Effects of adjuvant and conidial concentration on the efficacy of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> for the control of the two spotted spider mite, <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Greenhouse experiments were conducted on various crops (cucumber, tomato, eggplant, green bean) to ascertain the effects of Break-thru^® (polyether-polymethylsiloxane-copolymer, a silicone surfactant) and an oil emulsion, on Beauveria bassiana (Balsamo) Vuillemin (Bb) applications for the control of the two spotted spider mite, Tetranychus urticae Koch. The objectives were to compare a) the efficacy of Bb control when applied in aqueous Break-thru^® or an oil emulsion; b) the effects of various concentrations of Bb conidia, as affected by each surfactant; and c) the effects of Break-thru^® on the activity of the fungus. Conidia were suspended either in an aqueous Break-thru^® or an emulsifiable formulation at different conidial concentrations (1.05 × 10⁶, 2.1 × 10⁶ and 4.2 × 10⁶ conidia ml^?1) and sprayed onto leaves 2 weeks after artificial pest inoculation. Two sprays were performed, with an interval of one week from one spray to another, and T. urticae population counts (both motile and egg stages) were made on plant leaves 7 days after each spray. Bb conidia in Break-thru^® were more efficacious than conidia in emulsifiable formulation. With the highest rate of conidia (4.2 × 10⁶ conidia ml^?1), mortality of adult mites ranged from 60 ± 4.2 (mean ± SE) to 85.7 ± 4.3% in the Break-thru^® suspension and 39.4 ± 7 to 61.3 ± 6% in the oil emulsion. Leaf damage index was also substantially reduced from 70% in the unsprayed control to 40% by the application of Bb conidia at the highest rate with Break-thru^®. Break-thru^® can be combined with Bb in the integrated management of T. urticae and Isolate R444 is a promising candidate for the control of the pest.     

Comparison of aerial conidia and blastospores from two entomopathogenic fungi against Diaphorina citri (Hemiptera: Liviidae) under laboratory and greenhouse conditions

This study compared the insecticidal activity of liquid culture-produced blastospores and solid substrate-produced aerial conidia of Beauveria bassiana GHA and Isaria fumosorosea ARSEF3581 strains against Diaphorina citri adults. Insects exposed to 10⁷ propagules/ml in a spray residue contact leaf bioassay died within 6 days at 25°C, with no significant differences between fungal treatments. At higher concentrations (10⁸ propagules/ml), I. fumosorosea conidia killed psyllids faster compared to its blastospore formulation, i.e. 4 versus 5 days, respectively. In greenhouse tests, the same treatments applied to infested citrus plants (2?×?10⁶ spores/ml) all significantly reduced the number of nymphs compared with the untreated controls over 3 weeks; however, only I. fumosorosea blastospores significantly reduced the number of F1 adult psyllids when compared with controls. Similar results were observed in the follow-up greenhouse test, where I. fumosorosea blastospores were the most effective treatment overall, reducing D. citri populations by about 60% after 21 days; by contrast, imidacloprid killed almost 100% of psyllids within a week in both tests. Fewer psyllids exhibited mycosis in the greenhouse (i.e. ≈20 versus?≥?87% in the laboratory). This is the first report comparing both conidial and blastospore formulations of B. bassiana and I. fumosorosea for the control of a psyllid pest. Field testing is required to determine how successful different spore formulations might be under various environmental conditions.     

Effects of crop type on persistence and control efficacy of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> against the two spotted spider mite

The influence of five different crops (beans, cucumber, eggplant, maize, and tomato) on persistence and the control efficacy of Beauveria bassiana (Balsamo) Vuillemin to Tetranychus urticae Koch was investigated. Plants were artificially infested with T. urticae. B. bassiana conidia were suspended in Break-thru^® solution (0.01%) at three different concentrations (0.5, 1, 2 g l^?1) and sprayed once onto plants. Plants in the control treatment were sprayed with Break-thru^® solution alone. The number of conidia and levels of mite mortality were evaluated. Colony forming unit counts of conidia recovered from plant leaves declined over time regardless of the concentrations of B. bassiana applied. The rate of decline was different among crops and significantly higher on maize. However, more than 50% of the initial population of conidia were still viable on crops three weeks after application. The longer persistence of B. bassiana on crops did not result in better control of mites. Rather, mortality was positively correlated to the amount of inoculum deposited on leaves immediately after spraying. Mortality of mites was concentration-dependent and influenced by the host crop, with less control observed on maize and tomato than eggplant, beans and cucumber. Results were consistent between trials conducted and confirmed the hypothesis that the type of crop can influence the efficacy of B. bassiana against T. urticae.     

Susceptibility of <Emphasis Type="Italic">Diaphorina citri</Emphasis> (Hemiptera: Liviidae) and Its Parasitoid <Emphasis Type="Italic">Tamarixia radiata</Emphasis> (Hymenoptera: Eulophidae) to Entomopathogenic Fungi under Laboratory Conditions

Diaphorina citri (Kuwayama) is a global pest of citrus that transmits the bacteria associated with the disease, Huanglongbing. Entomopathogenic fungi and the parasitoid Tamarixia radiata (Waterston) are important biological control agents of this pest and likely to interact in D. citri populations. As a basis for interaction studies, we determined the susceptibility of nymphs and adults of D. citri and adults of the parasitoid T. radiata to six fungal isolates from the species Beauveria bassiana s.l. (Bals.-Criv.) Vuill. (isolates B1 and B3), Metarhizium anisopliae s.s. (Metsch.) (Ma129 and Ma65) and Isaria fumosorosea Wize (I2 and Pae). We conducted experiments evaluating infection levels in all three insect groups following inoculation with a series of conidial concentrations (1 × 10⁴–1 × 10⁸ conidia mL^?1). Results showed that D. citri nymphs and T. radiata were more susceptible to fungal isolates than D. citri adults. Overall, B. bassiana and M. anisopliae isolates caused the greatest infection compared with I. fumosorosea isolates in all three groups of insects. Isolates B1 (B. bassiana) and Ma129 (M. anisopliae) infected a greater proportion of adults and nymphs of D. citri, respectively. Both isolates of B. bassiana caused greater infection in T. radiata compared with isolates of the other fungal species. We propose that isolates B1 and Ma129 are the strongest candidates for control of D. citri. Our results represent the first report of entomopathogenic fungi infecting T. radiata, and the basis for future studies to design a biological control programme that uses both agents more efficiently against D. citri populations.     

Insecticidal activity of entomopathogenic fungi (Hypocreales) for potato psyllid,Bactericera cockerelli (Hemiptera: Triozidae): Development of bioassay techniques,effect of fungal species and stage of the psyllid

The potato psyllid, Bactericera cockerelli (?ulc), is a pest of potato, tomato, and some other solanaceous vegetables and has also been incriminated in the transmission of a bacterial pathogen, Candidatus Liberibacter solanacearum, resulting in a serious disease known as ‘zebra chip’. Although there are several reports of fungal pathogens in psyllids, there are none from B. cockerelli, nor have any fungi been evaluated against it. Five isolates of fungi, one Beauveria bassiana, two Metarhizium anisopliae and two Isaria fumosorosea, were bioassayed against B. cockerelli on potato leaves under ideal conditions for the fungi. All applications were made with a Potter spray tower. With the exception of concentration-effect studies, all other applications were made using 10⁷ conidia/mL in a 2-mL aqueous suspension. All isolates except B. bassiana, produced 95–99% mortality, corrected for control mortality, in adults 2–3 days after application of conidia and 91–99% in nymphs 4 days after application. The corrected mortalities for adults and nymphs treated with B. bassiana were 53 and 78%, respectively, 4 days after application. I. fumosorosea Pfr 97 produced 95% corrected mortality in both first and late third instar nymphs. M. anisopliae (F 52) produced 96% corrected mortality in first and third instar nymphs. Pfr 97 and F 52 were evaluated for insecticidal activity against third instar B. cockerelli using 10⁵, 10⁶, and 10⁷ conidia per mL. Mortality produced by I. fumosorosea Pfr 97 ranged from 83 to 97% and that of M. anisopliae F 52 was 88 to 95% at these concentrations.     

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.     

Potential of a combination of entomopathogenic fungal strains and a non-ionic surfactant to control the fall armyworm (Spodoptera frugiperda)

The fall armyworm, Spodoptera frugiperda, is an emerging invasive pest in Taiwan that feeds on a wide range of crops and causes serious damage. Herein, an entomopathogenic fungal library (EFLib) was constructed to identify potential microbes to control FAW. Twenty-eight indigenous entomopathogenic fungi (EPF) were isolated and investigated for their potential pathogenicity, with Metarhizium pinghaense (Mp-NCHU-124) and Beauveria bassiana (Bb-NCHU-157) exerting dose-dependent effects on the 4th instar FAW larvae. The non-ionic surfactant Silwet L-77 rapidly killed FAW larvae after spraying at a concentration of 300 mg/kg and the toxic effect of Silwet L-77 on FAW larvae was dose-dependent. When the EPF isolates (10⁶ conidia/mL) were applied to FAW larvae in combination with the non-ionic surfactant Silwet L-77 (30–90 mg/kg), the mortality rate dramatically increased and the LT₅₀ reduced, with increased fungal mycosis (Mp-NCHU-124: 38% to 72% and Bb-NCHU-157: 20 to 62%), indicating the high compatibility of EPF with the non-ionic surfactant. Thus, the Silwet L-77+EPF combined formulation has potential for practical field application for FAW pest control and sustainable agriculture in the future.     

The potential of Beauveria bassiana inoculum formulated into a polymeric matrix for a microbial control of spruce bark beetle

Two local strains of Beauveria bassiana originally isolated from naturally infected spruce bark beetles in Slovakia were tested for their virulence to Ips typographus (IT) and for their compatibility with a polymeric matrix composed of low-molecular polyethylene. Conidia could be homogenously immobilized in the low-molecular polyethylene matrix with no adverse effect on their viability and infectivity. At constant temperature (25°C), viability of immobilized conidial decreased only by 1–2% after 7 or 14 days when compared with non-formulated conidia. In field conditions, viability of conidia formulated in the matrix was even significantly higher than non-formulated conidia 35 days after their application in traps. Conidia incorporated into the polymeric matrix were infective to IT adults in laboratory bioassays. Mean values of LC₅₀ for native conidia (0.72–2.05?×?10⁶ conidia?ml^?1) and conidia immobilized in the polymeric matrix (0.64–1.03?×?10⁵ conidia?mm^?2) demonstrated high virulence. The efficacy of the local strains was significantly higher than that of B. bassiana strains from mycoinsecticides (Boverol^®, Botanigard^® ES and Naturalis-L^®). Results showed potential of this polymeric material for its use in microbial control of IT when mixed with conidia of B. bassiana.     

Beauveria bassiana ARP14 a potential entomopathogenic fungus against Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae)

The sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), and the greenhouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae), are important pests of protected crops grown in warm climates. We compared efficacy of a new strain of the entomopathogenic fungus Beauveria bassiana (ARP14) isolated from Riptortus pedestris (Hemiptera: Alydidae) with a commercial strain (GHA) against different life stages of both B. tabaci and T. vaporariorum. Eggs, nymphs, and adults were exposed to 1 × 10⁸ conidia/mL of each strain using the leaf-dipping method. The mycosis rate of B. tabaci eggs (as a proportion) was relatively low (0.13 for B. bassiana ARP14 and 0.10 for B. bassiana GHA), while, for T. vaporariorum eggs, mycosis rate was 0.44 for B. bassiana GHA and 0.27 for B. bassiana ARP14. However, mycosis rate of 1st instars of both whiteflies was much higher than for eggs, for both strains (ARP14 and GHA). The developmental period of B. tabaci eggs exposed to ARP14 was significantly shorter than for either eggs treated with GHA or the control. For 2nd and 4th instar nymphs and adults of both whiteflies there were no differences in mycosis rates between the two B. bassiana strains. These results suggest that, B. bassiana ARP14 could be commercialized as a native biological control agent for control of B. tabaci and T. vaporariorum.     

Application of hydrophilic–lipophilic balance (HLB) number to optimize a compatible non-ionic surfactant for dried aerial conidia of Beauveria bassiana

The hydrophilic–lipophilic balance (HLB) number system was used to optimize a compatible non-ionic surfactant, TDA (polyoxyethylene tridecyl ether) in formulations for two Beauveria bassiana strains, NI8 and GHA. The optimal HLB number for TDA was determined on the basis of wetting times for conidial powders. The results indicated that optimal HLB number of TDA for B. bassiana strain NI8 was 8, while the optimum HLB number for strain GHA was 10. The optimized TDA surfactants required significantly less wetting times than the commonly used laboratory surfactants, Triton X-100, Span 80, and Tween 80. These optimized TDA surfactants were further characterized on their ability to produce conidial suspensions of the two strains after 5 min of mixing, TDA HLB 8 and TDA HLB 10 produced suspensions of 1.8 × 10⁸ and 1.6 × 10⁸ conidia/ml for NI8 and GHA, respectively. These conidial levels were significantly higher than those in Triton X-100, Span 80, and Tween 80 suspensions after the same mixing time. Germination assays showed that TDA HLB 8 promoted significantly higher germination rates of strain NI8 than those observed in other commonly used laboratory surfactants. However, the germination rates of the GHA strain were unaffected by any of the surfactants tested. The efficacy of the conidial suspensions was confirmed with assays against Lygus lineolaris. Bioassay results indicated that there were no significant differences in mortalities because of surfactants. These results suggest optimization based upon HLB number will not negatively impact parameters associated with efficacy, while providing desirable physical properties.     

Reaction of some tomato cultivars to tomato leaf curl virus and evaluation of the endophytic colonisation with Beauveria bassiana on the disease incidence and its vector,Bemisia tabaci

Tomato line LA1478 and Pusa Ruby were resistant to tomato leaf curl virus (TLCV) disease. They registered higher plant height, number of branches, total phenol content and yield per plant than the other cultivars. Variety Peto 86 was tolerant to the disease while the other popular tomato cultivars, i.e. Ace, Early Pack, Money Maker, Prichard and Strain B were highly susceptible to the disease. Plant height and number of branches per plant revealed significantly positive association with fruit yield per plant. The disease index of TLCV exhibited significant negative correlations with plant height, total phenol content and fruit yield per plant – 0–4 and 5–25 adult whiteflies were observed on resistant susceptible cultivars. In the case of epiphytically colonisation by Beauveria bassiana conidia, not all developing hyphae on the leaf surface penetrated the whitefly cuticle. Many of the germ tubes elongated to a short distance before terminating its growth. On the other hand, the rapid staining of tomato tissues injected with B. bassiana conidial suspension indicates that the entomopathogenic fungus was established inside tomato tissues until the end time of the trial. The direct injection with the spore suspension yielded high post-colonisation, where the fungus was recovered from sites distant from the point of inoculation. This indicates that the fungus has the potential to move throughout the plant tissues. Laboratory bioassay of tomato whitefly feeding on tomato tissues containing B. bassiana conidial spores indicates that plant endophytic colonisation with entomopathogenic fungi may reduce insect survival on these plants. LT₅₀ values of the test diet were between three and four days. The mortality of Bemisia tabaci was high in the case of endophytically colonisation compared to epiphytically one (90.0% compared to 10.0% during three days) for whiteflies fed tomato tissues containing 1.5 × 10⁷ B. bassiana spores/ml. Application of B. bassiana as an artificial endophyte inside tomato plants can be an important component in the integrated control of tomato whiteflies. The endophytic colonising can achieve biocontrol effect based on induced disease resistance in plant tissues. According the available references, this is the first report on B. tabaci controlling by plant endophytic treatment.     

Virulence potential of some fungal isolates and their control-promise against the Egyptian cotton leaf worm,Spodoptera littoralis

A preliminary virulence test of four fungal isolates, Beauveria bassiana IMI 382302, Beauveria bassiana IMI 386701, Trichoderma harzianum T24 and Aspergillus flavus Link against larvae of Spodoptera littoralis was performed. The most effective isolates against larvae of S. littoralis were B. bassiana 302 and T. harzianum T24, which also showed the lower percentage of pupation compared with the other two isolates under the same conditions of treatments. Three concentrations (1 × 10⁶, 1 × 10⁷ and 1 × 10⁸ ml^?1) of the aqueous conidial suspension of the four tested isolates were carried out against both larval and pupal stages of S. littoralis within five days post-treatment. T. harzianum T24 showed 80% larval mortality only when applied at the highest conidial concentration, while A. flavus showed 100% pupal mortality only, at all of its conidial concentrations. However, B. bassiana IMI 382302 showed relatively high dose-dependant larval and pupal mortalities, while strain IMI 386701 of B. bassiana showed a very weak mortality against pupae at higher concentrations, and no virulence against larvae was recorded. Enzymatic and antibiosis bioassays of the four fungal isolates showed relatively high activities against Fusarium spp. for most of the tested isolates. Clear zone of enzyme activity on agar plates proportionally increased with increasing the concentration of enzyme substrate and prolongation of the incubation period. Mtabolites produced in the agar culture inhibited the growth of Fusarium spp. and the productivity differed greatly among isolates or strains of the same isolate. Volatile and non-volatile compounds produced by A. flavus Link showed a higher inhibition activity against Fusarium spp. compared with the other fungal isolates. The humoral antifungal response of insect host is relatively high compared to the anti-bacterial one. Injection of larvae with the immune sensitive bacteria Micrococcus luteus (5 × 10³ bacteria/larva) showed a detectable humoral response by 2 h, peaked around 12 h and became hardly detectable by 24 h post-injection. Injection of larvae with conidial suspension (5 × 10³ conidia/larva) from each of the fungal isolates showed humoral antifungal activity against B. bassiana IMI 386701 and A. flavus only. This activity was detectable by 12 h, peaked around 36 h and became hardly detectable by 48 h post-injection. Although the humoral antifungal response was started slowly compared to the antibacterial one, it lasted for longer and enabled larvae to withstand the infection with these immune-sensitive fungal strains. No humoral activity was detected against B. bassiana IMI 382302, although however, weak activity was detected against T. harzianum T24 only at the low conidial concentration but not at the higher one (1 × 10⁸ ml^?1). Thus, this study concludes that larvae of S. littoralis showed immune-dependant sensitivity to T. harzianum T24 and B. bassiana IMI 382302. Therefore, this study may recommend these two fungal isolates as mycoinsecticides in the battle against cotton leaf worm in Egypt. Hence, they have been selected for future comprehensive bioassays in the laboratory under conditions similar to that in the field. This, in fact, may help for developing effective mycoinsecticides against this pest. Penetration mechanims of insect cuticle by entomopathogenic fungi will be discussed.     

Potential of Metarhizium anisopliae and Beauveria bassiana to control Dinoderus porcellus (Coleoptera: Bostrychidae) infesting yam chips

The beetle Dinoderus porcellus Lesne is a serious storage insect pest that causes important losses by destroying stocks of yam chips. In the aim to found an alternative control method to the use of synthetic insecticides for its management, the virulence of the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin (isolate Bb115) and Metarhizium anisopliae (Metschnikoff) Sorokin (isolate Met 31) against adults of D. porcellus was evaluated under laboratory conditions (25 ± 2 °C and 70 ± 5% RH). Then, the effectiveness of the most virulent entomopathogenic fungus as biological agent against D. porcellus was assessed under farmer storage conditions. For each entomopathogenic fungus isolate, four conidial concentration (0, 10⁵, 10⁷, and 10⁹ conidia/mL) at the dose of 1 µL were inoculated topically on D. porcellus adults (3–5 days old). Observations focused on insect mortality, cadaver sporulation and weight loss of yam chips. Lethal dose and lethal time values were estimated using probit analysis. Both fungal isolates at all conidial dose caused more than 50% mortality on day 7, with the highest mortality (94.44%) achieved using B. bassiana at the 10⁹ conidia/mL. LT₅₀ values for B. bassiana and M. anisopliae isolates were 2.63 and 3.35 days, respectively, while their LT₉₀ values were 6.15 and 9.87 days, respectively. Yielding the lower LD₉₀ values and the highest rates of cadaver sporulation, B. bassiana isolate appeared as the most virulent against D. porcellus. After 3 months of storage, comparatively to the control, the B. bassiana isolate at the highest conidial dose (10⁹ conidia/mL) significantly reduced D. porcellus populations, and weight loss of yam chips. This study revealed the potential of B. bassiana and M. anisoplae isolates as biological control agent against D. porcellus for yam chips protection.     

Optimal concentration of Beauveria bassiana vectored by bumble bees in relation to pest and bee mortality in greenhouse tomato and sweet pepper

Greenhouse cage trials were conducted to determine the optimal concentration of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) (BotaniGard 22WP^® formulation) as vectored by the bumble bee, Bombus impatiens (Cresson) (Hymenoptera: Apidae) pollinator for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) on greenhouse tomato, tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) and green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) on greenhouse sweet pepper. Three inoculum concentrations of B. bassiana: low, 9 × 10⁹; middle, 6.24 × 10¹⁰; and high, 2 × 10¹¹ conidia g^?1 of inoculum and two controls (one with bees and heat-inactivated inoculum, and the other which contained only the host plants and pest species) were tested in a completely randomized block design. Beauveria bassiana killed 18, 54 and 56% of the adult T. vaporariorum and 33, 70 and 67% of the adult L. lineolaris, respectively, at the low, middle and high concentrations; but no infection from B. bassiana occurred in each of the control treatments. Internal infection rates after surface sterilization of the pest insects were 11, 34 and 35% for adult T. vaporariorum, 29, 54 and 58% for adult L. lineolaris, 22, 34 and 30% for nymphal M. persicae and 17, 29 and 32% for nymphal T. vaporariorum, respectively, at the low, middle and high concentrations. Significantly more bumble bees died at the high concentration of B. bassiana (42–45%) than at the other concentrations (9–15%) and the controls (5–7%). Spores of B. bassiana were collected throughout the plant canopy with the greatest numbers sampled from the top third of the canopy [ca. 1,200 colony forming units (CFU) per cm^?2]. The middle concentration was selected as the optimal concentration because it provided the best pest control with the least impact on the bees.     

Host plants influence susceptibility of whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to the entomopathogenic fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae)

We quantified the tritrophic effect of host plant on the susceptibility of the sweetpotato whitefly Bemisia tabaci (Genn.) to a fungal pathogen in the laboratory. Second-instar whiteflies reared on cucumber, eggplant, tomato and bean plants for six generations were exposed to conidial suspensions of Isaria fumosorosea isolate IF-1106. Our results did not detect differences in response (proportional survival or median lethal time, LT₅₀ days) among insect populations derived from different plants that were treated with 10⁷ conidia/ml. However, at concentrations ≤ 5×10⁶ conidia/ml, whiteflies reared on bean and tomato died significantly more quickly (i.e. LT₅₀ of 4–5 days) compared with cucumber and eggplant reared populations (5–7 days). Bean and tomato-reared populations were also more susceptible to mycosis (LC₅₀ ≈ 6 × 10⁵ conidia/ml) compared with those reared on cucumber (1.9 × 10⁶ conidia/ml) and eggplant (1.5 × 10⁶ conidia/ml). A separate study confirmed that this differential response of whitefly populations to I. fumosorosea was not explained by differences in deposition rate of conidia on leaf surfaces (i.e. a dosage effect). Our findings show that host plants affect the pathogenicity and virulence of a herbivore pathogen, but depend on the rate of exposure (inoculum) applied.     

New records of entomopathogenic fungi infecting Bemisia tabaci and Trialeurodes vaporariorum, pests of horticultural crops, in Argentina

The whiteflies Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) are major crop pests throughout the world. Although extensive research about biological control of whitefly by parasitoids and predators has been conducted, also entomopathogenic fungi can be considered as potential biological control agents. Surveys for entomopathogenic fungi were carried out in organic and conventional horticultural crops in greenhouses and open fields in Buenos Aires and Corrientes provinces, Argentina. These surveys resulted in the recovery and isolation of the following fungi from whiteflies: Lecanicillium lecanii (Zimmerm.) Zare & W. Gams, L. muscarium (Petch) Zare & W. Gams, L. longisporum (Petch) Zare & W. Gams, Isaria fumosorosea Wize and I. javanica (Frieder. & Bally) Samson & Hywel-Jones. Pathogenicity tests were conducted against T. vaporariorum nymphs using a conidial suspension (1 × 10⁷ conidia/ml) of the fungi. A mortality rate between 26.6% and 76.6% was obtained at 7 days post-infection. These are the first records of natural infections in the southernmost region of the South American continent of L. lecanii, L. muscarium, L. longisporum and Isaria javanica (Ascomycota: Hypocreales) on T. vaporariorum and also the first report of I. fumosorosea on B. tabaci.     

Influence of commercial fungicides on the germination,growth and virulence of four species of entomopathogenic fungi

The influence of 15 commercially available fungicides on the germination, growth and virulence of Metarhizium anisopliae, Beauveria bassiana, Isaria fumosorosea, and Lecanillium longisporum was evaluated. The influence of the fungicides on conidial germination was dependant on the fungicide type and dose. Most fungicides retarded conidial germination of all the fungi tested at 10× and at the recommended rate of application, however, their toxicity declined at lower concentrations. Most of the fungicides inhibited mycelial growth of B. bassiana, whereas L. longisporum growth was unaffected. Only two and eight fungicides influenced mycelial growth of I. fumosorosea and M. anisopliae, respectively. None of the fungicides influenced the virulence of B. bassiana and L. longisporum, however, tolylfluanid and azoxystrobin reduced the virulence of M. anisopliae and I. fumosorosea, respectively. These studies clearly show that certain fungicides have the potential to inhibit germination of entomopathogenic fungi in vitro but appear to have little or no effect on their virulence against target insects.     

Characterization and virulence of <Emphasis Type="Italic">Lecanicillium lecanii</Emphasis> against different aphid species

Seven isolates of Lecanicillium lecanii (Zimmermann) Zare &; Gams isolated in Spain from infected aphids were characterized using sequences of the Internal Transcribed Spacer (ITS) regions and also based on morphological and physiological characteristics. Four of these seven L. lecanii isolates were selected to assess their virulence against nymphs of Myzus persicae (Sulzer), Nasonovia ribisnigri (Mosley), Macrosiphum euphorbiae (Thomas) and Aphis gossypii Glover. Mortality (%), lethal concentration 50 (LC₅₀) and lethal time 50 (TC₅₀) were calculated. The analysis of the sequences of ITS region confirmed that the new isolates were clearly Lecanicillium lecanii. The set of isolates had similar radial growth (51.5–54.0 mm), except for ICAL1 (39 mm). The germination time 50 (GT₅₀) varied between 10.7 h (ICAL3) and 13 h (ICAL5). The isolate ICAL6 showed the highest value for conidial production (3.4 × 10⁸ con ml^?1) and also produced the highest mortality for M. persicae (95%) and was more virulent than the commercial product Vertalec^® (91.6%).     

Enhanced conidial thermotolerance and field efficacy of Beauveria bassiana by saccharides

Insecticide efficacy of Beauveria bassiana conidia was improved by optimizing the concentrations of conidial heat-protective saccharides (glucose, sucrose, maltose, trehalose, α-lactose, and mannitol) using response surface methodology. Two field trials in tea gardens were carried out to control leafhopper (Empoasca vitis) by spraying B. bassiana conidia together with the optimized saccharides (0.26 g glucose, 0.28 g lactose, 0.24 g mannitol per ml). In the field studies, B. bassiana conidia were applied to control Empoasca vitis with and without saccharides and compared with bifenthrin, a pyrethroid insecticide. With the optimal concentrations of saccharides, the conidial germination rate reached 72 % and the control efficacy of the saccharides group (65.7 %) was equal to the bifenthrin group (69.4 %), which improved by about 55 %.