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

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

Effects of Fluctuating Moisture and Temperature Regimes on Sporulation of Beauveria bassiana on Cadavers of Rhodnius prolixus

The effects of both moisture and temperature on the sporulation of an isolate of Beauveria bassiana , highly virulent to the Chagas' disease vector, Rhodnius prolixus , were studied in the laboratory under fluctuating regimes. Quantitative assays for conidial production from funguskilled cadavers from 10-day-old tests showed that recycling was highly dependent on the duration of exposure to high relative humidity (RH). On first-instar larval cadavers, sporulation reached more than 10 5 conidia/nymph under most regimes with a favourable phase combining high humidity (97% RH) and temperatures of 20 or 25 C for at least 12 h/day. Sporulation on third- and fifth-instar nymphs required a longer period (16 h/day or more) of favourable conditions (97% RH and 25 C) per day. The intensity of the conidial production from Rhodnius cadavers was enhanced when diurnal temperatures were high (28 and 35 C). From a vector control standpoint, daily high humidity requirements appear to be a crucial constraint. The recycling ability of B. bassiana on fungus-killed R. prolixus is most likely to contribute to the regulation of this triatomine vector if applications are made during the rainy seasons and in the most favourable habitats.     

Effect of temperature and relative humidity on the life cycle of Ornithodoros (Pavlovskyella) erraticus (Ixodoidea: Argasidae)

The effect of different temperatures (18, 22, 28, and 32.5 C, at constant 75% RH) and relative humidities (0, 15, 42, 60, 75, 84, and 92%, at constant 28 C) on the duration of the life cycle of Ornithodoros (Pavlovskyella) erraticus is studied in the laboratory. The egg incubation period is longer at 22 C than at the other temperatures tested; the percentage of hatched eggs was markedly increased at 28 C in comparison with other temperatures (T's) and relative humidities (RH's) tested. At constant 28 C, most larvae (86.2%) are ready to feed within 7.2 days posthatching; they feed for 5-52 min and molt to N1 in 7.8 days postfeeding. Five nymphal instars are recorded. Unfed N1-N5 survived for a longer period at 18 C than at other temperatures, whereas the effect of RH's was insignificant. After feeding, nymphal premolting periods differ from one instar to another and from one T or RH to another. At 28 C, the males emerge from N3, N4, and N5 in 9-15 days postfeeding, while females emerge only from N4 and N5 in 10-16 days. The overall sex ratio (3 male:5 female) is not affected by different T's and RH's. The female and male life spans were longer (means 720 and 500 days, respectively) at 22 C than at other T's and RH's. This study shows that the duration of the life cycle of O. erraticus decreases with rising T and increases with an increase in RH. However, the 28 C and 75% RH seem to be the optimum conditions for this species.     

Effects of fluctuating moisture and temperature regimes on the persistence of quiescent conidia of Isaria fumosorosea

Conidia of Isaria fumosorosea were submitted to three regimes of temperature and moisture to simulate microclimatic conditions which prevail in temperate (43% RH and 28 °C to 98% RH and 15 °C), subtropical (75% RH and 35 °C to 98% RH and 25 °C), and arid areas (13% RH and 40 °C to 33% RH and 15 °C) with daily fluctuating cycles. Germination, conidial viability, and virulence to Spodoptera frugiperda larvae were less affected after 20 days exposure under temperate cycling conditions than under arid and subtropical conditions. Exposure of conidia for 20 days to constant nocturnal simulated conditions of any tested regime weakly affected conidial persistence, whereas diurnal conditions exerted the most detrimental effects of high temperatures. However, when tested at both 45 °C and 50 °C at 33% RH for 160 h, the persistence of I. fumosorosea conidia was relatively higher than expected. These results emphasize that climatic conditions prevailing in environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies.     

STUDIES ON BIONOMICS OF LIPOSCELIS ENTOMOPHILA (PSOCOPTERA:LIPOSCELIDIDAE) INFESTING STORED PRODUCTS*

Abstract This paper deals with the biological characteristics of the psocid Liposcelis entomophila (Enderlein) on a diet composed of whole wheat flour and yeast (10: 1) under different temperatures (17.5–35C) and relative humidities (50%-90% RH). The results showed that at 75% RH development time from egg to adult varied from 71. 9 d at 20% to 21.7 d at 35C. At 28C it varied from 23.0 d at 90% RH to 34.4 d at 60% RH. The development threshold and the effective accumulated temperature for entire immature stages were estimated at 15. 7C and 460. 7 day-degree, respectively. The survival rate from egg to adult was 64. 5% at 27. 5C while at 20C and 35C it was only 32.1% and 37. 0%, respectively. At 28C the survival rate ranged from 31. 2% at 60% RH to 67.8% at 80% RH. L. entomophila could not survive at any humidity at 17. 5C and below 50% RH. The average longevity of adult ranged from 32.4 d at 35C and 64.4 d at 20C. At 75% RH the mean egg production varied from 27.1 at 27. 5 C and 13. 9 at 20C and the greatest fecundity occurred at 90% RH with 28C. The optimal ranges of temperature and humidity for L. entomophila population growth were 27. 5–30C and 80%—90% RH. The distribution and the reason for its serious infestation in China are discussed.     

Abiotic mortality factors of the coffee berry borer (Hypothenemus hampei)

Mortality of the coffee berry borer was studied under controlled laboratory conditions in Tapachula, Mexico. For adult female borers subjected to a range of relative humidities (RH) without food at 25°C, the longest mean survival time (20 days) was obtained at 93.5% RH. Adult borer survival was also studied at a range of temperatures for a fixed relative humidity (93.5% RH); at 20°C mean survival time was 28 days. Fecundity and mortality of borer stages in berries was studied for a range of humidities at 25°C. Maximum fecundity was obtained at 90 and 93.5% RH. Immature stages were ejected from the berry at 84% RH and above, which is interpreted as a form of brood hygiene.     

Common Leafspot of Alfalfa: Ascospore Germination and Disease Development in Relation to Moisture and Temperature

In a moist chamber Pseudopeziza medicaginis ascospores infected alfalfa (Medi sativa L.) moderately to abundantly within 6–10 h at 10–20 °C and within a longer time-span outside this temperature range. Approximate limits of the range were 2.5 and 28 °C; no infection took place at 30 °C. At 14°C ascospores infected alfalfa abundantly at 98 %relative humidity (RH) and above, moderately at 97%, sparsely at 95 and 96%, but not at 94% and below. Ascospores were hydrophilic, germinating best at or near 100%, RH but did not germinate at or below 93 % RH. After infection was established, tiny leafspots became visible within 6–7 days at constant temperatures of 15–25°, 10 days of 10°C, 13 days of 5 °C, and 25 days of 2.5 °C. They failed to develop into normal size spots within 4 weeks at constant temperatures near 30 °C, or near 10 °C and lower. Temporary exposure of incipiently diseased plants 1–6 days to 30–38 °C adversely affected subsequent leafspot development at 20–24°C. Inhibition depended on temperature and on the extent of post-infection disease development.     

Relative humidity preference and survival of starved Formosan subterranean termites (Isoptera: Rhinotermitidae) at various temperature and relative humidity conditions

Foraging groups of Formosan subterranean termites, Coptotermes formosanus Shiraki were tested for their relative humidity (RH) preference in a humidity gradient arena in the laboratory at a constant temperature of 26°C. Five RH levels (9%, 33%, 53%, 75%, and 98%) were maintained in the test arena comprising of a series of closed containers by using dry silica gel, saturated salt solutions, or distilled water alone. Termites gradually aggregated to the highest RH chamber in the arena. After 1 h, a significantly greater percentage of termites (≈46%) aggregated to the highest RH chamber (98%) than to the lower RH chambers (≤75%). After 12 h, > 97% of the termites aggregated to the 98% RH chamber. In survival tests, where termites were exposed to 15 combinatorial treatments of five RH levels (9%, 33%, 53%, 75%, and 98%) and three temperatures (20°C, 28°C, and 36°C) for a week, the survival was significantly influenced by RH, temperature, and their interaction. A significantly higher mortality was observed on termites exposed to ≤75% RH chambers than to 98% RH chamber at the three temperatures and significantly lower survival was found at 36°C than at 28°C or 20°C. The combination of temperature and RH plays an important role in the survival of C. formosanus.     

Environmental Effects on the Development and Survival of the Scale Insect Abgrallaspis cyanophylli (Signoret) (Homoptera: Diaspididae) with Reference to its Suitability for Use as a Host for Rearing Biological Control Agents

Developmental and survival rates of the locally important diaspidid pest, Abgrallaspis cyanophylli (Signoret) reared on Solanum tuberosum L . tubers were examined under light and dark conditions; humidities of 33, 53, 62 and 75% relative humidity (RH); varying population densities; constant temperatures in the range of 20 to 30oC and at cycling temperatures of 12 h at 14°C and 12 h at 30°C. Developmental rate was slightly lower under constant light conditions but mortality was higher in the dark, particularly amongst the males. At 26°C, there were no differences in developmental rate in relation to the various humidity levels. However, survival was significantly lower at 33% RH, with females suffering higher mortality than males. Population density was found to have no effect on developmental rate or size of the females. Overall mortality increased in line with population density although the result was poorly correlated. Within the range 20-28°C developmental rate increased with rising temperature but decreased at 30°C. Thermal summation and polynomial regression data show a theoretical lower thermal threshold for development of 12.47°C. The thermal constant was 541.7 degree days. Survival was lowest at 20°C and 30°C and highest at temperatures in the median range and under cycling conditions. Male survival was significantly higher than that of the females at 30°C and under the cycling regime of 14/30°C. The results suggest that the optimum conditions for rearing A. cyanophylli on potatoes would be at temperatures in the range 24-26°C and humidities of 55-65% RH.     

不同温湿度组合对安徽虫瘟霉 诱发桃蚜病害的影响

用孢子浴方法,对42批次桃蚜Myzus persicae（30～60头/批）接种大剂量（孢子79～90个/ mm²）安徽虫瘟霉Zoophthora anhuiensis的分生孢子,在20℃下保湿24 h后转入不同温度（10℃、15℃、20℃、25℃、30℃及自然变温1.5～16.6℃和8.5～20.2℃）和湿度(50%、65%、80%、90%、95%及100% RH)的组合条件下观察桃蚜的反应。结果表明,各组合条件下的桃蚜均能发病死亡,而且累计死亡率的显著差异存在于不同温度（F=7.46, P<0.01)和湿度间（F=12.54, P<0.01）。最适发病的温度为恒温20℃和变温8.5～20.2℃（日均温12.4℃）,死亡率随湿度升高而增大。在10～25℃和100% RH的组合中,温度的变化几乎不影响桃蚜的累计死亡率,但影响发病速率,在10℃、15℃、20℃和25℃下的致死时间LT₅₀值分别为8.4 天、7.1 天 、4.0 天和3.4 天。回归分析表明, 在100% RH下安徽虫瘟霉诱发桃蚜发病的起始温度为1.65℃。在10～15℃及自然变温下,病死蚜尸顺利产孢的湿度为80% RH;而在20～30℃下,蚜尸产孢的湿度为90% RH。在所有温湿组合的蚜尸中未见安徽虫瘟霉的休眠孢子发生。     

Thermal Requirements and Parasitism Capacity of Trissolcus brochymenae (Ashmead) (Hymenoptera: Scelionidae) Under Constant and Fluctuating Temperatures, and Assessment of Development in Field Conditions

In order to understand the relative importance of Trissolcus brochymenae , a common egg parasitoid of the predatory stinkbug Podisus nigrispinus in areas where this predator is released, the thermal requirements and developmental periods (egg to adult) at constant (17, 20, 25, 28 and 32°C) and fluctuating (10-20, 13-23, 15-25, 17-27, 20-30 and 25-35°C) temperatures, and the effect of constant and fluctuating temperatures systems on the longevity and parasitism capacity of T. brochymenae were investigated. Based on thermal requirements of the parasitoid and field day/night temperature variation in the regions where P. nigrispinus was released, we calculated monthly and yearly number of generations of the parasitoid. Parameters of biological and thermal requirements of T. brochymenae were not affected when the insects were reared under constant or fluctuating temperatures. It was shown that males have a shorter developmental period and lower thermal requirements than females. The lowest parasitism capacity and shortest longevity of T. brochymenae were observed under fluctuating temperature regimes of 10-20oC and 25-35°C. A higher parasitism capacity was obtained under a 20-30°C regime (96.0 ±33.6 offspring per female), while longevity was longer at a constant temperature of 27°C (17.6 ±0.6 days). T. brochymenae showed a continuous development during all seasons through the year under field conditions, accomplishing 2.7, 2.4, 2.9 generations per month in the CAF, Pains, and Refloralje areas. An average of 26.4 and 25.8, 25.8 and 25.3, and 24.7 and 23.6 generations per year under constant and fluctuating temperatures systems was estimated for the CAF, Pains, and Refloralje areas, respectively. No significant difference between thermal systems in each area was observed; however, a significantly smaller number of generations per year were estimated to occur in the Refloralje area. Implications of these results for the forecasting of parasitoid population development and its impact on the host stinkbug predator are discussed.     

Ripe pollen carbohydrate changes in Trachycarpus fortunei: the effect of relative humidity

Pollen of the palm Trachycarpus fortunei was kept at 25°C and relative humidities (RH) of 20, 55 and 98%. Changes in viability, water content and carbohydrates were measured over 2–17 days. Water content remained almost constant at 20 and 50% RH and increased dramatically at 98%. Pollen viability and germination rate remained almost constant over 14 days at 20% RH and decreased to about 2% after 7–9 days at 55% and to even less at 98% RH. Although the three experimental conditions were constant, qualitative and quantitative variations in pollen carbohydrates were recorded, even after pollen had lost its viability. The quantities of mono-, di- and polysaccharides varied with the period of pollen storage at the various RH. The greatest changes in glucose, fructose and sucrose content were recorded at 55 and 98% RH. At these relative humidities, maximum glucose and fructose content and minimum sucrose content occurred at maximum water content. Starch was not present in mature pollen but appeared and peaked after 7–9 days of pollen storage at 55 and 98%. Appearance of starch coincided with an increase in pectin content. PAS-positive cytoplasmic polysaccharides showed an increasing trend at 20% RH. A relation was found between pollen viability, water content and monosaccharide content. Pollen viability and germination capacity remained high at 20% RH for 14 days. At this relative humidity, pollen water, glucose and fructose contents remained almost constant, while sucrose reached its maximum value. The fluctuations of more complex carbohydrates (starch, pectins and PAS-positive cytoplasmic polysaccharides) were less easy to interpret. Changes observed under experimental conditions could simulate processes occurring in nature during pollen presentation and dispersal.     

Temperature Effects on Development and Reproduction of Heterodera cajani on Pigeonpea

Effects of constant and fluctuating temperature on development and reproduction of Heterodera cajani were studied on pigeonpea cv. ICPL 87 in growth chambers at 10, 15, 20, 25, and 30 C and in a greenhouse fluctuating between 22.2 and 37.8 C. Nematode penetration was greatest (P = 0.001) in roots at 25 C; there was no penetration at 10 C. The basal threshold temperature for development was calculated to be 11 C. Completion of one H. cajani generation required 17, 28, 35, and 66 days (323, 392, 315, and 264 degree-days) at 30, 25, 20, and 15 C, respectively, and 19 days (356 degree-days) at a fluctuating temperature. Survival was greater at 20 and 25 C than at 15 and 30 C. The greatest (P = 0.05) number of females (17.9 females per root) were produced at 25 C, compared with 13.2 at 20 C, 7.9 at 30 C, and 2.5 females at 15 C. Nematode reproduction was 1.6 to 7.1 times greater at 25 C than at other temperatures. Emergence of juveniles from egg sacs and cysts was greater at 25 and 30 C than at 15 and 20 C. Equations were developed to predict nematode development rate, cumulative juvenile emergence from egg sacs and cysts, and population increases as influenced by temperature.     

Effects of temperature and relative humidity on sporulation of Metarhizium anisopliae var. acridum in mycosed cadavers of Schistocerca gregaria.

The effects of relative humidity (RH) and temperature on the sporulation of Metarhizium anisopliae var. acridum on mycosed cadavers of desert locust, Schistocerca gregaria, were assessed in the laboratory. Quantitative assessments of conidial production over 10 days under constant conditions showed that sporulation was optimized at RH > 96% and at temperatures between 20 and 30 degrees C. Under both these conditions >10(9) conidia/cadaver were produced. At 25 degrees C, conidial yield was maximized under conditions in which cadavers remained in contact with damp substrate. Relatively little sporulation occurred at 15 degrees C (< 3 x 10(7) conidia/cadaver) and 40 degrees C (< 4 x 10(6) conidia/cadaver) and no sporulation occurred at 10 or 45 degrees C. Following incubation, conidial yield was closely related to the water content of locust cadavers. In separate tests, locust cadavers were incubated for 10 days under diurnally fluctuating temperature and RH that comprised favorable (25 degrees C/100% RH) alternating with unfavorable (40 degrees C/80% RH) conditions for sporulation. In this case, fewer conidia were produced compared with cadavers that were incubated under the favorable conditions for an equal period cumulatively but were not periodically exposed to unfavorable conditions. However, this reduced sporulation observed with the fluctuating condition was not observed when cadavers were similarly incubated under favorable/unfavorable conditions of temperature but were not periodically exposed to the low RH condition. This result implies that sporulation is a dynamic process, dependent not only on periodic exposure to favorable RH but also on the interrelation of this with low RH. Associated tests and the monitoring of changes in cadaver weights imply that the mechanism driving the reduced sporulation under fluctuating RH is the net water balance of cadavers, i.e. the cumulative ability of the fungus/cadaver to adsorb water necessary for sporulation at high RH is restricted by water loss associated with intermittent exposure to a low RH. The duration of daily exposure to high humidity appears to be a crucial constraint to the recycling ability of M. anisopliae var. acridum.     

Population growth and development of Liposcelis pearmani (Psocoptera: Liposcelididae) at constant temperatures and relative humidities

Psocids of genus Liposcelis are now considered serious pests of stored products. We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0°C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis pearmani Lienhard. L. pearmani did not survive at 37.5 and 40.0°C, at all relative humidities tested; at 43% RH, at all temperatures tested; and at 55% RH, at 32.5 and 35°C. The greatest population growth was recorded at 32.5°C and 75% RH (32-fold growth). L. pearmani males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 17, 63, and 20%, respectively. Female L. pearmani have two to five instars, and the percentages of females with two, three, four, and five instars were 5, 39, 55, and 1%, respectively. We developed temperature-dependent development equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. Based on 30-d population growth, L. pearmani cannot survive at temperatures >35.0°C; does not thrive at low relative humidities (55%), at temperatures above 25°C; and has a high optimum relative humidity for population growth (75%). Therefore, we expect it to have a more limited distribution compared with other Liposcelis species. These data provide a better understanding of how temperature and RH may influence L. pearmani population dynamics and can be used in population growth models to help develop effective management strategies for this psocid, and to predict its occurrence.     

Survival of Salmonella montevideo on Wheat Stored at Constant Relative Humidity

Eleven samples of Ottawa variety hard red winter wheat were inoculated with a standardized suspension of Salmonella montevideo. The contaminated wheat samples were placed in constant relative humidity (RH) chambers held at 25 C. Relative humidities were 7, 11, 22, 33, 43, 53, 62, 75, 84, 92, and 98%. Constant RH at 25 C was maintained with different saturated salt solutions in the sealed chambers. Periodic counts of viable S. montevideo cells per gram of wheat were made over a 28-week sampling period. Viable counts of S. montevideo on wheat held at 7, 11, and 22% RH decreased from an initial 10⁶ cells/g of wheat to a final count of 10⁴ cells/g in each sample. Samples stored at 33, 43, 53, and 62% RH decreased from 10⁶ viable cells/g to 3.6 × 10³, 10³, 10², and 20 viable cells/g, respectively. No viable S. montevideo cells were detected in the samples held at 75, 84, 92, and 98% RH after 22, 16, 26, and 16 weeks, respectively.     

Effect of temperature and relative humidity on the rate of development,fecundity and life table parameters of the red spider mite Oligonychus mangiferus (Rahman and Sapra) (Acari: Tetranychidae)

Studies on biology of Oligonychus mangiferus (Rahman and Sapra) at combination of eight constant temperatures and relative humidities (RHs) viz., 7.0°C with 85% RH, 10°C with 80% RH, 15.0°C with 75% RH, 23.0°C with 70% RH, 31.0°C with 65% RH, 34.0°C with 65% RH, 36.0°C with 60% RH and 40.0°C with 55% RH revealed that the optimal condition for the development of these mites are 15.0–31.0°C and 65–75% RH. The highest temperature and the lowest RH accelerated the rate of development and induced more reproduction of O. mangiferus. Its population also multiplied 30.81 times in a generation time of 27.36 days at 31.0°C and 65% RH, while the same population only increased 7.46 times in a generation time of 48.07 days at 15.0°C and 75% RH. Fecundity was highest at 31.0°C and 65% RH with 46.43 eggs per female. The highest intrinsic rate of natural increase was observed at 31.0°C as 0.125 per day.     

Biology of Ixodes Rubicundus Ticks under Laboratory Conditions: Observations on Oviposition and Egg Development

Observations on oviposition and egg development of Ixodes rubicundus were made under laboratory conditions. Engorged females were exposed to temperatures in the range 10–25°C and relative humidities (RHs) of 33 and 93%. The pre-oviposition period, oviposition period, incubation period, conversion efficiency index (CEI) values and fecundity were determined. The mean pre-oviposition period varied from 13.3 days (temperature 25°C and RH 33%) to 68.3 days (temperature 10°C and RH 93%). Oviposition extended from a mean of 39 days (temperature 25°C and RH 93%) to 201.7 days (temperature 10°C and RH 93%). The developmental zero temperature for the pre-oviposition period was 9.2°C. The mean total number of eggs produced by engorged I. rubicundus females varied from 2045.7 (temperature 10°C and RH 93%) to 3777.7 (temperature 20°C and RH 93%). Both female mass and RH significantly (p < 0.01) influenced the number of eggs produced. CEI values varied between 43.1–54.4% (RH 93%) and 34.1–42.5% (RH 33%). At 93% RH females produced between 14.2 and 17.7 eggs per mg body mass compared to the 13.2–14.6 eggs per mg body mass at 33% RH. The shortest mean incubation period recorded was 164.3 days (temperature 25°C and RH 93%). The developmental zero temperature for incubation was 6.5°C. Both the pre-oviposition and oviposition periods of I. rubicundus are more extended compared to other species of the genus. Ixodes rubicundus produces a large number of small eggs compared to other prostriate ticks.     

Enhanced ovicidal activity of an oil formulation of the fungus Metarhizium anisopliae on the mosquito Aedes aegypti

Abstract.  The effect of humidity on the activity of Metarhizium anisopliae IP 46 (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) formulated in sunflower oil against Aedes aegypti (L.) (Diptera: Culicidae) eggs was examined. After exposure of eggs at 75% relative humidity (RH) for ≤ 25 days, ovicidal activity was not increased by oil-in-water formulated conidia, hyphal bodies or pure-oil formulated conidia, compared with conidia or hyphal bodies prepared in water only. At optimal > 98% RH, eclosion was ≤ 13.7% after treatment with oil-in-water formulated propagules in ≤ 10% oil, and it was completely inhibited when conidia were applied in pure oil. At 86–100% RH, new conidia were found on eggs treated with oil-formulated conidia and incubated down to 91% RH. Ovicidal activity was still detected at 93% RH and was augmented with increasing humidity and time of exposure of eggs. Eclosion of larvae was distinctly reduced by IP 46 pure-oil formulated conidia after a minimal initial exposure of 3 days at > 98% RH, followed by: (a) a 12-day exposure at 75% RH before submersion in water; (b) a minimal 5-day exposure at > 98% RH and direct subsequent transfer of treated eggs to water, or (c) a minimal daily 20-h exposure at > 98% RH alternating with 4 h at 75% RH for 10 days. We demonstrate that oil-based formulations of conidia of M. anisopliae enhance ovicidal activity at high humidities and conclude that these formulations have potential in the integrated control of Ae. aegypti .     

Temperature and moisture requirements for conidial germination of an isolate of Beauveria bassiana,pathogenic to Rhodnius prolixus

The effects of temperature, relative humidity and water activity on germination of conidia of an isolate of Beauveria bassiana (Bals.) Vuill. pathogenic to the triatomine vector of Chagas' disease, Rhodnius prolixus Stål., were investigated in vitro. Germination occurred at temperatures between 15 °C and 35 °C under saturated atmosphere and the optima ranged from 25 °C to 3O °C. At the extreme temperatures tested (15 °C and 35 °C) the germination process was delayed, but germination rates reached more than 95%. Germination of B. bassiana conidia was strongly affected by moisture conditions. The availability of water, in both atmospheric and liquid conditions, caused changes in germination times as well as in germination rates. For example, at 25 °C + O.5 °C, germination took place within 20 h at 95.5% RH, whereas it needed 72 h of incubation at 90% RH. Germination times increased as the water activity declined from 0.96 a_w to 0.92 a_w. Below 0.92 a_w, o germination was observed after a 72 h incubation time.