Ana Morton

Efficacy of entomopathogenic nematodes against the tomato leafminer Tuta absoluta in laboratory and greenhouse conditions

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an important pest of tomato crops in South America and it has recently arrived in Europe affecting tomato plantations. The susceptibility of T. absoluta larvae and pupae to three species of entomopathogenic nematodes (Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora) was examined under laboratory conditions. Leaf bioassays were conducted to evaluate the nematode’s capability to reach the larvae and kill them within the galleries. The efficacy of the three nematode species after foliar application to potted tomato plants was evaluated under greenhouse conditions. High larval mortality (78.6–100%) and low pupae mortality (<10%) was determined in laboratory experiments. In the leaf bioassay a high level of larval parasitation (77.1–91.7%) was recorded revealing the nematode’s capacity to kill the larvae inside the galleries. In the pot experiments nematode treatment reduced insect infection of tomato plants by 87–95%. The results demonstrate the suitability of entomopathogenic nematodes for controlling T. absoluta.

Efficacy of entomopathogenic nematodes against neonate larvae of Capnodis tenebrionis (L.) (Coleoptera: Buprestidae) in laboratory trials

The efficacy of five entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae was tested against the neonate larvae of Capnodis tenebrionis. The nematode strains screened included two of Steinernema carpocapsae (Exhibit and M137), and one each of S. feltiae (S6), S. arenarium (S2), and Heterorhanditis bacteriophora (P4). Exposure of neonate larvae of Capnodis to 10 and 150 infective juveniles (IJs) per larva (equivalent to 3 and 48 IJs/cm2 respectively) in test tubes with sterile sand, resulted in mortality between 60–91% and 96–100%, respectively. At a concentration of 150 IJs/larva, all of the nematode strains were highly virulent. Both S. carpocapsae strains (Exhibit and M137) caused infection and mortality to larvae more quickly than the other strains. However, at a lower concentration assay (10 IJs/larva), S. arenarium was the most virulent strain. The penetration rate as an indicator of entomopathogenic nematode infection was also evaluated. The highest value was recorded for S. arenarium (36%), followed by H. bacteriophora (30.6%), S. feltiae (23.1%), and S. carpocapsae (20.7%).

Ecological characterization of entomopathogenic nematodes isolated in stone fruit orchard soils of Mediterranean areas

Entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae were isolated from stone-fruit orchards in two Mediterranean regions of Spain. A total of 630 soil samples (210 sites) from Catalonia and 90 soil samples (30 sites) from Murcia were evaluated resulting in 5.2% and 20% of the soils testing positive for nematodes, respectively. Ten steinernematid isolates and three heterorhabditid isolates were recovered using the Galleria mellonella baiting method. Based on morphometric data, molecular data, and cross-breeding experiments the nematode species were identified as Steinernemafeltiae and Heterorhabditis bacteriophora. Environmental tolerance to heat, desiccation and hypoxia, the effect of temperature on infectivity and reproduction and nematode migration in sand columns were compared among isolates and one Steinernema carpocapsae strain. Results showed differences among species and a great variability within species. Beneficial traits for each strain were added up to identify a superior candidate to control Mediterranean flat-headed rootborer, Capnodis tenebrionis. When all analyzed factors were considered, three S. feltiae isolates (Bpa, Sor and M116) obtained the best scores, and when hypoxia was removed, two of the strains (Bpa and Sor) continued ranking superior to other strains.

Field efficacy of the entomopathogenic nematode Steinernema feltiae against the Mediterranean flat‐headed rootborer Capnodis tenebrionis

The Mediterranean flat‐headed rootborer, Capnodis tenebrionis (L.) (Coleoptera: Buprestidae), is an economically important pest of stone fruit and seed fruit in Mediterranean areas. The potential control of the entomopathogenic nematode Steinernema feltiae (Filipjev) (strain Bpa), isolated from a dead C. tenebrionis larva, was tested in a cherry tree orchard in Ullastrell, Barcelona (Spain). Nematode infective juveniles (IJs) were applied by drench and injection. In both the treatments, a rate of 1 million IJs was applied per tree every week during 4 or 8 weeks, with a total dose of 4 × 106 IJs/tree and 8 × 106 IJs/tree. Number, stage and localization of insects in each tree trunk were recorded. In both the experiments, S. feltiae significantly reduced the population of C. tenebrionis providing control ranging from 88.3% to 97%. No significant differences were recorded between the different treatments. Persistence of nematodes was recorded until 6 weeks after application. Results indicate that the application of S. feltiae (Bpa) provides adequate control of C. tenebrionis in cherry trees.

Virulence of entomopathogenic nematodes to different stages of the flatheaded root borer, Capnodis tenebrionis (L.) (Coleoptera: Buprestidae).

The virulence of 14 Steinernema feltiae isolates, one S. carpocapsae and three Heterorhabditis bacteriophora isolates was compared in the laboratory against larvae, pupae and adults of the flatheaded root borer, Capnodis tenebrionis . Larval mortality ranged from 50 to 100% and pupae mortality from 0 to 70%. Adults were exposed to different nematode concentrations, 50 and 100 infective juveniles/cm 2 . Steinernema feltiae caused the highest mortality at the two doses tested, reaching 66.7% and 100%, respectively. Significant differences in mortality between C. tenebrionis males and females were observed. The differences in virulence observed at each stage of C. tenebrionis vary within a species and can be higher than differences among species. The results of this study suggest that some of the isolate strains have potential for improved biological control of C. tenebrionis .

Sex-related differences in the susceptibility of Periplaneta americana and Capnodis tenebrionis to the entomopathogenic nematode Steinernema carpocapsae

Entomopathogenic nematodes have a broad range of insect hosts, but efficacy varies depending on many factors including insect species and life stage of the host. In this study we examined the susceptibility of males and females of two insect species, the American cockroach Periplaneta americana and the flatheaded rootborer Capnodis tenebrionis to Steinernema carpocapsae by exposing adults to different concentrations. A separate study examined the routes of entry used by nematodes into males and females. Males of both species were more susceptible than females, with greater than 97% infection when a concentration of 50 IJs/cm(2) was applied, whereas mortalities lower than 58% were achieved against females 14 days post-infection. Infective juveniles were detected in similar number on the surface of both sexes, but when compared among internal regions the number of nematodes was significantly higher in gonads and ducts of males than of females for P. americana (5.49 in males; 0.02 in females) and C. tenebrionis (6.88 in males; 0.00 in females).

Synergistic effect of the herbicides glyphosate and MCPA on survival of entomopathogenic nematodes

Abstract The survival and infectivity of the infective juveniles of two species of entomopathogenic nematodes, Steinernema feltiae (Rhabditida: Steinernematidae) Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae), were determined after exposure for 72 h to two concentrations of the herbicides glyphosate and MCPA, as well as to the combination of the two herbicides (glyphosate + MCPA). For all herbicide treatments, concentrations and exposure times, S. feltiae was more tolerant to the herbicides than H. bacteriophora. The exposure of entomopathogenic nematodes to glyphosate + MCPA caused significantly higher mortality (26.33–57.33%) than glyphosate (0.67–15%) or MCPA (2.33–19%) alone. These results confirm the synergistic effect of the glyphosate + MCPA combination on the mortality in these nematodes. Nematode infectivity of Galleria mellonella larvae in response to the herbicides presence was evaluated in Petri dish assays containing sterile sand. Nematode infectivity was not significantly reduced by exposure to herbicides in S. feltiae but H. bacteriophora was less tolerant. Synergistic effect was obtained in the nematode mortality test but no synergistic effect was observed in the nematode infectivity assay. Our results suggest that possible synergistic effects of agrochemicals on survival of nematodes should be tested before mixing with entomopathogenic nematodes.

Isolation and virulence of entomopathogenic fungi against larvae of hazelnut weevil Curculio nucum (Coleoptera, Curculionidae) and the effects of combining Metarhizium anisopliae with entomopathogenic nematodes in the laboratory

Abstract An approach to ensure effective pest biocontrol would be to select native isolates of biological control agents (BCAs). A survey to isolate entomopathogenic fungi (EPF) from a hazelnut growing area has been carried out. EPF were recovered from 133 of the 295 soil samples. The main species isolated were Metarhizium anisopliae sensu lato (36%) and Beauveria bassiana sensu lato (42.8%). With regard to controlling abiotic factors, altitude had an effect on the distribution of B. bassiana, but not on M. anisopliae. Cropping system did not have an effect on the occurrence of these EPF, while pH appeared as a predictive variable for both. In addition, we tested the virulence of six of these isolates: three M. anisopliae and three of B. bassiana against larvae of Curculio nucum L. The highest larval mortality (reaching 80%) was due to M. anisopliae (strain 34) when applied in simultaneous combination with four entomopathogenic nematode species: Steinernema carpocapsae (strain B14), Steinernema feltiae (strain D114), Steinernema. sp. (strain D122) and Heterorhabditis bacteriophora (strain DG46). The effect of nematodes was greater and no antagonistic or synergistic effects were observed.

Virulence of entomopathogenic nematodes and their symbiotic bacteria against the hazelnut weevil Curculio nucum.

The virulence of different entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae, isolates from Catalonia (NE Iberian Peninsula), and their symbiotic bacteria was assessed with regard to the larvae and adults of the hazelnut weevil, Curculio nucum L. (Coleoptera: Curculionidae). The nematode strains screened included one Steinernema affine, five Steinernema feltiae, one Steinernema carpocapsae, one Steinernema sp. (a new species not yet described) and one Heterorhabditis bacteriophora. The pathogenicity of all the strains of nematodes was tested on larvae and only four of them on adults of the hazelnut weevil. Larval mortality ranged from 10% with S. affine to 79% with Steinernema sp. Adult mortality was higher in S. carpocapsae, achieving 100% adult weevil mortality. The pathogenicity of the symbiotic bacteria Xenorhabdus bovienii, X. kozodoii, X. nematophila and Photorhabdus luminescens was studied in larvae and adults of C. nucum. In the larvae, X. kozodoii showed a LT50 of 22.7 h, and in the adults, it was 20.5 h. All nematodes species except S. affine tested against larvae showed great potential to control the insect, whereas S. carpocapsae was the most effective for controlling adults.

Is Drosophila suzukii as susceptible to entomopathogenic nematodes as Drosophila melanogaster

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is the major invasive pest of small, soft-skinned and stone fruits, with a wide range of hosts. This study aims to test the susceptibility of this insect to entomopathogenic nematodes (EPNs) and their efficacy on infested fruits from first instar larvae to adult emergence. Drosophila suzukii and D. melanogaster (Meigen) (Diptera: Drosophilidae) were susceptible to Steinernema carpocapsae (Weiser) (Rhabditida: Steinernematidae), S. feltiae (Filipjev) (Rhabditida: Steinernematidae), Steinernema sp. (glaseri group) (Filipjev) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora (Poinar) (Rhabditida: Heterorhabditidae) on two substrates (filter paper and agar). The greater efficacy against D. suzukii was achieved by S. feltiae and S. carpocapsae (94 and 84%, respectively) with equal efficacy than that obtained using D. melanogaster as host (93.37 and 92.88%, respectively). The EPNs infected and could reproduce inside D. suzukii larvae. In contrast, pupae of both species were not infected by them. Nematodes proved to be able to reduce adult emergence of D. suzukii (up to 35% by S. feltiae) on strawberry fruit under laboratory conditions. These results show that D. suzukii is as susceptible as D. melanogaster to EPNs, confirming the potential of these nematodes as biological control agents against this important pest.