New Insights in the Life Cycle and Epidemics of Phytophthora porri on Leek

White tip, caused by Phytophthora porri, is a devastating disease in the autumn and winter production of leek (Allium porrum) in Europe. This study investigated the disease cycle of P. porri in laboratory and field conditions. Oospores readily germinated in the presence of non‐sterile soil extract at any temperature between 4 and 22°C, with the formation of sporangia which released zoospores. The zoospores survived at least 7 weeks in water at a temperature range of 0 till 24°C. Microscopic examinations revealed that zoospores encysted and germinated on the leek leaf surface and hyphae entered the leaf directly through stomata or by penetrating via appressoria. Oospores were formed in the leaves within 6 days, while sporangia were not produced. By monitoring disease progress in fields with a different cropping history of leek, it could be deduced that P. porri survives in soil for up to 4 years. Disease progress during three consecutive years was correlated with average daily rainfall in the infection period. Disease incidence on leek was reduced when rain splash was excluded by growing the plants in an open hoop greenhouse. Based on these findings, we propose a disease cycle for P. porri in which oospores germinate in puddles, and zoospores reach the leaves by rain splash and survive in water in the leaf axils, from where they infect the plant by direct penetration or via stomata. When conditions become unfavourable, oospores are produced in the leaves which again reach the soil when leaves decay. Secondary spread of the disease by sporangia does not seem to be important.     

Effect of temperature,hydrogen ion concentration and osmotic potential on oospore germination of fivePythium spp. isolated from pond water

Oospore germination occurred over a temperature ranging of 15–35°C forPythium coloratum, 10–35°C forP. diclinum, 15–30°C forP. dissotocum, 7–30°C forP. monospermum, and 10–30°C forP. pleroticum. Optimum temperature was 25°C for all species tested. In case of pH, oospore germination occurred over a range of 4.76–8.55 with an optimum of 6.40–7.40. The least germination occurred at pH 4.76 forP. coloratum, P. diclinum, P. monospermum andP. pleroticum, whileP. dissotocum germinated from pH 5.02. Oospores of the all tested pythia were able to germinate at –0.13 to –1.65 MPa and could not germinate at –3.40 MPa, with the highest germination rate at –0.27 to –0.47 MPa. The effect of temperature, pH and osmotic potential on oospore germination was discussed in relation to pollution of pond water.     

Assessment of the tolerance of Lactococcus lactis cells at elevated temperatures

When Lactococcus lactis strains were exposed directly to the lethal temperature of 50 C for 30 ;min, 0.1–31% of the cells survived. However, when pre-exposed to 40 °C, prior to exposure at 50 °C, 4–61% of the cells survived. A plasmid carrying a unique heat shock gene from the thermophile Streptococcus thermophilus was cloned into L. ;lactis. When the transformed cells were cultivated at 30 °C the introduction of the plasmid had no obvious effect on the growth of L. ;lactis. However, when the temperature was abruptly shifted from 30 °C to 42 °C at mid-growth phase the growth decreased by 50%.     

Storage and formulation of the entomopathogenicnematodes Heterorhabditis indica and H. bacteriophora

Successful control of insect pests through theapplication of entomopathogenic nematode dauerjuveniles of H. bacteriophora and H.indica can only be achieved when the nematodematerial reaches the end user in good condition.Storage and formulation techniques must provideoptimum conditions to guarantee a maximum survival andinfectivity of the nematodes. Nematode survival wastested at temperatures ranging between 5–25 °C.A maximum survival of H. indica was achieved at15 °C and the highest mortality at 5 °C.H. bacteriophora survived best at 7.5 °Cand least at 25 °C. An increase of the saltconcentration had positive effects on dauer juvenilesurvival in aqueous suspensions. Low pH between 6 and4 reduced the bacterial growth and prolonged survivalof stored dauer juveniles. Of the organic acidsascorbic, benzoic, citric and sorbic acid, onlyascorbic acid had a positive effect on H. indicasurvival. Extracts of the dried spice plants cinnamon,cloves, rosemary and oregano were tested. Enhancementof H. indica survival was recorded for cinnamonand cloves. Survival and infectivity of nematodesstored in attapulgite and bentonite clays and spongewere recorded over several weeks at different storagetemperatures. Infectivity was not influenced by thedifferent formulation materials. When stored insponge at 25 °C nematodes survived less than 1week and the formulation in clay could only prolongthis period for another week. At 5 °C thesurvival of H. bacteriophora in sponge wassuperior to that in clay, whereas H. indicasurvived less well in sponge than in clay at15 °C. Storage in aerated water at 5 °Cfor H. bacteriophora and at 15 °C for H. indica resulted in the lowest mortality. Forstorage at controlled conditions (temperature, pH andosmolarity), aerated water is superior to all othermethods tested and the addition of preservatives willincrease survival.     

Effects of temperature on survival and preimaginal development rates of Colorado potato beetle on potato and horse-nettle: potential role in host range expansion

The effect of temperature on the ability of Colorado potato beetles (Leptinotarsa decemlineata, Say) to use horse-nettle (Solanum carolinense L.) as a host plant was determined for larvae from colonies originating from two geographically separated populations, one adapted to horse-nettle (NC) and the other unadapted to horse-nettle (MA). Survival and developmental rate on horse-nettle and potato were measured for larvae from both colonies over a range of constant temperatures (12–30 °C) and one fluctuating temperature regime (22 °C to 30 °C). The ability of Colorado potato beetles to use horse-nettle as a larval host was strongly influenced by temperature, but the effects of temperature differed greatly between beetles from the two colonies. Survival of adapted larvae on horse-nettle was highest and comparable to that on potato at the constant 30 °C and the fluctuating temperature regime. Below 30 °C, survival of adapted larvae decreased drastically but some larvae survived at all temperatures except the lowest (12 °C). In contrast, survival of unadapted larvae to adult occurred only at 30 °C, and was low (10%). At lower temperatures, all larvae died. On potato, the effect of temperature was less dramatic, and consistent across colonies. At 12 °C, survival to adult was poor (ca. 10%), but at higher temperatures, survival increased sharply and larvae from both colonies survived equally well. On potato, small but statistically significant differences in developmental rates between beetle colonies were detected at the constant but not at the fluctuating temperature regimes. Also, the developmental day degree requirements (DD) and the low temperature development threshold (T0) values for the various developmental stages did not differ between colonies on potato. On horse-nettle, development times for both colonies were always significantly longer and DD requirements were greater than on potato. At 30 °C, the only constant temperature at which larvae from the unadapted colony completed development, the development rate to adult emergence was similar to that of beetles from the adapted colony. Differences between colonies in performance on horse-nettle were not a result of host-independent, genetically based differences in the thermal requirements of the two populations. Our findings are consistent with the hypothesis that adaptation to horse-nettle by Colorado potato beetle may be facilitated by a genotype × environment interaction involving temperature. These findings have important implications for host plant utilization, host range expansion and selection of pest biotypes adapted to plant resistance traits used in crop protection.     

Seed survival in small myrtaceous capsules subjected to experimental heating

Mature capsules of four small-fruited Myrtaceae (Eucalyptus regnans, Leptospermum laevigatum, L. myrsinoides and Kunzea ambigua) were heated in a muffle furnace over a range of temperatures (200–750° C) and for various lengths of time (15–300s). In addition, the rise in intracapsular temperature with time was measured at 250° C and the lethal seed temperature for K. ambigua determined by heating loose seed in a controlled-temperature water bath. Encapsulated seed survived heating for only short periods event at the lower range of experimental temperatures, with no seed surviving for more than 2 min at 200° C and the highest temperature survived being 650° C for 15 s by L. laevigatum. The species were ranked E. regnans, K. ambigua, L. myrsinoides and L. laevigatum in increasing order of insulating capacity of their capsules, based on survival times of encapsulated seed and the rate of increase of intracapsular temperatures. Seed of K. ambigua was killed when heated in water for a few seconds at 90–100° C. This result agrees closely with the threshold lethal temperature derived for all species by superimposing seed survival versus time and intracapsular temperature versus time curves for capsules heated at 250° C. These results demonstrate that despite their in situ efficacy during fire, small myrtaceous capsules hre mediocre seed insulators. They also suggest that in the field, survival times for encapsulated seed are likely to be in the order of seconds rather than minutes, which points to brief flame residence times in individual tree or shrub canopies. This work has the potential to be developed as a simple but powerful method for the measurement and mapping of fire intensities.     

Effects of salinity, temperature and pH on the survival of the nemertean Procephalothrix simulus Iwata, 1952

The salinity, temperature and pH tolerance of Procephalothrix simulus Iwata, 1952, were experimentally studied. In hypo-media, the nemerteans could survive 96 h in 3.3‰ solution at 10 °C (median lethal salinity [LS₅₀] was not determined at this temperature), and 96 h LS₅₀ were 7.3‰ and 13.5‰ at 20 °C and 30 °C, respectively. In hyper-media, 96 h LS₅₀ values were 53.9‰, 47.1‰ and 41.4‰ at 10 °C, 20 °C and 30 °C, respectively. The trend of body weight changes in diluted media indicated that this nemertean is a volume regulator. During a 96-h exposure in media at 0 °C, worms were thanatoid but could recover if the temperature was gradually elevated to 20 °C. In thermal tolerance experiments, the nemertean survived 96 h in seawater of 30 °C, and worms suffered high mortalities when the temperature exceeded 32 °C. Present results suggest that the interaction of temperature and salinity on the lethal effects on P. simulus is significant (P < 0.05). Elevated temperature (range 10-30 °C) decreased the worm's solute tolerance, and elevated salinity (range 18-38‰) decreased the worm's thermal tolerance. The survival pH level for this nemertean ranged from 5.00 to 9.20.     

Cold hardiness of the green gemmules of Spongilla lacustris L. (Porifera: Spongillidae)

Most green gemmules of Spongilla lacustris survived enclosure in ice at –20 °C for up to 30 days; however, their rate of germination at 20 °C was less rapid than that of control gemmules. The length of time spent at low temperature had little effect on gemmule survival. In contrast, repeated cooling to –20 °C and warming to 4 °C led to a progressive decline in gemmule viability. These results indicate that cold injury occurs primarily during transitions between high and low temperatures.     

Evaluation of host and pathogen responses for screening soil amendments to control Sclerotium rolfsii

Three strains of Bradyrhizobium, 280A, 2209A and 32H1, that nodulated peanuts (Arachis hypogaea L.), were tested for their ability to grow and survive at elevated temperatures of up to 42°C in laboratory culture. Strain 32H1 was unable to grow at 37°C and was more sensitive to elevated temperatures than the other two strains. All three produced heat-shock proteins of molecular weights 17 kDa and 18 kDa. Two greenhouse experiments were conducted to determine the effect of high root temperature on nodulation, growth and nitrogen fixation of peanut. Two peanut varieties (Virginia cv NC7 and Spanish cv Pronto) were inoculated and exposed to root temperatures of 30°, 37° and 40°C. Nodulation and nitrogen fixation were strongly affected by root temperature but there was no variety × temperature interaction. At a constant 40°C root temperature no nodules were formed. Nodules were formed when roots were exposed to this temperature with diurnal cycling but no nitrogen fixation occurred. Highest plant dry weight, shoot nitrogen content and total nitrogen were observed at a constant root temperature of 30°C. Increasing root temperature to 37°C reduced average nitrogen content by 37% and total nitrogen by 49% but did not reduce nodulation. The symbiotic performance of the strains corresponded to their abilities to grow and survive at high temperature in culture.     

Survival of adults and developmental stages ofSarcoptes scabiei var.canis when off the host

All life-stages ofSarcoptes scabiei var.canis survive in the hosts' environment for several days to several weeks depending on r.h. and temperature. Survival of larvae was comparable to males; survival of nymphs was comparable to females. Females and nymphs generally survived longer than larvae and males.Low temperature (10–15°) and high r.h. prolonged survival of all life stages. At 10–15°C, females and nymphs survived 1–3 weeks at 97% r.h., 1–2 weeks at 75% r.h. and 5–8 days at 45% r.h. At 20–25°C, survival was significantly reduced but all life-stages survived at least 2 days at 25% r.h. and 5–6 days at 75–100% r.h. Long survival off the host coupled with host-seeking behavior of these mites make it likely that environmental contamination is a source of scabies in domestic and wild mammals, and in humans.     

IGF-I and vitamin C promote myogenic differentiation of mouse and human skeletal muscle cells at low temperatures

In a previous study investigating the effects of low temperature on skeletal muscle differentiation, we demonstrated that C2C12 mouse myoblasts cultured at 30 °C do not express myogenin, a myogenic regulatory factor (MRF), or fuse into multinucleated myotubes. At this low temperature, the myoblasts continuously express Id3, a negative regulator of MRFs, and do not upregulate muscle-specific microRNAs. In this study, we examined if insulin-like growth factor-I (IGF-I) and a stable form of vitamin C (L-ascorbic acid phosphate) could alleviate the low temperature-induced inhibition of myogenic differentiation in C2C12 cells. Although the addition of either IGF-I or vitamin C alone could promote myogenin expression in C2C12 cells at 30 °C, elongated multinucleated myotubes were not formed unless both IGF-I and vitamin C were continuously administered. In human skeletal muscle cells, low temperature-induced blockage of myogenic differentiation was also ameliorated by exogenous IGF-I and vitamin C. In addition, we demonstrated that satellite cells of IGF-I overexpressing transgenic mice in single-fiber culture expressed myogenin at a higher level than those of wild-type mice at 30 °C. This study suggests that body temperature plays an important role in myogenic differentiation of endotherms, but the sensitivity to low temperature could be buffered by certain factors in vivo, such as IGF-I and vitamin C.     

Studies on the rust,Maravalia cryptostegiae,a potential biological control agent of rubber-vine weed,Cryptostegia grandiflora (Asclepiadaceae: Periplocoideae), in Australia,II: Infection

The parameters which govern infection of rubber-vine weed by the rustMaravalia cryptostegiae were investigated. The infection process, from appressorial formation to sporulation, is described and illustrated. Uredinioid teliospores have an optimum temperature range for germination at 22–27 °C, both in vitro and in vivo. However, germination on the rubber-vine leaf was more than double (81–92%) that in the absence of the host, and appressoria were formed only in vivo. An optimum temperature of 20–22°C and a dew period of 12 hours or more gave the highest level of infection as measured by sporulation density. The latent period from inoculation to pustule formation decreased with increasing temperature; the shortest period (8–11 days) being recorded at 25–27°C. At the lower temperatures (18°C), this was significantly extended (19–21 days). Four successive inoculations significantly reduced plant height and dry weight, although a compensatory growth flush occurred after the third inoculation. The addition of cryoprotectants had a negative affect on spore viability and subsequent infectivity. Cooling dry spores to –196°C at the rate of 10°C min^–1 gave the best results, with high germination (93–65%) up to 8 days after thawing.     

Thermotropic and structural evaluation of the interaction of natural sphingomyelins with cholesterol

The structural transitions in aqueous dispersions of egg-sphingomyelin and bovine brain-sphingomyelin and sphingomyelin co-dispersed with different proportions of cholesterol were compared during temperature scans between 20° and 50 °C using small-angle and wide-angle X-ray scattering techniques. The Bragg reflections observed in the small-angle scattering region from pure phospholipids and codispersions of sphingomyelin:cholesterol in molar ratios 80:20 and 50:50 could all be deconvolved using peak fitting methods into two coexisting lamellar structures. Electron density profiles through the unit cell normal to the bilayer plane were calculated to derive bilayer and water layer thicknesses of coexisting structures at 20° and 50 °C. Codispersions of sphingomyelin:cholesterol in a molar ratio 60:40 consisted of an apparently homogeneous bilayer structure designated as liquid-ordered phase. Curve fitting analysis of the wide-angle scattering bands were applied to correlate changes in packing arrangements of hydrocarbon in the hydrophobic domain of the bilayer with changes in enthalpy recorded by differential scanning calorimetry. At 20 °C the wide-angle scattering bands of both pure sphingomyelins and codispersions of sphingomyelin and cholesterol could be deconvolved into two symmetric components. A sharp component located at a d-spacing of 0.42 nm was assigned to a gel phase in which the hydrocarbon chains are oriented perpendicular to the bilayer plane. A broader symmetric band centered at d-spacings in the region of 0.44 nm was assigned as disordered hydrocarbon in dispersions of pure sphingomyelin and as liquid-ordered phase in codispersions of sphingomyelin and cholesterol. It is concluded from the peak fitting analysis that cholesterol is excluded from gel phases of egg and brain sphingomyelins at 20 °C. The gel phases coexist with liquid-ordered phase comprised of egg-sphingomyelin and 27 mol% cholesterol and brain-sphingomyelin and 33 mol% cholesterol, respectively. Correlation of the disappearance of gel phase during heating scans and the enthalpy change recorded by calorimetry in codispersions of sphingomyelin and cholesterol leads to the conclusion that a major contribution to the broadened phase transition endotherm originates from dilution of the cholesterol-rich liquid-ordered phase by mobilization of sphingomyelin from the melting gel phase.     

Geographical and experimental assessment of the distribution ofGracilaria species (Rhodophyta: Gigartinales) in relation to temperature

Tolerance and growth at temperatures from 0° to 36°C were investigated using 15 species and strains ofGracilaria Grev. isolated from tropical and temperate coasts of the Atlantic and eastern Pacific Oceans. All survived a minimum of 15°C and, with two exceptions, a maximum of 28°C. Only two species tolerated 34°C and none 36°C which was rapidly lethal. Isolates intolerant of temperatures less than 15°C were generally species known only from tropical waters, whereas species isolated from temperate waters tended to be eurythermal, and most seemed not to be restricted to cooler waters. Maximum growth of warm-water isolates tended to occur over a broad range of warmer temperatures, 20°C and higher, and usually extended to the upper limits of thermal tolerance. Isolates from temperate waters showed maximum growth at 20° or 15°C, and there was no appreciable growth of any of the isolates below 10°C. These experimental results are in accord with known distributional patterns ofGracilaria. There is a correlation between temperature and number of species, with most species reported from warm-water areas where the mean water temperature is 25°C or more. Where the 3-month mean minimum temperature is less than 20°C, there is a rapid decline in number of species. In the eastern Atlantic, the relationship is less obvious as few species have been reported from the warm-water region. This is quite likely the result of other environmental factors.NRCC No. 23817Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April 1984 at the Department of Marine Biology, Rijksuniversiteit Groningen (The Netherlands). Convenor: C. van den Hoek.     

Extreme temperatures and thermal tolerances for seedlings of desert succulents

Summary Extreme temperatures near the soil surface, which can reach 70°C at the main study site in the northwestern Sonoran Desert, markedly affect seedling survival. Computer simulations indicated that for the rather spherical barrel cactus Ferocactus acanthodes (Lem.) Britt. & Rose the maximum surface temperature decreased 8°C and the minimum temperature increased 3°C as the seedling height was increased from 1 mm up to 50 mm. Simulated changes in shortwave and longwave irradiation alone showed that shading could decrease the maximum temperature by about 5°C for the common desert agave, Agave deserti Engelm., and raise the minimum 1°C. Actual field measurements on seedlings of both species, where shading would affect local air temperatures and wind speeds in addition to irradiation, indicated that shading decreased the average maximum surface temperature by 11°C in the summer and raised the minimum temperature by 3°C in winter.Seedlings grown at day/iight air temperatures of 30°C/20°C tolerated low temperatures of about -7°C and high temperatures of about 56°C, as measured by the temperature where stain uptake by chlorenchyma cells was reduced 50%. Seedling tolerance to high temperatures increased slightly with age, and F. acanthodes was more tolerant than A. deserti. Even taking the acclimation of high temperature tolerance into account (2.7°C increase per 10°C increase in temperature), seedlings of A. deserti would not be expected to withstand the high temperatures at exposed sites, consistent with previous observations that these seedlings occur only in protected microhabitats. Based primarily on greater high temperature acclimation (4.3°C per 10°C), seedlings of F. acanthodes have a greater high temperature tolerance and can just barely survive in exposed sites. Wide ranges in photoperiod had little effect on the thermal sensitivities of either species. When drought increased the chlorenchyma osmotic pressure from about 0.5 MPa to 1.3 MPa, seedlings of both species became about 2°C less tolerant of high temperatures, which would be nonadaptive in a desert environment, and 2°C more tolerant of low temperatures, which also occurs for other species.In conclusion, seedlings of A. deserti and F. acanthodes could tolerate tissue temperatures over 60°C when acclimated to high temperatures and below -8°C when acclimated to low temperatures. However, the extreme environment adjacent to desert soil requires sheltered microhabitats to protect the plants from high temperature damage and also to protect them from low temperature damage at their upper elevational limits.     

Influence of freezing temperatures on a cactus,Coryphantha vivipara

Summary Coryphantha vivipara (Nutt.) Britton & Rose var. deserti (Engelm.) W.T. Marshall (Cactaceae) survived snow and tissue temperatures of-12°C in southern Nevada. However, the freezing point depression of the cell sap was only about 0.9°C. When the nocturnal air temperature in the laboratory was reduced from 10°C to-10°C for one night, the optimum temperature for CO₂ uptake shifted from 10°C to 6°C and uptake was reduced 70%, but full recovery to the original values occurred in 4 days. Nocturnal temperatures of-15°C killed 2 out of 5 plants and-20°C killed 5 out of 5, as judged by lack of net CO₂ uptake at night over a 2-month observation period. when the stems were cooled at 2° C/h, supercooling to about-6°C occurred followed by an exothermic reaction that presumably represented the freezing of extracellular water. When the subzero temperature was lowered further, no other exothermic reaction was observed and the cells became progressively dehydrated. Freezing-induced tissue death was ascribed to this cellular dehydration, which led to about 94% loss of intracellular water at-15°C. when the tissue temperature was lowered, the ability of chlorenchyma cells to plasmolyze and to take up a stain decreased, both being nearly 70% inhibited at-15°C and completely abolished at-20°C. Some cold-bardening occurred, since lowering the air temperature from 30° to-10°C in 10°C increments at weekly intervals caused the subzero temperature for 50% inhibition of staining to decrease from-10°C to-17°C. Extension of the range of C. vivipara to regions with wintertime freezing apparently reflects the tolerance of considerable freeze dehydration by its protoplasts.     

The effect of neonatal starvation on the growth,development and survival of larvae of the pine beauty moth,Panolis flammea (D & S)

Summary Mortality of neonatal pine beauty moth larvae varied from 0% to 100% depending on the duration of food deprivation and temperature. At 20°C and 100% RH all larvae had died by the fourth day of food deprivation, whereas at 10°C and 100% RH larvae survived for twelve days without food. Although larvae were able to survive at 15°C for up to seven days without food, establishment on thier host at this temperature was seriously affected by three days of starvation. No establishment took place after four days of starvation at 15°C. At 10°C establishment was significantly affected by starvation but not to such a marked degree. Establishment at both 15°C and 10°C was enhanced if the larvae were presented with a highly suitable host. The mean relative growth rate of those larvae reaching fifth instar was unaffected by the duration of their prefeeding starvation period. However, overall mean relative growth rates of the larvae were significantly affected by the duration of the starvation period. The implications of these results are discussed in relation to the population dynamics of this insect.     

Intracellular ice formation and growth in MCF-7 cancer cells

Direct cell injury in cryosurgery is highly related to intracellular ice formation (IIF) during tissue freezing and thawing. Mechanistic understanding of IIF in tumor cells is critical to the development of tumor cryo-ablation protocol. In aid of a high speed CMOS camera system, the events of IIF in MCF-7 cells have been studied using cryomicroscopy. Images of ‘darkening’ type IIF and recrystallization are compared between cells frozen with and without ice seeding. It is found that ice seeding has significant impact on the occurrence and growth of intracellular ice. Without ice seeding, IIF is observed to occur over a very small range of temperature (∼1 °C). The crystal dendrites are indistinguishable, which is independent of the cooling rate. Ice crystal grows much faster and covers the whole intracellular space in comparison to that with ice seeding, which ice stops growing near the cellular nucleus. Recrystallization is observed at the temperature from −13 °C to −9 °C during thawing. On the contrary, IIF occurs from −7 °C to −20 °C with ice seeding at a high subzero temperature (i.e., −2.5 °C). The morphology of intracellular ice frozen is greatly affected by the cooling rate, and no ‘darkening’ type ice formed inside cells during thawing. In addition, the intracellular ice formation is directional, which starts from the plasma membrane and grows toward the cellular nucleus with or without ice seeding. These results can be used to explain some findings of tumor cryosurgery in vivo, especially the causes of insufficient killing of tumor cells in the peripheral area near vessels.     

Combined effects of night-time temperature and allelochemicals on performance of a generalist insect herbivore

To assess the pattern of temperature influencing the effect of allelochemicals on growth of insect herbivores and to examine the potential effect of warmer nights due to global warming, we examined the simultaneous effects of allelochemicals and warmer night-time temperatures on an insect herbivore (Spodoptera exigua; Lepidoptera: Noctuidae). Dietary chlorogenic acid, rutin and tomatine levels reflected those occurring naturally in the leaves of tomato, a hostplant of this herbivore. We compared the effects of four thermal regimes having a daytime temperature of 26 °C , with the night-time temperature increased from 14 to 26 °C by increments of 4 °C . The effect of a particular allelochemical on developmental rate was similar among the four thermal regimes. Chlorogenic acid and tomatine each reduced final larval weight, but there was no effect of night-time temperature. In contrast, rutin had no effect on final weight, whereas final weight declined with increasing night-time temperature. Night-time temperature did not influence amount eaten. Larvae ate less when chlorogenic acid or tomatine was in the diet. For each allelochemical, there were no allelochemical by thermal regime interactions. In addition, we compared the effects of allelochemicals and the thermal regime of 26:14 °C and constant 20 °C , which was the average temperature of the 26:14 °C regime. Developmental rate was lower at the constant 20 °C regime, chlorogenic acid and tomatine each depressed developmental rate, and there were no allelochemical by thermal regime interactions. Thus, regardless of the specific allelochemical or amount, the pattern of response at the fluctuating regime was similar to that at the constant temperature. In contrast, comparison of the thermal regime of 26:22 °C and constant 24 °C , which was the average temperature of the 26:22 °C regime, showed several allelochemical by thermal regime interactions. At the 26:22 °C regime, developmental rate was disproportionatly higher at the maximal rutin concentration compared to that at constant 24 °C . At the constant 24 °C , final larval mass was disproportionately lower at the moderate tomatine concentration compared to that at the 26:22 °C regime. Because these results differ from that of other studies examining another species, it appears that the response to incremental changes in night-time temperature will reflect the allelochemicals and insect species tested. The contrast between the constant 24 °C and 26:22 °C regimes indicates that even small fluctuations (±2 °C ) in temperature over 24 h can yield differences in the response to an allelochemical.     

Effects of temperature on the establishment potential of the predatory mite Amblyseius californicus McGregor (Acari: Phytoseiidae) in the UK

Amblyseius californicus was introduced into the UK in the early 1990s as a biocontrol agent against glasshouse red spider mite Tetranychus urticae. This study investigated the effects of temperature on the establishment potential of A. californicus in the UK in the light of recent reports of their successful overwintering outside of glasshouse environments. The developmental thresholds were 9.9 and 8.6 °C respectively using simple and weighted linear regression. Using the day-degree requirement per generation calculated by weighted regression (143 day-degrees) in combination with climate data, it was estimated that up to seven generations would be possible annually outdoors in the UK. Non-diapausing adult females froze at −22 °C, with 100% mortality after reaching their freezing temperature. Up to 90% of mites died before freezing after short exposures to low temperatures. Significant acclimation responses occurred; 90% of acclimated individuals survived 26 days exposure at 0 °C and 11 days at −5 °C (acclimated mites were reared at 19 °C, 6L:18D followed by 1 week at 10 °C, 12L:12D). Non-diapausing adult females survived over 3 months outdoors in winter under sheltered conditions and oviposition was observed. The experimental protocol used in this study is discussed as a pre-release screen for the establishment potential of other Amblyseius species, and similar non-native biocontrol agents.