Group Movement in Entomopathogenic Nematodes: Aggregation Levels Vary Based on Context

Maintenance of an aggregated population structure implies within-species communication. In mixed-species environments, species-specific aggregations may reduce interspecific competition and promote coexistence. We studied whether movement and aggregation behavior of three entomopathogenic nematode species changed when isolated, as compared to mixed-species arenas. Movement and aggregation of Steinernema carpocapsae, S. feltiae and S. glaseri were assessed in sand. Each species demonstrated significant aggregation when alone. Mixed-species trials involved adding two species of nematodes, either combined in the center of the arena or at separate corners. While individual species became less aggregated than in single-species conditions when co-applied in the same location, they became more aggregated when applied in separate corners. This increased aggregation in separate-corner trials occurred even though the nematodes moved just as far when mixed together as they did when alone. These findings suggest that maintenance of multiple species within the same habitat is driven, at least in part, by species-specific signals that promote conspecific aggregation, and when the species are mixed (as occurs in some commercial formulations involving multiple EPN species), these signaling mechanisms are muddled.

A winning formula: sustainable control of three stored-product insects through paired combinations of entomopathogenic fungus, diatomaceous earth, and lambda-cyhalothrin

This research aimed to assess the effectiveness of Metarhizium robertsii, diatomaceous earth (Protect-It), and lambda-cyhalothrin, for the long-term protection of stored wheat against three destructive grain insect pests, Rhyzopertha dominica, Tribolium castaneum, and Trogoderma granarium. Different treatments were applied, both alone and in paired combinations in laboratory and persistence trials. Single treatments exhibited significantly lower mortality rates in comparison to the paired treatments for all tested insect species. Among the single treatments, lambda-cyhalothrin (Lamb) resulted in significantly higher mortality rates in laboratory trials, followed by diatomaceous earth (DE) and M. robertsii (Mr), with insignificant differences between Mr and DE. Evidently, DE exhibited the highest persistence after 120 days of storage for all insect species and initial exposures, although variations in mortality rates among treatments were mostly insignificant. Overall, the most effective treatment in terms of mortality in laboratory, and persistence trials, and progeny production was DE + Lamb, followed by Mr + Lamb, and Mr + DE for all tested insect species. In general, the most susceptible insect species was R. dominica, followed by T. castaneum and T. granarium. This research highlights the effectiveness of M. robertsii, DE, and lambda-cyhalothrin in providing prolonged protection of stored wheat against all the examined grain insect species.

Evaluating the Compatibility of Spinosad and Alpha-Cypermethrin for Controlling Six Insect Pests Infesting Stored Wheat

The deterioration of stored wheat due to pest infestations is a significant concern, with pests like Rhyzopertha dominica, Tribolium castaneum, Cryptolestes ferrugineus, Sitophilus oryzae, Oryzaephilus surinamensis, and Trogoderma granarium being major contributors. This study examined the efficacy of spinosad and alpha-cypermethrin, individually and in combination, against these pests under laboratory conditions. Spinosad was tested at two concentrations (0.05 and 0.1 mg/kg), while alpha-cypermethrin was applied at 0.05 mg/kg. The combined application of both insecticides led to significantly higher pest mortality compared to single treatments. Importantly, all treatments caused substantial pest mortality and exhibited the ability to suppress pest progeny production over time, as observed in both laboratory and persistence trials. Among the various treatment combinations, the joint application of 0.1 mg/kg spinosad and 0.05 mg/kg alpha-cypermethrin emerged as the most effective, resulting in elevated mortality and a marked reduction in pest progeny. Rhyzopertha dominica exhibited the highest susceptibility among the pests, followed by S. oryzae, T. castaneum, C. ferrugineus, O. surinamensis, and T. granarium. The remarkable performance of the joint action of alpha-cypermethrin and spinosad at low doses highlights this combination as an efficacious approach for safeguarding stored grain against these destructive insect pests, warranting further exploration.

Efficacy of entomopathogenic fungi, nematodes and spinetoram combinations for integrated management of Thrips tabaci

BACKGROUND

Two consecutive field trials using a blend of entomopathogens in combination with a new chemistry insecticide were conducted to determine treatment effects on onion thrips (Thrips tabaci Lindeman) populations, crop damage, plant development, crop yield and impact on natural enemies. Products were tested in an onion cropping system and included the insect pathogenic fungus Beauveria bassiana (isolate WG-11), an entomopathogenic nematode Heterorhabditis bacteriophora (strain VS) and the new-chemistry chemical insecticide spinetoram.

RESULTS

In all treatments, a significant decrease in thrips per plant population was detected in both trials. Overall, dual application of entomopathogens and insecticide was more effective than singly applied treatments. The lowest number of thrips larvae (1.96 and 3.85) and adults (0.00 and 0.00) were recorded when treated with dual application of B. bassiana and spinetoram at 7 days post application (DPA) after the second spray application in 2017and 2018, respectively. Damage on onion plants was considerably decreased in all treatments relative to the control. The lowest damage was observed on onion plants treated with B. bassiana + spinetoram at 7 DPA after the second spray application during both years. A significant decrease in the number of natural enemies (beetles, spiders, mites, lacewings, ants and bugs) on onion plants was recorded during both years. Insect pathogens when applied alone and in combination with each other considerably protected arthropod natural enemies compared to insecticide application applied alone. Significant increase in plant agronomic traits was observed compared to the control. Among all the treatments, B. bassiana + spinetoram produced maximum leaf length, leaf weight, total leaves, neck diameter, bulb diameter, number of rings per bulb, bulb weight, dry matter and plant yield following the 2017and 2018 applications, respectively.

CONCLUSION

The findings of the study reveal the potential of using insect pathogens and insecticide for control of T. tabaci. However, combinations containing spinetoram are harmful to nontarget organisms, whereas biological control agents help in protecting biodiversity in onion agroecosystems. © 2023 Society of Chemical Industry.

Natural Warriors against Stored-Grain Pests: The Joint Action of Beauveria bassiana and Steinernema carpocapsae

Tribolium castaneum, Trogoderma granarium, Oryzaephilus surinamensis, Sitophilus oryzae, Rhyzopertha dominica, and Cryptolestes ferrugineus are all major pests of stored grains. In this study, the efficiency of single and joint applications of the entomopathogenic nematode (EPN) Steinernema carpocapsae at two different doses (50 and 100 IJs cm-2) and the entomopathogenic fungus (EPF) Beauveria bassiana for the management of the aforementioned pests was estimated. At single treatments, both doses of S. carpocapsae caused higher mortality rates to all six pest species compared to B. bassiana. The combined treatment of EPF and EPN resulted in higher mortality compared to single treatments. Mortality was strongly influenced by the exposure interval and the application dose of the EPN at both single and combined treatments. Maximum mortality was observed for the application of the combined treatment at the high dose of S. carpocapsae and B. bassiana. Among the different insect species tested, the maximum mortality rate was observed for R. dominica (96.62%), followed by S. oryzae (90.48%), T. castaneum (87.23%), C. ferrugineus (76.05%), O. surinamensis (70.74%), and T. granarium (57.71%). The outcomes of this study demonstrate the potential of utilizing specific combinations of EPF and EPN as effective natural enemies against stored-grain pests.

Treatment of Four Stored-Grain Pests with Thiamethoxam plus Chlorantraniliprole: Enhanced Impact on Different Types of Grain Commodities and Surfaces

An insecticide containing the neonicotinoid thiamethoxam + the diamide chlorantraniliprole was evaluated against adults of Rhyzopertha dominica, Tribolium castaneum, Trogoderma granarium, and Sitophilus oryzae under laboratory bioassays both on freshly treated grain as well as on treated grain stored over 90 days for its persistence in efficacy. In laboratory bioassays, the insecticide was applied on wheat, maize, or rice at four doses, while in persistence bioassays on wheat at the same doses. Mortality and progeny were assessed in both laboratory and persistence bioassays. After 14 days of exposure, S. oryzae exhibited 100% mortality on all three commodities at the highest dose, while R. dominica showed complete mortality on wheat or rice and T. castaneum on wheat. For a period of 90 days, S. oryzae exhibited 42.69% mortality, followed by R. dominica (35.26%), T. castaneum (27.08%), and T. granarium (18.63%) at the highest dose. Progeny was successfully suppressed in all cases of complete mortality in laboratory bioassays and for S. oryzae for 90 days in persistence bioassays. Laboratory trials were also performed on plywood, concrete, ceramic tile, and steel at one dose. The highest mortality was observed on steel, followed by concrete, ceramic tile, and plywood for all insect species tested. This study demonstrates that thiamethoxam + chlorantraniliprole is effective against the tested species depending on exposure, storage period, surface, commodity, and dose.

The Potential of Two Entomopathogenic Fungi and Enhanced Diatomaceous Earth Mixed with Abamectin: A Comprehensive Study on Mortality, Progeny Production, Application Method, and Surface Application against Tribolium castaneum

This study determined the efficacy of Beauveria bassiana (Bals. -Criv.) Vuill., Metarhizium anisopliae (Metchnikoff) Sorokin, and diatomaceous earth mixed with abamectin (DEA) alone and in their combinations for the integrated management of larvae and adults of Tribolium castaneum (Herbst) from three field populations of Pakistan (Multan, Rawalpindi, and Rahim Yar Khan) and one laboratory population (Faisalabad). Treatments were applied on three surfaces, namely, viz. steel, concrete, and jute bags, implementing two application methods, dusting and spraying. The combined treatments were more effective in comparison with single treatments for both larvae and adults. Overall, the highest mortality rates were recorded in the Faisalabad population, followed by the Rehaim Yar Khan, Rawalpindi, and Multan populations. Progeny production was suspended 21 days after exposure to the combined treatment of DEA and both fungi in all populations except Rawalpindi. Larvae were found to be more susceptible than adults in all treatments and intervals. Dusting was more efficient than spraying for both larvae and adults and for all the populations studied. The present study provides a wholistic understanding of the impact of different factors on the success of the combined treatments using DEA and entomopathogenic fungi, supporting their use as surface treatments.

Development of Insecticide Resistance in Field Populations of Onion Thrips, Thrips tabaci (Thysanoptera: Thripidae)

The present study evaluated insecticide resistance in field populations of onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), collected from eight different onion-growing regions of Punjab, Pakistan. These field-collected populations were assessed for resistance development against eight commonly used active ingredients including deltamethrin, lambda-cyhalothrin, imidacloprid, acetamiprid, spinosad, spinetoram, cypermethrin, and abamectin. In leaf dip bioassays, T. tabaci adults showed varied levels of resistance towards different insecticides. Moderate or high levels of resistance to deltamethrin (58-86 fold), lambda-cyhalothrin (20-63 fold), and cypermethrin (22-54 fold) were observed in T. tabaci field populations. There were very low to moderate resistance levels to imidacloprid (10-38 fold), acetamiprid (5-29 fold), and abamectin (10-30 fold). The lowest levels of resistance were detected in thrips exposed to spinosad (3-13 fold) and spinetoram (3-8 fold). Insecticide resistance levels varied among populations collected from various geographic locations, but all populations exhibited elevated levels of resistance to deltamethrin. Thrips tabaci populations with higher resistance levels were most commonly found from the southern part of Punjab, Pakistan. Our findings revealed that spinosyns could be used as alternatives to conventional insecticides for the successful management of T. tabaci in onion fields.

Two are better than one: the combinations of Beauveria bassiana, diatomaceous earth, and indoxacarb as effective wheat protectants

The current study evaluates the efficacy of the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae), diatomaceous earth (DE) (Protect-It), and the oxadiazine indoxacarb, at single or combined applications on wheat kernels, for the management of the rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). The study was conducted between November 2020 and August 2021 in Faisalabad under a complete randomized block design. The combination of DE + indoxacarb was the most efficient as it caused higher overall mortalities ranging between 59.34 and 100%, and lower overall progeny production ranging between 8.35 and 33.70 individuals per vial, than all other treatments. Beauveria bassiana alone exhibited the lowest mortality rates ranging between 22.33 and 47.76%, and the highest offspring emergence, ranging between 51.33 and 78.55 individuals per vial. Similar pattern was observed when persistence bioassays were conducted. For a period of 120 days, the DE + indoxacarb was the most powerful combination against all tested species, providing overall mortality rates between 17.06 and 63.80%. The overall progeny production was lower for the insect individuals exposed on wheat treated with the DE + indoxacarb combination, ranging between 13.66 and 52.23 individuals per vial, and higher for those exposed to B. bassiana alone, ranging between 44.03 and 107.67 individuals per vial, for the entire duration of storage. However, the efficacy of all treatments decreased gradually during the course of storage. The findings of the current study indicate that the combinations of entomopathogenic fungi, DE, and indoxacarb can be used for the prolonged protection of stored wheat from the tested noxious insect species of stored products. Further research, which will include other inert dusts in combination with entomopathogenic fungi and indoxacarb, may provide additional knowledge towards an effective management of noxious species occurring in storages.

Combinations of Beauveria bassiana and spinetoram for the management of four important stored-product pests: laboratory and field trials

The current study examines the efficacy of the semi-synthetic insecticide spinetoram and entomopathogenic fungi Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) as wheat protectants against the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), and the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), under laboratory and field trials. One dose of B. bassiana, i.e., 1 × 107 conidia/kg wheat, two doses of spinetoram, i.e., spine1: 0.05 ppm (mg/kg wheat), spine2: 0.1 ppm, and their combinations (Bb + spine1, Bb + spine2) were evaluated at 20, 25, and 30 °C. All treatments provided significantly higher mortality at 30 °C compared with the other two temperatures. Maximum mortality levels were observed in the treatments where B. bassiana was combined with the higher dose of spinetoram (0.1 ppm). All treatments reduced progeny production in comparison with the control groups. Maximum progeny reduction was observed at 30 °C, on wheat treated with the Bb + spine2 combination. The combination Bb + spine2 also provided elevated mortality rates in both laboratory and field persistence trials, but at 180 days caused moderate mortality to all tested insect species. Concerning progeny, at laboratory persistence trials, the combination Bb + spine2 exhibited the lowest offspring emergence to all tested species compared to the other treatments and control. Overall, our study showed that R. dominica was the most susceptible species followed by S. granarius, T. castaneum, and T. granarium. Our findings revealed that the combination of B. bassiana and spinetoram may be a useful tool for efficient and advanced integrated pest management strategies for long storage periods under multiple temperatures.

Combined application of entomopathogenic nematodes and fungi against fruit flies, Bactrocera zonata and B. dorsalis (Diptera: Tephritidae): laboratory cups to field study

BACKGROUND

The peach fruit fly, Bactrocera zonata, and the Oriental fruit fly, B. dorsalis (Diptera: Tephritidae), are economically important fruit fly species in various regions of the world. We evaluated the effects of separate and combined applications of the entomopathogenic fungi (EPF) Beauveria bassiana (WG-18) and Metarhizium anisopliae (WG-02), and the entomopathogenic nematodes (EPNs) Heterorhabditis bacteriophora (VS strain) and Steinernema carpocapsae (ALL strain) against larvae, pupae and pharate adults, of B. zonata and B. dorsalis under laboratory, glasshouse and field cage conditions.

RESULTS

Combined applications of EPF and EPNs produced greater mortality than individual treatments under all conditions. Against both species, the combination of B. bassiana and H. bacteriophora consistently exerted strong effects that were similar to the combined application of B. bassiana and S. carpocapsae whereas M. anisopliae applied with S. carpocapsae was least effective in all combinations. In a laboratory bioassay, synergistic interactions were detected between B. bassiana and H. bacteriophora applied against larvae and pharate adults of both fly species, between B. bassiana and S. carpocapsae against larvae of both species and pharate adults of B. zonata, and between M. anisopliae and H. bacteriophora against B. zonata larvae. Other combined treatments resulted in additive effects, especially against fly pupae. In a potted soil bioassay, there were only additive interactions in all combinations against different stages of both flies. The 3rd instar of both flies was more susceptible than pharate adult and pupal stages. Additive interactions between EPNs and EPF were detected in the glasshouse against 3rd instars and pupae, and under field conditions against 3rd instars of both fly species.

CONCLUSION

These results indicate how particular combinations of entomopathogenic fungi and nematodes could be deployed in integrated pest management of tephritid fruit flies in orchard agro-ecosystems. © 2022 Society of Chemical Industry.

Laboratory and field studies on the combined application of Beauveria bassiana and fipronil against four major stored-product coleopteran insect pests

In the current study we have tested the application of Beauveria bassiana (Hypocreales: Cordycipitaceae) alone and in combination with fipronil at two doses against Tribolium castaneum (Coleoptera: Tenebrionidae), Rhyzopertha dominica (Coleoptera: Bostrychidae), Sitophilus granarius (Coleoptera: Curculionidae), and Trogoderma granarium (Coleoptera: Dermestidae) under laboratory and field conditions. At laboratory conditions, the combination of B. bassiana with the highest dose of fipronil produced the highest mortality. At different temperatures, mortality was increased with the increase in temperature. Maximum mortality was observed at 30 °C, followed by 25 °C and 20 °C for all tested species. Different treatments significantly reduced the progeny number in comparison to control groups for all tested species at all temperatures. In the persistence trial, all treatments that included the combinations of B. bassiana with fipronil produced significantly higher mortalities than the single treatments for all tested species over a period of 6 months. Furthermore, all treatments significantly reduced the number of progenies of all insect species in comparison with the control groups over the same storage period. In field trials, mortalities of all tested insect species were significantly higher on wheat treated with B. bassiana, fipronil, or their combinations than on controls for an entire storage period of 180 days. Overall, R. dominica was found the most susceptible species followed by S. granarius, T. castaneum, and T. granarium. The findings of the current study suggest that the use of B. bassiana and fipronil as grain protectants may provide elevated control against major stored-grain insect species during a prolonged period of storage.

Virulence of Entomopathogenic Nematodes to Pupae of Frankliniella fusca (Thysanoptera: Thripidae)

Tobacco thrips, Frankliniella fusca (Hinds) is an economically significant pest. Entomopathogenic nematodes (EPNs) have shown promise as biocontrol agents against certain thrips species, but they have not been explored for suppression of F. fusca. We investigated the potential of EPNs to manage F. fusca by conducting three different bioassays: 1) a small cup dose-response bioassay (25, 50, and 100 IJs cm-2) with four EPN species, 2) a broad virulence bioassay with eight EPN species at 100 IJs cm-2, and 3) a potted soil bioassay testing with four EPN species (100 IJs cm-2). In the dose-response bioassay, all treatments showed relatively lower adult emergence when compared with the control group, but the minimum adult emergence (30%) was observed at 7 d post-treatment when Heterorhabditis bacteriophora (FL1-1) was applied at the highest rate (100 IJs cm-2). In the broad virulence study, all EPN treatments caused significant reductions in F. fusca adult emergence (18.3-75.0%) in comparison with the control. H. bacteriophora (Fl1-1) was more virulent than other nematode treatments but statistically not different from Steinernema feltiae and Steinernema riobrave, while Steinernema rarum was the least virulent. In the potted soil bioassay, the lowest emergence (10.6%) was observed in H. bacteriophora (Fl1-1) treatment, followed by S. feltiae (SN), S. riobrave (355), and Heterorhabditis indica (HOM1) treatments. These results indicate that EPNs have the ability to suppress the soil dwelling stage of F. fusca and should be explored further under greenhouse and field conditions for biocontrol potential within an integrated pest management (IPM) context.

Persistence and efficacy of enhanced diatomaceous earth, imidacloprid, and Beauveria bassiana against three coleopteran and one psocid stored-grain insects

The residual efficacy of the enhanced diatomaceous earth (DE) formulation DEBBM alone and in combination with Beauveria bassiana (Hypocreales: Cordycipitaceae) or with the neonicotinoid insecticide imidacloprid against Tribolium castaneum (Coleoptera: Tenebrionidae), Rhyzopertha dominica (Coleoptera: Bostrychidae), Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), and Liposcelis paeta (Psocoptera: Liposcelididae) was investigated in the laboratory. The combination treatments were more effective compared to the single treatments against all examined species. The combinations of DEBBM and imidacloprid and imidacloprid with the highest dose rate of B. bassiana provided the highest mortality values against all tested species for 90 days of storage period. The combination of DEBBM plus B. bassiana resulted to the highest mortalities and to the lowest offspring production of all combinations tested after 180 days of storage. Mortality of adults for each test insect species was decreased over the storage period of 6 months, and the progeny production was increased with the extended storage period. Among the tested insect species, L. paeta was the most susceptible to all three grain protectants followed by C. ferrugineus, R. domina, and T. castaneum. The findings of the current study suggest that the use of DEBBM, imidacloprid, and B. bassiana as grain protectants may provide elevated control of major stored-grain insect species during a prolonged period of storage.

Virulence of Entomopathogenic Fungi to Rhagoletis pomonella (Diptera: Tephritidae) and Interactions With Entomopathogenic Nematodes

The objectives of this study were to quantify the virulence of four entomopathogenic fungal species to pupae of Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) and to determine the potential to combine entomopathogenic fungi (EPFs) and entomopathogenic nematodes (EPNs) for biological control of this pest. The four species of EPFs included Beauveria bassiana (strain GHA), Metarhizium brunneum (strain F52), Isaria javanica (wf GA17), and Isaria fumosorosea (Apopka 97 strain). In laboratory assays, all fungi reduced adult emergence but there were no differences between fungal species. Isaria javanica and M. brunneum were examined further in a EPFs and EPNs bioassay that also included the EPNs Steinernema carpocapsae (ALL strain) and S. riobrave (355 strain). All nematodes and fungi were applied either alone or in combination (fungus + nematode). There were no differences between species within the same entomopathogen group (fungi and nematodes). However, the treatment with S. riobrave resulted in lower R. pomonella emergence than either fungal species. The combination of S. riobrave and I. javanica resulted in the lowest R. pomonella emergence (3%) at fourth-week interval, which was significantly lower than any of the single-agent applications, yet virulence of the other three combination treatments was not different from their respective nematode treatments applied alone. Additive interactions were detected for all fungus-nematode combinations. This study suggests that application of entomopathogenic nematodes and fungi could be an effective option to suppress R. pomonella populations.

Interactions Between Two Invertebrate Pathogens: An Endophytic Fungus and an Externally Applied Bacterium

The members of family Noctuidae exist in diverse environments and many species from this group are of agriculture importance, particularly Helicoverpa spp. Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a major pest of many legumes and cereal crops. Due to environmental and regulatory concerns, safe alternatives to broad spectrum chemical insecticides are needed for the control of key noctuid pests such as H. armigera. A strain of Beauveria bassiana (Cordycipitaceae: Hypocreales) was evaluated for its ability to colonize endophytically in chickpea plants, and its effectiveness against second (L2) and fourth (L4) larval instars of H. armigera. B. bassiana was inoculated to chickpea plants through injection and endophytic establishment was confirmed by re-isolating the fungi from leaf samples. A detached leaf assay was used to evaluate pathogenicity. Bacillus thuringiensis was also applied to both larval stages through leaf dip method. In a novel approach, combined treatments of bacteria and endophytic fungi were compared with single-pathogen treatments. Relative to the single treatments, the combined pathogen treatments exhibited an increase in larval mortality, and decrease in pupation, adult emergence and egg eclosion. Specifically, synergistic effects on mortality were observed when larvae were exposed to simultaneous application of B. bassiana (1 × 108 conidia ml-1) with B. thuringiensis (0.75 μg ml-1). Both instars exhibited varying level of growth, development, frass production, diet consumption and fecundity when exposed to the chickpea leaves inoculated with endophytic B. bassiana and dipped with sub-lethal doses of B. thuringiensis. These findings indicate that the integrated application of endophytic colonized B. bassiana and B. thuringiensis can be effectively used against H. armigera.

Environmental tolerance of entomopathogenic nematodes differs among nematodes arising from host cadavers versus aqueous suspension

Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to -2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.

Integration of entomopathogenic fungi and eco-friendly insecticides for management of red palm weevil, Rhynchophorus ferrugineus (Olivier)

Red palm weevil (Rhynchophorus ferrugineus) is a voracious pest of date palm worldwide. Pakistan ranks sixth in date palm production globally. Losses to date palm plantations in Pakistan sometimes surpass 10%-20%. Most of the traditional management strategies used by farmers have been found insignificant to combat this voracious pest. The entomopathogenic fungi, Beauveria bassiana [QA-3(L) and QA-3(H)] and insecticides, Nitenpyram (Active 10% SL) [NIT (L) and NIT (H)] were applied to larval (2nd, 4th, and 6th), pupal and adult stages of R. ferrugienus. Integration or alone application of fungi with insecticides at different concentration under laboratory conditions. Combined application was depicted additive and synergistic interactions. Contrarily, highest cumulative mortality (100%) was recorded in 2nd instar larvae as compared to later instar larvae at combined application. The maximum pupal and adult mortality remained 89% and 66% respectively after treatment with [QA-3 (H) + NIT (L)]. The combination of B. bassiana at higher concentration whereas Nitenpyram at lower dose was found more lethal to larvae, pupae and adults of R. ferrugineus. This signifies the need of combining B. bassiana and bio-rational insecticides that can reduce the cost of management with least harm to environment and natural enemies.

Evaluating the combination of Metarhizium anisopliae and an enhanced form of diatomaceous earth (Grain-Guard) for the environmentally friendly control of stored grain pests

Stored grain pests cause great damage to various grain products, and protection against these pests is currently based on synthetic insecticides and fumigants. As a result, these chemicals cause problems, including grain contamination with chemical residues and the development of resistance by insect pests to these chemicals. Therefore, to combat this issue, in the present study, an enhanced form of diatomaceous earth (DE), Grain-Guard, and Metarhizium anisopliae (Metschnikoff) Sorokin (Ascomycota: Sordariomycetes) were evaluated alone and in combination against adults of Liposcelis paeta (Pearman) (Psocoptera: Liposcelididae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). M. anisopliae was used at a rate of 1.7 × 10⁴ conidia kg^-1 grain alone as well as with two doses of DE (25 and 50 ppm) on wheat under different exposure time courses (4, 7, and 14 days). It is worth mentioning that the combination of M. anisopliae and DE was highly effective against the adults of L. paeta, C. ferrugineus, R. dominica, and T. castaneum after 14 days of exposure. When DE and M. anisopliae were applied alone, DE showed more effectiveness than fungal conidia. Progeny emergence was decreased when modified DE was applied at a high dose rate with the fungus and suppressed at a low dose. The cadavers of all species in the trials showed a maximum percentage of mycosis, and sporulation (conidia/ml) also showed the same result when the fungus was tested alone, while low mycosis and sporulation were achieved under the application of a mixture with a high dose of modified DE. Our findings indicate the best possible combination of DE (at low dose rates) along with a fungus that might contribute to lowering health and environmental risks.

Potential of entomopathogenic nematodes against the pupal stage of the apple maggot Rhagoletis pomonella (Walsh) (Diptera: Tephritidae)

The apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), is considered a key pest of apples and is native to the eastern United States. The virulence of seven different species of entomopathogenic nematodes (EPN) was assessed against pupae of R. pomonella under laboratory conditions. Nematode species and strains included Steinernema carpocapsae (ALL strain), Steinernema feltiae (SN strain), Steinernema riobrave (355 strain), Steinernema glaseri (VS strain), Heterorhabditis bacteriophora (VS strain), Heterorhabditis indica (HOM1 strain), and Heterorhabditis megidis (UK211 strain). We conducted three bioassays: (i) short-term exposure cup bioassay (7 d), (ii) long-term cup bioassay (30 d), and (iii) pot bioassay (30 d). In the short-term exposure bioassay, all nematode strains (applied at 54 infective juvenile nematodes (IJs) cm-2) significantly reduced (range: 42.9-73.8%) insect survival relative to the control, but no differences were observed among the treatments. For the long-term exposure bioassay, using the same EPN application rate as the short exposure assay, all treatments reduced adult R. pomonella emergence compared with the control. Steinernema riobrave was the most virulent (28.3% survival), and S. glaseri and H. megidis were the least virulent (53.3% survival). In the pot experiment, S. riobrave and S. carpocapsae (applied at 27 IJs cm-2) had the highest virulence (23.3 and 31.7% survival of R. pomonella, respectively), while H. bacteriophora was the least effective (68.33% survival). Our results indicate that S. riobrave, S. carpocapsae, and S. feltiae have substantial potential to attack R. pomonella pupae, and their field application under the tree canopy (prior to adult emergence) in the spring when temperatures are conducive might be a good option for successful IPM of apple maggot fly.

The apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), is considered a key pest of apples and is native to the eastern United States. The virulence of seven different species of entomopathogenic nematodes (EPN) was assessed against pupae of R. pomonella under laboratory conditions. Nematode species and strains included Steinernema carpocapsae (ALL strain), Steinernema feltiae (SN strain), Steinernema riobrave (355 strain), Steinernema glaseri (VS strain), Heterorhabditis bacteriophora (VS strain), Heterorhabditis indica (HOM1 strain), and Heterorhabditis megidis (UK211 strain). We conducted three bioassays: (i) short-term exposure cup bioassay (7 d), (ii) long-term cup bioassay (30 d), and (iii) pot bioassay (30 d). In the short-term exposure bioassay, all nematode strains (applied at 54 infective juvenile nematodes (IJs) cm−2) significantly reduced (range: 42.9-73.8%) insect survival relative to the control, but no differences were observed among the treatments. For the long-term exposure bioassay, using the same EPN application rate as the short exposure assay, all treatments reduced adult R. pomonella emergence compared with the control. Steinernema riobrave was the most virulent (28.3% survival), and S. glaseri and H. megidis were the least virulent (53.3% survival). In the pot experiment, S. riobrave and S. carpocapsae (applied at 27 IJs cm−2) had the highest virulence (23.3 and 31.7% survival of R. pomonella, respectively), while H. bacteriophora was the least effective (68.33% survival). Our results indicate that S. riobrave, S. carpocapsae, and S. feltiae have substantial potential to attack R. pomonella pupae, and their field application under the tree canopy (prior to adult emergence) in the spring when temperatures are conducive might be a good option for successful IPM of apple maggot fly.

Biology and Control of the Khapra Beetle, Trogoderma granarium, a Major Quarantine Threat to Global Food Security

The khapra beetle, Trogoderma granarium, is a voracious feeder of stored products and is considered one of the most important quarantine pests globally. Its ability to survive for long periods under extreme conditions facilitates its spread through international commerce, which has led to invasions of new geographic regions. The khapra beetle is an important quarantine pest for many countries, including the major wheat-producing countries the United States, Canada, Russia, and Australia, and has been classified as one of the 100 worst invasive species worldwide. This species cannot always be controlled by insecticides and other nonchemical methods that are usually effective against other pests of stored products, particularly owing to its diapausing late larval stage. It can rapidly develop at elevated temperatures and under dry conditions, which are not favorable for many major stored-product insects. We synthesize key published work to draw attention to advances in biology, detection and control of the khapra beetle, and directions to consider for future research.

Resistance to commonly used insecticides and phosphine fumigant in red palm weevil, Rhynchophorus ferrugineus (Olivier) in Pakistan

The red palm weevil Rhynchophorus ferrugineus (Olivier) is an important pest of date palms in many regions of the world. This paper reports the first survey of insecticide resistance in field populations of R. ferrugineus in Pakistan which were collected from seven date palm growing areas across Punjab and Khyber Pakhtunkhwa (KPK) provinces, Pakistan. The resistance was assessed by the diet incorporation method against the formulated commonly used chemical insecticides profenophos, imidacloprid, chlorpyrifos, cypermethrin, deltamethrin, spinosad, lambda-cyhalothrin and a fumigant phosphine. Elevated levels of resistance were recorded for cypermethrin, deltamethrin and phosphine after a long history of insecticide use in Pakistan. Resistance Ratios (RRs) were 63- to 79-fold for phosphine, 16- to 74-fold for cypermethrin, 13- to 58-fold for deltamethrin, 2.6- to 44-fold for profenophos, 3- to 24-fold for chlorpyrifos, 2- to 12-fold for lambda-cyhalothrin and 1- to 10-fold for spinosad compared to a susceptible control line. Resistant R. ferrugineus populations were mainly found in southern Punjab and to some extent in KPK. The populations from Bahawalpur, Vehari, Layyah and Dera Ghazi Khan were most resistant to chemical insecticides, while all populations exhibited high levels of resistance to phosphine. Of the eight agents tested, lower LC50 and LC90 values were recorded for spinosad and lambda-cyhalothrin. These results suggest that spinosad and lambda-cyhalothrin exhibit unique modes of action and given their better environmental profile, these two insecticides could be used in insecticide rotation or assist in phasing out the use of older insecticides. A changed pattern of both insecticides can be used sensibly be recommended without evidence of dose rates and frequencies used.

Effects of single and combined applications of entomopathogenic fungi and nematodes against Rhynchophorus ferrugineus (Olivier)

This study was carried out to investigate the insecticidal properties of Beauveria bassiana, Metarhizium anisopliae and Heterorhabditis bacteriophora for their virulence against different larval instars of Rhynchophorus ferrugineus (Olivier). Both fungi were either applied alone or in combination, with H. bacteriophora simultaneously or 1 and 2 weeks after fungal application; EPN were also applied alone. Moreover, assessment of host development, diet consumption, frass production and weight gain were observed at sub-lethal dose rates. In combined treatments, additive and synergistic interactions were observed. Synergism was observed more frequently in H. bacteriophora + B. bassiana combinations than in H. bacteriophora + M. anisopliae combinations, and was higher in early instars than old instars. In 2^nd and 4^th instars, synergy was noted in H. bacteriophora + B. bassiana combinations at 0, 7 and 14 d intervals and in 6^th instar synergy was observed only in H. bacteriophora + B. bassiana combinations (at 0 and 7 d intervals). A decrease in pupation, adult emergence and egg hatching was enhanced in the combined treatments. Furthermore, reduced weights and variation in duration of insect developmental stages were observed among entomopathogens and enhanced in H. bacteriophora + B. bassiana combinations. Larvae treated with sub-lethal concentrations exhibited reductions in food consumption, growth and frass production and weight gain.

The efficacy of Beauveria bassiana, jasmonic acid and chlorantraniliprole on larval populations of Helicoverpa armigera in chickpea crop ecosystems

BACKGROUND

A robust integrated pest management (IPM) programme is needed to reduce the use of insecticides in controlling Helicoverpa armigera. Therefore, a 2 year field study was conducted to evaluate the use of alternative control measures (biochemical use) for H. armigera relative to exclusively using chemical insecticides. The entomopathogenic fungus Beauveria bassiana, jasmonic acid and the insecticide chlorantraniliprole were each applied twice during the chickpea growing season.

RESULTS

All three applied materials (either alone or combined) significantly (P ≤ 0.05) reduced the larval population of H. armigera and pod infestation. Effects increased with time, and the maximum difference was observed 7 days after the second application in each year. The lowest numbers of larvae per plant and pod infestation were in the B. bassiana 3.21 × 10⁶ + chlorantraniliprole treatment in both 2009/2010 and 2010/2011 year. The reduction in the larval population and pod infestation increased chickpea yield and the highest yield in both seasons, and the maximum yield was obtained in the B. bassiana 3.21 × 10⁶ + chlorantraniliprole treatment. The populations of natural enemies were highest in the jasmonic acid treatment.

CONCLUSION

The results suggest that B. bassiana, jasmonic acid and chlorantraniliprole may be useful components for the H. armigera IPM strategy. © 2016 Society of Chemical Industry.

Mitochondrial DNA Variation Among Populations of Rhynchophorus ferrugineus (Coleoptera: Curculionidae) From Pakistan

The Red Palm Weevil (RPW) Rhynchophorus ferrugineus (Olivier) is a voracious pest of palm species. In recent decades its range has expanded greatly, particularly impacting the date palm industry in the Middle East. This has led to conjecture regarding the origins of invasive RPW populations. For example, in parts of the Middle East, RPW is commonly referred to as the "Pakistani weevil" in the belief that it originated there. We sought evidence to support or refute this belief. First reports of RPW in Pakistan were from the Punjab region in 1918, but it is unknown whether it is native or invasive there. We estimated genetic variation across five populations of RPW from two provinces of Pakistan, using sequences of the mitochondrial cytochrome oxidase subunit I gene. Four haplotypes were detected; two (H1 and H5) were abundant, accounting for 88% of specimens across the sampled populations, and were previously known from the Middle East. The remaining haplotypes (H51 and H52) were newly detected (in global terms) and there was no geographic overlap in their distribution within Pakistan. Levels of haplotype diversity were much lower than those previously recorded in accepted parts of the native range of RPW, suggesting that the weevil may be invasive in Pakistan. The affinity of Pakistani haplotypes to those reported from India (and the geographical proximity of the two countries), make the latter a likely "native" source. With regards the validity of the name "Pakistani weevil", we found little genetic evidence to justify it.

Multiple Resistances Against Formulated Organophosphates, Pyrethroids, and Newer-Chemistry Insecticides in Populations of Helicoverpa armigera (Lepidoptera: Noctuidae) from Pakistan

Field populations of Helicoverpa armigera Hübner from 15 localities across the Punjab, Pakistan, were assessed by the leaf dip method for resistance against formulated organophosphates, pyrethroids, and newer insecticide groups. Resistance levels in H. armigera have been incrementally increasing for organophosphate and pyrethroid insecticides after decades of use in Pakistan. Resistance ratios (RRs) documented for organophosphates were 24- to 116-fold for profenofos and 22- to 87-fold for chlorpyrifos. For pyrethroids, RRs were 3- to 69-fold for cypermethrin and 3- to 27-fold for deltamethrin. Resistance levels against newer chemistries were 2- to 24-fold for chlorfenapyr, 1- to 22-fold for spinosad, 1- to 20-fold for indoxacarb, 1- to 18-fold for abamectin, and 1- to 16-fold for emamectin benzoate. Resistant populations of H. armigera were mainly in the southern part of the Punjab, Pakistan. The most resistant populations were collected from Pakpattan, Multan, and Muzzafargarh. Of the nine insecticides tested, LC50 and LC90 values were lower for newer insecticide groups; resistance levels were moderate to very high against organophosphates, very low to high against pyrethroids, and very low to low against the newer-chemistry insecticides. These findings suggest that the newer-chemistry insecticides with different modes of action could be included in insecticide rotations or replace the older insecticides. Supplementing the use of synthetic insecticides with safer alternatives could help to successfully lower the farmer's reliance on insecticides and the incidence of resistance due to repeated use of insecticides against major insect pests.

Naturally occurring entomopathogenic fungi infecting stored grain insect species in Punjab, Pakistan

The occurrence of entomopathogenic fungi isolated from stored grain insect pests sampled from various geographical regions of Punjab, Pakistan, was investigated. In total, 25,720 insects from six different species were evaluated, and 195 isolates from 24 different fungal species were recovered. These included the Ascomycetes Beauveria bassiana sensu lato (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae), Metarhizium anisopliae sensu lato (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae), Purpureocillium lilacinum (Thorn) Samson (Hypocreales: Ophiocordycipitaceae), and Lecanicillium attenuatum (Zare and W. Gams) (Hypocreales: Clavicipitaceae). The cadavers of red flour beetle Tribolium castaneum (Herbst.) (Coleoptera: Tenebrionidae) were significantly infected with the fungi followed by rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae), lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), rusty grain beetle Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae), and cowpea weevil Callosobruchus maculatus (F.) (Coleoptera: Bruchidae); however, the least were recovered from khapra beetle Trogoderma granarium (Everts) (Coleoptera: Dermestidae). The geographical attributes (altitude, longitude, and latitude) greatly influenced the occurrence of entomopathogenic fungi with highest number of isolates found from >400 (m) altitude, 33°-34' N latitude, and 73°-74' E longitude. The findings of the current surveys clearly indicated that the entomopathogenic fungi are widely distributed in the insect cadavers, which may later be used in successful Integrated Pest Management programs.