Print PageEntomopathogenic nematodes (EPNs) are important biological control agents of insects in natural and managed ecosystems but their role in soil food webs and the various factors that influence their spatial and temporal dynamics within and among habitats remain a matter of speculation. To address these issues, we used quantitative real–time PCR (qPCR) to study temporal and regional patterns of EPNs and some of their natural enemies in Florida citrus orchards. Our objective was to analyse the potential roles of abiotic and biotic soil components in regulating EPNs. We developed and used species-specific primers and probes to 11 EPN species, 8 species of nematophagous fungi (NF) and 2 species of Paenibacillus (bacterial ectoparasites of EPN). Food webs were characterized in 53 orchards among habitats categorized as Central Ridge (22 localities), Interior Flatwoods (19), and Coastal Flatwoods (12). The population changes of these organisms were also monitored monthly at two sites each in Flatwoods and Central Ridge.
Results/Conclusions
Five steinernematid and 2 heterorhabditid EPN species were detected. The well-drained, coarse sandy soils from the Central Ridge supported greater EPN diversity (P<0.01) compared to the poorly-drained, finer textured soils of the Coastal and Interior Flatwoods. EPN communities in Coastal Flatwoods were dominated by a single species (Heterorhabditis indica), whereas communities with Steinernema diaprepesi, Heterorhabditis zealandica and H. indica were encountered frequently on the Central Ridge. An exotic species, Steinernema scapterisci, imported in the 1980’s for mole cricket control in turf and pasture was occasionally detected in orchards in each habitat. Canonical correspondence analysis explained more than 84% of the species and physical properties inertia, and ongoing analyses of heavy metals and pesticides may reveal additional interrelationships that characterize these habitats. Numbers of S. diaprepesi were related to the species-specific ectoparasite Paenibacillus sp. in both the regional (r=0.40, P=0.003) and temporal surveys (r=0.35; P=0.001). The depth distributions of the most abundant EPN species (S. diaprepesi and H. indica) were seasonal, with more individuals detected below 15 cm depth in winter and above that in summer. Trapping NF, free living nematodes and fibrous root mass were consistently more abundant in the shallow soil horizon, whereas the most frequently encountered NF (endoparasitic Catenaria sp. and Myzocytium sp.) were more evenly distributed by depth. The temporal patterns of abundance of dominant species of EPN, NF and the phoretic bacteria were closely related between sites within regions, suggesting that relatively few key climatic variables modulate the population changes.
