玫烟色拟青霉对小菜蛾致病力的时间-剂量-死亡率模型模拟

小菜蛾Plutella xylostella是我国南方十字花科蔬菜上的重要害虫,已对田间常用的化学杀虫剂产生了严重的抗性。为寻找有效的小菜蛾生物防治措施,本实验研究了一株分离自家白蚁的玫烟色拟青霉Paecilomyces fumosoroseus (SCAU-PFCF01)对小菜蛾2～4龄幼虫的致病力。实验采用浸液法,供试浓度为1×10³、1×10⁴、1×10⁵、1×10⁶和1×10⁷个孢子/mL。结果表明：随玫烟色拟青霉孢子浓度的升高,小菜蛾的感病死亡率增加,在浓度为1×10⁷ /mL时,小菜蛾2、3和4龄幼虫的累计死亡率分别为96%、85%和80%。玫烟色拟青霉对小菜蛾各龄幼虫的致病力与供试龄期有关,其感病的敏感顺序为2龄、3龄和4龄。用时间 剂量 死亡率模型（time-dose-mortality model,TDM）对各龄幼虫的致病力数据进行模拟,所建模型均顺利通过Hosmer-Lemeshow拟合异质性检验,表明模型拟合良好,并由模型估计出了该菌株对小菜蛾各龄幼虫的致死剂量与致死时间。2龄幼虫接种后第7天、3龄幼虫接种后第5天、4龄幼虫接种后第4天的LC₅₀估计值分别为1.17×10⁴、1.44×10⁴和5.21×10⁴ /mL,LC₉₀估计值分别为1.98×10⁶、3.82×10⁷和1.29×10⁸ /mL。玫烟色拟青霉对小菜蛾幼虫的致死时间与浓度相关,供试各龄幼虫的LT₅₀值随着孢子悬浮液浓度的增加而递减,在1×10⁵～1×10⁷ /mL的范围内,2龄幼虫的LT₅₀值从3.16天降低到1.72天,3龄幼虫的LT₅₀从3.21天降低到1.83天,4龄幼虫的LT₅₀从3.69天降低到2.04天。即2龄幼虫致死所需的时间最短,其次为3龄幼虫,4龄幼虫致死所需的时间最长。结果显示了该株玫烟色拟青霉在小菜蛾的生物防治中具较强的应用潜力。     

Joint action of the entomopathogenic fungus Isaria fumosorosea and four chemical insecticides against the whitefly Bemisia tabaci

The strain IfB01 of Isaria fumosorosea (Paecilomyces fumosoroseus) is a promising myco-insecticide candidate for control of Bemisia tabaci. Joint action of strain IfB01 and four chemical insecticides [spirotetramat (Spi), acetamiprid (Ace), imidacloprid (Imi) and thiamethoxam (Thi)] against the whitefly B. tabaci was evaluated using the cooperative virulence index (c.f.). Substantial synergistic actions were found in the mixtures of IfB01 conidia with Spi, Imi and Thi 2–4 days after treatment. The greatest synergism was recorded in the mixture of IfB01 (2.5 × 10⁶ conidia/L) and Imi (12.5 mg/L), which had a c.f. value of 184 at day 3 after treatment. Furthermore, the shorter LT₅₀ values recorded in mixtures indicated that effectiveness improved when the conidia were applied with the chemical insecticides. However, no substantial synergisms were recorded with Ace and from day 5 onwards.     

Evaluation of the pathogenicity of Aschersonia aleyrodis on Bemisia tabaci in the laboratory and greenhouse

The entomopathogenic fungus Aschersonia aleyrodis (Webber) is a promising fungal species against whiteflies. In this work, the pathogenicity of A. aleyrodis isolate Aa005 against MEAM1 Bemisia tabaci (Gennadius) was evaluated under laboratory and greenhouse conditions. The bioassay results indicated that the percentage of larval mortalities was concentration and age dependent. A. aleyrodis showed high pathogenicity against second and third instars and pupae with LC₅₀ values of 7.93?×?10⁶, 1.08?×?10⁷, and 1.56?×?10^7?conidia?mL^?1, respectively. The median lethal time (LT₅₀) was lower (4.60 days) for second instars and was the highest (6.17 days) for pupae when inoculated with a concentration of 1?×?10^7?conidia?mL^?1. Weekly sampling of immatures showed that the per cent mortality caused by A. aleyrodis at a conidial concentration of 1?×?10^7?conidia?mL^?1 was 71.21% in small nymphs, 69.31% in large nymphs and 53.36% in pupae. The dispersion index (DI) and Lloyd’s Index of Patchiness (LIP) values indicated that the infected immatures had a tendency to aggregate. The study demonstrated that A. aleyrodis isolate A005 is an effective biocontrol agent for B. tabaci control under laboratory and greenhouse conditions.     

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.     

Effect of host plant on susceptibility of whitefly Bemisia tabaci (Homoptera: Aleyrodidae) to the entomopathogenic fungus Beauveria bassiana (Ascomycota: Hypocreales)

We determined host plant effect on susceptibility of whitefly Bemisia tabaci to the entomopathogenic fungus Beauveria bassiana under controlled conditions. Insects were reared on cucumber, eggplant, tomato or cabbage. Fungal suspensions of 1×10⁴, 10⁵, 10⁶, 10⁷ and 10⁸ conidia/mL were applied on second-instar nymphs. Nymphal survival significantly differed among different host plant species on which the nymphs were reared. Ten days after inoculation with 1×10⁸ conidia/mL, percent survival was 4.2±0.7, 9.6±0.4, 13.4±0.8, and 24.3±0.9% on cucumber, eggplant, tomato and cabbage, respectively. Average survival times of nymphs were also significantly influenced by host plant species. After inoculation with 1×10⁸ conidia/mL, survival times were 4.8±0.15, 6.0±0.11, 5.7±0.13, and 6.2±0.08 days for nymphs reared on cucumber, eggplant, tomato, and cabbage, respectively. Virulence also differed depending on host plant species; 10 days after inoculation, LC₅₀ values were 4.6×10⁴, 1.6×10⁵, 4.2×10⁵ and 2.1×10⁶ conidia/mL on cucumber, eggplant, tomato and cabbage, respectively. Nymphs on cucumber showed highest susceptibility.     

Time-concentration-mortality response of potato tuber moth pupae to the biocontrol agent Cordyceps tenuipes

ABSTRACT

The potato tuber moth (PTM) Phthorimaea operculella is a critical potato pest. Larvae infest both foliage and tubers and mature larvae pupate in the soil or other safe places. Cordyceps tenuipes, an entomopathogenic fungus, infect lepidopteran pupae. To determine the effectiveness of this fungus as a biocontrol agent for PTM, we evaluated the time-concentration-mortality (TCM) response of PTM pupae to C. tenuipes using the following bioassays: (1) direct immersion in conidial suspensions, (2) incubation in sterilised or (3) unsterilised soilpremixed with conidia, and (4) incubation in unsterilised soil drenched with conidial suspensions to simulate field conditions. Fungal infection caused 100%, 83.3%, 73.3%, and 85.0% mortality of PTM pupae in assays 1–4, respectively. At 10⁸ conidia/mL or conidia/g concentration, assays 1 and 4 had short lethal times (LT₅₀) of 2.2 and 2.6 days compared with 3.7 and 4.8 days for assays 2 and 3, respectively. On day 7 after inoculation, assays 1 and 4 also had low lethal concentrations (LC₅₀) of 1.69 × 10³ conidia/mL and 1.10 × 10⁵ conidia/g compared with those of assays 2 and 3, which showed low virulence, with LC₅₀ of 3.50 × 10⁵ and 3.60 × 10⁶ conidia/mL, respectively. Our results demonstrate that C. tenuipes is a promising candidate for PTM biocontrol at the pupal stage. Drenching the soil surface with conidial suspensions may be the most effective method of field application.     

Characterisation of Isaria fumosorosea isolates and their virulence toward the Diamondback Moth,Plutella xylostella

Some morphological and physiological characteristics of an Isaria fumosorosea isolate with diminished virulence, IFCF01-D, and its parent isolate, IFCF01, were evaluated and laboratory bioassays were performed to assess their virulence against Plutella xylostella. The relationship among these traits and virulence against P. xylostella is discussed. There were no significant differences in conidial viability, spore production and the time required for 50% germination (GT₅₀). Spore viability after incubation for 24 h at 25°C was greater than 98% for both isolates tested. Spore production on potato dextrose agar after 14 days incubation at 25°C was 4.68 × 10⁸ and 4.59 × 10⁸ conidia/mL for IFCF01 and IFCF01-D, respectively. When exposed to high temperatures (40, 45, 50 or 55°C) through a water bath for 10 min, conidial germination ranged from 0.83% to 84.0% for IFCF01 and 0% to 86% for IFCF01-D. Germination rate showed a negative relationship with the exposure temperature for both isolates. The per cent germination of isolate IFCF01 24 h after ultraviolet (UV) radiation (18 W, 240–260 nm) varied from 0% to 92% and 0% to 81% for IFCF01-D. Germination rate and the exposure time exhibited a negative correlation for both isolates tested. Conidial surface hydrophobicity of IFCF01 (60%) was significantly higher than that of isolate IFCF01-D (53%). Subsequently, using the cicada exuviae as the substrate for enzymatic analysis, Pr1 and chitinase activity demonstrated the contrasting virulence traits: higher specific activities for the more virulent IFCF01 and lower enzymatic levels for isolate IFCF01-D.     

Time-dose-mortality modelling and virulence indices for six strains of Verticillium lecanii against sweetpotato whitefly, Bemisia tabaci (Gennadius)

Bioassays of six strains of Verticillium lecanii (Zimmermann) Viégas were conducted with the sweet potato whitefly, Bemisia tabaci. For inoculation, batches of third‐instar whitefly nymphs on sweetpotato seedlings were immersed in conidial suspensions of five dosages at concentrations from 10³ to 10⁷ conidia/ml. Each dosage was used to inoculate 150–250 nymphs. The nymphs were maintained at 25°C, under 95% RH, photo phase of 16 : 8 (L : D) and observed daily for mortality. The resulting data were analysed over 8 days by a complementary log‐log (CLL) time‐dose‐mortality model, based on the Hosmer–Lemeshow test, analysing the time‐dose trends for five concentrations of six strains of V. lecanii simultaneously. The parameters from the model were used to estimate the virulence indices (the values of LC₅₀) of six strains against B. tabaci. Based on the time‐dose‐mortality relationships fitted and the virulence indices, the virulence of the six strains of V. lecanii for B. tabai was compared. Results indicated that the strain Vl6063 imported from Canada and the domestic strains V3450 and Vp28 derived from B. tabaci and a scale insect, respectively, were more virulent than the others with LC₅₀ values of 2.57 × 10⁵, 6.03 × 10⁵ and 6.03 × 10⁵, respectively.     

Isolation of dipicolinic acid as an insecticidal toxin from Paecilomyces fumosoroseus

Several entomopathogenic fungi produce toxins that could be used as bioinsecticides in integrated pest management programs. Paecilomyces fumosoroseus is currently used for the biological control of the whiteflies Bemisia tabaci and B. argentifolii. Supernatants from submerged batch culture, where the fungus produced abundant dispersed mycelium, conidia and blastospores, were toxic to the whitefly nymphs. The most abundant metabolite was purified by HPLC and identified by mass spectrometry and NMR as dipicolinic acid. Both the dipicolinic acid produced by the fungus and the chemically synthesized compound had insecticidal activity against third-instar nymphs of the insect. Dipicolinic acid was toxic to the whitefly nymphs in bioassays involving topical applications. In submerged culture, the specific growth rate of P. fumosoroseus was 0.054 h⁻¹, the specific glucose consumption rate was 0.1195 g g⁻¹ h⁻¹ and the specific dipicolinic acid production rate was 0.00012 g g⁻¹ h⁻¹. Dipicolinic acid was detected after 24 h when the fungus started growing; and dipicolinic acid production was directly correlated with fungal growth. Nevertheless, the yield was low and the maximal concentration was only 0.041 g l⁻¹. The maximal concentrations of conidia and blastospores (per milliliter) were 1.4×10⁸ and 7×10⁷, respectively.     

<Emphasis Type="Italic">Beauveria bassiana</Emphasis> pathogenicity to the cherry slugworm, <Emphasis Type="Italic">Caliroa cerasi</Emphasis> (Hymenoptera: Tenthredinidae) larvae

The cherry slugworm Caliroa cerasi is a significant destructive pest of sour cherries (Prunus cerasus) in Turkey. The potential of entomopathogenic fungi for controlling C. cerasi was evaluated. The effects of exposure methods and conidial concentrations (1 × 10⁶, 1.5 × 10⁶, 1 × 10⁷ and 1.5 × 10⁷ conidia/ml) on mature larvae of C. cerasi infected by Beauveria bassiana were investigated under laboratory conditions. Larvae sprayed directly with B. bassiana conidial suspensions and larvae exposed to B. bassiana-treated leaves resulted in 100% mortality within 2.90 and 2.77 days, respectively. The median lethal time (LT₅₀) and days to mortality were highest in the 1.0 × 10⁷ concentrations of conidia for both direct spray and leaf exposure. The present study suggests that B. bassiana has good potential for control of the cherry slugworm, C. cerasi.     

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.     

Host plant influences pathogenicity of Beauveria bassiana to Bemisia tabaci and its sporulation on cadavers

Laboratory bioassays were conducted to determine host plant effect on pathogenicity of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill. (Ascomycota: Hypocreales) to the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Fourth instar B. tabaci reared on cucumber, tomato, melon, green pepper, potato, eggplant, marrow, cabbage, bean or cotton, were treated with 1 × 10⁷ conidia/ml B. bassiana EABb 93/14-Tp isolate. Mortality caused by B. bassiana significantly increased with time and it was significantly affected by the host plant on which the nymphs were reared. Mean mortality of nymphs 8 days after inoculation ranged between 52.3±7.3 for nymphs reared on cotton and 91.8±5.8 for nymphs reared on cucumber. Average survival times of nymphs treated with the fungal suspensions were also significantly influenced by the host plant, with a mean of 4.7±0.1 days for nymphs reared on cucumber, 6.6±0.2 days for cotton and 6.9±0.1 days for green pepper. The production of newly formed conidia was also affected by host plant and varied from 111000±8600 conidia/cadaver for nymphs reared on cotton to 597000±28000 conidia/cadaver for those reared on melon.     

Susceptibility of Ceratitis capitata Wiedemann (Diptera: Tephritidae) to Entomopathogenic Fungi and Their Extracts

The effectiveness of seven strains of entomopathogenic fungi against Ceratitis capitata adults was evaluated in the laboratory. Adults were susceptible to five of seven aqueous suspensions of conidia. Metarhizium anisopliae and strain CG-260 of Paecilomyces fumosoroseus were the most pathogenic fungi, with 10-day LD₅₀ values of 5.1 and 6.1 × 10³ conidia/fly, respectively, when applied topically. Sublethal effects on fecundity and fertility of the fungal-exposed females were also studied. The most effective fungus in reducing fecundity was P. fumosoroseus CECT 2705, with reductions on the order of 65% at 1 × 10⁶ conidia/fly. M. anisopliae and Aspergillus ochraceus also showed significant reductions of fecundity (40–50% for most of the assayed concentrations). Fertility was moderately affected by the fungi. M. anisopliae at 1 × 10⁶ conidia/fly was the most effective fungus, showing egg eclosion reduction of over 50% compared with the control. In addition, culture broth dichloromethane extracts from the entomopathogenic fungi were tested for insecticide activity against C. capitata, including effects on fecundity and fertility. The extract from M. anisopliae was the most toxic, resulting in about 90% mortality at a concentration of 25 mg/g of diet; under these conditions, fecundity and fertility of treated females were reduced by 94 and 53%, respectively, compared with untreated controls.     

Screening of high toxic Metarhizium strain against Plutella xylostella and its marking with green fluorescent protein

Entomopathogenic fungus is proposed to be one of the best biocontrol agents against the destructive insect pest Plutella xylostella. In this study, we tested the virulence of 11 Metarhizium strain isolates against P. xylostella using a leaf dipping method, and found one strain, named 609, which had displayed the highest pathogenicity. Bioassay results showed that the accumulated corrected mortality rate was 86.7 % on the eighth day after inoculation with a spore concentration 1 × 10⁸ conidia/mL, and that the time to 50 % lethality was 5.7-day. The strain was identified as Metarhizium anisopliae var. acridum by internal transcribed spacer (ITS) region sequencing. A green fluorescent protein (GFP) marker containing vector, camben-gfp, was constructed and delivered into strain 609 by Agrobacterium tumefaciens-mediated transformation. Six positive clones expressing GFP were selected and tested for toxicity against P. xylostella, all of which displayed the same toxicity as the parental wild type strain. The survival rate of transformant T1 was investigated by monitoring GFP levels at 4-day intervals after inoculation into soil. We found that the concentration of Metarhizium spores decreased sharply from 1 × 10⁷ conidia/g to 1 × 10⁶ conidia/g in the first 5 days after inoculation. The decreasing trend then stabilized and the spore count declined to approximately 1 × 10⁴–10⁵ conidia/g after 1 month. The results of this study indicate that the expression of gfp gene in strain 609 does not alter the virulence capability of Metarhizium. This strain will therefore be useful for the control of P. xylostella and as a tool to study molecular biology properties and monitor colonization of M. anisopliae in the field.     

Effect of Beauveria bassiana on the ovarian development and reproductive potential of Anastrepha ludens (Diptera: Tephritidae)

We investigated the virulence of a native strain of Beauveria bassiana on the mortality, ovarian development, oogenesis, survival, fecundity and fertility of 4-, 8- and 12-day-old Anastrepha ludens females. In the first study, this strain caused 85% mortality in 8-day-old treated females, with a median lethal concentration (LC₅₀) of 3.1×10⁸ (2.1×10⁸–4.7×10⁸) conidia/mL and a median lethal time (LT₅₀) of 6.5 days. In the second study, the ovarian development and oogenesis of A. ludens females treated with 1×10⁹ conidia/mL were monitored daily in sacrificed flies. The fungus infection did not significantly affect ovarian development of the treated females, although there was a delay in vitellogenesis and a reduction in the quantity of mature basal oocytes and oviposition index in these flies. Moreover, the lowest net fecundity was found in 4-, 8- and 12-day-old treated females, and reduced fertility was observed in 4-day-old treated females. An application to test the potential use of this strain under field conditions is discussed.     

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.     

Enhanced mortality of Bemisia tabaci nymphs by Isaria javanica combined with sublethal doses of chemical insecticides

The aim of this current study was to evaluate the mortality of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) nymphs by the combination between the entomopathogenic fungus Isaria javanica (Friedrichs & Bally) Samson & Hywel‐Jones and synthetic chemical insecticides. The bioefficacy of I. javanica and the insect growth regulators named spiromesifen and buprofezin was tested alone and in combination against B. tabaci nymphs under screenhouse conditions. The in vitro compatibility between these two control agents was previously assessed under laboratory conditions. The sublethal concentration (LC₂₅) of these insecticides towards second‐instar nymphs was determined and then mixed with the fungal treatments to investigate the type of interaction. All I. javanica isolates at 5 × 10⁷ conidia/ml inflicted nymphal mortality by up to 62.4%. The insecticides did not influence the germination and mycelial growth of the selected I. javanica isolate CG1282. In general, the insecticide–fungus combinations increased nymphal mortalities in comparison with their single counterparts. Combinations with the fungus and buprofezin or spiromesifen augmented nymphal mortality by 10% and 24%, respectively, in comparison with the fungus alone. Additive interaction was found with the combination of the I. javanica CG1282 at 1 × 10⁶ conidia/ml and spiromesifen at 1.56 ppm, and additive and synergistic interactions were achieved with the fungus at 5 × 10⁶ conidia/ml and spiromesifen at 3.12, 6.25 and 12.5 ppm. Additive interactions were also observed from mixtures of fungus at 5 × 10⁶ and buprofezin at 3.12 and 6.25 ppm. Only combinations of I. javanica with spiromesifen reduced to some extent the mycosis on dead nymphs. The joint action of I. javanica with sublethal doses of these insecticides may be a promising tool to assist in the integrated management system for B. tabaci.     

Influence of <Emphasis Type="Italic">Lecanicillium attenuatum</Emphasis> on the development and reproduction of the cotton aphid, <Emphasis Type="Italic">Aphis gossypii</Emphasis>

The activity of entomopathogens on insect pests has been investigated for many species but the influence of entomopathogenic fungi on factors other than mortality relating to population increase has not been frequently studied. The influence of Lecanicillium attenuatum CS625 (=Verticillium lecanii CS625) on development and reproduction of cotton aphid (Aphis gossypii) was investigated. A conidia suspension of the isolate was applied onto first instar nymphs. Increased spore concentration did not significantly affect each nymphal stage, total nymphal period, pre-reproductive period and the age of first larviposition. A significant dose effect on reduction of life span, reproductive period and fecundity was observed in 1st and 3rd instars after spore application. When conidia were applied to 1st instars, life span was significantly reduced to 10.8 and 8.4 days at 1 × 10⁴ and 1 × 10⁸ conidia/ml, respectively from 12.2 days in the control. During the life span, total fecundity was 41 ± 7.3, 26 ± 0.8 and 22 ± 5.7 nymphs per female at 1 × 10⁴, 1 × 10⁶ and 1 × 10⁸ conidia/ml, respectively compared with 51 ± 2.0 nymphs per untreated female. Reproduction period was also significantly shortened with increasing spore concentration. Application of spores to 3rd instars showed a similar trend. However, daily fecundity of individual aphids was not affected by spore dose. It was concluded that the isolate of L. attenuatum is able to affect populations of cotton aphid by reducing life span and total fecundity as well as by killing the aphids directly.     

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.     

Acute oral intragastric pathogenicity and toxicity in mice of <Emphasis Type="Italic">Paecilomyces fumosoroseus</Emphasis> isolated from whiteflies

Paecilomyces fumosoroseus, monospore culture EH-506/3, isolated in Mexico from Bemisia tabaci whitefly was tested for acute oral intragastric pathogenicity and toxicity in CD-1 mice. Animals were inoculated by gavage with only one dose (10⁸ conidia/animal) of viable (72 mice), heat-killed (24 mice) fungus and compared to 18 control mice. Clinical observations were done daily; mycological and histological tests were performed during necropsies at days 3, 10, 17, and 21 after the inoculation. No mice were clinically ill or died. At the end of the study, their mean weight corresponded to healthy adults. Positive fungal cultures of feces were obtained only 24 h after inoculation. Positive cultures were found in 15 out of 360 organs (liver, spleen, kidney, brain, lung) in 12 of 72 mice inoculated with viable conidia. Gross pathology exhibited splenomegaly and liver paleness in mice inoculated with viable and heat-killed fungus. Non-germinated conidia were observed in studied organs, without any pathological tissue reaction, suggesting no mycological or histopathological evidence of fungal multiplication. The fungus was able to persist, but did not cause permanent damage to the host. This study supports the non-pathogenic/toxic status of P. fumosoroseus EH-506/3 when administered intragastrically in mice.