Albrecht M. Koppenhöfer

Effects of microbial and other antagonistic organism and competition on entomopathogenic nematodes

Antagonistic factors, broadly identified as antibiosis, competition and natural enemies, impact on entomopathogenic nematodes. Antibiosis can occur through the release of plant chemicals from the roots into the soil, which may adversely affect the host-finding behavior of the infective stage nematode, or the presence of these chemicals in the host insect may negatively affect nematode reproduction. In laboratory studies, intra-specific and inter-specific competition reduces nematode fitness, and inter-specific competition can cause local extinction of a nematode species. For example, after concomitant infection of a host, a steinernematid species usually excludes a heterorhabditid species. The mechanism for the steinernematid superiority has been postulated to be a bacteriocin(s) produced by Xenorhabdus, the symbiotic bacterium of the steinernematid, which prevents Photorhabdus, the symbiotic bacterium of the heterorhabditid, from multiplying. Inter-specific competition between two steinernematid species ...

Synergism of imidacloprid and entomopathogenic nematodes against white grubs: the mechanism.

Entomopathogenic nematodes and the chloronicotinyl insecticide, imidacloprid, interact synergistically on the mortality of third‐instar white grubs (Coleoptera: Scarabaeidae). The degree of interaction, however, varies with nematode species, being synergistic for Steinernema glaseri (Steiner) and Heterorhabditis bacteriophora Poinar, but only additive for Steinernema kushidai Mamiya. The mechanism of the interaction between imidacloprid and these three entomopathogenic nematodes was studied in the laboratory. In vials with soil and grass, mortality, speed of kill, and nematode establishment were negatively affected by imidacloprid with S. kushidai but positively affected with S. glaseri and H. bacteriophora. In all other experiments, imidacloprid had a similar effect for all three nematode species on various factors important for the successful nematode infection in white grubs. Nematode attraction to grubs was not affected by imidacloprid treatment of the grubs. Establishment of intra‐hemocoelically injected nematodes was always higher in imidacloprid‐treated grubs but the differences were small and in most cases not significant. The major factor responsible for synergistic interactions between imidacloprid and entomopathogenic nematodes appears to be the general disruption of normal nerve function due to imidacloprid resulting in drastically reduced activity of the grubs. This sluggishness facilitates host attachment of infective juvenile nematodes. Grooming and evasive behavior in response to nematode attack was also reduced in imidacloprid‐treated grubs. The degree to which different white grub species responded to entomopathogenic nematode attack varied considerably. Untreated Popillia japonica Newman (Coleoptera: Scarabaeidae) grubs were the most responsive to nematode attack among the species tested. Untreated Cyclocephala borealis Arrow (Coleoptera: Scarabaeidae) grubs showed a weaker grooming and no evasion response, and untreated C. hirta LeConte (Coleoptera: Scarabaeidae) grubs showed no significant response. Chewing/biting behavior was significantly increased in the presence of nematodes in untreated P. japonica and C. borealis but not in C. hirta and imidacloprid‐treated P. japonica and C. borealis. Our observations, however, did not provide an explanation for the lack of synergism between imidacloprid and S. kushidai.

Subterranean, Herbivore-Induced Plant Volatile Increases Biological Control Activity of Multiple Beneficial Nematode Species in Distinct Habitats

While the role of herbivore-induced volatiles in plant-herbivore-natural enemy interactions is well documented aboveground, new evidence suggests that belowground volatile emissions can protect plants by attracting entomopathogenic nematodes (EPNs). However, due to methodological limitations, no study has previously detected belowground herbivore-induced volatiles in the field or quantified their impact on attraction of diverse EPN species. Here we show how a belowground herbivore-induced volatile can enhance mortality of agriculturally significant root pests. First, in real time, we identified pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene) from citrus roots 9–12 hours after initiation of larval Diaprepes abbreviatus feeding. This compound was also detected in the root zone of mature citrus trees in the field. Application of collected volatiles from weevil-damaged citrus roots attracted native EPNs and increased mortality of beetle larvae (D. abbreviatus) compared to controls in a citrus orchard. In addition, field applications of isolated pregeijerene caused similar results. Quantitative real-time PCR revealed that pregeijerene increased pest mortality by attracting four species of naturally occurring EPNs in the field. Finally, we tested the generality of this root-zone signal by application of pregeijerene in blueberry fields; mortality of larvae (Galleria mellonella and Anomala orientalis) again increased by attracting naturally occurring populations of an EPN. Thus, this specific belowground signal attracts natural enemies of widespread root pests in distinct agricultural systems and may have broad potential in biological control of root pests.

Comparison of neonicotinoid insecticides as synergists for entomopathogenic nematodes

Abstract In previous greenhouse and field studies, the neonicotinoid insecticide imidacloprid and the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema glaseri interacted synergistically against third-instars of the Japanese beetle, Popillia japonica , the oriental beetle, Exomala (= Anomala ) orientalis , and three masked chafer species, Cyclocephala hirta , C . pasadenae , and C . borealis (Coleoptera: Scarabaeidae). We tested whether this interaction would also occur with other neonicotinoids, primarily thiamethoxam. In laboratory, greenhouse and field experiments, imidacloprid provided stronger and more consistent synergism with nematodes than thiamethoxam. White grub mortality resulting from nematode–neonicotinoid combinations was synergistic/additive/antagonistic in 75/25/0% of our observations with imidacloprid and 37/42/21% of our observations with thiamethoxam. Neonicotinoid–nematode interactions varied with white grub species. Imidacloprid always interacted synergistically with nematodes against E . orientalis and P . japonica , whereas no enhancement occurred against Rhizotrogus majalis and Maladera castanea . Against E . orientalis , imidacloprid interacted synergistically with five nematode species, H . bacteriophora , H . megidis , H . marelatus , S . glaseri , and S . feltiae . Synergistic combinations of nematodes and a neonicotinoid insecticide could be used for curative treatments of white grub infestations, especially against E . orientalis and P . japonica . This combination may allow spot-treatment of turf areas that exceed damage thresholds, thereby limiting the environmental impact of the insecticide application.

Steinernema scarabaei for the control of white grubs.

Abstract The efficacy of the new entomopathogenic nematode species, Steinernema scarabaei , isolated from white grubs in New Jersey for the control of economically important white grub species (Coleoptera: Scarabaeidae) was compared to that of two strains of Steinernema glaseri , four strains/isolates of Heterorhabditis bacteriophora (including two fresh isolates from scarab larvae), and an undescribed Heterorhabditis species from Korea. The efficacy was tested against the oriental beetle, Exomala (= Anomala ) orientalis , the Japanese beetle, Popillia japonica , and the northern masked chafer, Cyclocephala borealis , under laboratory, greenhouse, and field conditions, and against the European chafer, Rhizotrogus majalis , in the laboratory. Under laboratory and greenhouse conditions, S. scarabaei was highly pathogenic to P. japonica , E. orientalis , and R. majalis , but was less effective against C. borealis . However, S. scarabaei provided excellent control of P. japonica , E. orientalis , and C. borealis under field conditions. P. japonica was the most nematode-susceptible white grub species. Against this species the superiority of S. scarabaei over the other nematodes tested became only apparent under field conditions and with very low nematode rates in the laboratory. C. borealis was less susceptible to all nematodes tested and only in a field experiment did S. scarabaei clearly outperform H. bacteriophora . Both E. orientalis and R. majalis were highly susceptible to S. scarabaei but showed moderate to low susceptibility to all other nematodes tested. In a field experiment, S. scarabaei also controlled P. japonica and E. orientalis larvae more quickly than H. bacteriophora . There was weak synergism between S. scarabaei and the neonicotinoid insecticide imidacloprid against E. orientalis larvae but not against P. japonica and C. borealis larvae. Overall, S. scarabaei shows exceptional potential for the biological control of white grubs.

Survival of entomopathogenic nematodes within host cadavers in dry soil

Abstract Our objectives were to determine whether entomopathogenic nematode emergence from host cadavers is influenced by soil moisture, whether the nematodes can survive adverse desiccating conditions in the soil by remaining within the host cadaver, and whether differences in such an adaptation occur among species. In the first experiment, wax moth larvae killed by Steinernema glaseri, Steinernema carpocapsae, Steinernema riobravis , or Heterorhabditis bacteriophora were placed in soil water potentials ranging from −500 MPa (very dry) to −0.006 MPa (moist). No infective juveniles (Us) emerged from cadavers at −500 MPa, and only few S. glaseri and S. carpocapsae emerged at −40 MPa. Large numbers of IJs emerged at ≥ −5 MPa from cadavers containing S. carpocapsae, S. glaseri , or H. bacteriophora. S. riobrauis emerged only at ≥ −0.3 MPa. In the second experiment, cadavers were left in dry soil (−40 MPa) for various periods of time before being rehydrated. The number of Us emerging per cadaver and the infectivity of the emerged IJs were determined. IJ emergence declined with the time that the cadavers were left in dry soil. Regression analysis predicted that IJ emergence from cadavers with S. glaseri, S. carpocapsae, H. bacteriophora , or S. riobravis would stop after 27, 62, 80, and 111 days, respectively, in dry soil. We hypothesize that S. carpocapsae , a sit-and-wait forager, survives longer than S. glaseri because it is adapted to infect insects near the soil surface, whereas S. glaseri , an actively searching forager, is adapted to infect insects deeper in the soil profile. Cadavers colonized by S. carpocapsae , therefore, are more likely to be exposed to dehydrating conditions. H. bacteriophora , an actively searching forager, may survive longer within cadavers because the gummous consistency of its host cadavers retains moisture very efficiently. S. riobrauis may survive for considerable lengths of time within cadavers in adaptation to the subtropical, semiarid climate of its geographic area of origin.

Biological Control Agents for White Grubs (Coleoptera: Scarabaeidae) in Anticipation of the Establishment of the Japanese Beetle in California

Abstract We tested biological control agents for the control of 3rd-instar scarab turfgrass pests, both for the masked chafer Cyclocephala hirta LeConte and the Japanese beetle, Popillia japonica Newman. The former species is endemic in California whereas the latter, although not yet established, constitutes a permanent serious threat to agriculture and horticulture in California. We conducted experiments using C. hirta in California and P. japonica in New Jersey. A field trial conducted in 2 different California turfgrass sites compared the field persistence in the absence of hosts of Bacillus thuringiensis Berliner subspecies japonensis Buibui strain, the milky disease bacterium, Paenibacillus (= Bacillus) popilliae (Dutky), and the entomopathogenic nematodes Steinernema kushidai Mamiya and Heterorhabditis bacteriophora Poinar to that of the organophosphate diazinon. Soil samples taken 0–70 d after applications were bio-assayed with P. japonica. Only diazinon and the entomopathogenic nematode S. kushidai caused substantial mortality and S. kushidai activity persisted significantly longer than diazinon activity. In greenhouse experiments, combinations of entomopathogenic nematode species usually resulted in additive mortality of scarab larvae. Combinations of S. kushidai and diazinon also resulted in additive mortality. In field trials, the efficacy of H. bacteriophora and especially S. kushidai and S. glaseri, was comparable to that of diazinon over 14–18 d. However, it is likely that at least S. kushidai would have outperformed diazinon over an extended period because of its longer persistence and potential for recycling in the hosts. S. kushidai, should it become commercially available, deserves further examination as an alternative to chemical white grub control especially as a highly compatible component of sustainable turfgrass management.

Steinernema scarabaei n. sp. (Rhabditida: Steinernematidae), a natural pathogen of scarab beetle larvae (Coleoptera: Scarabaeidae) from New Jersey, USA.

Steinernema scarabaei n. sp. (Rhabditida: Steinernematidae) is a new entomopathogenic nematode isolated from larvae of the scarab beetles Anomala(= Exomala)orientalis and Popillia japonica from turfgrass in New Jersey, USA. Morphology, hybridisation and molecular studies indicated the distinctness of S. scarabaei n. sp. from other Steinernema spp. Distinctive diagnostic characters include: the presence of a mucronated tail in both first generation adults; the presence of a ventrally bifurcated mucro in the first generation female tail; the size and shape of the spicules and gubernaculum and the arrangement of the genital papillae of the male; third-stage infective juvenile with total body length of 890-959 μm and lateral field with eight longitudinal ridges. RFLP analysis of the ITS region of rDNA showed S. scarabaei n. sp. to be distinct from 50 other Steinernema species and isolates. In addition, phylogenetic interpretation of sequence data from the LSU of rDNA provided further evidence for autapomorphies and separate species status for S. scarabaei n. sp.

Pathogenicity of Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei (Rhabditida: Heterorhabditidae, Steinernematidae) Against 12 White Grub Species (Coleoptera: Scarabaeidae)

We compared the pathogenicity of the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei against third instars of 12 white grub species. The Japanese beetle (Popillia japonica) was highly susceptible to all nematode species. Oriental beetle [Exomala (=Anomala) orientalis], European chafer (Rhizotrogus majalis), Asiatic garden beetle (Maladera castanea), and the May/June beetles Phyllophaga crinita, Ph. congrua, and Ph. (Subgenus Phytalus) georgiana were highly susceptible to S. scarabaei but had mediocre to low susceptibility to H. bacteriophora and S. glaseri. The black turfgrass ataenius (Ataenius spretulus) was very susceptible to H. bacteriophora but had mediocre susceptibility to S. glaseri and S. scarabaei. Northern (Cyclocephala borealis) and southern masked chafer (C. lurida) had mediocre and southwestern masked chafer (C. pasadenae) and green June beetle (Cotinis nitida) had low susceptibility to all nematode species.

Ecological characterization of Steinernema scarabaei, a scarab-adapted entomopathogenic nematode from New Jersey

This study describes the basic ecological characteristics of the entomopathogenic nematode Steinernema scarabaei (Rhabditida: Steinernematidae) that was originally isolated from epizootics in scarab populations in New Jersey turfgrass areas. Under laboratory conditions, S. scarabaei infected a limited range of insect species and appeared best adapted to scarab larvae as hosts. It uses a widely ranging foraging strategy with a low attachment rate to mobile hosts on the soil surface but with excellent infection of sedentary host placed at >or=2 cm soil depth. It has a wide thermal activity range with optimum infectivity from 17.5 to 25 degrees C. Because of its foraging strategy and adaptation to scarab larvae as hosts, S. scarabaei has outstanding potential for the control of scarab pests.