Biological control agents and levels of parasitism of <i>Agrotis segetum</i> (Lepidoptera: Noctuidae) in grain production regions of South Africa

Vegetation drives assemblages of entomopathogenic nematodes and other soil organisms: Evidence from the Algarve, Portugal

False codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), is a priority pest on citrus, stone fruit, and table grapes. Current control focuses on the adult stage; however, each stage of the life cycle of the insect should be targeted. The potential of local biocontrol agents against FCM immature stages was investigated. Several entomopathogenic nematode (EPN) and entomopathogenic fungus (EPF) species were identified from soil samples collected from orchards and vineyards throughout the Western Cape province in South Africa. The eggs were proven to be susceptible (30–65%) to several EPN species, at 200 infective juveniles (IJs) per 50 µl. Xenorhabdus indica, the symbiotic bacterium of Steinernema yirgalemense Nguyen et al., caused significantly more mortality than the control. The EPNs were highly virulent against the FCM larvae, with S. yirgalemense causing 100% mortality in all trials. Metarhizium robertsii (78%), M. anisopliae (50%), and Beauveria bassiana (75%) caused high mortality in FCM larvae. The fully formed pupae were the most resistant of the immature stages, with the EPNs causing low mortality at 100 IJs per insect. As the FCM larvae were highly susceptible to S. yirgalemense and M. robertsii under laboratory conditions, they should be further tested, separately and in combination, in field conditions to illustrate the benefits of including them in a FCM‐IPM programme.

Previous laboratory studies have indicated the potential of some entomopathogenic nematode (EPN) species for the control of larvae of the black cutworm (BCW). To determine the most promising EPN species and the most susceptible BCW stages, a more in-depth evaluation of seven EPN species against different BCW instars was carried out, the efficacies of in vitro- and in vivo-produced EPNs were compared and the suitability of BCW instars for EPN reproduction was examined. Heterorhabditis megidis was the most virulent species, irrespective of larval stage in small arenas, followed most often by H. bacteriophora. In pots with grass, Steinernema carpocapsae tended to be the most virulent species, followed by H. bacteriophora, H. megidis and S. riobrave. Fourth and/or fifth instars were the most susceptible stages to most EPN species, and pupae the least susceptible. Furthermore, H. bacteriophora, H. megidis and S. carpocapsae successfully reproduced in fifth and sixth instars and pupae. In vivo-produced H. megidis and S. carpocapsae controlled fifth instars better than the corresponding in vitro-produced products; production method did not affect H. bacteriophora and S. riobrave efficacy. Several in vitro-produced commercial EPN strains were highly virulent to BCW and warrant further testing under field conditions, along with some in vivo-produced strains.

Entomopathogenic nematode food web assemblages in Florida natural areas

Simple SummaryThe plum curculio, a snout beetle native to North America, is one of the most important fruit-feeding pests of cultivated blueberry in New Jersey. Application of certain entomopathogenic nematode (EPN) species has shown efficacy in plum, peach, and apple orchards when targeting the larval stage of plum curculio in soil. Prior to our research, however, EPNs have never been tested for control of this pest in highbush blueberries. In 2020, laboratory and field studies were conducted to: (1) determine the persistence of different EPN species in acidic blueberry soil; (2) compare the virulence of these EPNs to plum curculio larvae and pupae; and (3) compare the efficacy of these EPNs to control this pest in blueberry fields. In 2021, field studies were conducted to confirm the efficacy of one of the EPN species. Steinernema riobrave persisted better in blueberry sand, was the most virulent EPN against plum curculio larvae and pupae and was highly efficacious for suppression of larvae and pupae of this pest in blueberry fields. Steinernema riobrave has the potential to become an important component in the management of plum curculio in highbush blueberry.Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae) is a key pest of stone and pome fruits in the United States. Application of certain entomopathogenic nematode (EPN) species has shown efficacy in some crops when targeting the larval stage of C. nenuphar in soil. To date, however, no EPNs have been tested for the control of this pest in highbush blueberries. In 2020, laboratory and field studies were conducted to: (1) determine the persistence of Steinernema riobrave, S. carpocapsae, S. feltiae, and Heterorhabditis bacteriophora in acidic blueberry soil; (2) compare the virulence of these EPNs to C. nenuphar larvae and pupae; and (3) compare the efficacy of these EPN species to control this pest in blueberry fields. The greatest persistence in blueberry soil was exhibited by S. riobrave followed by S. carpocapsae. Superior virulence was observed in S. riobrave against C. nenuphar larvae and pupae. Promising levels of virulence were also observed in S. carpocapsae and S. feltiae against the larvae, but S. scarabaei had low virulence. In the field, S. riobrave provided significantly higher levels of C. nenuphar suppression (90%) than the other EPNs. The field efficacy of S. riobrave against C. nenuphar at low and high rates was confirmed in 2021. Steinernema riobrave has the potential to become an important component in the management of C. nenuphar in highbush blueberry.

One of the constraints in the use of entomopathogenic nematodes as biological control agents is their interaction with other soil microorganisms. Competition studies with two species of entomopathogenic nematodes, particularly a heterorhabditid and a steinernematid, indicate that incompatibilities exist within an insect host usually resulting in the death of both nematode species. Although these incompatibilities occur within a host, the coexistence of two nematode species with different attack strategies may be possible because of spatial and temporal separation of the species. Similarly, entomopathogenic nematodes and the entomopathogenic fungus Beauveria bassiana are antagonistic to one another within the same host. Yet, coexistence in the soil is likely because the nematodes are not attracted to fungus-infected insects. The combined application of both pathogens should provide better reduction of a susceptible pest than either pathogen alone. The milky disease bacterium, Bacillus popilliae, a pathogen of scarabaeid larvae, and a heterorhabditid nematode show compatibility. Thus, B. popilliae may be used as a stressing agent to make scarabaeid larvae more susceptible to heterorhabditid infection. Finally, nematode-parasitic fungi may be antagonistic to entomopathogenic nematodes. For example, the fungus Hirsutella rhossiliensis infects several species of entomopathogenic nematodes. However, its infectivity varies between nematode species and a less-susceptible nematode species may be more efficacious against an insect pest in soils infested with this fungus.

Entomopathogenic nematode (EPN) species richness merits studies towards making rational decisions for effective management of Caribfly, Anastrepha suspensa (Loew) in southern Florida. Competition for Caribfly and efficacies of EPN biodiversity were examined under laboratory conditions. Similar EPN species treatments to Caribfly-infested fruits, periodically obtained from the ground in groves which were also infested by the parasitoid Diachasmimorpha longicaudata Ashmead (Braconidae), were studied in a series of field trials. Treatments with individual EPN species and their mixtures caused similar mortalities of Caribfly larvae, though the various EPN species competed for larvae in multiple-species treatments. Laboratory trials showed that mortalities of EPN-treated Caribfly pupae were mostly inversely related to EPN diversity. In the field, population densities of emerging adult Caribfly increased with increasing number of EPN species combined in treatments. Thus, single-EPN species treatments proved to be more effective for the management of fruit-to-soil stages of Caribfly. Relative to controls, the proportions of surviving adult Caribfly observed in EPN treatments with Heterorhabditis bacteriophora (exotic in Florida), Steinernema feltiae (exotic EPN) and Heterorhabditis indica (the endemic species) in field plots were 22.5 ± 6, 45 ± 13 and 47 ± 13%, respectively. Number of emerging D. longicaudata in each of EPN species treatments was similar to that observed in control, suggesting that none of the EPN species significantly affected the emergence of D. longicaudata, a parasitoid of Caribfly. Heterorhabditis bacteriophora will be more promising, with insignificant side effects on D. longicaudata in Caribfly-integrated pest management.

Surveying and screening South African entomopathogenic nematodes for the control of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann)

Relative virulence, host finding ability, and reproductive capacity of entomopathogenic nematodes for control of the goat biting louse Bovicola caprae (Phthiraptera: Trichodectidae).

Entomopathogenic nematodes, fungi, and low risk insecticides were evaluated for the management of the wheat stem sawfly, Cephus cinctus Norton, in winter wheat at two locations (Devon and Western Triangle Ag Research center) in the Golden Triangle area of Montana (USA) in 2013. Two fungi (Beauveria bassiana and Metarhizium brunneum), four nematodes species (Steinernema carpocapsae, Steinernema kraussei, Steinernema feltiae, and Heterorthabditis bacteriophora), an insect growth regulator (diflubenzuron/dimilin), and a botanical-based chemical (azadirachtin/Aza-direct) were used as foliar sprays. These control agents significantly reduced damage caused by C. cinctus larvae, compared to the untreated control or treatment with water alone. No yield differences were observed among entomopathogenic fungi, nematodes, and low risk insecticides. The effectiveness of azadirachtin, diflubenzuron, the entomopathogenic fungi, and the nematodes persisted at the 28th day post application, by which time the wheat had been harvested. Stubbles collected after harvest showed significantly fewer sawfly larvae in the plots treated with entomopathogenic fungi, nematodes, diflubenzuron, and azadirachtin compared to the untreated and water spray plots, indicating that these biorational pesticides have potential to be used as alternatives to conventional pesticides for controlling the wheat stem sawfly larvae.

Entomopathogenic nematodes as biological control agent against Bactrocera zonata and Bactrocera dorsalis (Diptera: Tephritidae)

Mechanized production and delivery of biological pesticides presents challenges because the biological agents must remain viable during these processes. This study evaluates the effect of flow through an abrupt contraction, where flow characteristics similar to that found within bioprocesses and spray equipment are developed, on damage to a benchmark biological pest control agent, entomopathogenic nematodes (EPNs). An opposed-pistons, contraction flow device generated volumetric flow rates ranging between 8.26 cm(3)/s and 41.3 cm(3)/s. Four EPN species were evaluated: Heterorhabditis bacteriophora, Heterorhabditis megidis, Steinernema carpocapsae, and Steinernema glaseri. Damage was quantified by counting living and dead EPNs. Optical and cold field emission scanning electron microscope (CFE-SEM) images provided qualitative information to describe how the damage occurred. The experimental flow field was completely described using FLUENT, a computational fluid dynamics program. Local flow parameters computed in FLUENT were compared to EPN damage. The type and extent of damage varied between EPN species. Damaged Heterorhabditis spp. generally remained whole with an internal rupture located near the center of the body, while Steinernema spp. most often broke into several pieces. The fast-transient stress field generated at the entrance to the contraction caused a momentary tensile loading and then relaxation that damaged the EPNs. At high flow rates, the tensile stresses became large enough to cause failure of the EPN structural membrane. The relative elasticity of the EPN structural membrane may explain the differences in damage observed between the species. It is speculated that the internal rupture of the Heterorhabditis spp. occurred during the processes of stretching and relaxing at the contraction entrance. Appreciable damage was observed at lower average energy dissipation rates for H. bacteriophora (1.23E + 8 W/m(3)), H. megidis (1.72E + 8 W/m(3)), and S. glaseri (2.89E + 8 W/m(3)) compared to S. carpocapsae (3.70E + 8 W/m(3)). Energy dissipation rates within an equipment component should be kept below 1E + 8 W/m(3) to avoid hydrodynamic damage to EPNs. The relationship between average energy dissipation and EPN damage provides important information for future simulation efforts of actual spray equipment components.

Pieris canidia is one of the serious pests of cruciferous crops causing extensive damage to agricultural crops. Entomopathogenic nematodes (EPNs) therefore represent ideal candidates for biological control of the pest. In this study, the efficacy of four indigenous EPNs species, Heterorhabditis indica, Heterorhabditis baujardi, Steinernema sangi, and Steinernema surkhetense from Mizoram was evaluated against P. canidia under laboratory condition. Different concentrations of nematodes, 10, 25, 50, 100, and 200 infective juveniles per larva (IJs/larva) were used to evaluate larval mortality rate, host penetration rate, and progeny production in insect cadaver. All the four EPN species showed high pathogenicity against the pest for different nematode concentrations and observation periods. At a concentration of 200 IJs/larva, cent percent mortality of the pest was recorded at 72 hr post-incubation for S. surkhetense, 96 hr for S. sangi and H. indica, and 120 hr post-incubation for H. baujardi. Based on the values of LC50 and LT50, H. indica was the most pathogenic among the four nematode species while S. sangi was the least pathogenic. After 24 hr of incubation, the LC50 values of H. indica, H. baujardi, S. surkhetense, and S. sangi were 88.60, 98.29, 113.26 and 95.61 IJs/larva, respectively. At 10 IJs/larva, the LT50 values of H. indica, H. baujardi, S. sangi, and S. surkhetense were 88.12, 90.69, 88.102.30, and 88.11 hr, respectively. The study also disclosed that all the four EPN species successfully infect the pest and showed high rate of penetration into the host. Furthermore, all the nematode isolates were capable of producing large numbers of IJs in larval cadaver of P. canidia that significantly varies between the EPN species. The isolate H. baujardi produced the highest number of IJs followed by H. indica, S. surkhetense, and S. sangi. Our findings therefore reveal that all the four EPN isolates have the potential to be developed as biological control agents for P. canidia.

Boring-insects as factors in tropical industries

Chapter 20 - Microbial Control of Sugarcane Insect Pests