[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

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R. CAMPOS-HERRERA ET AL.
infection peg of fungal spores did not penetrate beyond the second stage cuticle that is
retained as a protective sheath by IJ (3rd stage) heterorhabditids. Steinernematid IJs
generally cast the second stage cuticle shortly after emerging into the soil from insect
cadavers (Timper & Kaya, 1989, 1992).
A variety of mechanisms other than protective sheaths modulate predation by
NF on nematodes. For example, fungi that form adhesive networks trap plantparasitic
root-knot nematodes much more effectively than cyst nematodes (neither of
which retain a cast cuticle), whereas fungi producing constricting rings trapped both
types of nematodes with equal efficiency (Jaffee, 1998). El-Borai et al. (2007)
showed that in sand microcosms the predation rates of five species of endoparasitic
and trapping NF on 5 EPN species, all commonly isolated from citrus orchards,
were highly species specific. Two endoparasitic NF species that infect via zoospores
were highly lethal to all EPN species except H. indica, which was unaffected by
these fungi in the microcosm assays. Conversely, large endemic steinernematids
such as S. diaprepesi and Steinernema sp. (previously identified as S. glaseri) were
relatively unaffected by several species of Arthrobotrys (trapping NF), compared to
significant predation by these fungi on the smaller exotic S. riobrave and the
heterorhabditids H. zealandica and H. indica. Thus, the report by El-Borai et al.
(2007) did not support causality of the relationships between NF and S. diaprepesi
or H. zealandica reported by Duncan et al. (2007). The lack of predation by
zoosporous NF on just H. indica is intriguing, however, since these commonly
encountered NF require free water for zoospore movement and H. indica was the
sole EPN species reported from several low lying coastal areas, which tend to have
relatively wet soils (Fisher-Le Saux et al., 1998; Mauléon et al., 2006; Table 1).
Organisms other than predators and parasites might influence the abundance of
EPNs. Paenibacillus is a bacterial genus that is intimately associated with
arthropods. Phoretic associations between Paenibacillus and EPNs were recently
reported and demonstrate remarkable convergence of bacterial species adapting to
two paraphyletic nematode genera (Enright & Griffin, 2004, 2005; El-Borai,
Duncan, & Preston, 2005). Paenibacillus spp. associated with heterorhabditids have
spindle shaped spores that adhere exclusively to the nematode sheath (2nd-stage
cuticle) whereas those associated with steinernematids have oval spores that adhere
only to the 3rd-stage cuticle (Fig. 4). Paenibacillus nematophilus spores attached to
all tested heterorhabditid species and those in the closely-related order Stongylida
(Enright & Griffin, 2004). In contrast, a Paenibacillus sp. associated with S.
diaprepesi appears to be species specific (El-Borai et al., 2005). Paenibacillus spp.
are frequently observed on all known endemic species of EPNs in Florida but not on
the introduced species S. riobrave. Like the entomopathogenic bacteria P. popilliae
and P. lentimorbus, the Paenibacillus species that are phoretic on EPN complete
their life cycle in the insect cadaver but they are not entomopathogenic and they do
not appear to affect the reproduction of EPN species. The only known adverse affect
to the nematode is impaired motility in proportion to the degree to which a nematode
is encumbered with spores. Spore-free steinernematids and heterorhabditids move
further and infect more insects that do spore-encumbered nematodes. However, the
degree to which Paenibacillus spp. can modulate EPN abundance in nature is
unknown.