锈褐原花蝽在不同温度下的发育与积温必需条件

阿月浑子树木虱Agonoscena pistaciae Burckhardt and Lauterer （半翅目: 木虱总科）是伊朗园林树木阿月浑子树上常见的最具破坏性的害虫,其捕食性天敌锈褐原花蝽Anthocoris minki pistaciae Wagner在伊朗阿月浑子树种植区为该害虫的生防因子。本研究在17.5~35℃的8个恒温以及相对湿度55%±5%,光照周期16L∶8D的控制条件下,在A. pistaciae若虫上饲养这种捕食性花蝽的同时,调查温度对其发育的影响。结果表明：这种捕食性花蝽在17.5~32℃下可成功发育;然而在35℃下,卵不能孵化,且只有10%的若虫进入成虫阶段。30℃下从卵至成虫羽化的发育历期最短。据测算估计,这种捕食性花蝽的卵、若虫发育以及整个发育（卵至成虫）的积温分别为77,200和263度·日;卵、若虫和整个发育的低温度阈值分别为8.53, 9.2 和9.47℃。这些结果为建立阿月浑子树木虱的综合防治计划提供了宝贵的信息。     

Life history parameters of the coccinellid beetle, Oenopia conglobata contaminata, an important predator of the common pistachio psylla, Agonoscena pistaciae (Hemiptera: Psylloidea)

The predatory beetle, Oenopia conglobata contaminata, is associated with the common pistachio psylla, Agonoscena pistaciae, the major pistachio pest in Iran. Successful development and reproduction on both A. pistaciae and Aphis gossypii (the major weed aphid in the pistachio orchards) indicated they were suitable prey for O. conglobata contaminata. Under ample prey supply, larval development on A. pistaciae was shorter and mortality was lower compared to those reared on A. gossypii. Furthermore, this ladybird attacks and destroys a large number of psyllid nymphs during the whole of its larval period (620±17 fourth stage nymphs) and also in its adult stage (191±7.5 4^th stage nymphs daily). The optimum temperature for development was 30°C, the theoretical threshold for development was 13°C and thermal requirements from egg to adult was estimated as 196 degree-days (°D). Fecundity for the first 21 days of adult life was 387 and 355 eggs when females fed on A. pistaciae and A. gossypii nymphs, respectively. The intrinsic rate of increase (r_m) at 27.5°C was 0.19 and 0.18 when ladybirds were fed on psyllid and aphid nymphs, respectively. In a laboratory choice experiment, the adult ladybirds showed a strong preference for A. pistaciae compared to A. gossypii. This was in agreement with our field observation that O. conglobata contaminata is almost always found on psyllid colonies, even when aphids were plentiful on weeds in the pistachio orchards. The influence of the predator on psyllid seasonal population under natural condition was not studied in this investigation and this subject must be measured in subsequent trials.     

Effects of photoperiod and temperature on the development of Bonagota cranaodes

Abstract.  The Brazilian apple leafroller, Bonagota cranaodes (Meyrick) (Lepidoptera: Tortricidae) is reared in the laboratory under a long-day (LD 14 : 10 h) and a short-day (LD 7 : 17 h) photoperiod at 22 °C, and under two different temperatures (10–13 °C and 21–22 °C). The development time from larval to adult eclosion do not differ between the two photoperiods, but did between the two temperature regimes. However, the larvae do not enter diapause, even under short day conditions and low temperatures. The number of adults obtained does not differ with temperature and light conditions. Field captures with pheromone traps show that Brazilian apple leafroller occurs in apple orchards throughout the year and the population densities are lower in winter. Accordingly, control measures should be taken during the off-season.     

Photoperiod and temperature effects on gametogenesis in winter flounder Pseudopleuronectes americanus

The winter flounder is an in‐shore flatfish living in shallow waters on the east coast of North America from Labrador to Georgia. In the St Lawrence estuary, the reproductive season is May and June. Our objective was to test the effects of winter‐spring photoperiod and temperature conditions on the timing of sexual maturation in both males and females. Groups (16 animals each) of winter flounder breeders were maintained from mid‐January to mid‐May under five different experimental conditions: (1) natural photoperiod and temperature conditions; (2) natural photoperiod, 6° C; (3) 15L : 9D, natural temperature conditions; (4) 15L : 9D, 6° C; (5) accelerated photoperiod increase from winter to spring conditions, 6° C. Natural photoperiod and temperature conditions correspond to a gradual increase in light period from 8L : 16D (January) to 15L : 9D (May) and in temperature from −1° C (January to April) to 6° C (May). GSI and condition factor did not differ among the treatments ( P  > 0·05). In males, milt production occurred simultaneously in the different treatments and histological examination did not indicate any significant effect of either photoperiod or temperature on testes development. In females, seven stages of oocyte development were observed. Both the number of oocytes at the cortical alveoli stage and number of atretic oocytes increased at 6° C (warm temperature conditions). Overall, neither photoperiod nor temperature modified the reproductive period. Warm winter‐spring temperature conditions, however, may decrease egg numbers and egg quality.     

The disproportionate effect of global warming on the arrival dates of short-distance migratory birds in North America

Recent studies have shown that, in response to global climate change, diverse avian taxa are now nesting measurably earlier (< 10 days) in both the United States and Britain. Similarly, several studies on European birds have now demonstrated that a variety of species (although not all) are arriving increasingly early. However, surprisingly, widespread changes in North American migrant phenology have not been demonstrated. It is hypothesized that short-distance migrants (birds that winter in the southern United States) may be quicker to adapt to climate change than long-distance migrants (birds that winter south of the United States), as short-distance migrants can respond to meteorological cues indicating weather conditions to the north whereas long-distance migrants must rely on photoperiod. This study examined the first arrival dates of 103 migrant birds in New York and Massachusetts and found that, on average, all migrants arrived significantly earlier during the period 1951–1993 than the period 1903–1950. From 1951–1993 birds wintering in the southern United States arrived on average 13 days earlier while birds wintering in South America arrived 4 days earlier. Although a change in observer effort cannot be quantified and may be a source of bias, a comparison of the numbers of reporting observers during the 1930s and the 1980s revealed no significant difference. These results are consistent with those expected under a scenario of global warming.     

Hatching of cladoceran resting eggs: temperature and photoperiod

Summary 1. We identified temperature and photoperiod conditions under which the hatching of 45 cladoceran species could be elicited. Identification of appropriate hatching cues is of primary importance for the exploration of the ties between active and diapausing stages.
2. Incubation temperature affected the hatching success of resting eggs isolated from Danish, Belgian/Dutch and Spanish sediments. In general, most hatchlings and species were retrieved at 15 °C. Danish and Belgian/Dutch resting eggs hatched more successfully under a long day photoperiod than in continuous illumination.
3. Most species could be retrieved after incubation of resting eggs isolated from a limited amount of sediment (0.4 kg) under a single, well chosen combination of temperature and photoperiod. Processing additional sediment samples under seven more incubation regimes only allowed detection of 21% (Spain) to 34% (Denmark) more species.
4. The incubation period for resting eggs to hatch was strongly influenced by incubation temperature. Our results show that hatching experiments aimed at assessing cladoceran species richness and conducted at 15 °C should be continued for a period of at least 2 weeks, after which a random subset of hatchlings (e.g. n  = 100) can be selected from the total hatchling assemblage.     

Effect of Vernalization and Red Light Illumination of Seedlings of Bread Wheat (Triticum aestivum L.) on the Temperature Profile of cAMP Phosphodiesterase Activity

Phenotypic manifestations of Vrn(vernalization) and Ppd (photoperiod) genes responsible for transition of bread wheat Triticum aestivumL. to generative growth (flowering) are mutually related. Since the mechanism of phytochrome-induced photoperiodism involves the enzymes of cyclic adenosine monophosphate metabolism, and phosphodiesterase in particular, we tested involvement of phosphodiesterase in the process of winter wheat vernalization and formation of flowering competence in alternate wheat requiring a long photoperiod but no vernalization for its transition to flowering. We studied temperature dependence of phosphodiesterase activity in vernalized and unvernalized winter wheat on the one hand and in etiolated and red light illuminated seedlings of alternate wheat on the other hand. Short-term experiments demonstrated that red light illumination is similar to long photoperiod by the effect on the long-day plants. Both influences induced a pronounced inversion of the temperature profile of phosphodiesterase activity in the 28–45°C range. We propose that phosphodiesterase is involved in vernalization and can serve as a receptor of low temperature in winter wheat. Changed temperature profile is a radical control mechanism of phosphodiesterase activity in response to the influences (red light and vernalizing temperatures) responsible for competence of various bread wheat forms for generative growth.     

Effects of photoperiod and temperature on the termination of diapause in the univoltine seed wasp Eurytoma plotnikovi

Abstract Mummified pistachios containing fully grown diapause larvae of Eurytoma plotnikovi Nikol'skaya (Hym., Eurytomidae) were collected in early August and late September in coastal northern Greece and subjected to various photoperiod and temperature treatments, then maintained at 19 or 26°C and a long-day (LD 16:8 h), a changing, or a short-day (LD 10:14 h) photoperiod until pupation. In larvae of early August (beginning of diapause) subjected for 20 weeks to 19°C under a long, a changing, or a short photophase, followed by 19°C and a long photophase, 50% of the larvae pupated after 24, 18 and 13 weeks respectively. After exposure for 20 or even 12 weeks to a short photophase and low temperatures (10 or 4°C), pupation occurred after only 7–8 weeks and was more synchronous. The ranges of temperature for diapause development and post-diapause morphogenesis overlap. After exposure for 12 weeks to short days and low temperature, larvae of late September pupated much sooner under long days than under short days and sooner at 26° than at 19°C. E.plotnikovi depends on both temperature and photoperiod for diapause development, low temperature having a strong favourable effect on the earlier part and long day on the later part of diapause. In a few larvae of another pistachio seed wasp, Megastigmus pistaciae Walker, after a long enough period of low temperatures, diapause was terminated normally at 26°C and long days, or at 19°C and long or short days.     

Effects of temperature and photoperiod on vegetative growth of white clover (Trifolium repens) ecotypes

Effects of photoperiod and temperature on vegetative growth of seedling populations and clones of white clover ( Trifolium repens L.) originating from various latitudes (58°48'–69°54'N) and altitudes (up to 1100 m above sea level) were studied in a phytotron. Dry matter production, stolon elongation, petiole elongation and leaf lamina size were enhanced by long photoperiod. The requirement for long photoperiod increased with decreasing temperature. At 6°C the maximum growth was recorded under 24-h daylength. At 18°C already an increase in photoperiod from 12 to 15 h significantly enhanced growth, and maximum growth was obtained at 21-h photoperiod. The studied populations responded similarly to daylength, and the results did not indicate photoperiodic ecotypes in the material. The southernmost clones and populations generally had the highest dry matter production at all temperature treatments (6–18°C). Variation between clones within one location was, however, significant, and rapidly growing clones were found also in high-latitude locations. Dry matter production was poorly correlated with the morphological characters observed, but in some cases significant correlation with leaf lamina size was found.     

Photoperiod and temperature affect the life cycle of a subtropical cockroach, Opisoplatia orientalis: seasonal pattern shaped by winter mortality

Abstract.  Opisoplatia orientalis is an ovoviviparous cockroach living in the subtropical areas in Japan. Both adults and nymphs overwinter on Hachijo Island (33°N). The nymphs sampled before and after overwintering showed a similar pattern in frequency distribution of head widths with a definite peak of fifth instars. The present study was conducted to determine how this pattern was formed by investigating the effects of photoperiod and temperature on development and reproduction. Photoperiod influenced the number of nymphal instars, resulting in a longer duration of nymphal development at LD 12 : 12 h than at LD 16 : 8 h. However, the rate of development at each instar was only affected to a small extent by photoperiod and no sign of diapause was detected. It was suggested that the photoperiodic response controlling the number of nymphal instars might have evolved to adjust the timing of adult emergence and reproduction to the favourable season. The prereproductive period and time intervals between nymph depositions were prolonged as temperature declined, but there was no evidence for diapause in adults. Mortality occurred in eggs and embryos inside of the body of the females during winter. Thus, it was inferred that female adults would reset ovarian development in spring and deposit nymphs in summer simultaneously, and these nymphs would reach the fifth instar before winter comes. This winter mortality hypothesis was supported by experiments in which reproductive activity and mortality were monitored for field-collected adults under either constant or changing temperature conditions simulating those in the field.     

Energy Allocation Changes in Overwintering Adults of the Common Pistachio Psylla, Agonoscena pistaciae Burckhardt & Lauterer (Hemiptera: Psyllidae)

The common pistachio psylla, Agonoscena pistaciae Burckhardt & Lauterer (Hemiptera: Psyllidae), is known as the key pest of pistachio orchards in Iran. This pest passes the winter as adults. In this study, energy allocation changes in relation to ambient temperature were investigated in field-collected adults by measuring total body sugar, trehalose, glucose, sorbitol, myoinositol, glycogen, lipid, and protein contents. Glycogen content decreased with decrease in ambient temperature. The decrease in glycogen content was proportional to the increase in total body sugar, trehalose, myoinositol, and sorbitol contents. In January, with mean ambient temperature of 5.4°C, glycogen content was at the lowest level, whereas total body sugar, trehalose, glucose, and sorbitol were at the highest level. Total body sugar, trehalose, myoinositol, and sorbitol contents increased as temperature decreased from 22.7°C in October to 5.4°C in January. In conclusion, low molecular weight carbohydrates and polyols may play a role in winter survival and adaptation to cold of the common pistachio psylla by providing the required cryoprotection. Also, overwintering adults of the common pistachio psylla may store energy in the form of lipid for later utilization during the overwintering.     

Effects of temperature of adults and eggs on the induction of embryonic diapause in the band-legged ground cricket, Dianemobius nigrofasciatus

Abstract.  Eggs laid by adult female Dianemobius nigrofasciatus , reared under long-day (LD 16 : 8 h, 25 °C) or short-day (LD 12 : 12 h, 25 °C) conditions from the nymphal stage, are kept at several constant temperatures. At 22.5–30.0 °C, eggs laid by long-day adults show lower incidences of diapause than those laid by short-day adults. In both eggs laid by adults under long-day conditions and those under short-day conditions, the higher the temperature at which the eggs are kept, the lower the incidence of diapause. When eggs of long-day adults are exposed to a low-temperature pulse (10 °C, 24 h) on the day of deposition (day 0), the incidence of diapause increases. The low-temperature pulse on day 1 does not increase the incidence of diapause. By contrast, when the eggs of short-day adults are exposed to a high-temperature pulse (35 °C, 24 h) on day 0 or day 1, the incidence of diapause decreases. The temperature pulses on day 0 are more effective at diapause prevention. Staining of diapause eggs by the Feulgen–Rossenbeck method shows that the eggs enter diapause at the blastoderm stage, which is on day 1 or day 2 at 25 °C. The exposure of adults to long days and higher temperatures prevents the eggs from entering diapause. In D. nigrofasciatus , embryonic diapause is controlled by maternal effects, adult photoperiod and temperature, and egg temperature before or at diapause.     

Observations on the effect of photoperiod on the control of polymorphism in Psylla pyricola

ABSTRACT. Psylla pyricola Forster (Homoptera) occurs as two adult morphs, a summer form (f. typica) and a winter form (f. simulans). The latter is larger, darker and overwinters in ovarian diapause. Eggs laid by either morph under LD 12:12 (short days) or under LD 18:6 or 16:8 (long days) gave f. typica when reared under long days. When reared under short days, almost all were f. simulans. No interforms were recorded. When the photoperiod was switched during the nymphal stage (whether from long to short days, diapause induction; or from short to long days, diapause termination), nymphs were progressively less sensitive with increasing age, with no morph changes when the switch occurred in the fifth instar. Nymphs derived from f. simulans reared under long days tended to be more sensitive to a change to short days in the early instars than when the nymphs were first reared under short days and then switched to long days. Interforms were frequent when the switch occurred during the nymphal stage, particularly in the third instar. Wing lengths varied within morphs depending on the timing of the switch. The largest f. simulans were derived from f. typica when maintained under short days, and the smallest f. typica from either morph when maintained under long days, as would be expected under field conditions. No f. simulans were found under field conditions in the first f. typica generation, but a small percentage were present in the second generation. It is concluded that, even within a given generation, not all P. pyricola are equally sensitive to photoperiod, but that photoperiod is one of the major factors controlling the change to f. simulans in the autumn. Whilst under laboratory conditions photoperiod can also affect the switch to f. typica in the spring, in the field it may be less important than low temperatures.     

Neuroendocrine Regulation of the Development of Seasonal Forms of the Asian Comma Butterfly, Polygonia c-aureum L

In the butterfly, Polygonia c-aureum , development of seasonal forms controlled by the photoperiod and temperature was shown to involve a neuroendocrine system of the brain-corpus cardiacum-corpus allatum complex.
For analysis of the neuroendocrine system concerned, the innervation of the complex was investigated first by cobalt chloride perfusion staining and then by severance of axons, ablation of the candidate cells, injection of a homogenate of these cells and transplantation of corpora cardiaca using pupae programmed to be either summer-form or autumn-form adults.
The results suggested that medial nerve cells produce what is called material producing the summer form.
The seasonal forms of the Asian comma butterfly, Polygonia c-aureum L., summer and autumn forms (Fig. la, b), are determined by the photoperiod and the temperature during the larval period (1–3). Previous studies have given the following results on the physiological mechanism involved in the effect of environmental factors in inducing these seasonal forms. First, the mechanism involves neurosecretory cells located somewhere in the brain (2). Second, the nervous connections between the brain and the corpus cardiacum (NCC I+II (4)) and between the right and left brain lobes are indispensable for the effect (2, 5–7).
The present study consisted of two series of experiments. One was designed to demonstrate morphologically the axonal connection of the corpus cardiacum with the corpus allatum in this butterfly, like that shown in several other insects (8–13). The other series was designed to locate the neurosecretory cells producing material related to the seasonal form and to see if this material is also present in the corpus cardiacum.     

Electrophysiological identification of cold receptors on the antennae of the ground beetle Pterostichus aethiops

Abstract.  In single-sensillum extracellular electrophysiological recordings, terminal campaniform sensilla at the tip of antennae of the ground beetle Pterostichus aethiops (Pz., 1797) show action potentials of three sensory cells, A-, B- and C-cells, distinguished by differences in their spike amplitudes. Only the A-cell, with the largest spike amplitude, is highly sensitive to temperature fluctuations, showing remarkable changes in its firing rate induced by changes in temperature of 0.1 °C. The firing rate of A-cells at 23 °C varies from 15–52 Hz among different beetles. Mean impulse frequency of A-cells is found to be a function of steady temperature, the firing rate decreasing with temperature increase. A-cells respond to a rapid temperature drop with a strong phasic-tonic reaction; larger decreases in temperature evoke higher peak frequency values. Maximum peak frequencies, varying from 380–630 Hz in different beetles, are induced by temperature decreases of 3–10 °C, whereas temperature rise strongly inhibits impulse activity of the A-cell. The first manifestation of rapid warming in the nerve impulse sequence is a very long interspike period, followed by diminished activity. Both the length of the long interspike period and the rate of following impulse activity are functions of temperature change; hence, A-cells respond to temperature changes as typical cold receptors, similar to coeloconic and short hair-like sensilla in other insects.     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Control of summer and winter diapause in the leaf-mining fly Pegomyia bicolor Wiedemann (Dipt., Anthomyiidae)

Effects of photoperiod and temperature on diapause induction and termination were investigated in both aestival and hibernal pupae of Pegomyia bicolor Wiedemann under field and laboratory conditions. In the field, summer diapause had occurred already in part of the first pupal population; the proportion of diapause gradually rose as the day length and temperature increased. This fly is a short-day species with a pupal summer and winter diapause. Summer diapause was induced by both long day-lengths and mild temperatures. The whole larval life is sensitive to photoperiod. Winter diapause was induced mainly by low temperatures, especially in the first 10 days after pupation. High temperatures strongly enhanced summer diapause induction regardless of photoperiod. The diapause-averting influence of short photoperiods was fully expressed only at moderately low temperatures. High temperatures delayed diapause development, resulting in a rather long summer diapause; whereas low temperatures hastened it, leading to a short winter diapause and showing a low thermal threshold for diapause development. In the field, the post-diapause development started in January, the coldest month, suggesting that the thermal requirements for post-diapause development is also low.     

Seasonal variation in foliar carbon exchange in Pinus radiata and Populus deltoides: respiration acclimates fully to changes in temperature but photosynthesis does not

We investigated seasonal variation in dark respiration and photosynthesis by measuring gas exchange characteristics on Pinus radiata and Populus deltoides under field conditions each month for 1 year. The field site in the South Island of New Zealand is characterized by large day-to-day and seasonal changes in air temperature. The rate of foliar respiration at a base temperature of 10 °C ( R ₁₀) in both pine and poplar was found to be greater during autumn and winter and displayed a strong downward adjustment in warmer months. The sensitivity of instantaneous leaf respiration to a 10 °C increase in temperature ( Q ₁₀) was also greater during the winter period. The net effect of this strong acclimation was that the long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures. Seasonal changes in photosynthesis were sensitive to temperature but largely independent of leaf nitrogen concentration or stomatal conductance. Over the range of day time growth temperatures (5–32 °C), we did not observe strong evidence of photosynthetic acclimation to temperature, and the long-term responses of photosynthetic parameters to ambient temperature were similar to previously published instantaneous responses. The ratio of foliar respiration to photosynthetic capacity ( R _d/ A _sat) was significantly greater in winter than in spring/summer. This indicates that there is little likelihood that respiration would be stimulated significantly in either of these species with moderate increases in temperature – in fact net carbon uptake was favoured at moderately higher temperatures. Model calculations demonstrate that failing to account for strong thermal acclimation of leaf respiration influences determinations of leaf carbon exchange significantly, especially for the evergreen conifer.     

Photoperiod and cell mediated immunity of clinically normal dogs

Abstract

Previously, the authors have reported seasonal variations in cell mediated immunity in the dog during the period July, 1977 ‐ October 1978 as measured by whole blood lectin‐induced lymphocyte transformation. Peak activity occurred in the summer, suggesting association with photoperiodicity. Here the authors report on immune response of dogs kept indoors ‐ under controlled physical environment ‐ with a natural (outdoor) photoperiod or under a 12:12 h (LD) regime, and a control group kept in outdoor kennels. Peak immune activity in 1979 occurred in the winter, in both indoor groups as well as the outdoor groups subject to natural photoperiod. Since the indoor dogs were kept at a constant temperature and humidity in clean (filtered) air, photoperiod, temperature, and particulate air contaminants probably are not associated with seasonal variations in immunity. The underlying cause for either the seasonal variations or the shift from peak activity in the summer of 1978 to winter of 1979 is unknown. Dogs under LD = 12:12 light regime had a significantly lowered immunity relative to the dogs with the natural photoperiod.     

Inducing the sexual forms and hatching the eggs of pea aphids

In temperate climates, pea aphids (Acyrthosiphon pisum) produce a single sexual generation each year in response to declining photoperiod and temperature. Mating occurs in the fall and the eggs have an obligatory winter diapause. Genetic recombination during the sexual phase is thought to be an important source of genetic variability within cyclically parthenogenetic aphid populations. Methods for reliably producing sexual forms and hatching the eggs of aphids are therefore central not only to the study of evolutionary change in aphid populations, but also for a general understanding of the origin of agriculturally important variation in destructiveness within pest species.Here, sexual forms of six pea aphid clones were induced in the laboratory and eggs were successfully hatched by creating conditions that closely mimicked those found in field situations. A declining photoperiod was produced by controlling artificial lighting using a timer with variable cycle length. Using these conditions, sexual forms were successfully produced for all six clones tested, which were then mated in all combinations. Eggs were exposed to a daily cycle of freezing and thawing in an incubator under a short-day photoperiod. Egg hatch averaged 60%, but was as high as 89% for some crosses. These methods will permit testing of evolutionary hypotheses and execution of detailed genetic studies of sources of variability within pea aphid populations. They are thus important tools for both evolutionary and agricultural studies.