Short-term biochemical ill effects of insect growth regulator (IGR) pesticides in Cyphoderus javanus Borner (Collembola: Insecta) as potential biomarkers of soil pollution.

The insect growth regulator (IGR) chemicals are considered as safe alternatives to synthetic organic pesticides, but only scant information are available on their possible impact on non-target and ecologically important soil insect fauna of croplands. Previous studies by the authors showed that recommended agricultural doses of IGRs buprofezin (Applaud 25SC at 250 g a.i. ha(-1)), flubendiamide (Takumi 20WG at 50 g a.i. ha(-1)) and novaluron (Rimon 10EC at 100 g a.i. ha(-1)) produced less mortality of adults of a non-target soil insect Cyphoderus javanus Borner (Collembola) but decreased major life history parameters namely moulting, fecundity and egg hatching success. This detritivorous microarthropod is very sensitive to soil characteristics and is ecologically relevant to the tropical soils. Present microcosm study showed strong biochemical impact of the above doses of IGRs on tissue nutrient levels and digestive enzyme activities in C. javanus within 7 days of exposure to treated sandy loam soil. The levels of tissue proteins, carbohydrates, lipids and free amino acids declined significantly and persistently in the specimens reared in IGR-treated soils than in the specimens of untreated soil. Similarly, α-amylase, cellulase and protease activities declined significantly in the specimens of IGR-treated soil. These nutritional scarcities would reduce metabolism, growth and reproduction in the affected insects. Therefore, the observed biochemical responses, especially the levels of tissue proteins, carbohydrates and α-amylase activity in C. javanus are early warning indices and potential biomarkers of soil pollution in croplands.

Biomonitoring insecticide pollution using non-target soil microarthropods.

The scope of biomonitoring insecticide pollution in soil is discussed with the help of field and laboratory findings on the density, prey-predator ratio and fecundity of non-target microarthropod fauna. Field experiments were conducted in small plots with mustard, wheat and lady's finger crops and insecticides namely heptachlor 20EC (3.25 kg ai/ha = 16.25 lit/ha) and endosulfan 35EC (0.875 kg ai/ha = 2.5 lit/ha) applied at the seedling stages. Soil microarthropod population estimated at fortnightly intervals in the treated and untreated control plots revealed a general trend of adverse effect of the insecticides, prominently on the density and relative abundance of major prey groups like Collembola and Acari leading to notable decline in prey-predator ratio. Comparison of the percentage reductions of major taxonomic and trophic groups between pre-treatment and post-treatment intervals also demonstrated the ill effect of both heptachlor and endosulfan, notably on Collembola and the prey category. In the laboratory the survival success and fecundity of Cyphoderus javanus (Collembola) and Archegozetes longisetosus (Acari) were compared by exposing freshly emerged adults to sub-lethal concentrations of heptachlor and endosulfan for varying durations. The untreated control sets recorded high fecundity for both C. javanus and A. longisetosus, but chronic toxicity of the insecticides on adults confined to the treated soil resulted into very low fecundity. Even short duration exposure to heptachlor and endosulfan treated soil for 24 or 72 hours only was found to delay the egg-laying and decrease the fecundity of both the species. It is concluded that population responses and reproductive sensitivity in non-target soil microarthropods are potential eco-toxicological parameters for detecting pesticide pollution in soil and for ecological health assessment since the results are based on the bioactivity of toxicants.

Biomonitoring of anticholinesterase pesticides in the soil: usefulness of soil Collembola.

The impact of Methyl parathion and Carbaryl was evaluated on an ecologically important soil Collembola, Cyphoderus sp. Enzyme characteristics demonstrate substrate optimum at 1 10(-2) mol/L temperature optimum at 30 degrees C with a pH requirement of 8.0. In vivo inhibition of whole body AChE reveals higher degree of inhibition by LD50 dose of Methyl parathion as compared to that of Carbaryl where maximum inhibition was noticed at the agricultural dose.

Impact of insecticides on nontarget microarthropod fauna in agricultural soil.

Ecologically important soil microarthropods were used to evaluate the direct and residual toxicities of some insecticides under field and laboratory conditions. The density of total microarthropods and major groups, namely Acarina and Collembola, suffered a statistically significant and persistent decline in the aldrin 30 EC (0.25%)- and endosulfan 35 EC (0.33%)-treated soil of wheat fields. But dimethoate 30 EC (0.125%) and phosphamidon 85 EC (0.03%) applied in mustard fields produced only a temporary decline. Laboratory studies showed that all the above insecticides and monocrotophos 36 EC (0.2%), methyl parathion 50 EC (0.05%), chlordane 20 EC (0.125%), and carbaryl 50 WP (0.625%) had a direct knockdown effect on Cyphoderus sp. but another collembolan species, Xenylla sp., appeared to be somewhat resistant. Only endosulfan was toxic to a common soil Acarina species, Lancetoppia sp. Among four soil media, toxicity was maximum in pure sand, followed by sandy loam, clay, and organic soil. The residual toxicity of phosphamidon, dimethoate, methyl parathion, and endosulfan was more prolonged for Cyphoderus sp. than for Xenylla sp. Only the larval stage of Lancetoppia sp. was susceptible to the residual effect of endosulfan. LD50 and bioassay studies showed that Cyphoderus sp. can be employed as a potential biomonitor of insecticide pollution in soil.