Reproductive and developmental biology of Gonatocerus ashmeadi (Hymenoptera: Mymaridae), an egg parasitoid of Homalodisca coagulata (Hemiptera: Cicadellidae)

The reproductive and developmental biology of Gonatocerus ashmeadi Girault, a parasitoid of the glassy-winged sharpshooter Homalodisca coagulata (Say), was determined at five constant temperatures in the laboratory: 15; 20; 25; 30; 33 °C. At 30 °C, G. ashmeadi maintained the highest successful parasitism rates with 46.1% of parasitoid larvae surviving to adulthood. Lifetime fecundity was greatest at 25 °C and fell sharply as temperature either increased or decreased around 25 °C. Temperature had no effect on sex ratio of parasitoid offspring. Mean adult longevity was inversely related to temperature with a maximum of 20 days at 15 °C to a minimum of eight days at 33 °C. Developmental rates increased nonlinearly with increasing temperatures. Developmental rate data were fitted with the modified Logan model for oviposition to adult development times across each of the five experimental temperatures to determine optimal and upper lethal temperature thresholds. The lower developmental threshold estimated by the Logan model and linear regression were 1.10 and 7.16 °C, respectively. Linear regression of developmental rate for temperatures 15–30 °C indicated that 222 degree-days were required above a minimum threshold of 7.16 °C to complete development. A temperature of 37.6 °C was determined to be the upper development threshold with optimal development occurring at 30.5 °C. Demographic parameters were calculated and pseudo-replicates for intrinsic rate of increase (r_m), net reproductive rates (R_o), generation time (T_c), population doubling time (T_d), and finite rate of increase (λ) were generated using the bootstrap method. Mean bootstrap estimates of demographic parameters were compared across temperatures using ANOVA and nonlinear regression.     

Effects of temperature on development, survival, longevity, and fecundity of the Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) predator, Axinoscymnus cardilobus (Coleoptera: Coccinellidae)

Axinoscymnus cardilobus (Homoptera: Aleyrodidae) is an important predator of Bemisia tabaci (Coleoptera: Coccinellidae) that occurs in high population density of B. tabaci. Temperature among other factors is observed to play an important role in the development of arthropods. The effect of temperature on the development of A. cardilobus was studied at seven constant temperature regimes (14, 17, 20, 23, 26, 29, 32 °C). The results indicated that the duration of egg, larval and pupal stages were significantly influenced by increased temperature. The rate of development gradually increased with increase in temperature from 14 °C to 26 °C, but declined from 26 °C to 32 °C. The survival rates of different insect stages were stable at temperatures between 20 °C and 26 °C, but at extreme temperatures of 32 °C and 14 °C, a sharp decrease was evident. Ovipositional period of the female decreased when temperatures were increased from 17 °C to 32 °C. The highest fecundity of the female (225.7 eggs per female) was recorded at 23 °C. Life tables of A. cardilobus were constructed based on the experimental results at temperatures of 14–32 °C. The reproductive rate (R₀), the innate capacity for increase (r_m) and the finite rate of increase (λ) reached the maximum values at 23 °C, of 70.7, 0.059 and 1.062, respectively. The mean generation time (T) decreased with increased temperature from 17 °C to 32 °C, the highest and least values recorded at 17 °C and 32 °C were 112.7 and 38.7, respectively. These results offer valuable insight on the importation and establishment of A. cardilobus into new environments with diverse temperature regimes.     

The Effect of Rearing Temperature on Flight Initiation of Trichogramma sibericum Sorkina at Ambient Temperatures

Trichogramma sibericum Sorkina was reared in the laboratory at three temperatures: 16, 21, and 26°C. Individuals from each of these treatments were then tested for propensity to initiate flight at one of four ambient temperatures: 16, 19, 21, or 26°C. Both rearing and ambient temperatures had significant effects on flight initiation. Insects reared at 16°C had the highest mean proportion of flyers; insects reared at 26°C had the lowest. The proportion of insects initiating flight increased with increasing ambient temperature. Also, the interaction of these two temperature experiences was significant. Insects reared at 16°C were more likely to initiate flight at 16°C than insects reared at 21 or 26°C. These results indicate that performance (as assessed by flight initiation) at ambient temperature is dependent on the temperature previously experienced during rearing.     

The RustPuccinia abruptavar.partheniicola,a Potential Biocontrol Agent of Parthenium Weed: Environmental Requirements for Disease Progress

The rust fungusPuccinia abruptavar.partheniicola,a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination temperatures as well as dew period durations and temperatures were investigated to determine some of the environmental requirements for disease establishment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20°C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26°C or 18/13°C; day/night). Urediniospores germinated best at 12 ± 1°C, with lower germination rates at 5°C or above 20°C. No infection occurred when the plants were exposed to dew periods of ≤3 h, regardless of the incubation temperature. The disease progressed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 ± 1°C. The disease progressed most slowly following inoculation at dew periods of 6 h or less. Disease progress was more rapid when the plants were exposed to a cool-temperature regime (18/13°C) than when exposed to a warm-temperature regime (30/26°C). This suggests that good infection of parthenium weed could be obtained when the urediniospores arrive on the plants during the afternoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected.     

Effect of temperature on survival, development and reproduction of the predatory lacewing Dichochrysa prasina (Neuroptera: Chrysopidae) reared on Ephestia kuehniella eggs (Lepidoptera: Pyralidae)

Preimaginal development and adult longevity and reproduction of Dichochrysa prasina Burmeister were studied at six constant temperatures (15, 20, 25, 27, 30 and 33 °C) and a photoperiod of 16:8 (L:D). Eggs of the flour moth Ephestia kuehniella (Zeller) were used as food throughout preimaginal development, whereas the adults of D. prasina fed on a liquid diet of water, yeast hydrolysate, sugar and honey. At the highest tested temperature of 33 °C no larvae completed their development. At the rest of the tested temperatures the egg to adult developmental period ranged from approximately 92 days at 15 °C to 25 days at 30 °C. Percentages of adult emergence ranged from 36% at 15 °C to 84% at 30 °C. Both adult longevity and fecundity were significantly affected by temperature and the intrinsic rate of increase (r_m) reached its maximum value at 27 °C. These results could be useful for the establishment of a small scale rearing and mass production of D. prasina.     

Effect of Temperature on the Life History of Cirrospilus sp. near lyncus (Hymenoptera: Eulophidae), a Parasitoid of Phyllocnistis citrella (Lepidoptera: Gracillariidae)

The effect of four constant temperatures on the life history of Cirrospilus sp. near lyncus was examined in the laboratory. This species is one of the most abundant generalist indigenous parasitoids of the citrus leafminer, Phyllocnistis citrella Stainton, in Spain. Adult lifespan of C. sp. near lyncus decreased from 50.2 to 9.1 days as temperatures increased from 15 to 30°C, respectively. Both gross fecundity and host-feeding were highest at 20°C (170.48 eggs and 32.33 hosts). Oviposition rates were optimal at higher temperatures (5.22 eggs per day at 25°C and 4.79 eggs per day at 30°C) and were dependent on female age. In contrast, host-feeding rates for a given temperature did not depend on age. Generation time decreased with increasing temperatures from 68.05 days at 15°C to 12.19 days at 30°C. Net reproduction peaked at 20°C (68.86 viable females per female). Intrinsic rate of increase doubled from 15°C (0.059 females per female per day) to 20°C (0.127 females per female per day) and almost doubled again from 20 to 30°C (0.210 females per female per day). Given these parameters, C. sp. near lyncus could perform optimally in the area occupied by P. citrella in the Mediterranean region.     

Growth of dinoflagellates, Ceratium furca and Ceratium fusus in Sagami Bay, Japan: The role of temperature, light intensity and photoperiod

Seasonal changes of field populations and growth rates of two dinoflagellates, Ceratium furca and Ceratium fusus, were examined in the temperate coastal water of Sagami Bay, Japan. Weekly field sampling was conducted from August 2002 to August 2003, and laboratory experiments were also carried out to investigate effects of temperature, irradiance and photoperiod on the growth rates of these two Ceratium species. In the field, the abundances of both species increased significantly from April to August 2003, were gradually decreased from November 2002 and were not observed in January 2003. C. fusus was able to increase at lower temperatures in February 2003 compared to C. furca. In the laboratory, the two species did not grow at <10 °C or >32 °C. The highest specific growth rate of C. furca was 0.72 d⁻¹ at 24 °C and 600 μmol m⁻² s⁻¹. Optimum growth rates (>0.4 d⁻¹) of C. furca were observed at temperatures from 18 to 28 °C and at irradiances from 216 to 796 μmol m⁻² s⁻¹. The highest growth rate of C. fusus was 0.56 d⁻¹ at 26 °C and 216 μmol m⁻² s⁻¹. Optimum growth rates of C. fusus were observed at the same irradiance rage of C. furca, whereas optimum temperature range was narrower (26–28 °C). The growth curves of both species indicated saturation of the growth rates when light intensity was above 216 μmol m⁻² s⁻¹, and did not show photoinhibition at irradiances up to 796 μmol m⁻² s⁻¹. The specific growth rates of both Ceratium species were clearly decreased at L:D = 10:14 relative to those at L:D = 14:10 and L:D = 12:12. The present study indicates the two Ceratium species can adapt to a wide range of temperature and irradiance.     

Thermotolerance and gene expression following heat stress in the whitefly Bemisia tabaci B and Q biotypes

The whitefly Bemisia tabaci (Gennadius) causes tremendous losses to agriculture by direct feeding on plants and by vectoring several families of plant viruses. The B. tabaci species complex comprises over 10 genetic groups (biotypes) that are well defined by DNA markers and biological characteristics. B and Q are amongst the most dominant and damaging biotypes, differing considerably in fecundity, host range, insecticide resistance, virus vectoriality, and the symbiotic bacteria they harbor. We used a spotted B. tabaci cDNA microarray to compare the expression patterns of 6000 ESTs of B and Q biotypes under standard 25 °C regime and heat stress at 40 °C. Overall, the number of genes affected by increasing temperature in the two biotypes was similar. Gene expression under 25 °C normal rearing temperature showed clear differences between the two biotypes: B exhibited higher expression of mitochondrial genes, and lower cytoskeleton, heat-shock and stress-related genes, compared to Q. Exposing B biotype whiteflies to heat stress was accompanied by rapid alteration of gene expression. For the first time, the results here present differences in gene expression between very closely related and sympatric B. tabaci biotypes, and suggest that these clear-cut differences are due to better adaptation of one biotype over another and might eventually lead to changes in the local and global distribution of both biotypes.     

The effects of water temperature and ration size on growth and body composition of fry of common carp, Cyprinus carpio

Experiment was conducted with the aim of determining the effect of varying water temperature and ration size on growth and body composition of fry of the common carp, Cyprinus carpio. Common carp fry with an initial body weight (BW) of 0.86 g were fed a diet (34.9% protein, 18.3 KJ/g diet) at four ration sizes 4%, 5%, 6% and 7% of their body weight per day and reared at two water temperatures 28 and 32 °C for 60 days. Fry fed with 6% ration showed the highest mean final body weight at 28 °C. Final body weight was significantly (P<0.05) affected by ration and temperature. Cyprinus carpio fry raised at 28 °C had higher feed efficiency (FE) (44.36%) than the fry reared at 32 °C (40.98%) with 4% ration. Further, feed efficiency decreased with increase in ration levels in both temperatures. Protein efficiency ratio (PER) was higher (1.26) at 28 °C than at 32 °C (1.17). At 6% ration, common carp fry showed highest specific growth rate (SGR) (3.82%/day) at 28 °C as compared with at 32 °C (3.57%/day). A linear increase in protein and lipid contents was evident with increasing ration levels up to 6% body weight at both temperatures 28 and 32 °C. Second-order polynomial regression analysis of weight gain and SGR indicated the breakpoints at ration level 6.04% and 6.08% body weight per day at 28 and 32 °C. Hepatosomatic index (HSI) not affected by temperature and ration size while, viscerosomatic index (VSI) influenced (P<0.05) by ration size and temperature. Based on the above results, it may be concluded that 6% BW/day ration is optimal for growth of Cyprinus carpio fry at both the temperatures 28 and 32 °C.     

An autecological study of the potentially toxic dinoflagellate Alexandrium affine isolated from Vietnamese waters

The potentially toxic dinoflagellate species Alexandrium affine isolated from Ha Long Bay (Tonkin Gulf), Vietnam was cultured and maintained for morphological, physiological and toxicological studies. Classical morphological examinations including plate pattern were in good agreement with the international nomenclature of the species. The fine structure of A. affine, including morphology of its developmental stages during vegetative and sexual reproduction was found to be typical of other species in the genus. Two general trends in growth of A. Affine from Vietnamese waters were apparent: (1) growth rates were low at low salinities (10 and 15 psu) in all experimental temperatures (21–27 °C); (2) growth rates were high at salinities 25, 30, and 35 psu in all temperatures. There were no significant differences in growth rates at different salinities at low temperature (21 °C), and the most significant difference in growth rate was between high temperature–high salinity and high temperature–low salinity. The optimum temperature and salinity for growth were 24 °C and 30 psu. Maximum division rates per day (0.5–0.7) were at salinities 30 and 35 psu and at temperatures 24 and 27 °C. But the best conditions for division rate were 21 and 24 °C at salinities 30 and 35 psu. Toxicity analyses indicated A. affine to be both toxic and non-toxic at certain times. In the former case, toxicity was very low, 2.28 fmol  per cell; the toxicity component of A. affine was compared with that of A. leei and the mussel Perna viridis including neoSTX, STX, and GTX₁–GTX₄.     

Effects of temperature, salinity and irradiance on the growth of the red tide dinoflagellate Gyrodinium instriatum Freudenthal et Lee

The effects of temperature, salinity and irradiance on the growth of the red tide dinoflagellate Gyrodinium instriatum Freudenthal et Lee were examined in the laboratory. Exposed to 45 different combinations of temperature (10–30 °C) and salinity (0–40) under saturating irradiance, G. instriatum exhibited its maximum growth rate of 0.7 divisions/day at a combination of 25 °C and a salinity of 30. Optimum growth rates (>0.5 divisions/day) were observed at temperatures ranging from 20 to 30 °C and at salinities from 10 to 35. The organism could not grow at ≤10 °C. In addition, G. instriatum burst at a salinity of 0 at all temperatures, but grew at a salinity of 5 at temperatures between 20 and 25 °C. It is noteworthy that G. instriatum is a euryhaline organism that can live under extremely low salinity. Factorial analysis revealed that the contributions of temperature and salinity to its growth of the organism were almost equal. The irradiance at the light compensation point (I₀) was 10.6 μmol/(m² s) and the saturated irradiance for growth (I_s) was 70 μmol/(m² s), which was lower than I_s for several other harmful dinoflagellates (90–110 μmol/(m² s)).     

Thermal requirements for the embryonic development of Periplaneta americana (L.) (Dictyoptera: Blattidae) with potential application in mass-rearing of egg parasitoids

The embryonic development of oothecae of Periplaneta americana was evaluated under four different constant temperatures (5, 10, 15, 20, 25, 30, and 35 °C) and also at different exposure times at <5 °C. Their suitability as hosts after the treatment for the parasitoids Evania appendigaster and Aprostocetus hagenowii was also assessed. Temperatures of 5, 10, 15, and 35 °C adversely affected the development of the cockroaches, and exposure times to <5 °C longer than 5 days sufficed to kill all the embryos in the oothecae. The lower thermal threshold for complete development of P. americana was estimated to be 6.8 °C, with a required total amount of 900.9 degree-days. Cold-killed oothecae were still fit for the development of parasitoids. Parasitism rates of A. hagenowii were higher than those of E. appendigaster, although with lower emergence rates. Our results can be useful in aiding mass-rearing of these parasitoids for biological control programmes of P. americana, and may help forecast the time of emergence of nymphs of American cockroaches in infested areas.     

Laboratory evaluation of two diatomaceous earth formulations against Blattisocius keegani fox (Mesostigmata, Ascidae) and Cheyletus malaccensis oudemans (Prostigmata, Cheyletidae)

Diatomaceous earths (DEs) are very promising natural-origin pesticides against stored-product pests, but there is still inadequate information about the effect of DEs against stored-product mites. For this purpose, laboratory bioassays were conducted to assess the effects of DEs against the predatory mites Blattisocius keegani Fox (Mesostigmata, Ascidae) and Cheyletus malaccensis Oudemans (Prostigmata, Cheyletidae). Two DEs were used: SilicoSec, which contains 92% SiO₂, and PyriSec which contains 95.7% SilicoSec, 1.2% natural pyrethrum and 3.1% piperonyl butoxide. As prey, eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) were used. The tests were conducted at three temperatures, 20, 25 and 30 °C, on wheat treated with DEs at two dose rates, 500 and 1000 ppm and mortality of mite individuals was measured after 7 days of exposure. For B. keegani, protonymphs were proved significantly less susceptible in comparison with adults, in most temperature/DE combinations examined. Also, for both DEs, significantly more B. keegani adults were dead at 30 °C than at the other two temperatures. C. malaccensis protonymphs were less susceptible than adults, for both DEs tested, with the exception of PyriSec at 30 °C. In the case of adults, in SilicoSec-treated wheat, significantly fewer individuals were dead at 30 °C in comparison with the other two temperatures, but this was reversed for PyriSec. The results of the present work indicate that both species are susceptible to the two DEs tested, but this susceptibility is highly determined by several factors such as formulation, dose rate and temperature.     

Effects of the multiple stressors high temperature and reduced salinity on the photosynthesis of the hermatypic coral Galaxea fascicularis

This study investigates the physiological responses in the hermatypic coral Galaxea fascicularis exposed to salinity stress (from 37 ppt to 15 ppt) for 12 h, combined effects of reduced salinity (from 37 ppt to 20 ppt) and two temperatures (26 °C and 32 °C) for 12 h and combined effects of reduced salinity (from 37 ppt to 25 ppt) and two temperatures (26 °C and 29.5 °C) for 10 d. The results demonstrate that the coral is tolerant to 12 h exposure to extremely low salinity (15 ppt). The study also shows that combined effects of temperature and low salinity aggravate the damage on the photosynthesis of the symbiotic dinoflagellates in 12 h exposure to 20 ppt sea water. This study suggests that high temperature (29.5 °C) aggravates the damage of trivially low salinity (30 ppt) on the holobiont (the coral and its symbiotic dinoflagellates) in 10 d exposure. However, high temperature (29.5 °C) may have an antagonistic effect between temperature and low salinity (25 ppt) on metabolism of the holobiont. Based on the above results, we suggest that (1) the true mechanism of corals exposed to combined effects of low salinity and high temperature is complicated. This calls for more studies on different corals. Future studies should aim at investigating long-term low-level stress in order to simulate in situ conditions more accurately; (2) when corals exposed to extremely severe combined stressors for short-term or trivially severe stressors for relative long-term, the combined effects of two stressors (such as low salinity and high temperature) may be negative, otherwise, the effects may be additive.     

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment (sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.     

Citrate synthase and pyruvate kinase activities during early life stages of the shrimp Farfantepenaeus paulensis (Crustacea,Decapoda, Penaeidae): effects of development and temperature

Energy metabolism in early life stages of the shrimp Farfantepenaeus paulensis subjected to temperature reduction (26 and 20 °C) was determined using the activities of citrate synthase (CS) and pyruvate kinase (PK). At both temperatures, weight-specific activity of CS decreased throughout the ontogenetic development from protozoea II (PZ II) to postlarva XII–XIV (PL XII–XIV). PK activity reached a pronounced peak in PL V–VI, followed by a further decrease in PL XII–XIV. Temperature reduction produced variation in oxygen consumption rates (QO₂), ammonia–N excretion and in enzyme activities. Ammonia–N excretion was higher at 20 °C in mysis III (M III), PL V–VI and PL XII–XIV, resulting in substantially lower O:N ratios in these stages. QO₂ was increased in protozoea II (PZ II) and mysis I (M I) at 26 °C, while no difference in QO₂ was detected in the subsequent stages at either temperature. This fact coincided with higher CS and PK activities in M III, PL V–VI and PL XII–XIV at 20 °C compared with 26 °C. Regressions between individual enzyme activities and dry weight exhibited slope values of 0.85–0.92 for CS and 1.1–1.2 for PK and temperature reduction was reflected by higher slope values at 20 than at 26 °C for both enzymes. Weight-specific CS activity was positively correlated with QO₂ at 20 and 26 °C, and may thus be used as an indicator of aerobic metabolic rate throughout the early stages of F. paulensis. The variation in enzyme activities is discussed in relation to possible metabolic adaptations during specific ontogenetic events of the F. paulensis life cycle. Here, the catalytic efficiency of energy-metabolism enzymes was reflected in ontogenetic shifts in behaviour such as larval settlement and the adoption of a benthic existence in early postlarvae. In most cases, enhanced enzyme activities appeared to counteract negative effects of reduced temperature.     

Germination responses of Diplotaxis harra to temperature and salinity

Diplotaxis harra (Forssk.) Boiss, an annual herb in the family of Brassicaceae, is widely distributed in many sandy and gypseous areas in southern Tunisia. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and recovery responses after seed transfer to distilled water. The germination responses of the seeds in complete darkness were determined over a wide range of temperatures (5, 10, 15, 20, 25 and 30 °C) and salinities (0, 50, 100, 150 and 200 mM NaCl). Germination was inhibited by either an increase or decrease in temperature from the optimal temperature (15 °C). Highest germination percentages were obtained under non-saline conditions and an increase in NaCl concentrations progressively inhibited seed germination. Rate of germination decreased with an increase in salinity at all temperatures but comparatively higher rates were obtained at 15 °C. Salt stress decreased both the percentage and the rate of germination. An interaction between salinity and temperature yielded no germination at 200 mM NaCl. Seeds were transferred from salt solution to distilled water after 20 days, and those from low salinities recovered at all temperatures. At NaCl concentration of 200 mM, the recovery of germination was completely inhibited.     

Evaluation of the Entomopathogenic Fungi Beauveria bassiana and Paecilomyces fumosoroseus for Microbial Control of the Silverleaf Whitefly, Bemisia argentifolii

Collaborative research was conducted at the USDA-ARS Subtropical Agricultural Research Center in southern Texas to assess the microbial control potential of Beauveria bassiana and Paecilomyces fumosoroseus against Bemisia whiteflies. Laboratory assays demonstrated the capacity of both pathogens to infect Bemisia argentifolii nymphs on excised hibiscus leaves incubated at relative humidities as low as 25% at 23 ± 2°C (ca. 35% infection by B. bassiana and P. fumosoroseus resulted from applications of 0.6–1.4 × 10³ conidia/mm² of leaf surface). In small-scale field trials using portable air-assist sprayers, applications at a high rate of 5 × 10¹³ conidia in 180 liters water/ha produced conidial densities of ca. 1–2.5 × 10³ conidia/mm² on the lower surfaces of cucurbit leaves. Multiple applications of one isolate of P. fumosoroseus and four isolates of B. bassiana made at this rate at 4- to 5-day intervals provided >90% control of large (third- and fourth-instar) nymphs on cucumbers and cantaloupe melons. The same rate applied at 7-day intervals also provided >90% control in zucchini squash, and a one-fourth rate (1.25 × 10¹³ conidia/ha) applied at 4- to 5-day intervals reduced numbers of large nymphs by >85% in cantaloupe melons. In contrast to the high efficacy of the fungal applications against nymphs, effects against adult whiteflies were minimal. The results indicated that both B. bassiana and P. fumosoroseus have strong potential for microbial control of nymphal whiteflies infesting cucurbit crops.     

Temperature effects on growth and cell size in the marine calcareaous dinoflagellate Thoracospaera heimii

Growth experiments were carried out on the marine calcareous dinoflagellate Thoracosphaera heimii. Two strains (A603, GeoB 86) of the phototrophic, predominantly vegetative coccoid T. heimii were cultured at different temperature and nutrient levels. For the temperature experiment a gradient box was developed to allow the simultaneous testing of a wide range of temperatures on phytoplankton. During the investigations T. heimii was growing from 14 to 27°C. Exponential growth rates do not show an unimodal response curve vs. temperature: values rise with increasing temperatures toward maximal growth rates around 27°C. At low temperatures exponential growth is extremely long (over 50 days). In f/2 culture medium T. heimii (A603) is less efficient at high temperatures than at low temperatures, final yield was about five times higher at 16°C than at 27°C. Growth rate and final yield at 27°C are approximately the same for all experiments, despite different nutrient levels. Mean shell diameters show no clear relation to growth temperature. Calcification of T. heimii shells is inversely related to temperature.