Conidiation of Hirsutella thompsonii var. synnematosa in submerged culture

Fourteen monosporal isolates of Hirsutella thompsonii grew vegetatively in various liquid media producing typical phialidic-like conidiophores. Hirsutella thompsonii var. synnematosa from Ivory Coast (HtIC) was the only pathotype which produced true conidia in submerged culture. HtIC began producing conidia after 3 days incubation reaching a peak ranging from 6.8 × 10⁵ to 9.7 × 10⁷ conidia/ml between 6 and 11 days. A concentration of 10 g/liter of corn steep liquor and 0.2% Tween 80 were essential for maximum conidiation. Submerged conidia had a smooth but somewhat rugose conidial walls, whereas aerially formed conidia were distinctly verrucose. Germination of submerged conidia ranged from 5.2 to 12.9% and were virulent causing 32.5% infection to adult citrus rust mites when sprayed on citrus foliage at 1.2 × 10⁹ conidia/ml.     

Genetic diversity in <Emphasis Type="Italic">Hirsutella thompsonii</Emphasis> isolates based on random amplified polymorphic DNA analysis

Hirsutella thompsonii Fisher is a host-specific fungal pathogen of the diverse group of arthropods known as the Acari. It particularly affects eriophyid mites, and the identification of its isolates is a difficult task due to its pleomorphic nature. Seven isolates of H. thompsonii var. thompsonii and H. thompsonii var. synnematosa collected from various agro-climatic regions of India were subjected to PCR analysis using random decamer primers to differentiate between them. Random amplified polymorphic DNA analysis revealed that all of the isolates from the citrus rust mite, Phyllocoptruta oleivora Ashmead (Acari: Eriophyidae), clustered together, with the exception of one, HtCRMB. The only isolate of H. thompsonii from Aceria guerreronis keifer (Acari: Eriophydae), HtPDBC, clustered separately.     

Selection of entomopathogenic fungi for use in combination with sub-lethal doses of imidacloprid: perspectives for the control of the leaf-cutting ant <Emphasis Type="Italic">Atta sexdens</Emphasis><Emphasis Type="Italic">rubropilosa</Emphasis> Forel (Hymenoptera: Formicidae)

In the first part of this study, four isolates of the fungus Beauveria bassiana (Bals.) Vuillemin (LPP1, LPP2, CG05 and CG24) and one isolate of Metarhizium anisopliae (Metsch.) Sorokin (CG46) were tested against adult foragers of Atta sexdens rubropilosa. Ants were allowed to walk on filter paper discs, inside Petri dishes, previously impregnated with 1 ml of a conidia suspension (2 × 10⁷ conidia ml⁻¹), maintained at 80% RH and 26°C for 24 h and subsequently, transferred to sterile Petri dishes, maintained at 23°C, 80% RH, 24 h dark. The mean values of LT₅₀ for LPP2, LPP1, CG46, CG24 and CG05 were 3.5, 3.7, 3.8, 4.2 and 4.4 days, respectively. Control insects for all tests in this study showed less than 10% mortality. Experiments were carried out to test the toxicity of imidacloprid (IMI) to A. sexdens rubropilosa. Mortality was evaluated 10 days following a 24 h exposure to the insecticide. Percent mortality caused by 500, 200, 100 and 10 ppm IMI was 77.8, 56.7, 45.5 and 5.5 respectively. Insects treated with 10 ppm IMI were observed to have reduced locomotor activity 24 h after exposure to the insecticide. The LC₅₀ of IMI was 154.3 ppm. Subsequent tests were carried out to evaluate the combination of a sub-lethal dose of IMI (10 ppm) and infection by CG24 (1 × 10⁷ conidia ml⁻¹). Mortality due to fungal infection alone was 43.3%. Mortality of insects treated with IMI followed by exposure to the fungus was 64.3%. These results indicate that IMI significantly increases the susceptibility of ants to infection by B. bassiana CG24.     

Pathogenicity of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> and <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> to the tobacco spider mite <Emphasis Type="Italic">Tetranychus evansi</Emphasis>

Seventeen isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and two isolates of Beauveria bassiana (Balsamo) Vuillemin were evaluated for their pathogenicity against the tobacco spider mite, Tetranychus evansi Baker & Pritchard. In the laboratory all the fungal isolates were pathogenic to the adult female mites, causing mortality between 22.1 and 82.6%. Isolates causing more than 70% mortality were subjected to dose–response mortality bioassays. The lethal concentration causing 50% mortality (LC₅₀) values ranged between 0.7×10⁷ and 2.5×10⁷ conidia ml⁻¹. The lethal time to 50% mortality (LT₅₀) values of the most active isolates of B. bassiana and M. anisopliae strains varied between 4.6 and 5.8 days. Potted tomato plants were artificially infested with T. evansi and treated with B. bassiana isolate GPK and M. anisopliae isolate ICIPE78. Both fungal isolates reduced the population density of mites as compared to untreated controls. However, conidia formulated in oil outperformed the ones formulated in water. This study demonstrates the prospects of pathogenic fungi for the management of T. evansi.     

Infection of Blissus antillus (Hemiptera: Lygaeidae) Eggs by the Entomopathogenic Fungi Metarhizium anisopliae and Beauveria bassiana

This study determined the pathogenicity and virulence of Beauveria bassiana and Metarhizium anisopliae to eggs of the chinch bug Blissus antillus (Hemiptera: Lygaeidae). Eggs were inoculated under laboratory conditions by immersion in concentrations of 1 × 10⁴ and 5 × 10⁶ conidia/ml. Inoculated eggs were kept under controlled conditions. Evaluations were carried out daily for 20 days. M. anisopliae isolates were highly virulent to eggs, even at 1 × 10⁴ conidia/ml. All B. bassiana isolates tested were considered to be of low virulence or avirulent. The most virulent isolate tested was ESALQ 818 (M. anisopliae), which caused 96.7% infection, when eggs were immersed in suspensions of 1 × 10⁴ conidia/ml. Conidial production on infected eggs was observed to be highest for M. anisopliae isolate CG144, with a mean value of 11.6 × 10⁵ conidia/ml/egg. Infection of Blissus eggs oviposited on plant stems was greater when M. anisopliae isolate CG144 was formulated in mineral oil (63.5% mortality) than when formulated in Tween 80 (27.1% mortality).     

Pathogenicity of Beauveria bassiana (Deuteromycotina: Hypomycetes) to Larvae of the Small Poplar Longhorn Beetle, Saperda populnea (Coleoptera: Cerambycidae)

The small poplar longhorn beetle, Saperda populnea is an important pest of Lombardy poplars (Populus nigra L.) in Turkey. A survey for natural entomopathogenic fungi of S. populnea larvae was made in Erzurum, Turkey, during the period 2004–2005. Larvae (13.5%) infected with a strain of the fungus Beauveria bassiana were found. The pathogenicity of B. bassiana strain 46 was conducted with different concentrations of conidia (10⁶, 10⁷ and 10⁸ conidia/ml) of this isolate on S. populnea larvae. The lowest concentration (10⁶ conidia/ml) caused about 56% mortality within 6 days. One hundred percent mortality was achieved after median lethal time (LT₅₀) of 4.6 and 4.4 days for 10⁷ and 10⁸ conidia/ml, respectively. There were no significant differences between median lethal times. This is the first record of natural infection of S. populnea larvae by B. bassiana.     

Pathogenicity and specificity of Neozygites tanajoae and Neozygites floridana (Zygomycetes: Entomophthorales) isolates pathogenic to the cassava green mite

The cassava green mite (CGM), Mononychellus tanajoa, a native of South America was accidentally introduced into Africa where it causes serious crop losses. The possibility of introducing classical biological agents from the native home of CGM into Africa was investigated. Thus, we conducted a series of laboratory assays of the native fungal pathogens, Neozygites tanajoae from Brazil and Neozygites floridana from Colombia and Brazil, and compared them with N. tanajoae isolates from Benin. Infectivity of both fungal species, was assayed against the twospotted spider mite, Tetranychus urticae, and against the red mite, Oligonychus gossypii. Pathogenicity against CGM and host range studies were conducted by transferring adult females of each mite species to leaf discs containing sporulated cadavers with a halo of conidia of each fungal isolate. All isolates caused some degree of infectivity to CGM. None of the isolates of N. floridana and N. tanajoae tested were pathogenic to O. gossypii, and only two isolates infected T. urticae. Most isolates from Brazil were highly virulent and infected only CGM. Sixteen N. tanajoae isolates caused more than 89% mortality and more than 62% of the CGM became mummified. A mummified CGM is characteristically a swollen, brown fungus-killed mite that has great potential to produce conidia. However, high mortality was not always associated with high mummification. The median mummification time ranged from 4.4 to 6.7 days. Five Brazilian isolates caused >75% mummification with a median mummification time <5 days. Isolates that cause high mummification in a short period of time would be more likely to cause epizootics and to establish in the new environment. Therefore, these isolates would be the best candidates for introduction to Africa.     

Pathogenicity, formulation and storage of insect pathogenic hyphomycetous fungi tested against Diabrotica speciosa

Studies were conducted tosearch for fungal strains with potentialpathogenicity against Diabrotica speciosa(Germar) (Coleoptera: Chrysomelidae).Among sixteen fungal isolates screenedthe most virulent was a Beauveria bassiana(Balsamo) Vuillemin isolate (FHD13) thatcaused 70% mortality of D. speciosathird instar larvae. The LC₅₀ value ofB. bassiana isolate FHD13 was3.48 × 10¹⁰ conidia/ml.Different temperatures (4, 17 and 26 °C)and vegetable oils (corn, sunflower and canola)used for storage did not significantly affectviability of conidia. A pathogenicity trialagainst D. speciosa larvae performed withthe corn oil formulation (1 × 10⁸ conidia/mlof oil) caused 65% of mortality.     

Effect of entomopathogenic fungi upon adults of Stomoxys calcitrans and Musca domestica (Diptera: Muscidae)

The pathogenicity and virulence of 10 isolates of entomopathogenic fungi from the soil of lodging pens of dairy production units in Aguascalientes, Mexico, on adults of Stomoxys calcitrans and Musca domestica were determined. All isolates were pathogenic when exposed by aspersion to a concentration of 1×10⁸ conidia/ml, causing between 20.3 and 91.7% mortality in S. calcitrans and between 31 and 91.7% in M. domestica at 7 days post-exposure; in S. calcitrans isolates of Beauveria bassiana (Bb114) and Metarhizium anisopliae (Ma135), sensu lato, were the most noteworthy as mortality reached above 90% with an LC₅₀ of 3.5×10⁵ conidia/ml for Bb114, while for Ma135 reached 1.6×10⁴ conidia/ml. In M. domestica Ma134 and Ma135 showed mortality above 90% with an LC₅₀ of 4.3×10⁴ and 1.4×10⁵ conidia/ml, respectively.     

Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia bipunctata

Harmonia axyridis is a predatory coccinellid, native to central and eastern Asia. It has been available in many countries for use as a biological control agent of pest aphids and scale insects. In many of these countries, including the USA, H. axyridis has established. It is now considered an invasive alien species for a number of reasons, including its impact on functional biodiversity. Beauveria bassiana is known to be a natural mortality agent of overwintering coccinellids and is a potential candidate for the biological control of H. axyridis. In this paper we compare the susceptibility of three species of coccinellid, H. axyridis (cultures derived from Japan and UK), Coccinella septempunctata and Adalia bipunctata to infection by B. bassiana (commercial strain GHA) after exposure at three doses (10⁵, 10⁷, 10⁹ conidia ml⁻¹). The two subpopulations of H. axyridis (Japan and UK) were more resistant to B. bassiana infection than either A. bipunctata or C. septempunctata. This is exemplified by the median lethal doses at 10 days post-inoculation (LD₅₀) of 10^6.2, 10^6.0, 10^8.3, 10^9.6 conidia ml⁻¹ for A. bipunctata, C. septempunctata, H. axyridis (Japan) and H. axyridis (UK), respectively. Only doses of 10⁹ conidia ml⁻¹ resulted in mortality of H. axyridis, in contrast, 80% of C. septempunctata and 70% of A. bipunctata exposed to 10⁷ conidia ml⁻¹ of B. bassiana succumbed to infection. The fecundity (cumulative mean egg production over 10 days) of A. bipunctata and H. axyridis (UK) was also assessed. The fecundity of C. septempunctata could not be assessed because this species requires diapause prior to the onset of reproduction and these studies were on beetles that had recently eclosed (2–8 weeks). Harmonia axyridis (Japan) produced no eggs in most treatments including the control and so was excluded from analysis. High dose (10⁹ conidia ml⁻¹) inoculation reduced the fecundity of A. bipunctata to zero but egg production was similar for individuals inoculated with doses of 10⁵, 10⁷ conidia ml⁻¹ and control individuals. In contrast, all doses of B. basssiana reduced H. axyridis (UK) egg production dramatically. We discuss these results in relation to the potential for control of H. axyridis using B. bassiana.     

Virulence of Different Isolates and Formulations of Beauveria bassiana for House Flies and the Parasitoid Muscidifurax raptor

Adult house flies (Musca domestica) were susceptible (94-100% mortality) to Beauveria bassiana when conidia of the Hf88 isolate were applied to plywood boards at 10⁷ conidia/cm²; a starch dust formulation was more effective than a liquid suspension. Adult flies were also susceptible (90-99% mortality) to this isolate when they were con fined with treated water (10⁸ conidia/ml) or food (10⁸ conidia/100 mg). House fly larvae were not affected by treatments with up to 10⁸ conidia/cm³ of rearing medium. A 2-year survey of house flies cm from New York dairies indicated that most natural infections of house flies occurred in September and October, although prevalence rates never exceeded 1%. Thirteen single-fly isolates obtained during this survey were compared with the Hf88 isolate for virulence against flies; the 2 most virulent isolates were slightly more virulent for flies than for the fly parasitoid Muscidifurax raptor. Incorporation of conidia into a sucrose bait (10⁸ conidia/100 mg) in cages gave high levels of house fly control (78-100% mortality) 5 days after exposure.     

Hirsutella thompsoniU a fungal pathogen of mites. II. Host-pathogen interactions

The moniliaceous fungus, Hirsutella thompsoniU grown on potato-dextrose agar (PDA) or on sterile wheat bran, was highly pathogenic to the carmine spider mite, Tetranychus cinnabarinus, and, grown on PDA, to the oriental spider mite, Eutetranychus orientalis. The fungus penetrated the mites' integument mainly through the legs and formed hyphal bodies in chains in the haemolymph. Hyphae, on which the spores were produced, began to emerge through the genital and anal apertures and then all over the body. Various mycophagous mites, a predaceous species and the tick Argas persicus were immune. H. thompsonii grew well on cadavers of diverse insects and mites. The fungus killed most mites and quickest, usually by the 2nd day, at 25^o, 27^o and 30 ^oC; least at 13^o and 35 ^oC. It sporulated best on mites at 24^o, 27^o and 30 ^oC (full sporulation at 27 ^oC took place within 12 h after death); it was good, but slower, at 13^o and 35 ^oC. The fungus germinated, penetrated mites and sporulated there very poorly below 100% r.h. When the daily number of hours at 100% r.h. was reduced from 24 to 18 or 6 h, fungus-associated mortality dropped greatly. In the field, use of the fungus for mite control would be suitable particularly in tropical and humid subtropical areas, and its success in Israel would not be assured. In glasshouses, H. thompsonii could induce epizootics in Israel and elsewhere only if humidities were raised to saturation and the daytime temperature kept below 37 ^oC.     

Beauveria bassiana submerged conidia production in a defined medium containing chitin,two hexosamines or glucose

Summary Beauveria bassiana in liquid culture can produce blastospores and occasionally submerged conidia. For use as a bioinsecticide, conidia have definite advantages. Numerous studies have investigated conidia production in liquid cultures using synthetic and industrial grade media supplemented with glucose. We have studied growth, development and sporulation in microcultures using growth media containing chitin monomers. For the production of submerged conidia growth media containing N-acetyl-d-glucosamine (GlcNAc) proved to be better than yeast extract-peptone-glucose (YPG), glucose plus ammonium salts (Glc+NH₄Cl) or N-acetyl-d-galactosamine (GalNAc). Sixty-one percent of the spores in the GlcNAc medium were submerged conidia with the remainder being blastospores. The concentration of submerged conidia reached 8.0 × 10⁵/ ml after two days in GlcNAc medium as compared to 8.9 × 10⁵/ml in YPG medium. Therefore, in terms of percentage of submerged conidia produced, GlcNAc medium generated more submerged conidia in spite of its lower cell yields. Growth in a medium containing chitin, a polymer of GlcNAc, resulted in 86.3% of the spores as submerged conidia exceeding 10⁶/ml after 48 h. Growth under phosphate limitation resulted in an increased percentage of submerged conidia for all media tested. Electron microscopy and spore protein analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed that structural and compositional differences exist between the spore types.     

Hirsutella thompsonii, a fungal pathogen of mites. I. Biology of the fungus in vitro

Hirsutella thompsonii, a moniliaceous fungus pathogenic to mites, grew and sporulated on sterilised wheat bran. The effects of environmental factors were studied on the fungus grown on potato-dextrose-agar (PDA). The fungus was mesothermophilic. Growth, sporulation and conidial germination were best at 25^o-30 ^oC. Conidia kept at 37 ^oC for 5 days on PDA died, but those held at 5 ^oC germinated upon a subsequent removal to 25 ^oC. Almost all conidial germ tubes survived an 8 h exposure to 3–5% r.h. and to 60% r.h., but subsequently the former grew poorly at 100% r.h. H. thompsonii sporulated equally well in continuous darkness or light, and produced typical chlorinous to light olive-green mycelium and conidia under all conditions. A 2 h exposure of naked mycelium and conidia (which have melanised walls) to u.v. irradiation failed to kill the fungus.     

Beauveria Bassiana Pathogenicity to the Citrus Rust Mite Phyllocoptruta Oleivora

The pathogenicity of Beauveria bassiana to one of the major pests of citrus crops, Phyllocoptruta oleivora, was assessed by inoculating mites with different concentrations of conidia (1×10⁶, 5×10⁶, 1×10⁷, 5×10⁷ and 1×10⁸). Treated mites were kept at controlled conditions (25 ± 0.5°C, 12 h photoperiod and 98% relative humidity) and mite survivorship was evaluated daily. Mortality was found to increase in time and was dependent on the conidia concentration, with values ranging from 24 to 91% for the lowest and highest conidia concentration, respectively. The calculated LC₅₀ on the fifth day was 4.23×10⁶ conidia/ml. Mean lethal time was 3.98, 9.79, 3.09 and 2.74 days for 5×10⁶, 1×10⁷, 5×10⁷ and 1×10⁸ conidia/ml, respectively. Conidia were found to adhere all over the mite body surface, especially at the anal region, where vegetative mycelium was found entering the mite body. We noticed the formation of small crystals inside the mite’s body that were produced during colonization of the body cavity by the fungus. This is the first report of B. bassiana pathogenicity for this species.     

An Entomopathogenic Strain of Beauveria bassiana against Frankliniella occidentalis with no Detrimental Effect on the Predatory Mite Neoseiulus barkeri: Evidence from Laboratory Bioassay and Scanning Electron Microscopic Observation

Among 28 isolates of Beauveria bassiana tested for virulence against F. occidentalis in laboratory bioassays, we found strain SZ-26 as the most potent, causing 96% mortality in adults at 1×10⁷ mL⁻¹conidia after 4 days. The effect of the strain SZ-26 on survival, longevity and fecundity of the predatory mite Neoseiulus (Amblyseius) barkeri Hughes were studied under laboratory conditions. The bioassay results showed that the corrected mortalities were less than 4 and 8% at 10 days following inoculation of the adult and the larvae of the predator, respectively, with 1×10⁷ conidia mL⁻¹ of SZ-26. Furthermore, no fungal hyphae were found in dead predators. The oviposition and postoviposition durations, longevity, and fecundity displayed no significant differences after inoculation with SZ-26 using first-instar larvae of F. occidentalis as prey in comparison with untreated predator. In contrast, the preoviposition durations were significantly longer. Observations with a scanning electron microscope, revealed that many conidia were attached to the cuticles of F. occidentalis at 2 h after treatment with germ tubes oriented toward cuticle at 24 h, penetration of the insect cuticle at 36 h, and finally, fungal colonization of the whole insect body at 60 h. In contrast, we never observed penetration of the predator''s cuticle and conidia were shed gradually from the body, further demonstrating that B. bassiana strain SZ-26 show high toxicity against F. occidentalis but no pathogenicity to predatory mite.     

Effect of acaricide resistance on reproductive ability of the honey bee mite Varroa destructor

The reproduction of pyrethroid-resistant Varroa destructor mite, a brood parasite of honey bees, was observed in Weslaco, Texas, and the results compared with known susceptible mite populations from other studies. Seven Apis mellifera colonies that had mite populations resistant to the acaricide Apistan^™ were used. Pyrethroid-resistance was confirmed when only 17% rather than 90% of mites confined in dishes containing Apistan^™ died after 12 h of exposure. The average number of eggs laid by resistant mites invading worker and drone cells was 4.4 and 5.4 respectively. This is similar to the number of eggs laid by susceptible mites in worker (4.4–4.8) or drone (4.7–5.5) cells. Also the average number of fertilised V. destructor female mites produced by resistant mites in worker (1.0) and drone (2.1) cells were similar to the number produced by susceptible mites in worker (0.9) and drone (1.9–2.2) cells. In addition, no major differences between the resistant and susceptible mite populations were observed in either worker or drone cells when six different reproductive categories and offspring mortality rates were compared. Therefore, it appears that there is little or no reproductive fitness cost associated with pyrethroid resistance in V. destructor in Texas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of relative humidity and origin of isolates of Neozygites tanajoae (Zygomycetes: Entomophthorales) on production of conidia from cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae), cadavers

Neozygites tanajoae is a very specialized fungus pathogenic to the cassava green mite (CGM), Mononychellus tanajoa, an important cassava pest introduced to Africa from the Neotropics. Conidial discharge from cadavers of CGM that died from infections with 14 isolates of N. tanajoae collected from diverse climates of Brazil was quantified to help select potential candidate strains for introduction to Africa. Studies aimed to identify isolates with lower requirements for relative humidity for sporulation and isolates that discharged more conidia during short periods of moisture. At 96 ± 0.5% RH, production of conidia was variable and even isolates from the Brazilian semi-arid region, e.g., Petrolina and Itaberaba, produced few conidia. Significant differences in the numbers of conidia produced by diverse Brazilian isolates were observed after 6, 9 and 12 h at 100% RH. At 100% RH, production of primary conidia increased considerably from an average of 57 ± 4 conidia at 6 h to 509 ± 37 conidia at 12 h. The isolate sporulating least (BIN21) discharged only 45.7% of the number of conidia produced by isolate BIN1, one of the isolates producing the most spores. Results from this study demonstrate that differences in production of conidia among isolates should be considered when selecting Neozygites isolates for new biological control introductions.     

Selection of Beauveria bassiana isolates for control of the whiteflies Bemisia tabaci and Trialeurodes vaporariorum on the basis of their virulence, thermal requirements, and toxicogenic activity

As part of a 3-fold approach to select potential mycoinsecticides for whitefly control, we evaluated infectivity, thermal requirements, and toxicogenic activity of the entomopathogenic fungus Beauveria bassiana (Ascomycota: Clavicipitaceae) under laboratory conditions. Twenty-five native B. bassiana isolates and a commercially available mycoinsecticide (based on B. bassiana) were evaluated for virulence to fourth instar nymphs of sweetpotato whitefly, Bemisia tabaci, and greenhouse whitefly, Trialeurodes vaporariorum, at a concentration of 1 × 10⁷ conidia/ml. All isolates were pathogenic for both whitefly species, whereas mortality rates varied from 3 to 85%. A second series of bioassays was conducted on 10 selected isolates using four 10-fold concentrations ranging from 1 × 10⁵ to 1 × 10⁸ conidia/ml. Median lethal concentrations (LC₅₀) of the four most virulent isolates varied from 1.1 × 10⁵ to 6.2 × 10⁶ conidia/ml and average survival time (AST) of treated nymphs from 5.9 to 7.4 days. T. vaporariorum were significantly more susceptible to all B. bassiana isolates than B. tabaci. The thermal biology of the eight most virulent isolates to both whitefly species was investigated at six temperatures (10–35 °C). The colony radial growth rate was estimated from the slope of the linear regression of colony radius on time and data were then fitted to a modified generalized β function that accounted for 90.5–99.3% of the data variance. Optimum temperatures for extension rate ranged from 23.1 to 27.1 °C, whereas maximum temperatures for fungal growth varied from 31.8 to 36.6 °C. On the basis of their virulence and thermal requirements, three isolates showed promise as candidates for whitefly management in Mediterranean greenhouses. Whilst in vitro production of macromolecular compounds toxic to Galleria mellonella larvae was not a requisite for virulence, ASTs of larvae injected with Sephadex G-25 fractions from candidate isolates ranged from 1.4 to 3.7 days compared with 5–6 days for non-toxic G-25 fractions. In addition, proteinase K treatment significantly reduced their toxic activity suggesting that they were proteins and revealing the potential of these isolates to be further improved through biotechnology to kill the pest more quickly.     

Influence of humidity on the infection of western flower thrips, <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> (Thysanoptera: Thripidae), by <Emphasis Type="Italic">Beauveria bassiana</Emphasis>

The insecticidal activity of Beauveria bassiana GHA derived from a commercial mycoinsecticide BotaniGard ES against Frankliniella occidentalis was determined in a bioassay by dipping the female adults into a conidial suspension. The 90% lethal concentration of B. bassiana GHA was estimated to be 9.7 × 10⁶ conidia/ml. The lethal times for achieving 90% mortality of thrips inoculated with a 1/500-diluted solution of BotaniGard ES and a 10^7.5 (3.16 × 10⁷) conidia/ml suspension of B. bassiana GHA were estimated to be five and six days, respectively. When the treated thrips were exposed to a high relative humidity (RH) of over 99% for various periods and then transferred to 60% RH, the requisite lengths of the high-humidity period to achieve 90% mortality of the thrips at six days after inoculation were estimated to be 46 and 47 h in BotaniGard ES and B. bassiana GHA, respectively. Fungal multiplication in the thrips was detected between 48 to 60 h after inoculation by measuring Beauveria-specific DNA in the host following inoculation with a B. bassiana GHA suspension of 10^7.5 conidia/ml using a real-time quantitative PCR. The mycelial growth in the host hemocoel was not influenced by the low-humidity condition.