Baris Gulcu

Trophic Relationships of Entomopathogenic Nematodes in Agricultural Habitats

Entomopathogenic nematodes (EPNs) play several roles in the soil ecosystem. While EPNs are generally thought of in the context of reducing the density of pest populations when they are applied, they are also natural components of soil food webs and exert considerable influence on the population dynamics of many players in the system in addition to the intended targets of biological control efforts (Hodson, Siegel, & Lewis, 2012). They are lethal parasites of insects, but not all of the species they infect are the targets for which they are applied. They are also prey and hosts to a variety of other soil organisms. Here, we attempt explain the fate of EPNs after they are applied to soil in the context of the complicated interactions among members of soil food webs.

Laboratory evaluation of Turkish entomopathogenic nematodes for suppression of the chestnut pests, Curculio elephas (Coleoptera: Curculionidae) and Cydia splendana (Lepidoptera: Tortricidae).

Abstract The lepidopteran, Cydia splendana, and the coleopteran, Curculio elephas, are the most serious pests of chestnut fruit in Turkey. We evaluated the biological control potential of three Turkish entomopathogenic nematode species, Steinernema feltiae, S. weiseri and Heterorhabditis bacteriophora, against the last instar larvae of C. splendana and C. elephas, both of which occur in the soil from fall (October–November) until mid-summer (August). The optimal temperature for infection, time to death of the hosts, and reproductive potential of the nematodes were determined at 10, 15, 20 and 25°C for both pest species. Cydia splendana was more susceptible to nematode infection than C. elephas. Temperature had a significant effect on the infectivity and development of entomopathogenic nematodes. The cold-adapted S. weiseri and S. feltiae were the most virulent species at 10 and 15°C, whereas the warm-adapted H. bacteriophora was the most effective at 20 and 25°C. In soil pot experiments conducted at 15°C, S. weiseri was the most virulent species against C. elephas and C. splendana. However, our data show that C. elephas larvae had a lower and C. splendana larvae had a higher susceptibility to the nematode species tested. Accordingly, we recommend that future efforts of using entomopathogenic nematodes, especially S. weiseri, be directed against C. splendana and that there be a continued effort to find more virulent nematode isolates against larvae of C. elephas.

Molecular variability of Schistonchus caprifici (Nematoda: Aphelenchoididae) from Ficus carica in Turkey

An extensive biogeographical survey was conducted from 2004 through part of 2007 of nematodes associated with the edible fig, Ficus carica, in seven different regions of Turkey. Figs (syconia) were collected, dissected and harvested for nematodes from 308 apparently wild or naturalised F. carica trees along roadsides and trails. Nematode specimens were examined morphologically and molecular analyses of sequences of the D2/D3 expansion segments of the large subunit (LSU) rDNA and partial mitochondrial DNA COI (mtCOI) were done. Of the 308 fig trees, 150 (49%) were positive for what was morphologically confirmed to be Schistonchus caprifici. Figs on one tree in Kahramanmaras city, South East Turkey, were found to contain S. caprifici and dauer juveniles of what appears to be a diplogastrid nematode. Molecular analyses produced congruent trees for both sequenced loci supporting the hypothesis that S. caprifici from different locations in Turkey are part of a well supported clade with some inherent variability. No geographic patterns were observed for either locus suggesting that the sequences generated represent inherent intraspecific variation for S. caprifici and that human activities related to the culture of the edible fig have allowed for mixing of any previously allopatric lineages.

Response of three cyprinid fish species to the Scavenger Deterrent Factor produced by the mutualistic bacteria associated with entomopathogenic nematodes.

The symbiotic bacteria, Photorhabdus and Xenorhabdus associated with entomopathogenic nematodes (EPNs) in the genera Heterorhabditis and Steinernema, respectively, produce a compound(s) called the Scavenging Deterrent Factor (SDF). SDF deters a number of terrestrial insect scavengers and predators and one bird species from feeding on host insects killed by the nematode-bacterium complex but has not been tested against aquatic vertebrates. Moreover, the Heterorhabditis-Photorhabdus association is believed to have evolved in an aquatic environment. Accordingly, we hypothesized that SDF will deter fish from feeding on nematode-killed insects and tested the responses of three omnivorous fresh water fish species, Devario aequipinnatus, Alburnoides bipunctatus, and Squalius pursakensis, to SDF in the laboratory. When the fish were exposed to Galleria mellonella larvae killed by the Heterorhabditis- or Steinernema-bacterium complex at 2 or 4days post-infection, all three fish species made several attempts to consume the cadavers but subsequently rejected them. However, all fish species consumed freeze-killed control larvae. In a choice test, when D. aequipinnatus or A. bipunctatus were offered a pair of nematode-killed larvae, both fish species rejected these cadavers; when offered a nematode-killed larva and a freeze-killed larva, both fish species consumed the freeze-killed larva but not the nematode-killed one. In further tests with D. aequipinnatus, there was no significant difference in the number of 2-day-old Bacillus thuringiensis subsp. kurstaki-killed (Btk) larvae consumed compared to freeze-killed larvae, but significantly fewer 4-day-old Btk-killed larvae were consumed compared to freeze-killed larvae. When D. aequipinnatus was fed G. mellonella larvae killed by the symbiotic bacteria, the fish rejected the cadavers. When given freeze-killed or nematode-killed mosquito (Aedes aegypti) larvae, the fish consumed significantly more of the former larvae (99%) compared to the latter (55%). When D. aequipinnatus was placed in a symbiotic cell-free supernatant for 18h, a significant reduction in consumption of freeze-killed larvae compared to cell-free Btk or control broth supernatant was observed. We showed that SDF protects the nematode-killed insects from being consumed by omnivorous fishes and suggests that they will have minimal effects on recycling of EPNs in the aquatic environment.

Biological control potential of native entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) against Spodoptera cilium (Lepidoptera: Noctuidae) in turfgrass

In laboratory studies, we demonstrated that five native entomopathogenic nematode species/isolates caused 100% mortality of Spodoptera cilium larvae, a soil surface-feeding pest of turfgrass. At 25 infective juveniles/cm2 applied to sod, two selected Turkish species, Steinernema carpocapsae and Heterorhabditis bacteriophora (Sarigerme isolate), averaged 77% and 29% larval mortality, respectively.

Reverse Taxonomy Reveals Pristionchus maupasi (Diplogasterida: Diplogastridae) Association with the Soil-Dwelling Bee Andrena optata (Hymenoptera: Andrenidae) in Turkey

Summary Previous molecular operational taxonomic unit (MOTU) survey work with diplogastrid dauers from the abdominal glands of adult female soil-dwelling andrenid bees in Turkey had suggested commensal relationships between species of the genus Andrena and a new species of Koerneria and several species from an unidentified nematode clade near “Mononchoides” (based upon comparisons with GenBank at the time). We used reverse taxonomy on dauer nematodes from Andrena optata from Turkey to successfully culture, morphotype, and sequence adult nematodes that fully matched Pristionchus maupasi and one of the MOTUs previously isolated as dauers from the abdominal glands of A. limata and A. flavipes, and previously designated as belonging to the clade near “Mononchoides.” This study demonstrates the value of reverse taxonomy for resolving MOTU identification issues as the depth of the reference sequence database increases and successful cultures or environmental samples of adults are made available for morphotypic and genotypic comparisons. In addition, it has helped expand our knowledge of the potential host range and biogeographical distribution of P. maupasi which was originally thought to be relatively host specific on scarab beetles, and has raised questions about the chemical ecology of dauers for this species in the wild.