Effects of humidity on eggs and immatures of Neoseiulus fallacis,Amblysieus andersoni,Metaseiulus occidentalis and Typhlodromus pyri (Phytoseiidae): implications for biological control on apple,caneberry, strawberry and hop

The lethal humidity (LH₅₀) responses at 20°C of eggs of two strains of Neoseiulus fallacis (Garman) were 71.6 and 69.7%; of three strains of Amblyseius andersoni (Chant) were 62.9, 62.0 and 62.4% and of one strain each of Typhlodromus pyri Scheuten and Metaseiulus occidentalis Nesbitt were 55.0 and 28.4%, respectively. Eggs of three genetically distinct strains of A. andersoni from Oregon, the Netherlands and Italy did not respond differently from one another nor did eggs of freely hybridizing N. fallacis from Michigan and Oregon. Mortality of larvae through development to early protonymphs at 50% RH, 20°C. was 91.9, 82.3, 46.2 and 31.0% for fed mites and 98.1, 83.2, 67.0 and 89.7% for unfed mites of Oregon strains of N. fallacis, A. andersoni, T. pyri and M. occidentalis, repectively. Fed larvae-protonymphs of M. occidentalis and T. pyri were more tolerant of low humidity than fed larvae-protonymphs of N. fallacis and A. andersoni. Mortality was less for fed than unfed larvae-protonymphs of M. occidentalis and T. pyri, but there were no differences for A. andersoni and N. fallacis. Levels of feeding by predator larvae on T. urticae and cannibalism by phytoseiid protonymphs contributed to species differences. Responses to humidity are discussed in relation to geographic and host plant distributions and biological control by single or mixed species populations of phytoseiids.     

Allopatric populations of the invasive larch casebearer differ in cold tolerance and phenology

1. Traits of non-native insect herbivores may vary spatially due to local genetic differences, rapid post-introduction evolution, and/or novel host plant associations. 2. Populations of larch casebearer, Coleophora laricella Hübner, originally from Europe have likely been isolated for > 60 years in North America on eastern larch, Larix laricina (Du Roi) K. Koch, and western larch, Larix occidentalis Nutt. 3. This study investigated cold tolerance and phenology of larvae collected from eastern larch in Minnesota, and western larch in Oregon, Idaho, and Montana, U.S.A. 4. Mean supercooling points of larvae from Minnesota were up to 10 °C lower than supercooling points of larvae from Oregon, Idaho, and Montana. 5. At ambient environmental conditions in spring, overwintering larvae from Minnesota required a mean (± SE) of 172 ± 19 degree-days above 5 °C to break winter quiescence and actively wander, significantly more than required by larvae from Oregon (66 ± 4), Idaho (64 ± 1), and Montana (60 ± 2). 6. Across all assays and despite substantial latitudinal and elevational variation among western larch sites, no significant differences in any traits were detected among larvae collected from western larch. 7. Spatial variation in cold tolerance and phenological traits of larch casebearer may be attributable to insect genetic differences and/or host plant effects, but exact mechanisms remain unknown. Differences in thermal biology between regions may result in disparate effects of climate change on insect populations and should be accounted for when forecasting insect dynamics across large spatial scales.     

Thermal response in pre‐imaginal biology of Ochlerotatus albifasciatus from two different climatic regions

The biological processes on mosquito could be variable in response to local climatic characteristics. The thermal effects on time and the rate larval development, immature survival and adult size in local populations of Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) from cold (Sarmiento) and temperate (Buenos Aires) regions from Argentina were evaluated. This species affects livestock production and human health. Larvae of both regions were placed in breeding thermal baths (11–32 °C range). Development and survival were recorded daily until adult emergence. The development temperature threshold and thermal constant for Sarmiento (4.59 ± 3.08 °C, 204.08 ± 7.83 degree days) was lower and higher than Buenos Aires, respectively (8.06 ± 1.81 °C, 149.25 ± 2.6 degree days). At cold temperatures (11–16 °C), Sarmiento larvae demonstrated 5 days faster development and higher survival (56%) than Buenos Aires (15%), whereas at warm temperatures (20–32 °C) were up to 2 days slower and similar survival (16% vs. 18%). The size did not show differences between populations. An Ochlerotatus albifasciatus population seems to present local thermal responses. The favourable temperature for survival and rate of development would vary within a cold or warm range, and these differential responses would explain the wide geographical distribution in different climatic regions of southern South America.     

Test for latitudinal variation of life history,behavior and mortality in the strictly univoltine damselfly Sympecma fusca (Zygoptera: Lestidae)

A wealth of evidence shows that combinations of ecological stressors interact in shaping life history traits, but little is known about how ecological stressors combine with different seasonal time constraints to shape life history, behavior and mortality across populations. We studied life history, behavior and mortality rate in two latitudinally distant populations of the strictly univoltine, adult‐overwintering damselfly Sympecma fusca. Results from laboratory common‐garden and outdoor experiments indicated countergradient variation of larval development time and growth rate: the more time‐constrained larvae showed faster development and a higher growth rate. This finding led to larger size at emergence in the more time‐constrained individuals. Under conditions of intraspecific interaction (outdoor experiment), northern individuals showed lower survival than southern ones, presumably due to cannibalism. In the absence of intraspecific interactions (laboratory experiment), northern and southern larvae did not differ in survival. Finally, laboratory‐grown northern and southern larvae did not differ in activity level. This is the first time that compensation for seasonal time constraints has been shown in a temperate odonate species that overwinters in the adult stage.     

Effects of environmental humidity on the survival and development of pine caterpillars, Dendrolimus tabulaeformis (Lepidoptera: Lasiocampidae)

The pine caterpillar, Dendrolimus tabulaeformis is one of the most important pests on Pinus tabulaeformis and other pine species in North China. In the present study, effects of relative humidity (RH) on the development and survival of pine caterpillars and soil moisture (SM) on their diapausing larvae were investigated. Low RH (20%) deferred the development of eggs and larvae, reduced egg hatching and larval surviving compared to 40%, 60% and 80% RH. Both low (20%) and high (100%) RH reduced egg hatching, but only 20% RH deferred the development of larvae, prolonged developmental duration and reduced the body mass and body length of larvae. The SM influenced the survival of diapausing larvae significantly. The dry treatment significantly reduced the supercooling points (SCPs), whereas increased the mortality and reduced body mass from 56.9 to 36.5 mg and body water content from 78% to 63% after 2 weeks' exposure. Therefore, higher RH is more favorable for the development of early instars and survival of diapausing larvae of the pine caterpillars.     

Biosystematics ofAmblyseius andersoni andA. potentillae (Acarina: Phytoseiidae): Implications for biological control

Populations ofAmblyseius andersoni Chant from Verona, Italy and Oregon, U.S.A. and ofA. potentillae (Garman) from The Netherlands were hybridized in reciprocal crosses and examined for evidence of genetic isolation and morphological or isozyme discrimination. Hybridization studies showed that all crosses between the three populations produced viable and fertile female offspring. Backcrosses of F₁ hybrid females to males of the maternal strain likewise showed no evidence of genetic isolation. It is concluded that the populations are conspecific, and thatA. potentillae should be recognized as a junior synonym ofA. andersoni.Morphological examination showed that the Oregon and Netherlands biotypes were more similar to one another than either was to the Italian biotype. A linear discriminate-function analysis correctly classified the mites 78.3% of the time, with only 5% of the misclassifications involving the Italian biotype. Polyacrylamide gel electrophoresis of esterase isozymes showed distinct bands of enzyme activity with significantly differentR _f values for each of the three populations. The genetic continuity between the biotypes should allow us to incorporate specific biological traits of value for biological control in Oregon by hybridization with the other populations, while the morphological and electrophoretic markers may allow us to track the degree of establishment and dispersal which occurs under field conditions when foreign biotypes are introduced.     

Microgeographic variation in temperature-induced plasticity in an isolated amphibian metapopulation

Variation in local environments may lead to variation in the selection pressures and differentiation among local populations even at microgeographic scale. We investigated variation in temperature-induced plasticity in larval life-history traits among populations of an isolated pool frog (Rana lessonae) metapopulation in Central Sweden. Successful breeding of this northern fringe metapopulation is highly dependent on early summer temperature, however, the metapopulation shows very little variation in molecular genetic markers suggesting limited potential for local differentiation. We exposed larvae from three closely-located populations to two temperatures (20 and 25°C) in laboratory to investigate their growth and development responses to temperature variation. In general, larvae exposed to warmer temperature experienced higher survival and metamorphosed faster, but at a smaller size than those at low temperature. We found differences among the populations in both trait mean values and in the plastic responses. Among-family variation within populations was found in growth rate and time to metamorphosis, as well as in plasticity suggesting that these traits have a capacity to evolve. Our results indicate ample phenotypic variation within and among these closely-located populations despite the low molecular genetic variation. The differences in pond temperature characteristics detected in the study in the three localities may suggest that differential selection is acting in the populations. The strong differentiation found in the larval traits implies that understanding the factors that influence the potential of the populations to adapt to environmental changes may be essential for successful conservation strategies.     

Factors affecting entomopathogenic nematode infection ofPlutella xylostella on a leaf surface

We investigated the ability of entomopathogenic nematodes to infect diamondback moth (DBM),Plutella xylostella (L.) (Lepidoptera: Plutellidae) on a leaf surface. In a leaf disk assay, mortality of late stage DBM larvae ranged from <7% caused bySteinernema kushidai Mamiya to >95% caused byS. carpocapsae (Weiser) All strain. LC₅₀ values forS. carpocapsae, S. riobravis Cabanillas, Poinar & Raulston, andHeterorhabditis bacteriophora Poinar NC1 strain were 14.6, 15.4, and 65.4 nematodes/larva, respectively.S. carpocapsae, S. riobravis, andH. bacteriophora caused 29%, 33%, and 14% mortality of DBM pupae, respectively. DBM mortality caused byS. carpocapsae on radish declined at low (<76%) to moderate (76–90%) RH, because nematode survival and infectivity declined at low (<76%) to moderate (76–90%) RH. However, DBM mortality caused byS. riobravis did not decline with RH.S. riobravis survival declined with RH, but infectivity did not. Overall, nematode survival and infectivity to DBM larvae were lower forS. riobravis than forS. carpocapsae. In addition, DBM mortality was higher on radish plants (pubescent leaves) than on cabbage plants (glaborous leaves).     

Genome-wide SNP analysis of three moose subspecies at the southern range limit in the contiguous United States

Genome-wide evaluations of genetic diversity and population structure are important for informing management and conservation of trailing-edge populations. North American moose (Alces alces) are declining along portions of the southern edge of their range due to disease, species interactions, and marginal habitat, all of which may be exacerbated by climate change. We employed a genotyping by sequencing (GBS) approach in an effort to collect baseline information on the genetic variation of moose inhabiting the species’ southern range periphery in the contiguous United States. We identified 1920 single nucleotide polymorphisms (SNPs) from 155 moose representing three subspecies from five states: A. a. americana (New Hampshire), A. a. andersoni (Minnesota), and A. a. shirasi (Idaho, Montana, and Wyoming). Molecular analyses supported three geographically isolated clusters, congruent with currently recognized subspecies. Additionally, while moderately low genetic diversity was observed, there was little evidence of inbreeding. Results also indicated?>?20% shared ancestry proportions between A. a. shirasi samples from northern Montana and A. a. andersoni samples from Minnesota, indicating a putative hybrid zone warranting further investigation. GBS has proven to be a simple and effective method for genome-wide SNP discovery in moose and provides robust data for informing herd management and conservation priorities. With increasing disease, predation, and climate related pressure on range edge moose populations in the United States, the use of SNP data to identify gene flow between subspecies may prove a powerful tool for moose management and recovery, particularly if hybrid moose are more able to adapt.

     

Functional response of Euseius finlandicus and Amblyseius andersoni to Panonychus ulmi on apple and peach leaves in the laboratory

The functional response of adult females of the predatory mites Euseius (Amblyseius) finlandicus and Amblyseius andersoni to larvae and adult females of the fruit tree red spider mite Panonychus ulmi was determined on apple and peach leaf disks in the laboratory at 25°C and 16:8 (L:D). For adult females of P. ulmi the predation efficiency of E. finlandicus was higher on peach than on apple, whereas that of A. andersoni was higher on apple than on peach. Efficiency of predation on larvae of P. ulmi by either predator did not differ significantly between apple and peach. On both plants, A. andersoni had a higher predation rate than E. finlandicus on larvae of P. ulmi. It is concluded that in the laboratory the host plant has a substantial effect on predation efficiency of A. andersoni and E. finlandicus when they preyed on adults but not when they preyed on larvae of P. ulmi.     

Larval survival and feeding by immature Metaseiulus occidentalis,Neoseiulus fallacis,Amblyseius andersoni and Typhlodromus pyri on life stage groups of Tetranychus urticae Koch and phytoseiid larvae

When 20 newly hatched larvae either of Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Amblyseius andersoni Chant or Typhlodromus pyri Scheuten were held in arenas without food at 95% RH and 20°C, the percentages of mites surviving to protonymphs were 5.0, 81.3, 86.3, and 83.8%, respectively. Unfed M. occidentalis larvae starved within 2–3 days, while immatures of the other three species lived up to 12–14 days, with some becoming adults by cannibalizing and/or scavenging. Phytosciid larvae given eggs, larvae/protochrysalis/protonymphs (L/P), deutochrysalis/deutonymphs (D) or teleiochrysalis/female adult (T/A) of Tetranychus urticae Koch, fed at different incidences during 6 h tests. Larvae of T. pyri never fed, but almost all larvae of M. occidentalis fed on eggs and L/Ps and 60–70% of M. occidentalis larvae fed on Ds and T/As. N. fallacis and A. andersoni larvae fed at incidences from 20–75% depending on the stage of spider mite given. Larvae fed more commonly on eggs and L/Ps than Ds and T/As for M. occidentalis and N. fallacis but not A. andersoni. Protonymphs and deutonymphs of all four species, readily fed on T/As after 3 h of exposure, but incidences were higher for A. andersoni and T. pyri. Feeding on phytoseiid larvae by protonymphs and deutonymphs also was more common for A. andersoni and T. pyri. Except for M. occidentalis, deutonymphs fed more than protonymphs on phytoseiid larvae. Results are discussed in relation to individual species life histories and the value of these traits in predicting a species role in a biological control system.     

Variation in the demographics of a rare central Oregon endemic, Astragalus peckii Piper (Fabaceae), with fluctuating levels of herbivory

Understanding variation in plant vital rates (survival, growth, and reproduction) and population demographic parameters for rare plant taxa facilitates effective management for long-term persistence. We evaluated demographics of the rare plant Astragalus peckii (Fabaceae), a state-listed Threatened plant in Oregon, USA, with particular emphasis on how a microlepidopteran herbivore, Sparganothis tunicana, impacted vital rates and population growth. Stage-based transition matrix models were used to compute population growth rate (λ) and elasticity from 2006 to 2009 at two populations: Bull Flat, which was located in the main population center; and Chiloquin, a naturally isolated population. Population growth at Bull Flat was stable to slightly declining (λ = 0.96, 95 % CI 0.91–1.00) whereas at Chiloquin, the isolated population, population growth was increasing (λ = 1.20, 95 % CI 1.15–1.24). Microlepidopteran herbivory was associated with different plant responses in each population. At Bull Flat, plant survival was lower with greater herbivore presence. At Chiloquin, reproduction was reduced in plants when herbivores were active earlier in the growing season. Despite these effects on plant vital rates, we found lower population growth only during one transition period at Bull Flat when we compared matrices with and without herbivory. In addition to herbivory, we also address the potential role precipitation plays as a contributor to site differences and temporal variation within sites. Overall, we illustrate how two populations can have different responses to the same disturbance factor and highlight implications for management of different populations across the landscape.     

Effect of climatic variation on the morphological characteristics of 37‐year‐old balsam fir provenances planted in a common garden in New Brunswick,Canada

The extent of the effect of projected changes in climate on trees remains unclear. This study investigated the effect of climatic variation on morphological traits of balsam fir [Abies balsamea (L.) Mill.] provenances sourced from locations spanning latitudes from 44° to 51°N and longitudes from 53° to 102°W across North America, growing in a common garden in eastern Canada. Lower latitude provenances performed significantly better than higher latitude provenances (p < .05) with regard to diameter at breast height (DBH), height (H), and crown width (CW), a distinction indicative of genotypic control of these traits. There was, however, no significant difference among provenances in terms of survival (p > .05), an indication of a resource allocation strategy directed at survival relative to productivity in higher latitude provenances as seen in their lower DBH, H, and CW compared to the lower latitude provenances. Temperature had a stronger relationship with DBH, H, and CW than precipitation, a reflection of adaptation to local conditions in populations of the species along latitudinal gradients. Both climatic variables had some effect on tree survival. These results suggest that the response of balsam fir to climatic variation will likely not be uniform in the species, but differ based on genetic characteristics between populations located in the northern and southern parts of the species’ range. Population differences in response to climatic variation may be evident earlier in growth traits, compared to survival in balsam fir. The findings of this study will facilitate modeling in the species that is reflective of genetic variation in response to climatic conditions, and guide provenance selection for utilization in terms of productivity or resilience as well as breeding programs directed at obtaining species that possibly combine both traits.     

Evaluating mulches together with Heterorhabditis zealandica (Rhabditida: Heterorhabditidae) for the control of diapausing codling moth larvae,Cydia pomonella (L.) (Lepidoptera: Tortricidae)

The potential of using an entomopathogenic nematode, Heterorhabditis zealandica Poinar, together with different test mulches (pine chips, wheat straw, pine wood shavings, blackwood and apple wood chips) to control diapausing codling moth, Cydia pomonella (L.) larvae was evaluated. Mesh cages were identified as a suitable larval-containment method. High levels of codling moth mortality were obtained when using pine wood shavings as mulch (88%) compared to pine chips, wheat straw, blackwood and apple wood chips (41–88%). Humidity (>95% RH) has to be maintained for at least 3 days to ensure nematode survival. It was also proven that nematodes had the ability to move out of infected soil into moist mulch, to infect the codling moth larvae residing at heights of up to 10 cm. Field experiments showed the importance of climatic conditions on nematode performance. Low temperatures (<15°C) recorded during the first trial resulted in low levels of control (48%), as opposed to the 67% mortality recorded during the second trial (temperatures ranged between 20 and 25°C). Low levels of persistence (<10%) were recorded in the mulches post-application. The study conclusively illustrated some of the baseline requirements fundamental to the success of entomopathogenic nematodes together with mulches for the control of codling moth.     

Effects of Earlier Sea Ice Breakup on Survival and Population Size of Polar Bears in Western Hudson Bay

ABSTRACT Some of the most pronounced ecological responses to climatic warming are expected to occur in polar marine regions, where temperature increases have been the greatest and sea ice provides a sensitive mechanism by which climatic conditions affect sympagic (i.e., with ice) species. Population-level effects of climatic change, however, remain difficult to quantify. We used a flexible extension of Cormack-Jolly-Seber capture-recapture models to estimate population size and survival for polar bears (Ursus maritimus), one of the most ice-dependent of Arctic marine mammals. We analyzed data for polar bears captured from 1984 to 2004 along the western coast of Hudson Bay and in the community of Churchill, Manitoba, Canada. The Western Hudson Bay polar bear population declined from 1,194 (95% CI = 1,020-1,368) in 1987 to 935 (95% CI = 794-1,076) in 2004. Total apparent survival of prime-adult polar bears (5–19 yr) was stable for females (0.93; 95% CI = 0.91-0.94) and males (0.90; 95% CI = 0.88-0.91). Survival of juvenile, subadult, and senescent-adult polar bears was correlated with spring sea ice breakup date, which was variable among years and occurred approximately 3 weeks earlier in 2004 than in 1984. We propose that this correlation provides evidence for a causal association between earlier sea ice breakup (due to climatic warming) and decreased polar bear survival. It may also explain why Churchill, like other communities along the western coast of Hudson Bay, has experienced an increase in human-polar bear interactions in recent years. Earlier sea ice breakup may have resulted in a larger number of nutritionally stressed polar bears, which are encroaching on human habitations in search of supplemental food. Because western Hudson Bay is near the southern limit of the species' range, our findings may foreshadow the demographic responses and management challenges that more northerly polar bear populations will experience if climatic warming in the Arctic continues as projected.     

Effects of fluctuating moisture and temperature regimes on the infection potential of Beauveria bassiana for Rhodnius prolixus

The effect of both moisture and temperature on the infective potential of Beauveria bassiana to the Chagas' disease vector, Rhodnius prolixus, was studied under fluctuating regimes. At constant 25 degrees C, contaminated first-instar nymphs exposed to increasing daily periods of initial exposure to 97% RH, followed by transfer to reduced humidity (43, 53, 75, and 86% RH), showed a significant reduction in mortality when the 97% RH exposure time declined from 12 to 8 h per day. The duration of disease incubation depended on the daily 97% RH exposure time. Under fluctuating regimes of both humidity (97% RH versus 75% RH) and temperature (15/28, 20/25, 25/28, and 25/35 degrees C), first-instar mortality was affected by weather conditions, daily 97% RH exposure time (8, 12, and 16 h per day), and number of temperature and humidity fluctuations before transferring tested insects to constant unfavorable conditions. In most cases, at 12/12 h alternating cycles, high and rapid mortality required five cycles. Under these fluctuating regimes, fungus-induced mortality and mortality time were similarly affected in third- and fifth-instar nymphs by the daily 97% RH exposure time. Despite a lower susceptibility of older larval stages, mortality rates in insects exposed for at least 12 h per day at 97% RH remained very high except at 15 degrees C. Moisture and temperature regimes at 12/12 h cycling significantly affected the dose-mortality response in first-instar nymphs. The most favorable conditions consisted of 97%-20 degrees C combined with either 75%-25 degrees C or 43%-25 degrees C. Under less favorable alternating conditions (lower and higher temperatures) the amounts of inoculum required for killing 50% of first-instar nymphs were 10 or 20 times higher. From a vector control standpoint, daily high humidity appears to be the most crucial climatic constraint. B. bassiana has the potential to control R. prolixus populations with applications made during the rainy seasons when humidity is high.     

Fitness costs associated with low genetic variation are reduced in a harsher environment in amphibian island populations

A basic premise of conservation geneticists is that low levels of genetic variation are associated with fitness costs in terms of reduced survival and fecundity. These fitness costs may frequently vary with environmental factors and should increase under more stressful conditions. However, there is no consensus on how fitness costs associated with low genetic variation change under natural conditions in relation to the stressfulness of the environment. On the Swedish west coast, natterjack toad Bufo calamita populations show a strong population genetic structure and large variation in the amount of within-population genetic variation. We experimentally examined the survival of natterjack larvae from six populations with different genetic variation in three thermal environments corresponding to (a) the mean temperature of natural ponds (stable, laboratory), (b) a high temperature environment occurring in desiccating ponds (stable, laboratory) and (c) an outdoor treatment mimicking the natural, variable thermal conditions (fluctuating, semi-natural). We found that larvae in the outdoor treatment had poorer survival than larvae in the stable environments suggesting that the outdoor treatment was more stressful. Overall, populations with higher genetic variation had higher larval survival. However, a significant interaction between treatments and genetic variation indicated that fitness costs associated with low genetic variation were less severe in the outdoor treatment. Thus, we found no support for the hypothesis that fitness costs associated with low genetic variation increase under more stressful conditions. Our results suggest that natural thermal stress may mask fitness losses associated with low genetic variation in these populations.     

Hardening trumps acclimation in improving cold tolerance of Drosophila melanogaster larvae

Abstract Chill‐susceptible insects are able to improve their survival of acute cold exposure over both the short term (i.e. hardening at a relatively severe temperature) and longer term (i.e. acclimation responses at milder temperatures over a longer time frame). However, the mechanistic overlap of these responses is not clear. Four larval stages of four different strains of Drosophila melanogaster are used to test whether low temperature acclimation (10 °C for 48 h) improves the acute cold tolerance (LT₉₀, ～2 h) of larvae, and whether acclimated larvae still show hardening responses after brief exposures to nonlethal cold or heat, or a combination of the two. Acclimation results in increased cold tolerance in three of four strains, with variation among instars. However, if acclimation is followed by hardening pre‐treatments, there is no improvement in acute cold survival. It is concluded that short‐term thermal responses (e.g. hardening) may be of more ecological relevance to short‐lived life stages such as larvae, and that the mechanisms of low temperature hardening and acclimation in D. melanogaster may be antagonistic, rather than complementary.     

Development rates of two Xenopsylla flea species in relation to air temperature and humidity

The rate of development of immature fleas, Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) was studied in the laboratory at 25 degrees C and 28 degrees C with 40, 55, 75 and 92% relative humidity (RH). These fleas are separately associated with the host jird Meriones crassus Sundevall in different microhabitats of the Ramon erosion cirque, Negev Highlands, Israel. This study of basic climatic factors in relation to flea bionomics provides the basis for ecological investigations to interpret reasons for paratopic local distributions of these two species of congeneric fleas on the same host. Both air temperature and RH were positively correlated with duration of egg and larval stages in both species. Change of humidity between egg and larval environments did not affect duration of larval development at any temperature. At each temperature and RH, the eggs and larvae of X. ramesis did not differ between males and females in the duration of their development, whereas female eggs and larvae of X. conformis usually developed significantly faster than those of males. For both species, male pupae developed slower than female pupae at the same air temperature and RH. Air temperature, but not RH, affected the duration of pupal development. At each humidity, duration of the pupal stage was significantly longer at 25 degrees C than at 28 degrees C: 15.3+/-1.7 vs. 11.7+/-1.2 days in X. conformis; 14.1+/-2.0 vs. 11.5+/-1.7 days in X. ramesis, with a significantly shorter pupal period of the latter species at 25 degrees C. These limited interspecific bionomic contrasts in relation to basic climatic factors appear insufficient to explain the differential habitat distributions of X. conformis and X. ramesis.