FIGURE 1: Sting nematode adult female
Sting nematodes Belonolaimus longicaudatus is a large nematode, reaching sizes of about 1/8-inch long when mature (Figure 1). Size may particularly matter in the case of the stylet of this nematode,
which is long and allows the nematode to feed deep within root tissues (Figure 2). This nematode feeds on root meristem tissues (root tips) and this fact likely helps explain why it causes damage even at low threshold numbers (most labs indicate a damage threshold of about 20 per 100 cc of soil). Feeding by this nematode, when numbers are high enough, leads to a shallow, stunted root system. Wounds from the nematode feeding allow other soil organisms to colonize and further debilitate the host plants (Figure 3, page 18). Sting nematode is an ectoparasitic feeder: its body remains outside of the host tissues as it feeds, and it can move short distances to reach other roots for further feeding. As an ectoparasite, it is presumed to be more susceptible to nematicides. Sting nematode is a southern nematode in the United States: it does not survive in frozen soils for long periods of time, and also is limited to soils of at least 80% sand. Belonolaimus and related species also occur in other parts of the world in turf and are recognized as major pathogens. It has been pointed out before (Peacock, 1989), and is obvious, that sand-based rootzones are naturally ideal habitats for sting and other nematodes. Besides being good habitats for the nematodes themselves, sand-based rootzones are inherently nutrient deficient and prone to drought stress. Therefore, root parasites, such as nematodes, are particularly important in sandy soils. 17
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In the Southern states, arguably, the most important nematodes include sting, root-knot species, and lance nematodes. This is not to say that others, if counts from assays are high enough, cannot also cause significant damage or contribute to damage from other stresses. These might include nematodes such as stunt, stubby root, ring and spiral nematodes (Dickerson, et al, 2000). Generally, nematodes are broadly recognized as ‘ectoparasites’ and ‘endoparasites’. Ectoparasitic nematodes remain outside the host roots and feed by piercing plant cells with their needle-like stylets. Endoparasitic nematodes actually penetrate the plant roots and can move through root systems (‘migratory endoparasites’), while feeding. Others, such as the root knot nematodes, can penetrate and remain immobile (‘sedentary endoparasites’). Lance nematodes are an example of ‘migratory’ semi-endoparasites which can occur in root system as well as the soil around the roots. Knowing these details has implications on sampling and also on difficulty in control with traditional nematicides.
FIGURE 2: Sting nematode head showing stylet
