Pesticide Residues in Soil Invertebrates - Pesticides: Evaluation of Environmental Pollution - page 347

possess many characteristics that make them ideal as bioindicators for soil health assess-
ment (Bongers and Ferris 1999), and their fauna composition, together with its ecological
indices, has emerged as a useful monitor of environmental conditions and soil ecosystem
function (Neher 2001).
There is a growing concern over the impacts of such pesticides on nontarget free-living
nematodes. Yardim and Edwards (1998) studied the responses of nematode communities
to mixtures of insecticides (carbaryl, endosulfan, and esfenvalerate), fungicides (chloro-
thalonil), and herbicides (trifluralin and paraquat) in a tomato field and found that the
temporal community dynamics of different nematode trophic groups differed with the
pesticide applications. Yeates et al. (1999) reported that the diversity of the nematode com-
munity was increased and bacterivores were consistently low in herbicide-treated plots
over a 7-year period. Chen et al. (2003) monitored the effect of acetochlor on the nema-
tode community structure in a soybean field. The results showed that the soil nematode
community structure could be greatly influenced by acetochlor, and the numbers of total
nematode and trophic groups were reduced, and species richness (SR) was effective in
distinguishing the differences between the acetochlor plots and the control plots. Pen-
Mouratov and Steinberger (2005) investigated the effect of two pesticides, Nemacur and
Edigan, on soil nematodes in a desert system, and the results indicated that the numbers
of total nematodes, fungivores, and bacterivores were decreased in the pesticide treat-
ments. Wada and Toyota (2008) conducted a pot test to evaluate the toxicity of imicya-
fos and fosthiazate to nontarget organisms and reported that the two organophosphorus
nematicides effectively suppressed a plant-parasitic nematode Pratylenchus penetrans but
had little impact on free-living nematodes and the soil microbial community. Smith et al.
(2000) showed that long-term application of benomyl in a tall grass prairie had no effect on
herbivorous nematodes but reduced populations of certain groups of fungal-feeding and
predatory nematodes. Wardle et al. (1995) have suggested that evidence for direct negative
effects of herbicides on nematode populations were more likely to be indirect effects from
changes arising in the quantity and quality of plant inputs (e.g., dead organic matter from
weeds) to the soil.
12.3.5 Effect of Pesticides on Microarthropods
Soil arthropods play important roles in breaking down plant remains and controlling
crop pests by parasitism and predation and are food sources for larger animals. For
sprays, the concentration of pesticides will be greatest at the soil surface immediately
after application, and the species most vulnerable to potential adverse effects are
those that live on the soil surface. Examples of such species include spiders as well as
ground and rove beetles belonging to the Carabidae and Staphylinidae families that are
predators of aphids and that may contribute to the control of these insect pests. Many
regulatory authorities require an assessment of the effects of pesticides on nontarget
terrestrial arthropods, particularly if the compound is intended for application to soil
(Oomen 1998).
Soil fauna including microarthropods (collembolans, mites) and microfauna (proto-
zoa) may be affected by soil-applied pesticides with possible flow-on consequences for
organic matter mineralization. Collembola are among the most abundant soil arthropods
and play an important role in decomposer food webs (Petersen 2002). Collembola are
known to be food generalists (Scheu and Folger 2004). The diet of most species is com-
posed of a mixture of detritus, algae, bacteria, and fungi and varies with season (Wolters
1985). Due to their feeding activity, Collembola affect decomposition processes and the