Relative susceptibility of <Emphasis Type="Italic">Spodoptera litura</Emphasis> pupae to selected entomopathogenic fungi

The pupae of Spodoptera litura (Fab.), (Lepidoptera: Noctuidae), a polyphagous pest affecting common crops in Indian subcontinent, were treated with different concentrations of conidia of four isolates of entomopathogenic fungi belonging to three species, Metarhizium anisopliae var. anisopliae (Metschnikov) Sorokin (ARSEF 7487), Lecanicillium muscarium (Petch) Zare & W Gams (two isolates ARSEF 7037 and ARSEF 6118) and Cordyceps cardinalis Sung & Spatafora (ARSEF 7193) under laboratory conditions. Suspensions (10⁸/ml) of conidia harvested from Sabouraud dextrose agar yeast extract (SDAY) plates resulted in the highest mortality (85.8%) with M. anisopliae and the lowest mortality (57.3%) with C. cardinalis. The values of LC₅₀ and LC₉₀ suggested that M. anisopliae was the most virulent fungal strain followed by L. muscarium (ARSEF 7037). However, C. cardinalis was the least virulent species among the fungi used in the bioassay. In soil bioassays, drenching the soil with conidial suspensions of ARSEF 7487 and ARSEF 7037 (10⁸ conidia/g of soil) reduced the adult emergence from pupa by 81.3% and 72.5%, respectively, while premixing the sterile soil with conidia killed lesser number of pupae (62.9% by ARSEF 7487 and 54.6% by ARSEF 7037). Our findings suggest that M. anisopliae (ARSEF 7487) and L. muscarium (ARSEF 7037) are potent entomopathogens and could be developed into biocontrol agents against rice cutworm in IPM programs. Handling editor: Helen Roy     

Isolation and virulence of entomopathogenic fungi against the great spruce bark beetle,Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae)

Twelve fungal strains including Lecanicillium muscarium (Petch.) Zare and Gams, Isaria farinosa (Holmsk.) Fr., Fusarium sp., Beauveria bassiana Sensu Lato and Beauveria sp. were isolated from larvae and adults of D. micans. In addition, virulence of these isolates against this pest was determined. Conidia suspensions of 1×10⁶ conidia mL^–1 were applied to larvae and adults. The highest mortality and mycosis for larvae were obtained from isolate ARSEF 9271 (Beauveria bassiana) with 90% mortality and mycosis within 10 days. ARSEF 9271 also produced 93% mortality and mycosis in adults. On the other hand, the highest mortality and mycosis for adults were obtained with isolate ARSEF 9272 (Beauveria sp.), with 100% mortality and 80% mycosis within 10 days. These results indicate that isolates ARSEF 9271 and ARSEF 9272 seem to be the most promising potential fungal biocontrol agents against D. micans.     

Effects of successive subculturing on stability, virulence, conidial yield, germination and shelf-life of entomopathogenic fungi

Aims: To determine the stability and conidial yield of two strains of the entomopathogenic fungus Metarhizium anisopliae and one strain of M. brunneum, being developed for the control of insect pests. Methods and Results: The conidial yields and the shelf‐life of the conidia of two commercially viable strains of M. anisopliae V275 (=F52) and ARSEF 4556 and one strain of M. brunneum (ARSEF 3297) were determined after harvesting conidia from in vitro subcultures on Sabouraud dextrose agar (SDA) and broken basmati rice. The strains were stable and showed no decline in virulence against Tenebrio molitor, even when subcultured successively 12 times on SDA. Conidia‐bound Pr1 protease activity decreased in conidia harvested from SDA and mycosed cadavers after the 1st subculture, but increased in conidia produced on rice. The C:N ratio of conidia from mycosed cadavers was lower than that of conidia from rice or SDA. Irrespective of the number of subcultures, strain ARSEF 4556 produced significantly higher conidial yields than ARSEF 3297 and V275. The 12th subculture of V275 and ARSEF 3297 produced the lowest conidial yield. Shelf‐life studies showed that conidia of strain ARSEF 4556 had a higher conidial viability than V275 and ARSEF 3297 after 4 months, stored at 4°C. Conclusions: The current study shows that determining strain stability and conidial yield through successive subculturing is an essential component for selecting the best strain for commercial purposes. Significance and Impact of the Study: This is the first study to compare quality control parameters in the production of conidia on rice, and it shows that the level of Pr1 is comparatively high for inoculum produced on rice.     

Selection of promising fungal biological control agent of the western flower thrips Frankliniella occidentalis (Pergande)

Aims: Larval stages of Frankliniella occidentalis are known to be refractory to fungal infection compared with the adult stage. The objective of this study was to identify promising fungal isolate(s) for the control of larval stages of F. occidentalis. Methods and Results: Ten isolates of Metarhizium anisopliae and eight of Beauveria bassiana were screened for virulence against second‐instar larvae of F. occidentalis. Conidial production and genetic polymorphism were also investigated. Metarhizium anisopliae isolates ICIPE 7, ICIPE 20, ICIPE 69 and ICIPE 665 had the shortest LT₅₀ values of 8·0–8·9 days. ICIPE 69, ICIPE 7 and ICIPE 20 had the lowest LC₅₀ values of 1·1 × 10⁷, 2·0 × 10⁷ and 3·0 × 10⁷ conidia ml^?1, respectively. Metarhizium anisopliae isolate ICIPE 69 produced significantly more conidia than M. anisopliae isolates ICIPE 7 and ICIPE 20. Internally transcribed spacers sequences alignment showed differences in nucleotides composition, which can partly explain differences in virulence. Conclusion: These results coupled with the previous ones on virulence and field efficacy against other species of thrips make M. anisopliae isolate ICIPE 69 a good candidate. Significance and Impact of the Study: Metarhizium anisopliae isolate ICIPE 69 can be suggested for development as fungus‐based biopesticide for thrips management.     

Conidial water affinity is an important characteristic for thermotolerance in entomopathogenic fungi

The interspecific thermotolerance of several species of entomopathogenic fungi was evaluated based on the conidial water affinity. The species were divided between hydrophilic and hydrophobic conidia. The species with hydrophobic conidia were Beauveria bassiana (ARSEF 252), Metarhizium brunneum (ARSEF 1187), Metarhizium robertsii (ARSEF 2575), Isaria fumosorosea (ARSEF 3889) and Metarhizium anisopliae s.l. (ARSEF 5749). The species with hydrophilic conidia were Tolypocladium cylindrosporum (ARSEF 3392), Tolypocladium inflatum (ARSEF 4877), Simplicillium lanosoniveum (ARSEF 6430), Lecanicillium aphanocladii (ARSEF 6433), S. lanosoniveum (ARSEF 6651), Aschersonia placenta (ARSEF 7637) and Aschersonia aleyrodis (ARSEF 10276). The conidial surface tension of each isolate was also studied. Conidial suspensions were exposed to 38, 41 or 45 °C. After exposure, the suspensions were inoculated on media and conidial germination was evaluated. Considerable differences in thermotolerance were found among the 12 entomopathogenic fungal species. Species with hydrophobic conidia were generally more thermotolerant than species with hydrophilic conidia. All isolates with hydrophobic conidia showed higher conidial surface tension than the isolates with hydrophilic conidia.     

Virulence of entomopathogenic hypocrealean fungi infecting <Emphasis Type="Italic">Anoplophora glabripennis</Emphasis>

Twenty isolates of four species of entomopathogenic hypocrealean fungi (Beauveria bassiana, Beauveria brongniartii, Isaria farinosa, and Metarhizium anisopliae) were found to be pathogenic to adults of the Asian longhorned beetle, Anoplophora glabripennis. Survival times for 50% of the beetles tested (ST₅₀) ranged from 5.0 (M. anisopliae ARSEF 7234 and B. brongniartii ARSEF 6827) to 24.5 (I. farinosa ARSEF 8411) days. Screening studies initially included strains of B. brongniartii, which is registered as a microbial control agent in Europe, Asia and South America but not in North America. At that time, we could not confirm that this fungal species is native to North America which added uncertainty regarding future registration of this species for pest control in the USA. Therefore, subsequent bioassays documented median survival times for three M. anisopliae isolates (5–6 days to death) and two of these isolates are suggested for further development because they are already registered for pest control in the USA. An erratum to this article can be found at     

Reduction in fitness of female Asian longhorned beetle (Anoplophora glabripennis) infected with Metarhizium anisopliae

Bioassays were conducted to document the effects of Metarhizium anisopliae infection on adult female Asian longhorned beetle (Anoplophora glabripennis) reproduction before death and subsequent survival of offspring. The effect of infection on fecundity was evaluated for females already laying eggs and for newly eclosed females using M. anisopliae isolates ARSEF 7234 and 7711, respectively. Decreased longevity and oviposition compared with controls were observed in females that were already laying eggs when exposed to M. anisopliae ARSEF 7234. Newly eclosed females exposed to M. anisopliae ARSEF 7711 displayed shortened longevity (10.0 ± 0.7 days vs 74.3 ± 6.8 days for controls) and decreased oviposition (1.3 ± 0.7 eggs per ARSEF 7711-exposed female vs 97.2 ± 13.7 eggs per female for controls) compared with controls. Percentages of eggs that did not hatch were greater for both groups of fungal-treated females compared with controls and 60.0% of unhatched eggs contained signs of fungal infection. The percentage of larvae dying within 9 weeks of oviposition was higher for sexually mature females exposed to ARSEF 7234 compared with controls and >40% of dead larvae displayed signs of fungal infection. Thus, for both stages of females and both fungal isolates, fewer surviving larvae were produced after female fungal infection compared with controls. M. anisopliae infection affects female fitness by decreasing female longevity, by decreasing female oviposition before death and through horizontal transmission of M. anisopliae to offspring.     

LABORATORY SUSCEPTIBILITY OF PLUTELLA XYLOSTELLA TO METARHIZIUM ANISOPLIAE AND NOMURAEA RILEYI*

Abstract Five isolates of Metarhizium anisopliae and one isolate of Nomuraea rileyi were bioassayed against larvae of Plutella xylostella. Larvae were treated by exposing cabbage leaf discs previously immersed in conidial suspension, and were then incubated at 25^oC and observed daily. One of M. anisopliae isolates, F11248, originally from Mastotermes darwiniensis was found being most virulent against P. xylostella. The LC₅₀ was estimated as 2.03 times 10⁴conidia/ml with 9 d mortality data, and the LT₅₀ was 4.97 d at concentration of 10⁷conidia/ml. Isolate F163 (N. rileyi) showed virulence to P. xylostella in both tests, but no cadavers sporulated.     

Evaluation of Metarhizium anisopliae for the control of Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae), the principal vector of bluetongue virus in Australia

Four isolates of the entomopathogenic fungus Metarhizium anisopliae were tested for their potential to control the biting midge Culicoides brevitarsis, the principal vector of bluetongue virus in Australia. Adult C. brevitarsis died three to eight days after walking on paper substrate treated with 0.7 g/m² conidia of any of the isolates, indicating that M. anisopliae has potential as a surface treatment or topical application control strategy. Incorporation of the fungus into freshly excreted cattle dung at rates of between 0.25 and 1 g conidia/kg reduced the emergence of adult midges by up to 98.5% compared to untreated dung indicating that M. anisopliae has the potential to control C. brevitarsis larvae in cattle dung. Three of the isolates produced similar mortality rates on adult and immature C. brevitarsis while the fourth isolate produced lower, but still significant, mortality rates on adult and immature stages.     

Impact of culture age on conidial germination,desiccation and UV tolerance of entomopathogenic fungi

The impact of culture age on conidial yields, germination and tolerance to UV exposure of freshly harvested and dry conidia produced by five entomopathogenic fungal (EPF) isolates was studied. Beauveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii and Lecanicillium muscarium were grown on potato dextrose agar (PDA) medium for 7 or 14 days at 25°C. While the age of cultures had a significant impact on the germination rate of conidia produced by isolates L. lecanii CBS 122.175 and B. bassiana LMSA 1.01.093, other EPF isolates germinated at the same rate regardless of the culture age. When exposed to UV radiation, conidia produced by all isolates germinated at a lower rate compared to the non-irradiated conidia, although this decrease in germination (20–80% decrease) was unaffected by the culture age. Air-drying had only a slight impact on conidial germination (0–60% decrease). Under the conditions of this study, the stability of irradiated conidia produced by M. anisopliae LMSA 1.01.197 and B. bassiana CBS 110.25 was significantly increased when conidia were dried prior to UV exposure. This increase in tolerance to stress of dried conidia might be caused, at least partially, by the low metabolic activity associated with dehydration.     

Virulence of Hypocreales fungi to pecan aphids (Hemiptera: Aphididae) in the laboratory

There is need for efficacious biocontrol agents for aphids in commercial orchards. As a preliminary step to this end we determined the virulence of several Hypocreales fungi to pecan aphids. In the first experiment we tested the virulence of Isaria fumosorosea (ARSEF 3581) blastospores to three pecan aphids Monellia caryella, Melanocallis caryaefoliae, and Monelliopsis pecanis under laboratory conditions. Rates of 1 × 10⁷ or 1 × 10⁸ spores per ml were applied in 2 ml via a spray tower to 90 mm Petri dishes containing 10 aphids each. Mortality and mycosis were determined after 24, 48 and 72 h. Treatment effects were observed by 48 h post-application, and by 72 h the higher application rate caused >90% mortality and mycosis in M. caryella and M. caryaefoliae, whereas <70% was observed in M. pecanis.We conducted two subsequent experiments (Experiments 2 and 3), using the same methodology, to compare the virulence of several Hypocreales species and strains against the aphid of primary economic concern to most pecan growers, M. caryaefoliae. In Experiment 2, we compared blastospores and conidia of two I. fumosorosea strains (ARSEF 3581 and ATCC 20874 [= strain 97]). The blastospores of ARSEF 3581 and conidia of ATCC 20874 showed higher virulence than other treatments and thus were included in Experiment 3, which also compared the virulence of conidia of Beauveria bassiana (GHA strain) and Metarhizium anisopliae (F52 strain). Results in Experiment 3 indicated the highest virulence in I. fumosorosea 3581 blastospores and M. anisopliae (F52) followed by I. fumosorosea (20874) conidia. The detection of pathogenicity to pecan aphids establishes the potential for commercial usage and additional study. Results reported here will narrow treatments to test in future greenhouse and field trials.     

不同寄主来源的根虫瘟霉菌株对小菜蛾幼虫的毒力比较

在不同寄主来源的4株根虫瘟霉Zoophthora radicans对小菜蛾 Plutella xylostella 2龄幼虫的生物测定中,发现源于小菜蛾的菌株ARSEF1100毒力最强,在0.53～319.32/mm²的孢子剂量下,接种后第8 天累计死亡率为2.38%～97.44%,虫尸全部表现典型的虫瘟霉症状;源于叶蝉的ARSEF2699和F99101菌株的同日累计死亡率分别为2.38%～50.00% (剂量为1.56～314.84/mm²孢子)和2.38%～57.89% (剂量为1.84～484.08/mm²的孢子);而源于菜粉蝶的ARSEF1342菌株在3.54～633.0/mm²的孢子剂量下只引发6.52%～13.63%的累计死亡率,后3个菌株致死的小菜蛾幼虫仅部分表现典型症状。所获数据经时间剂量-死亡率模型模拟分析,剂量效应参数依次为ARSEF1100 (1.89) > F99101 (1.48) > ARSEF2699 (1.23) > ARSEF1342 (0.37),相互间差异均达极显著水平。接种后4～8 天内,ARSEF1100的LD₅₀值分别为231.68、113.08、71.41、40.87和35.30/mm²的孢子,其毒力远高于其余3个菌株;ARSEF2699的相应LD₅₀值为1344.43、922.39、555.58、410.06和397.07/mm²的孢子;F99101的LD₅₀值为666.86、451.64、413.82、350.65和332.57/mm²的孢子,而ARSEF1342的毒力太弱难以估计。这些结果表明,ARSEF1100菌株最有希望用于小菜蛾的微生物防治。     

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.     

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).     

Identification of Metarhizium strains highly efficacious against Aedes,Anopheles and Culex larvae

Entomopathogenic fungi, such as Metarhizium anisopliae and Beauveria bassiana, have been shown to be efficacious in killing mosquito larvae of different mosquito species. The current study compared the pathogenicity and efficacy of two formulations of three fungal strains against different instars of three mosquito species with the aim of identifying the most virulent strain for use under field conditions. Three strains of Metarhizium, ARESF 4556, ARSEF 3297 and V275, were assayed against early (L_2?3) and late (L_3–4) instar larvae of Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. Two formulations of the fungi were tested, dry conidia and aqueous suspensions (i.e. ‘wet’ conidia). Effects of all combinations of conidia, mosquito species, instar, fungal strain and concentration on mosquito mortality were analysed using Cox regression and Kaplan–Meier analyses. Strain ARSEF 4556 was more virulent than ARSEF 3297 and V275, with LT₅₀ values ranging from 0.3 to 1.1 days, with Anopheles and Culex being more susceptible than Aedes. Early and late instars were equally susceptible independent of species. Although the formulation did influence mortality rates, both ‘wet’ and ‘dry’ conidia applications were highly effective in killing mosquito larvae. Viable spores were more efficacious than heat killed spores. The latter did cause mortality but only at high concentrations. Metarhizium sp. has proved to be effective in reducing survivability of all larval stages of Aedes, Anopheles and Culex under laboratory conditions. Aedes larvae were generally more tolerant than Anopheles and Culex irrespective of fungal strain.     

Isolation and identification of entomopathogenic fungus from Eastern Ghats of South Indian forest soil and their efficacy as biopesticide for mosquito control

The repeated usage of chemical insecticides, responsible for insecticide resistance in mosquitoes and environmental toxicity. Currently effective and environmental-safe control strategies are needed for the control disease-vector mosquitoes. Entomopathogens can be an effective alternative to chemical insecticide. Herein we isolated and tested 46 soil-borne entomopathogenic fungi belonging to six genera, namely Beauveria sp., Metarhizium sp., Fusarium sp., Aspergillus sp., Trichoderma sp., and Verticillium sp., fungi conidia were tested on Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus larvae. Bioassays results show that M. anisopliae fungal isolate causes a 100%, 98.6% and 92% mortality within six days, on Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus, respectively. M. anisopliae treated three mosquito larvae have lower lifetime with LT₅₀ values in A. stephensi, 2.931 days; A. aegypti, 2.676 days and C. quinquefasciatus, 3.254 days. 18 s rDNA sequence analysis confirmed that the isolated fungus are belonging to the genus of M. anisopliae-VKKH3, B. bassiana-VKBb03, and V. lecanii-VKPH1. Our results clearly show that M. anisopliae has good potential, as a low-cost, environmentally safe tool for the control of A. aegypti, A. stephensi, and C. quinquefasciatus mosquitoes.     

Lethal effects of Gliocladium virens,Beauveria bassiana and Metarhizium anisopliae on the malaria vector Anopheles albimanus (Diptera: Culicidae)

Control of Anopheles albimanus, the main vector of malaria on the coast of the State of Chiapas, is based mainly on application of chemical insecticides, which has resulted in resistance to most registered insecticides. Strategies for biological control may provide sustainable alternatives. We report on the lethal effects of a native isolate of Gliocladium virens on An. albimanus larvae and adults, compared to that of strains of Beauveria bassiana and Metarhizium anisopliae. Conidial suspensions of G. virens, B. bassiana and M. anisopliae cultured on Sabouraud agar were tested in bioassays with An. albimanus larvae and adults. Mosquito larvae were more susceptible to all fungi, compared to adults. On early and late instar larvae, M. anisopliae showed the most pathogenic effect (LC₅₀ of 1.4×10⁵ conidia/mL in early instars; 1.1×10⁵ conidia/mL in late instars), followed by G. virens (LC₅₀ of 3.3×10⁵ conidia/mL in early instars and 3.5×10⁶ conidia/mL in late instars). Metarhizium anisopliae sensu lato and the native G. virens could be considered good choices for An. albimanus control in southern Mexico.     

The development and multiple uses of a standardised bioassay method to select hypocrealean fungi for biological control of aphids

A technically standardised bioassay method was designed, evaluated and used to assess virulence and host range of hypocrealean fungi against aphids. A track mounted sprayer was used to apply conidia because hand held versions of the same sprayer can be used for field applications, thereby allowing the outcome from laboratory experiments to predict activity in the field accurately. Eighteen fungal isolates were assessed in single concentration bioassays against the black bean aphid Aphis fabae Scopoli. Isolates comprised commercially available mycoinsecticides (based on Beauveria bassiana and Lecanicillium longisporum) and isolates of B. bassiana, Lecanicillium spp., Paecilomyces fumosoroseus and Metarhizium anisopliae. Aphid mortality was in excess of 80% for 15 isolates, and HRI 1.72 (L. longipsorum), Z11 (P. fumosoroseus), Mycotech strain GHA (B. bassiana) and ARSEF 2879 (B. bassiana) were studied further. Multiple concentration bioassays identified HRI 1.72 as the most virulent isolate against A. fabae with significantly smaller LC₅₀ and LT₅₀ values compared to other isolates. A precise LC₅₀ value (2.95 × 10² conidia ml⁻¹) was calculated for HRI 1.72 using a second multiple concentration assay with smaller concentrations of conidia. The four isolates were applied at a single concentration (1 × 10⁸ conidia ml⁻¹) against Myzus persicae, A. fabae, Acyrthosiphon pisum, Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi. A ranking of aphid susceptibility was obtained, such that S. avenae > M. persicae, A. pisum, A. fabae > R. padi. Results indicate the importance of standardising bioassay methods to reduce bioassay variability without compromising the ability to use the bioassay to investigate fungus–host interactions under varying abiotic and biotic conditions.     

Transmission of <Emphasis Type="Italic">Metarhizium brunneum</Emphasis> conidia between male and female <Emphasis Type="Italic">Anoplophora glabripennis</Emphasis> adults

Transmission of conidia between mates of the Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), was studied using two isolates of the entomopathogenic fungus Metarhizium brunneum Petch (Hypocreales: Clavicipitaceae) (formerly M. anisopliae). After one beetle was inoculated and caged with a mate for 6 h, conidia were rinsed off each beetle using Tween-80 and pentane to count conidia transferred. Treated males transmitted more conidia to females than treated females transferred to males. Untreated partners did not die as quickly as their inoculated mates, but died significantly faster than controls. For beetles inoculated with ARSEF 7711, the difference in time to death between inoculated beetles and their untreated mates was shorter when males were inoculated than when females were inoculated. We hypothesize that greater conidial transmission from males to females was due to their relative positions during copulation and the prolonged post-copulatory mate-guarding characteristic of males.     

Comparative laboratory studies on three fungal pathogens of the elm bark beetle Scolytus scolytus: Pathogenicity of Beauveria bassiana,metarhizium anisopliae, and Paecilomyces farinosus to larvae and adults of S. scolytus

The entomogenous fungi Beauveria bassiana (nine isolates), Metarhizium anisopliae (seven isolates), and Paecilomyces farinosus (four isolates) were tested as pathogens of larvae of the elm bark beetle, Scolytus scolytus. Single isolates of B. bassiana and M. anisopliae were also tested against adult beetles. Of the 21 isolates tested as conidial suspensions against larvae, all proved pathogenic. The three most and least virulent isolates were, respectively, isolates of B. bassiana and M. anisopliae. The other isolates fell between these two extremes, with the four P. farinosus isolates all moderately virulent. Spore retention on larvae following inoculation was estimated by washing conidia off the larvae. From the results it was possible to relate larval mortality to the approximate spore dose causing infection at different spore concentrations. Thus, application of spores of the three pathogens at a concentration of 10³ spores/ml resulted in limited mortality. At this concentration, an average of only a single spore was recovered from the inoculated larva. Adult bark beetles also proved susceptible to infection by isolates of B. bassiana and M. anisopliae. They were exposed to discs of elm bark dipped in a conidial suspension. It was estimated that a dose of less than 100 spores could cause infection of beetles following feeding on the elm bark discs.