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.     

Performance of a semiochemical‐baited autoinoculation device treated with Metarhizium anisopliae for control of Frankliniella occidentalis on French bean in field cages

The performance of an autoinoculation device was evaluated in field cage experiments for control of Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in French bean, Phaseolus vulgaris L. var. Samantha (Fabaceae). Treatments consisted of a fungus‐treated device with and without semiochemical (Lurem‐TR), and a fungus‐free device as control; the fungus used was Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae). The overall mean number of conidia acquired by a single insect was higher in the fungus‐treated semiochemical‐baited device than in the device without semiochemical: 5.0 ± 0.6 × 10⁴ vs. 2.2 ± 0.4 × 10⁴ conidia per insect. The overall thrips mortality was also higher in the semiochemical‐baited device than in the device without the semiochemical: 59.3 ± 3.9 vs. 41.7 ± 3.5%. Conidial viability was not affected in the M. anisopliae‐treated device without semiochemicals, 7 days after treatment, whereas it was considerably decreased – from 81.0 ± 1.3 to 6.5 ± 1.1%, 2 and 7 days post‐inoculation – in the M. anisopliae‐treated semiochemical‐baited device. Thrips mortality was positively correlated with M. anisopliae conidial viability, and conidial viability was negatively correlated with conidial acquisition. This suggests that the semiochemical volatiles reduced the conidial viability, which in turn resulted in significant reduction in thrips mortality, despite the highest conidial acquisition in the semiochemical‐baited fungus‐treated device. Thrips density per plant was significantly reduced in both fungus‐treated treatments (with semiochemical: 8.7 ± 1.7 adults per plant; without semiochemical: 6.6 ± 1.4 adults per plant) compared with the fungus‐free control (19.8 ± 2.6 adults per plant). These results demonstrate the potential for an autoinoculation device strategy for the control of thrips, particularly in screenhouses.     

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.     

Importance of timing of application of the entomopathogenic fungus,metarhizium anisopliae for the control of legume flower thrips,megalurothrips sjostedti and its persistence on cowpea

Field experiments were conducted for two seasons to evaluate the timing of application of the entomopathogenic fungus, Metarhizium anisopliae for the control of legume flower thrips, Megalurothrips sjostedti on cowpea. One application of M. unisopliae timed at flower bud stage and another at flowering stage did not protect cowpea yield against M. sjostedti as does chemical insecticide, Karate (Lambda‐cyhalothrin). Instead, one application of the fungus given at flower bud stage and two applications given at flowering were required to keep M. sjostedti population in check through these stages, which are very sensitive to thrips damage with a concomitant increase in cowpea yield which was significantly higher than the Karate treatment. Studies of persistence showed that M. anisopliae remained active in the field for 3–4 days.     

The entomopathogenic nematode Steinernema kraussei and Metarhizium anisopliae work synergistically in controlling overwintering larvae of the black vine weevil,Otiorhynchus sulcatus,in strawberry growbags

Previously, the combination of reduced rate of entomopathogenic nematodes (EPN) and fungus caused additive or synergistic mortality to third-instar black vine weevil (BVW), Otiorhynchus sulcatus. In this study, we examined this interaction in unheated glasshouses during winter and compared a combination of commercial formulation of a cold-tolerant EPN, S. kraussei (Nemasys L?) and fungus Metarhizium anisopliae strain V275 against overwintering third-instar BVW. The combination of M. anisopliae with S. kraussei at a rate of 1×10¹⁰ conidia+250,000 nematodes/growbag resulted in additive or synergistic effects, providing 100% control of overwintering larvae.     

Effects of Metarhizium anisopliae on searching,feeding and predation by Orius albidipennis (Hem., Anthocoridae) on Thrips tabaci (Thy., Thripidae) larvae

The generalist predator Orius albidipennis Reut. (Hem., Anthocoridae) and entomopathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin (Ascomycota: Clavicipitaceae) are important biocontrol agents of Thrips tabaci Lindeman (Thys., Thripidae) in most greenhouses. In this study, we estimated searching time, feeding time and predation rate in O. albidipennis feeding on untreated and treated thrips larvae which had been inoculated with three concentrations of M. anisopliae V275 at four time intervals; 0, 24, 48 and 72 h after infestation. Applied concentrations were 1×10³, 2×10⁴ and 2×10⁵ conidia/mL which roughly correspond to the LC₂₅, LC₅₀ and LC₇₅ for second instar-larvae. O. albidipennis responded to the presence of the M. anisopliae on the treated hosts by increasing the searching time and decreasing feeding time and predation rate levels. It was also able to detect and avoid treated patches.     

Combined use of entomopathogenic nematodes and Metarhizium anisopliae as a new approach for black vine weevil,Otiorhynchus sulcatus,control

Combined use of the entomopathogenic nematodes (EPNs), Heterorhabditis bacteriophora Poinar (Heterorhabditidae), Steinernema feltiae Bovien, and Steinernema kraussei Steiner (Steinernematidae) and the insect‐pathogenic fungus, Metarhizium anisopliae (Metsch.) Sorokin (Clavicipitaceae) was evaluated for control of third‐instar black vine weevil, Otiorhynchus sulcatus Fabricius (Coleoptera: Curculionidae). Black vine weevil larvae were exposed to various concentrations of M. anisopliae and EPNs and mortality was assessed weekly or at 3‐day intervals under laboratory and greenhouse conditions. The EPNs were added simultaneously, or 1 or 2 weeks after application of M. anisopliae. Throughout the experiments, the combined application of EPNs with M. anisopliae resulted in increased efficacy against black vine weevil. When the EPNs were applied 1 or 2 weeks after application of the fungus, 100% larval mortality was obtained, even when the biocontrol agents were used at reduced rates. The interactions observed suggest that EPN and M. anisopliae work together synergistically in potted Euonymus fortunei Blondy (Celastraceae) under greenhouse conditions and may provide a powerful and economically feasible approach for black vine weevil larval control.     

Effects of post-application irrigation and substrate moisture on the efficacy of entomopathogenic nematodes against western flower thrips, Frankliniella occidentalis

The efficacy of entomomatogenic nematodes (Steinernema bicornutum Tallosi, Peters and Ehlers and/or Heterorhabditis indica LN2 Poinar, Karunakar and David) against the soil‐dwelling life stages of western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) was assessed under different moisture conditions in a commercial plant‐growing substrate in laboratory experiments. In the first experiment, both nematode species were tested at substrate moisture ranges of 67, 78, 88, or 95% relative moisture content, that were maintained before applying the nematodes at 100 or 400 infective juveniles (IJs) cm^?2. In the second experiment, 10, 25, 50, 100, or 120 ml irrigation water, resulting in relative moisture contents of 72, 81, 90, 99%, or more than the saturation level of the substrate, respectively, was applied to the substrate. Heterorhabditis indica LN2 was applied either in 3 ml water and followed by irrigation, or by suspending the infective juveniles in the water amounts indicated above to apply the nematodes in higher volume. Results indicated that at the higher application rate, initial moisture content did not significantly affect the efficacy of H. indica LN2. On the other hand, increasing moisture content resulted in an improved efficacy of H. indica LN2 and S. bicornutum at lower and higher application rates, respectively. Similar thrips control levels of 44 and 60% at the lower and higher application rate of H. indica LN2, respectively, were obtained at 88% relative moisture content. In the second experiment, higher and statistically similar thrips mortality of 40 and 50% at lower and higher application rates of H. indica LN2, respectively, were obtained when the infective juveniles were applied in a high volume suspension of 100 ml, or when followed by irrigation with 25 ml water, resulting in both cases in 81% relative moisture content. Generally, efficacies of the nematodes for thrips control can be improved by using an appropriate moisture content and/or post‐application irrigation. Thus, the high nematode application rates required for successful F. occidentalis control can be partly attributed to substrate moisture content and/or post‐application irrigation.     

An immuno-marking technique for thrips

Rabbit immunoglobulin G (R‐IgG) was used successfully as an external mark for thrips. Females of both Thrips tabaci Lindeman and Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) were marked with 1 mg ml^?1 R‐IgG solution with 1%‘Tween 20’ by the contact exposure method. Determining the retention of the mark was by running the rinsing solution of individual thrips in an enzyme‐linked immunosorbent assay (ELISA). The sandwich ELISA method was used with an additional biotin–avidin step. The threshold for a positive marking score was defined as three times the mean optical density readings of the negative control thrips. Under laboratory conditions, on bean pods, all marked thrips scored positive up to 6 days after marking (DAM). When marked thrips were kept in the laboratory on marigold flowers for 2 days, they all scored positive. When marked and unmarked thrips were placed together on these flowers, the mark was transferred to 10–20% of the unmarked thrips and they became positive. Under field conditions, on sticky traps covered with water‐base glue, 100, 80, and 20% of the marked T. tabaci scored positive by the 3rd, 6th, and 9th DAM, respectively. Under the same conditions 100, 90, and 10% of the marked F. occidentalis scored positive by the 3rd, 6th, and 9th DAM, respectively. The retention of the R‐IgG decreased significantly under conditions of wetness and high humidity. After 6 days on chive plants kept at 80–100% r.h., all marked thrips scored negative while on plants kept at 40–60% r.h., 85% of the marked thrips scored positive. Rabbit IgG can be used as an external marker for thrips. The suitability of this marking method for dispersal studies of these important pests needs to be evaluated.     

Effects of tomato spotted wilt virus (TSWV) isolates, host plants, and temperature on survival, size, and development time of Frankliniella fusca

The effects of different isolates of the tomato spotted wilt tospovirus (TSWV), host plants, and temperatures on Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), the most important vector of TSWV in North Carolina, were measured in the laboratory. Thrips were reared at either 18.3, 23.9, or 29.4 °C until adult eclosion on excised leaves of Datura stramonium L. or Emilia sonchifolia (L.). Plants were either infected with the TSWV isolates CFL or RG2, or left uninfected (control). The results revealed a positive relationship between larval survival and temperature, regardless of host plant or TSWV isolate. Both survival to adult and percentage transmission of TSWV by F. fusca were significantly affected by the interaction between host plant and TSWV isolate. The consequence of this interaction was that the cohort‐based percentage transmission from infected E. sonchifolia plants for CFL was 1.3‐fold greater than that of RG2, whereas the percentage transmission from infected D. stramonium plants for RG2 was twice that of CFL. Both host plant and TSWV isolates showed significant effects on thrips development time to adult and head capsule width of adult thrips, as well as on the incidence of thrips infection with TSWV. The infection status of these thrips was determined by ELISA for the NSs viral protein. Infected thrips reared on infected host foliage took longer to develop to adult and were smaller than non‐infected thrips which had also been reared on infected host foliage, demonstrating a direct effect of the TSWV on thrips. However, non‐infected thrips reared on non‐infected leaves took longer to develop than non‐infected thrips reared on infected leaves, suggesting an effect of the plant tissue on thrips. In addition, adult thrips reared on TSWV‐infected D. stramonium at 29.4 °C developed smaller head capsules than thrips developing on infected foliage at lower temperatures and on non‐infected leaves of D. stramonium or E. sonchifolia. Both TSWV isolates and host plants differentially affected females more than males. In conclusion, both the infection of thrips by TSWV and TSWV‐mediated changes in host plant quality were found to have significant biological effects on F. fusca.     

Phoxim and manure enhanced the population rebound and preservation of Metarhizium anisopliae applied in soil

We investigated the population dynamics of Metarhizium anisopliae during peanut growth and the effect of phoxim and manure on population dynamics. The applied population of M. anisopliae initially decreased rapidly, then slowly, and finally stabilised or revived. The 50% decline in the original three rates of treatment appeared at 41.8–57.6 days; however, the populations decreased towards similar levels at harvest time. Phoxim clearly inhibited the fungal growth and conidiation on the medium. Germination was reduced by half or was completely absent when conidia were inoculated on media containing 25 or 100 ppm phoxim. The colony number decreased by 20–65%, and the colonies grew more slowly, conidiated less and faded in colour on media containing 25–200 ppm phoxim. However, normal growth and enhanced conidiation were restored when they were subsequently subcultured on normal media. Adding phoxim or manure to the fungal treatment in potting soil caused the population to decrease faster within the first 16 days but rebound and level off after 30 days. In the field, the M. anisopliae populations at peanut harvest dropped to approximately 10% of their initial levels, regardless of whether the fungus was applied alone or with phoxim or manure. We speculated that low concentrations of phoxim might stimulate M. anisopliae sporulation and proliferation, and that manure might increase space and nutrient competition between soil microbes and increase M. anisopliae proliferation.     

Effect of culture medium on the production and virulence of submerged spores of Metarhizium anisopliae and Beauveria bassiana against larvae and adults of Aedes aegypti (Diptera: Culicidae)

Three Metarhizium anisopliae and three Beauveria bassiana isolates were cultivated in media containing casamino acids, soybean flour or sunflower seed flour and were shaken for three days. M. anisopliae presented similar yields of around 10⁶ submerged spores/ml without significant differences among them, whereas B. bassiana produced yields of around 10⁸ spores/ml, of which GHA strain produced more submerged spores in the casamino acids medium. The other two strains showed no significant difference in the production of submerged spores in the three media used. Differences in mortality on Aedes aegypti larvae were observed with the submerged spores of Metarhizium depending on isolate and medium used. M. anisopliae 2157 caused significantly higher mortality (40%) when cultivated in casamino acids medium. It presented an LC₅₀ of 8.93 × 10⁵ submerged spores/ml water against mosquito larvae five days after application, whereas it caused 27% mortality in Ae. aegypti adults 10 days after application. In conclusion, fungal nutrition affected virulence of some isolates of M. anisopliae against Ae. aegypti larvae while such an effect was not noted for B. bassiana isolates.     

The combined effect of soil‐applied azadirachtin with entomopathogens for integrated management of western flower thrips

Performance of soil application of azadirachtin products with entomopathogens was evaluated as single treatments, in multiple combinations and in different concentrations against the soil stages of western flower thrips, Frankliniella occidentalis (Pergande), in French beans Phaseolus vulgaris L. Treatments consisted of NeemAzal‐T solution, neem pellets, Steinernema carpocapsae (Weiser) Nemastar^®, isolates of Metarhizium anisopliae (Metschnikoff) Sorokin (IPP 2539 and ICIPE‐69) and Beauveria bassiana (Balsamo) – Naturalis^®. All treatments were analysed for the number of emerging adults, while emerged adults in fungi‐based treatments were analysed additionally for the retarded development of mycosis as a possible cause of secondary mortality. Possible interactive effects in combined treatments were analysed using a generalized linear model (GLM) approach, and three levels of dose–response combinations of the selected treatments were further tested. Bioassay results of the single treatments indicated between 43% and 60% reduction in adult emergence with NeemAzal‐T solution thus proving to be the most efficient. However, most cadavers with entomopathogenic fungi (EPF) treatments showed the development of mycosis. Therefore, the reduction in adult emergence attributed to the EPF was altogether >87%. Combined treatments with Steinernema, Metarhizium (ICIPE‐69), NeemAzal‐T and neem pellets resulted in total reduction in adult emergence of 95–97% when late mortality by mycosis was considered. Of the treatment combinations, two showed synergistic, four additive and one an antagonistic response. Combining low concentration of entomopathogenic nematode (EPN) (100 IJ/cm²) with NeemAzal‐T resulted in satisfactory control compared to the operational dose of EPN, while the highest concentration of M. anisopliae (10⁸ conidia) combined with Steinernema showed the best performance with 74% reduction in adult emergence.     

Interactions among vegetable-infesting aphids,the fungal pathogen Metarhizium anisopliae (Ascomycota: Hypocreales) and the predatory coccinellid Cheilomenes lunata (Coleoptera: Coccinellidae)

Entomopathogenic fungi are among biocontrol agents being considered for the control of aphids on a variety of crops. Predatory coccinellids, although generalist, are also among important natural enemies that must be conserved for aphid management. Laboratory studies were carried out to investigate the interaction between three vegetable-infesting aphids, Metarhizium anisopliae isolate ICIPE 62 and the coccinellid predator Cheilomenes lunata. At a concentration of 1?×?10⁸?conidial?ml^–1, the fungus was found to cause mortality of 7.5% to C. lunata, compared to 2.5% mortality in the control at 10?days post-treatment. Female adult C. lunata to which fungus-infected aphids were offered as prey never accepted them as food source in non-choice bioassays. However, live and dead non-infected aphids were fed upon. In choice bioassay, a total of 1–3 out of 24 infected non-sporulating aphids per species (average of 0.1–0.4 aphids per arena) were consumed by 48?h-starved C. lunata within a period of 60?min, but avoided sporulating cadavers. Foraging adult C. lunata enhanced the spread of conidia of M. anisopliae from infected cadavers to fourth instars Aphis gossypii feeding on okra (0.8–15.0% mortality), Brevicoryne brassicae (3.3–15.0% mortality) and Lipaphis pseudobrassicae (0.8–14.2% mortality) on kale plants. Results of this study demonstrate compatibility between M. anisopliae and C. lunata, and could provide a sustainable strategy for effective management of aphids on crucifers and okra cropping systems.     

Antioxidant,anti‐inflammatory,and enzyme inhibitory activity of natural plant flavonoids and their synthesized derivatives

The synthesized flavonoid derivatives were examined for their antioxidant, anti‐inflammatory, xanthine oxidase (XO), urease inhibitory activity, and cytotoxicity. Except few, all the flavonoids under this study showed significant antioxidant activity (45.6%–85.5%, 32.6%–70.6%, and 24.9%–65.5% inhibition by DPPH, ferric reducing/antioxidant power, and oxygen radical absorption capacity assays) with promising TNF‐α inhibitory activity (42%–73% at 10 μM) and IL‐6 inhibitory activity (54%–81% at 10 μM) compared with that of control dexamethasone. The flavonoids luteolin, apigenin, diosmetin, chrysin, O^3?, O⁷‐dihexyl diosmetin, O^4?, O⁷‐dihexyl apigenin, and O⁷‐hexyl chrysin, showed an inhibition with IC₅₀ values (4.5‐8.1 μg/mL), more than allopurinol (8.5 μg/mL) at 5 μM against XO and showing more than 50% inhibition at a final concentration (5 mM) with an IC₅₀ value of ranging from 4.8 to 7.2 (μg/mL) in comparison with the positive control thiourea (5.8 μg/mL) for urease inhibition. Thus, the flavonoid derivatives may be considered as potential antioxidant and antigout agents.     

Entomopathogenicity of beauveria bassiana and metarhizium anisopliae to the cowpea aphid,aphis craccivora koch (homoptera: Aphididae)

The pathogenicity of four isolates each of the entomopathogenic fungi, Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae (Metsch.) Sorok. to apterous adult Aphis craccivora Koch was evaluated in the laboratory at 4 concentrations of conidia. All fungi isolates tested were found to be pathogenic to the insect but their virulence varied among species and isolates within species. Three isolates, B. bassiana CPD 11 and M. anisopliae CPD 4 and 5 caused significantly higher mortality than the other isolates at the various concentrations tested causing mortality of between 58–91%, 64 to 93% and 66–100%, respectively, at 7 days post treatment. At the highest concentration of 1 × 10⁸conidiaml^‐1, these isolates produced the shortest LT₅₀s of 3.5, 3.6 and 3.4 days, respectively. Their LC₅₀s were 6.8 × 10⁵, 3.1 × 10⁵ and 2.7 × 10⁵ conidia ml^‐1, respectively. The results indicate that these isolates are promising candidates for the control of the cowpea aphid but their pathogenicity to various aphid non‐target beneficial organisms within the cowpea agroecosystem warrant further investigation before initiating field control.     

Pathogenicity of the Hyphomycete Fungi Verticillium lecanii and Metarhizium anisopliae to the Western Flower Thrips,Frankliniella occidentalis

The pathogenicity of several isolates of the hyphomycete fungi Verticillium lecanii and Metarhizium anisopliae to Frankliniella occidentalis was investigated. Treatment of adult thrips with M. anisopliae resulted in at least 94% mortality at 7 days post-inoculation. In contrast, V. lecanii isolates only gave mortalities of between 20 and 70%. Detailed studies were made on the most virulent isolate of M. anisopliae (275) to determine its efficacy at different doses and temperatures. At 23 C the LC was ca. 3 105 conidia ml-1 after 5 days and the LTs were 50 50 3 and 4.5 days at 10 7 and 106 conidia ml-1 respectively. Temperature influenced fungal virulence to adult thrips; the LT at 18 and 20 C was ca. 4 days and at 23 or 26 C it was ca. 3 days. 50 Larvae were less susceptible to infection than adult thrips (27% versus 100% mortality), presumably due to the inoculum being shed with the exuvium during ecdysis. Conidia of M. anisopliae isolate 275 germinated rapidly on the surfaces of larvae, pupae and adults, with most germlings producing appressoria within 24 h post-inoculation. Fungal elements were present in significant amounts in the body 3 days after treatment.     

Synergism between Metarhizium anisopliae (Deuteromycota: Hyphomycetes) and Boric Acid against the German Cockroach (Dictyoptera: Blattellidae)

Mortality of German cockroaches, Blattella germanica (L.), caused by Metarhizium anisopliae (Metschnikoff) Sorokin strain AC-1 alone and in combination with different formulations of boric acid, was evaluated in laboratory bioassays. Topical application of M. anisopliae alone (8.96 × 10⁹ conidia/m²) required 28 days to cause >92% cockroach mortality (LT₅₀ = 10 days). In contrast, in combination with boric acid (topically applied as a dust or in drinking water), M. anisopliae killed cockroaches significantly faster than without boric acid. M. anisopliae conidial dust (8.96 × 10⁸ conidia/m²) with either 12.5% (w/w) boric acid dust or 0.1% (w/v) boric acid in drinking water killed 100% of the cockroaches in only 8 days (LT₅₀ = 5 days) and 10 days (LT₅₀ = 6 days), respectively, without compromising the fungus emergence from cadavers. Replacement of M. anisopliae with flour dust or heat-killed M. anisopliae conidia eliminated this effect, demonstrating that it was not the consequence of greater boric acid ingestion due to more extensive cockroach grooming upon exposure to M. anisopliae conidia. Moreover, injections of a low dose of M. anisopliae, which caused only 30% mortality, together with sublethal concentrations of boric acid into the cockroach hemocoel resulted in a doubling of mortality. Statistical analysis demonstrated a synergistic interaction between these two insecticides.     

Decreased preference and reproduction, and increased mortality of Frankliniella occidentalis on thrips-resistant pepper plants

The effect of thrips resistance in pepper (Capsicum annuum L.) – previously shown to result in impeded thrips population development (Maris PC, Joosten NN, Goldbach RW & Peters D (2003a) Restricted spread of Tomato spotted wilt virus in thrips‐resistant pepper. Phytopathology 93: 1223–1227. Maris PC, Joosten NN, Goldbach RW & Peters D (2003b) Spread of Tomato spotted wilt virus and population development of Frankliniella occidentalis in pepper resistant to thrips. Proceedings of the Section Experimental and Applied Entomology Netherlands Entomological Society (NEV) Amsterdam 14: 95–101.) – on thrips’[Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)] reproduction, mortality, host preference, and behaviour was investigated. Reproduction, studied by oviposition and larval survival, was negatively affected by the thrips‐resistant (TR) phenotype, whereas the offspring's developmental rate did not differ on TR and the thrips‐susceptible (TS) phenotype. While thrips’ behaviour was hardly affected by thrips resistance, a significant preference for TS plants over the TR plants was found in different tests. When released on either a TR or a TS plant, thrips dispersed at significantly higher rates from the TR plants, demonstrating that not only an impeded reproduction, but also a reduced residence time adds to the reported lower thrips numbers on TR plants.     

Ovicidal effects of entomopathogenic fungal isolates on the invasive Fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae)

Maize is a major staple food for over 300 million people in sub‐Saharan Africa. Sustainable productivity of this primary crop has been recently threatened by Fall armyworm (FAW), Spodoptera frugiperda invasion. Due to lack of environmentally safe management strategies, immediate responses by growers and governments to tackle FAW are based on rampant use of pesticides. Looking for efficient biopesticides, twenty entomopathogenic fungal isolates (14 Metarhizium anisopliae and 6 Beauveria bassiana) were screened for their efficacy against eggs and second instar larvae of FAW. A single discriminating concentration of 1 × 10⁸ conidia ml^?1 and four replicates per treatment were used in all experiments. Isolates were assessed for their ability to cause mortality of FAW second instar larvae, eggs and the neonate larvae that emerged from treated eggs. Among the isolates tested, only B. bassiana ICIPE 676 caused moderate mortality of 30% to second instar larvae. Metarhizium anisopliae ICIPE 78, ICIPE 40 and ICIPE 20 caused egg mortalities of 87.0%, 83.0% and 79.5%, respectively, and M. anisopliae ICIPE 41 and ICIPE 7 outperformed all the others by causing 96.5% and 93.7% mortality to the neonate larvae, respectively. The cumulated mortality of eggs and neonates was highest with M. anisopliae ICIPE 41 (97.5%), followed by M. anisopliae ICIPE 7, 655, 40, 20 and 78 with total mortality of 96.0%, 95.0%, 93.5%, 93.0% and 92.0%, respectively. These isolates with high cumulated mortality (≥92%), especially ICIPE 78 and 7, which are already commercialized for spider mites and ticks control respectively, would be good candidates for development as biopesticides for management of FAW in Africa if further evidence of their efficacy is obtained in the field.