) for determination of the AKH content in CNS (brain + corpora cardiaca + corpora allata) and haemolymph of adult macropterous and brachypterous females of the bug Pyrrhocoris apterus. The tests revealed that the AKH content fluctuates between 1 and almost 4 pmol/CNS during the first 14 days of adult life and significantly increased in order diapausing brachypters<reproductive brachypters<macropters. The titre of AKH in haemolymph is detectable mostly only in macropterous females during that period; in reproductive or diapausing brachypterous females keeps mostly below the detectable limit—1 fmol/μl. There are significant changes of AKH content in CNS and haemolymph of 10-day-old macropterous females during a 24 h period, with the highest values at about 10 h after the onset of light and at second half of the light period, respectively. The diel changes of AKH content in CNS are positively correlated with diel changes of adipokinetic response to AKH. Immunohistochemistry revealed that almost all reactive material is localized in the posterior part of the corpora cardiaca, and just a small amount in a few cell groups and axons distributed over the whole brain.

Ocorrência de diapausa em Tenuipalponychus tabebuiae Aguilar, Flechtmann &amp; Ochoa (Acari, Tetranychidae) no Estado de São Paulo, Brasil

This paper reports the occurrence of diapause in Tenuipalponychus tabebuiae Aguilar, Flechtmann & Ochoa, 1991, for the first time in tropical region, and describes the morphological differences between the diapausing and no-diapausing females.

Photoperiodic regulation of the phospholipid molecular species composition in thoracic muscles and fat body of Pyrrhocoris apterus (Heteroptera) via an endocrine gland, corpus allatum

In the conventional view, the winter adaptation of membrane lipids is induced by temperature decrease. We propose that winter remodelling of membranes in Pyrrhocoris apterus is triggered by short-day photoperiod before the temperature decrease and changes caused by cold temperature represent the later phase of adaptation. The induction of diapause by short-day photoperiod results in an accumulation of phosphatidylethanolamine (PE) molecular species with C 16:0/C 18:2 acyl chains esterified to sn-1/ sn-2 positions of glycerol at the expense of C 18:0/C 18:2. Proportions of C 16:0/C 18:2-PE are enhanced in short-day compared to long-day insects in both thoracic muscles (TM, 15.0 vs. 8.2%) and fat bodies (FB, 24.9 vs. 13.6 %). Proportions of C 16:0/C 18:2-PE are further enhanced during cold acclimation (to 26.5% in TM, 33.6 % in FB) at the expense of a more saturated species, C 18:0/C 18:1-PE. These changes are less prominent in phosphatidylcholines (PC). The effect of photoperiod seems to be mediated via the corpus allatum. Long-day non-diapause females deprived of their corpus allatum have the phospholipid molecular species profile similar to that found in short-day diapausing females. While the acyl chain remodelling is regulated by both photoperiod and temperature, the head group composition is regulated by temperature only. Similar to most other organisms, the level of PE is higher (50.3 vs. 43.5% in TM, 44.3 vs. 37.8% in FB) and that of PC is lower (35.9 vs. 40.2% in TM, 41.6 vs. 46.1 % in FB) at cold temperatures (≤1°C) compared to warm temperatures (≥16°C). In contrast to a general rule, the PE is less unsaturated than PC. In both TM and FB, proportions of unsaturated/unsaturated molecular species are consistently high in PC (56.3–67.5% in TM, 59.2–66.6% in FB), while they are consistently low in PE (19.1–26.7% in TM, 12.1–15.1% in FB). An adaptive significance of changes in the phospholipid composition for the low temperature and/or dehydration stress is discussed in relation to known physical properties of phospholipids.

Differences in diapause attributes between two clinal forms distinguished by male‐to‐male aggression in a subsocial spider mite, Schizotetranychus miscanthi Saito

The nest‐weaving spider mite Schizotetranychus miscanthi Saito showed a cline in male‐to‐male aggression intensity with minimum winter temperature. The altered kin structure in spring nests, which might be caused by winter harshness, was hypothesized to be a key factor responsible for the cline in male‐to‐male aggression. In Japan, we found two forms (high‐ and low‐aggression forms) that showed different clinal trends with similar regression slopes and different intercepts. The former is characteristic of local populations from milder climates, whereas the latter occurs in harsher climates. We hypothesized that the intensity of female diapause, which may determine whether males are produced during late winter, was one of the factors separating these two clinal forms. In the four populations studied, short day length during the developmental period (egg to adult emergence) induced diapause in females. Diapause intensity varied greatly among populations, and particularly between the high‐aggression and low‐aggression forms. These data, together with data on winter harshness between the localities, led us to believe that female diapause is one of the factors affecting relatedness between interacting males in nests and can explain why the two forms of S. miscanthi have different clinal trends in male aggression in Japan.

A trade‐off between diapause duration and fitness in female parasitoids

Abstract 1. Diapause allows insects to cope with adverse weather conditions but also poses substantial fitness costs, e.g. through reduced survival of the diapausing stage or sublethal effects in the following season.2. The energetic costs of diapause in females of the parasitoid Asobara tabida Nees (Hymenoptera: Braconidae) were assessed using experimental manipulation of diapause duration.3. An increase in diapause length not only led to higher mortality among diapausing pupae but also caused a significant decrease in egg load, fat reserves, and dry weight of the emerging adult females.4. Only larvae with sufficient resources were able to survive the entire diapause period and there was a trade‐off between the metabolic costs of diapause and adult fitness components.5. In contrast, the size (tibia length) of emerging females increased with increasing diapause duration. It is proposed that this may be due to a genetic correlation between larval dry weight and adult size, so that selection for heavier larvae would result in larger adults even when resources are limited.6. Ultimately, the evolution of diapause duration and its consequences for adult performance will depend on the costs of overwintering and the ecological conditions in the habitat.