Pesticide Residues in Soil Invertebrates - Pesticides: Evaluation of Environmental Pollution - page 349

Foliar and soil insecticides were found to be lethal to Collembola, and insecticide appli-
cations resulted in a strong decline in the density of total Collembola. The application of
chlorpyrifos reduced collembolan density to a greater extent than dimethoate; the effect
of the combined application on total collembolan numbers was similar to that of chlorpy-
rifos only. The foliar insecticide, dimethoate, significantly decreased the density of epigeic
Collembola (Christiansen 1964), including the genera Isotoma and Lepidocyrtus, and also
tended to decrease the density of Entomobrya and Sminthuridae . In contrast, the density of
endogeic genera remained little affected. Probably, the effect of the application of dimetho-
ate, which functions as a contact pesticide, was restricted to surface-living species and its
effect penetrated little into the soil. Joy and Chakravorty (1991) reported that dimethoate
is lethal to many species of Collembola; however, its effect in the field is likely to vary
between species depending on exposure. In addition to reducing overall collembolan
abundance, the application of insecticides changed the dominant structure of the collem-
bolan community.
Overall, the soil insecticide caused such a strong change in the composition of the collem-
bolan community that the additional application of foliar insecticide had no further effect.
In fact, the soil insecticide application virtually eradicated most species of Collembola
(Endlweber et al. 2006). The nematicide, carbofuran, for example, has been shown in many
studies to have a negative impact on soil microarthropods, particularly Collembola and
predatory mites (Prostigmata and Mesostigmata), with populations taking up to a year
to recover (Reddy 1999). A similar effect has been noted with the insecticide dimethoate
(Martikainen et al. 1998). Long-term use of the fungicide mancozeb in vineyards has also
been reported to reduce populations of the predatory mite Typhlodromus pyri (Auger et al.
2004). Herbicides, however, have generally been found to have negligible effects on soil
microarthropod populations (Martikainen et al. 1998; Cortet et al. 2002), although some
early reports have shown that atrazine, simazine, glyphosate, and paraquat can cause tem-
porary reductions in microarthropod activity (Edwards 1989). More recently, Rebecchi
et al. (2000) reported that the sulfonylurea herbicide triasulfuron caused a decrease in
some collembolan species in an agricultural soil. Effects of insecticides and fungicides
on protozoan and nematode populations are also more pronounced than those of herbi-
cides (Gupta and Yeates 1997). For example, Petz and Foissner (1989) found that mancozeb
altered the community structure but not the absolute number of protozoans in a field soil,
while Ekelund (1999) demonstrated that various groups of protozoa (notably flagellates)
were reduced by field application rates of the fungicide fenpropimorph.
A 5-month durational period of the recolonization of soil arthropods was monitored on
endosulfan-treated soil from April to August 2007, within the 5-10 cm depth at varying
concentrations of the pesticide (Iloba and Ekrakene 2010). The result showed that there
was consistent decrease in the mean numbers of soil arthropod sampled from April to
June and the decrease was more as the concentration of applied endosulfan increased.
However, July to August witnessed a very remarkable increase in the mean soil arthro-
pod sampled compared to the control stations, an indication of recolonization. Among
the seven groups of soil microarthropod sampled, the mean number from groups were
statistically different (p < 0.05) at all concentrations compared to the control with Acarina,
Collembola, Coleoptera, and Myriapoda being the most abundant while Hymenoptera,
Isoptera, and Crustacea being the least in abundance. The most recovered group was the
Acarina while the least was Crustacea with recolonization ability being greatest in stations
with higher concentrations.
The application of the insecticide dimethoate, particularly in the autumn, has led
to reductions in the numbers of ground-dwelling beetles in cereals and other crops.