Effects of temperature on growth and efficiency of food utilization in fifth-instar caterpillars of the tobacco hornworm, Manduca sexta

Fifth-instar larvae of Manduca sexta were reared from hatching on artificial diet at 15, 20, 25, 30 and 35°C. Total development time decreased with increasing temperature. Very few larvae (12%) survived at 15°C, so this temperature was not considered further. There was some mortality at 30°C (11%), and at 35°C (50%).The absolute rate of growth in the fifth instar was faster at 25 than at 20°C, but was similar at 25, 30 and 35°C. This was true both for caterpillars that were chronically exposed to experimental temperatures (i.e. since hatching) and for those acutely exposed (i.e. reared up to fifth instar at 25°C).There was a progressive decrease with higher rearing temperatures in both the initial and final sizes of chronically exposed fifth-instar larvae. Acutely exposed caterpillars matched for initial size showed smaller temperature related differences in final size. Because of these size differences there were differences in relative growth rate which did not reflect true differences in absolute growth rate.Total food consumed by chronically exposed caterpillars was greatest at the lowest temperature (20°C), and decreased progressively with increasing temperature. The absolute rate of food consumption increased from 20 to 25°C, but did not vary significantly between 25 and 35°C. Differences in the sizes of the insects at the different temperatures meant that there were differences among relative measures of consumption that did not reflect absolute food consumption.For chronically exposed caterpillars, none of the three usual indices of food conversion efficiency (AD, ECI and ECD) varied significantly with temperature between 20 and 35°C. This implies that the effects of temperature on metabolic costs are closely matched to food consumption.Oxygen consumption increased with temperature between 20 and 25°C but was temperature compensated between 25 and 35°C.These findings are discussed in terms of their implications for the optimal temperature for growth in Manduca.     

Upper temperature tolerance and the effects of temperature on byssus attachment in the queen scallop, Chlamys opercularis (L.)

The upper temperature tolerance ( LD₅₀-48 h) have been established for three size groups of Chlamys opercularis (L) at different acclimation temperatures In large and intermediate-sized scallops mortlaity was between 19 and 24°C, and in spat between 24 and 25°C. These mortalities varied according to the thermal history of the animals.The rate of byssus formation in spat was found to be maximum at 18°C.     

The combined effects of temperature and diet on development and survival of a crab spider,Misumenops tricuspidatus (Fabricius) (Araneae: Thomisidae)

In the present study, the combined effects of temperature and diet on development and survival of a crab spider, Misumenops tricuspidatus (Fabricius) (Araneae: Thomisidae) in laboratory conditions were investigated. The experiments were carried out at five constant temperatures ranging from 15°C to 35°C on two kinds of diets, fruit flies (Drosophila melanogaster) and a mixed diet of fruit flies and dung flies. It was found that development rate of eggs increased with successive temperature increments, reaching a maximum at 30°C, then declined at 32°C and that eggs survived well between 20°C and 30°C (>70%), but no eggs survived to hatching at 35°C regardless of whether the spiders were fed on single or mixed diet. Juveniles completed development on both diets at all constant temperatures tested, but survival was low at the extreme temperatures. Juvenile development times decreased over successive temperature increments up to 30°C, then increased at 32°C. Females developed faster than males. Diet also influenced development time, survival and number of moults to reach maturity. Juveniles raised on the mixed diet composed of fruit flies and dung flies developed faster, survived better, and required fewer moults to reach maturity than on a diet composed of only fruit flies. Plots of development rates (reciprocal of mean development times) and survival rates (expressed as percentages) against constant temperatures indicated that M. tricuspidatus is well adapted to low temperatures, but detrimentally affected by high temperatures. Using linear regression, the lower development threshold (LDT) and the sum of effective temperatures (SET) for all life stages of M. tricuspidatus on each diet were estimated. LDT and SET varied among developmental stages and between diets.     

The influence of temperature on growth rate and length of larval life of the gastropod, Crepidula plana Say

The relationship between rate of larval development and the potential to prolong larval life was examined for larvae of the marine prosobranch gastropod Crepidula plana Say. Larvae were maintained in clean glass dishes at constant temperatures ranging from 12–29°C and fed either Isochrysis galbana Parke (ISO) or a Tahitian strain of Isochrysis species (T-ISO). Under all conditions, larvae grew at constant rates, as determined by measurements of shell length and tissue biomass. Most larvae eventually underwent spontaneous metamorphosis. Regardless of temperature, faster growth was associated with a shorter planktonic stage prior to spontaneous metamorphosis. Within an experiment, higher temperatures generally accelerated growth rates and reduced the number of days from hatching to spontaneous metamorphosis. However, growth rates were independent of temperature for larvae fed ISO at 25 and 29°C and for larvae fed T-ISO at 20 and 25°C. Where growth rates were unaffected by temperature, time to spontaneous metamorphosis was similarly unaffected. Maximum durations of larval life at a given temperature were shorter for larvae of Crepidula plana than for those of the congener C. fornicata (L.), although both species grew at comparable rates. Interpretations of the ecological significance of these interspecific differences in delay capabilities will require additional data on adult distributions and larval dispersal patterns in the field.     

Constant and fluctuating temperature acclimations have similar effects on phenotypic plasticity in springtails

Much interest exists in the extent to which constant versus fluctuating temperatures affect thermal performance traits and their phenotypic plasticity. Theory suggests that effects should vary with temperature, being especially pronounced at more extreme low (because of thermal respite) and high (because of Jensen's inequality) temperatures. Here we tested this idea by examining the effects of constant temperatures (10 to 30 °C in 5 °C increments) and fluctuating temperatures (means equal to the constant temperatures, but with fluctuations of ±5 °C) temperatures on the adult (F2) phenotypic plasticity of three thermal performance traits – critical thermal minimum (CT_min), critical thermal maximum (CT_max), and upper lethal temperature (ULT₅₀) in ten species of springtails (Collembola) from three families (Isotomidae 7 spp.; Entomobryidae 2 spp.; Onychiuridae 1 sp.). The lowest mean CT_min value recorded here was -3.56 ± 1.0 °C for Paristoma notabilis and the highest mean CT_max was 43.1 ± 0.8 °C for Hemisotoma thermophila. The Acclimation Response Ratio for CT_min was on average 0.12 °C/°C (range: 0.04 to 0.21 °C/°C), but was much lower for CT_max (mean: 0.017 °C/°C, range: -0.015 to 0.047 °C/°C) and lower also for ULT₅₀ (mean: 0.05 °C/°C, range: -0.007 to 0.14 °C/°C). Fluctuating versus constant temperatures typically had little effect on adult phenotypic plasticity, with effect sizes either no different from zero, or inconsistent in the direction of difference. Previous work assessing adult phenotypic plasticity of these thermal performance traits across a range of constant temperatures can thus be applied to a broader range of circumstances in springtails.     

The influence of temperature,sexual condition,and season on the metabolic rate of the lizardPsammodromus hispanicus

Summary Male and femalePsammodromus hispanicus from southern Europe were acclimated to four seasonal conditions of photoperiod and night time temperature. During the dark period, the lizards' body temperatures fell to ambient air temperature but during the light period the lizards were allowed to thermoregulate behaviourally and at such times the lizards' mean body temperature varied from 29.0°C to 32.6°C. The resting metabolic rate of these lizards was measured in 5°C steps from 5°C to 30°C or 35°C. Sexual condition had little effect on resting metabolic rate, but at low temperatures lizards acclimated to winter or spring seasonal conditions had lower resting metabolic rates than those acclimated to summer or autumn conditions. At temperatures above 20°C seasonal acclimation had no effect on resting metabolic rate. It is considered that the reduction in low temperature metabolic rate in spring and winter is induced by low night time temperatures and serves to conserve energy during those seasons when lizards must spend long periods at low temperature without being able to feed.     

Effects of salinity and cyclic temperature on survival of two sympatric species of grass shrimp (Palaemonetes), and their relationship to natural distributions

Survival and respiration of the grass shrimp Palaemonetes pugio Holthuis and P. vulgaris (Say) from the Newport River estuary were measured after exposure to cyclic and constant winter temperatures, to rapid decreases in temperature, and to various temperature-salinity combinations. Both species were subjected to nine temperature-salinity combinations including temperature regimes of cyclic 7–13°C, constant 7° and 10°C, and salinities of 5, 20, and 35%.. Based on the laboratory and field results, the differences in physiological tolerance to winter temperatures and salinities were examined in relation to habitat partitioning by these sympatric species.Survival after continuous exposure to cyclic temperature regimes at medium to high salinities was similar to that observed for comparable constant temperatures; however, at low salinities mortality was significantly lower under the cyclic regime than under either constant regime. This suggests that cyclic temperatures may be detrimental in combination with some other stress. A rapid, transient decrease in temperature from either 7° or 10°C to 2°C had no measurable effect on survival or rate of oxygen consumption at any temperature-salinity acclimation. Neither salinity (except in areas intermittently subjected to salinities below 3 %.) nor winter temperatures appear to affect habitat partitioning in grass shrimp.     

Mating duration and egg production of the predaceous mite Neoseiulus californicus (Acari: Phytoseiidae) vary with temperature

Effects of constant temperature on mating duration and total fecundity of Neoseiulus californicus females mated once were investigated at 18 °C, 25 °C, 30 °C, and 35 °C with a photoperiod of 16L:8D. Adult mites grown and maintained at 25 °C mated for 315.3 min on average and produced 46.1 eggs per female. These values varied significantly by temperature: 553.6 and 13.9 (18 °C), 261.2 and 26.6 (30 °C), and 253.6 and 23.9 (35 °C), respectively. Duration of copulation was negatively correlated with temperature. However, total egg production peaked at 25 °C and decreased at lower and higher temperatures. Reduced sperm transfer and/or survival rate of sperm in the female body may account for decreased egg production when temperatures are not optimal.     

Temperature dependent development and temperature thresholds of Rhyncaphytoptus ficifoliae Keifer (Diptilomiopidae)

The effects of temperature on developmental rate of Rhyncaphytoptus ficifoliae Keifer (Diptilomiopidae) were determined at six constant temperatures (17, 20, 25, 30, 33 and 36 °C) on fig leaves. The total developmental time of females decreased as temperature increased from 17 (21.62 days) to 33 °C (6.02 days), and then increased at 36 °C (6.47 days). Using the ordinary and Ikemoto and Takai (2000) linear models the estimated lower temperature thresholds (T_min) for total developmental time of females were 10.78 and 10.37 °C and the constant temperatures (k) were 140.25 and 144.78°-days (DD), respectively. Data also were fitted to SSI nonlinear temperature-dependent model. The estimated T_L, intrinsic optimum temperature (T_Ф) and T_h for total immature stages of females by SSI model were 11.11, 23.72 and 37.98 °C, respectively. With use of the obtained data from rearing R. ficifoliae under constant temperatures in laboratory and temperature data in Khorramabad region in 2017, the real developmental rate of this mite in natural conditions was described. The highest (100%) and lowest values (51.67%) of survival rate for immature stages were found at 25 and 36 °C, respectively. The presented information could be used to predict the population dynamics of main pest R. ficifoliae for an effective management.     

Some effects of temperature on the hour glass photoperiod timer in the aphid Megoura viciae

“Resonance” experiments conducted at 3 temperatures do not support the view that the Megoura photoperiod (scotophase) timer has an oscillatory component. The main effects of temperature, which are consistent with an hour glass model, have been examined by exposing the aphids to temperatures ranging from −3 to 30°C for the first 4 h of the scotophase, subsequently returning them in each cycle to 15°C for measurement of the critical night length. During the temperature treatments the insects were removed from the plant to avoid indirect effects resulting from changes in the rate of development (this procedure causes a slight shift in the critical night length from 9.5 to 9.0 h). The timer was found to be almost perfectly compensated between 6 and 20°C, but at lower temperatures it runs slow, only one quarter the normal elapsed time being measured at −3°C. At higher temperatures (25 and 30°C) considerable irregularities appear, eventually resulting in the elimination of the critical night length. The results suggest that the timer may sometimes be stopped.Light perception was assessed by cooling the aphids in light. Photoreception was impaired in some individuals at temperatures as high as +6°C and became negligible at −3°C. The illuminated phase was then accepted as a dark interval of equal duration. Yet at this temperature the timer was still operating, albeit slowly. Their differing temperature thresholds point to some degree of separation in these two functions.High-temperature (25°C) experiments with continously feeding aphids showed that although scotophase heating was more effective, there was a distinct response when high temperatures were synchronized with the photophase. This was attributed to the operation of a “photoperiod counter” mechanism.     

Importance of temperature for the performance and biocontrol efficiency of the parasitoid Perilitus brevicollis (Hymenoptera: Braconidae) on Salix

With the prospect of warmer temperatures as a consequence of ongoing climate change, it is important to investigate how such increases will affect parasitoids and their top-down suppression of herbivory in agroecosystems. Here we studied how the performance and biocontrol efficiency of the willow “bodyguard” Perilitus brevicollis Haliday (Hymenoptera: Braconidae) were affected at different constant temperatures (10, 15, 20, 25°C) when parasitizing a pest insect, the blue willow beetle (Phratora vulgatissima L., Coleoptera: Chrysomelidae). Parasitism did not reduce herbivory at all at 10°C, indicating poor biocontrol efficiency at low temperatures. At higher temperatures, however, parasitism reduced herbivory substantially, implying that biocontrol may be promoted by a warmer climate. Parasitoid performance (survival and development rate) generally increased with increasing temperature up to 20°C. The only exception was body size, which followed the temperature–size rule and decreased with increasing temperature. Our results indicate that a warmer climate may enhance the biocontrol of the blue willow beetle in environments that currently are cooler than the parasitoid’s optimal temperature for development.     

Effect of initial freezing temperature on the semen characteristics of frozen-thawed ram spermatozoa in a semi-arid tropical environment

Ram spermatozoa are sensitive to extreme changes in temperature during the freeze-thaw process. The degree of damage depends on a combined effect of various factors including initial freezing temperature. The present study was conducted to observe the effect of initial freezing temperature on post-thawing motility of ram spermatozoa of native and crossbred rams maintained in a semi-arid tropical environment. Good quality semen obtained from native Malpura and crossbred Bharat Merino rams were pooled within breed and diluted at a rate of 1000 million spermatozoa per milliliter in TEST—yolk–glycerol extender. Diluted semen samples were loaded in 0.25 ml straws and cooled to −25, −75 or −125 °C freezing temperature at the rate of −25 °C/min under controlled conditions before plunging into liquid nitrogen for storage. The thawing of straws was performed at 50 °C in a water bath for 10 s and motility characteristics of the frozen-thawed spermatozoa were assessed by a computer-assisted spermatozoa analysis technique. Initial freezing temperature significantly affected the post-thawing motility of sperm in both the breeds. The post-thawing % motility and rapid motile spermatozoa were significantly higher at initial freezing temperature of −125 °C and lower at −25 or −75 °C. The percentage medium motile sperm were similar at all three initial freezing temperatures. The percentage of slow motile and linearity of sperm varied (P<0.01) between the different freezing temperatures. The curvilinear velocity, average path velocity and straight line velocity of spermatozoa were higher (P<0.01) at −125 °C than −25 or −75 °C. Although the lateral head displacement of spermatozoa did not vary significantly between the different initial freezing temperatures, the stroke frequency was significantly lower at −25 °C than −75 or −125 °C. Except for % linearity, the average path velocity and straight line velocity, other spermatozoa characteristics were not significantly different between breeds. The interaction between freezing temperature and breed was significant only for the % motility and linearity of the spermatozoa. The study indicates that initial freezing temperature has a significant effect on spermatozoa motility and velocity following post-thawing. The best motile spermatozoa following thawing were achieved at −125 °C freezing temperature.     

Influence of temperature on the biological parameters of the anholocyclic species Cinara tujafilina (Hemiptera: Aphidoidea)

Aphids are a good model to study insect reaction to habitat change. Temperature is one of the main factors that influences insects. This paper examines the influence of temperature on developmental stages, fecundity, survival rate and demographic parameters of Cinara tujafilina (Hemiptera: Aphidoidea, Lachnidae), connected with decorative plants of the Cupressaceae family. C. tujafilina was reared in a laboratory on T. orientalis at five constant temperatures of 10, 15, 20, 25 and 28°C, 70% humidity and 14L:10D. The pre-reproduction stage varied from 7 at 25°C to 19 days at 10°C. Developmental threshold was assigned at 3.5°C. The longest reproduction stage for the aphids developing was recorded at 25°C, namely 33 days, while the shortest, at the temperature of 10°C, lasted 8 days. At 25°C this species is characterised by the shortest pre-reproduction stage, the highest fecundity, the highest survival rate and the highest demographic parameters, particularly r_m (0.17). The results suggest that the optimal temperature for the species is 25°C, and indicate that climatic change will favourably influence its development and increase its role as a pest of decorative plants.     

The influence of temperature variations and thermal pollution on various aspects of the biology of the prawn Palaemon pacificus (Stimpson)

The influence of different temperatures 10, 15, 20, and 25°C on the food consumption, growth, moulting rate, and respiration of Palaemon pacificus (Stimpson) from Langebaan Lagoon, west coast of South Africa, was studied under laboratory conditions. At 10°C mortality was high so that food consumption and moulting rate could not be determined as these were very low. At higher temperatures, food consumption was found to be temperature dependent, the rate at 25°C being twice that at 15°C. Growth rate was most favourable at 25°C. At 28°C growth rate was lower than at 20°C but higher than at 15°C. The intermoult period was 17 days at 15°C, and 11 and 10 days at 20, and 25°C, respectively. It seems that from an energetic point of view, 25°C is the most favourable temperature for P. pacificus. Several indices of growth efficiency at different temperatures are presented. The appearance of this prawn in South African west coast localities such as Langebaan during the summer and its disappearance during winter, can be explained by its temperature preferences. The possibility that thermal pollution from a nuclear power station may be beneficial to this prawn, is discussed.     

Prey consumption by phytoseiid spider mite predators as affected by diurnal temperature variations

The consumption rate of an ectothermic predator is highly temperature-dependent and is a key driver of pest-predator population interactions. Not only average daily temperature, but also diurnal temperature variations may affect prey consumption and life history traits of ectotherms. In the present study, we evaluated the impact of temperature alternations on body size, predation capacity and oviposition rate of the predatory mites Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus McGregor (Acari: Phytoseiidae) when presented with eggs of their natural prey, the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae). For both predators, mean daily temperature as well as temperature alternation had a substantial impact on the number of prey consumed. At lower average temperatures, more eggs were killed under an alternating temperature regime (20 °C/5 °C and 25 °C/10 °C) than at the corresponding mean constant temperatures (15 and 20 °C). At higher average temperatures (>25 °C), however, the opposite was observed with higher numbers of prey killed at constant temperatures than at alternating temperatures. At 25 °C, temperature variation had no effect on the predation capacity. A similar trend as for the predation rates was observed for the oviposition rates of the phytoseiids. Body size of N. californicus was affected both by average daily temperature and temperature variation, with smaller adult females emerging at alternating temperatures than at constant temperatures, whereas for P. persimilis, temperature variation had no impact on its body size. Our results demonstrate that temperature variations are likely to affect biological control of T. urticae by the studied phytoseiid predators.     

The development of milky disease under laboratory and field temperature regimes

The effect of temperature on the development of milky disease agent, Bacillus popilliae var. rhopaea, in third-instar Rhopaea verreauxi larvae was studied in two experiments. In the first experiment, only small differences were found between the probit lines of final percentage infection against dose under five temperature regimes (constant 18, 23, and 28°C; alternating 13–23°C, and 18–28°C). The disease developed more slowly at the lower temperatures while alternating temperatures gave shorter ET₅₀ values than the equivalent constant temperatures. In the second experiment, a higher incidence of disease was obtained under field conditions than under any of the laboratory conditions tested. It was concluded that for up to 6 months/year temperature is not likely to limit the development of B. popilliae var. rhopaea in the field, and that, under field conditions, most larvae would achieve a Phase IV infection.     

Effects of temperature on food ingestion rate and absorption,retention, and equilibrium burden of phosphorus in an aquatic snail,Goniobasis clavaeformis Lea *

The effects of sublethal temperatures on feeding rates and phosphorus dynamics of a freshwater snail, Goniobasis clavaeformis Lea, were determined and feeding rates were measured at four temperatures. The food source was aufwuchs labelled with radioactive phosphorus. A model was developed to elucidate the results of this type of study. Food ingestion rate increased with increasing temperature up to 14°C and then decreased at temperatures above 14°C. The elimination rate of absorbed phosphorus increased with increasing temperature throughout the entire range of experimental temperatures, 10-19.3°C. Mean retention times of absorbed phosphorus i n Goniobasis were estimated to be 34, 24, 10, and 6 days at 10, 13.8, 15, and 193°C, respectively. Mean retention time of unabsorbed ³²P in the gut of this species as a function of temperature followed the same temperature relationship as that of ingestion rate. The absorption efficiency of phosphorus was estimated to be constant at about 39% for ail experimental temperatures, although the data suggest that the absorption ePRciency may have been related inversely to the rate of gut clearance or directly to the residence time of food in the gut. The equilibrium body load of phosphorus at each experimental temperature was estimated based on concentrations of stable phosphorus in the food source and the kinetics of ³²P in Goniobasis. The equilibrium body burden of phosphorus in Goniobasis increased with increasing temperatures up to a maximum at 11–12°C and then decreased at temperatures above 12°C.     

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT₅₀ (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.     

Temperature-induced changes of malondialdehyde, heat-shock proteins in relation to chlorophyll fluorescence and photosynthesis in Conocarpus lancifolius (Engl.)

The effect of variable temperatures (10–50 °C) on photosynthesis and chlorophyll fluorescence in Conocarpus lancifolius was evaluated. Additionally, the ability of the species to synthesize heat-shock proteins (HSPs) to protect against high temperatures, and malondialdehyde (MDA) as a by-product of lipid peroxidation was investigated. Plants at 10 °C showed virtually no measurable growth, leaf discoloration and a few brown lesions, while high temperatures (40 and 50 °C) promoted growth and lateral branch development. Chlorophyll content index, photochemical efficiency (F _v/F _m) of PS II, electron transport rate and photosynthetic rate declined with decreasing temperature but increased significantly at higher temperatures. Heat-shock protein (HSP 70 kDa) was produced at temperatures 30–50 °C and an additional 90 kDa protein was also produced at 50 °C. Increase in the efficiency of excitation energy captured by the open PS II reaction centers (F _v/F _m) increased linearly (P ≤ 0.05) with the accumulation of HSP 70 at higher temperatures. However, at low temperatures the concentration of MDA increased significantly, indicating lipid peroxidation due to oxidative stress. The production and accumulation of HSP 70 and 90 kDa coupled with increased electron transport rate and photochemical efficiency can be used to assess survival, growth capacity and to some extent the tolerance of C. lancifolius to elevated temperatures.     

Effect of temperature on germination,growth, and infectivity of the mosquito pathogen Tolypocladium cylindrosporum (deuteromycotina; hyphomycetes)

The mosquito pathogen Tolypocladium cylindrosporum was examined with regard to its response to temperature. Similar temperature ranges were found for growth, germination, and infectivity of blastospores and conidia. Germination occurred at 8° and 33°C but not at 6° and 35°C. Optimal germination and growth was noted between 24° and 27°C for both spore types. Infectivity of blastospores and conidia at different temperatures was examined by exposing L₂Aedes sierrensis larvae to concentrations of 5 × 10⁵ blastospores/ml or 5 × 10⁶ conidia/ml. Larvae were incubated at 12°, 15°, 25°, and 30°C. Infection occurred at all temperatures tested with LT₅₀ values ranging from 22.7 days (12°C) to 5.6 (25°C) days for conidia and 4.7 days (12°C) to 0.6 day (25°C) for blastospores. These results confirmed earlier findings that blastospores infected and killed host larvae more rapidly than conidia and suggested that this difference is largely due to the more rapid germination rate of blastospores. These experiments demonstrated that T. cylindrosporum can be active against mosquito larvae over a broad range of temperatures encompassing both the cold-water habitat of certain temperate mosquito species as well as the habitat of tropical vector species.