Effect of some carbamate pesticides on nodulation,plant yield and nitrogen fixation byPisum sativum andVigna sinensis in the presence of their respective rhizobia

Summary Six carbamate pesticides namely 1-naphthol, sevin, dimetilan, trematan, NaDDC and dymid were studied to see their effect on nodulation and nitrogen fixation inPisum sativum andVigna sinensis. Low concentrations of the pesticides have little effect on nodulation and nitrogen fixation, whereas higher concentrations adversely effect these processes. The results also indicate that then sensitivity depends upon the species of the Rhizobium and also the type of the pesticide. Pesticides belonging to the carbamate group differ in their capacity to affect nodulation and nitroge fixation.     

The effect of insecticides on the distribution of foracing parasitoids,Diaeretiella rapae [Hym.: Braconidae] on plants

Foraging aphid parasitoids,Diaeretiella rapae M'Intosh, were exposed to sublethal doses of the insecticides pirimicarb, permethrin and malathion on brusslls sprouts plants. Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and, while on these plants, tended to concentrate activity on unsprayed surfaces. For permethrin and malathion, pesticide residues reversed the stereotypic upward foraging pattern of the wasp. Negative consequences of sublethal pesticide doses for parasitoid foraging efficiency are discussed.      

Biological comparative study between Wolbachia-infected Aedes aegypti mosquito and Wolbachia-uninfected strain,Jeddah city,Saudi Arabia

In this study, samples of Wolbachia-infected Aedes aegypti mosquitoes were collected from Al-Safa district in Jeddah city, Saudi Arabia. The presence of Wolbachia bacteria in mosquitoes was confirmed by PCR technique and they were reared and propagated in the laboratory. Comparative studies were conducted between Wolbachia-infected A. Aegypti and the Wolbachia-uninfected laboratory strain in terms of their ability to withstand drought, resist two types of insecticides and the activities of pesticide detoxification enzymes. The Wolbachia-infected A. aegypti strain proved less able to withstand the drought period, as the egg-hatching rate of the Wolbachia-uninfected strain was greater than that of the Wolbachia-infected strain after one, two and three months of dry periods. Compared to the Wolbachia-uninfected strain, the Wolbachia-infected strain demonstrated a relatively greater resistance to tested pesticides, namely Baton 100EC and Fendure 25EC which may be attributed to the higher levels of the detoxification enzymes glutathione-S-transferase and catalase and the lower levels of esterase and acetylcholine esterase.     

Influence of a carbamate pesticide on growth,respiration (14C)-carbon metabolism and symbiosis of aRhizobium sp.

Summary Addition of aldicarb (2 methyl-2(methyl thio) propionaldehyde-0-methyl carbamoyl oxime) in the growth medium enhanced the growth ofRhizobium sp. (cowpea group) at 2 ppm level while an inhibition was observed at the normal (5 ppm) and higher (10 ppm) concentrations. Respiration of the cells was also inhibited by 5 and 10 ppm levels of the chemical eventhough a stimulation was observed at 2 ppm (lower) concentration. The insecticide, when incorporated at 5 and 10 ppm levels in the medium increased the¹⁴C-glucose incorporation and considerably altered the assimilation of the radioactive carbon in different fractions of rhizobium cells. Soil application of this insecticide (Temik 10 G) reduced the number of nodules formed and the total nitrogen content in cowpea plants inoculated with theRhizobium sp. but enhanced the dry matter production of cowpea plants.Based on the M. Sc. thesis submitted by the first author to the Tamil Nadu Agricultural University, Coimbatore-3.     

Interaction of DDT (1,1,1-trichloro-2,2-BIS(p-chlorophenyl)-ethane with liposomal phospholipids

The influence of $\text{1,1,1-}\text{trichloro}\text{-2,2-}\text{bis}\text{(p-}\text{chlorophenyl}\text{)}\text{ethane}$ (DDT) and several other pesticides on the physical state of membrane phospholipids was investigated using model lipids. The thermal dependence of fluorescence intensity of the probe parinaric acid in dipalmitoylphosphatidylcholine liposomes and lipid vesicles of mixed composition were recorded. DDT was incorporated into the liposomal bilayer. The insecticide lowered the phase transition temperature and broadened the temperature range of the transition. The effects were concentration-dependent.The results may be interpreted as a sort of blurred and facilitated phase transition of bilayer lipids caused by intercalation of DDT between fatty acyl chains of membrane phospholipids.     

Biochemical and proteomic effects in Procambarus clarkii after chlorpyrifos or carbaryl exposure under sublethal conditions

In vivo effects of two sublethal doses of chlorpyrifos and carbaryl were studied in Procambarus clarkii after 2 and 7 days of exposure, and after pesticide removal. Chlorpyrifos inhibited carboxylesterase activity in a concentration-dependent manner, but acetylcholinesterase was less sensitive. Compared with chlorpyrifos, carbaryl had a less marked effect on esterase activity. The effects of selected pesticides on biotransformation or oxidative stress biomarkers were contradictory. Chlorpyrifos lowered ethoxyresorufin-O-deethylase (EROD), catalase and oxidized glutathione (GSSG) levels but raised glutathione-S-transferase activity, while carbaryl raised EROD, catalase and glutathione-S-transferase, but lowered glutathione peroxidase and reduced glutathione (GSH) levels. The effects on protein expression patterns depending on pesticide type and the tissue used for analysis were studied in parallel by 2-DE. In gill and nervous tissue about 2000 spots (pI 4–7) were resolved, with quite different expression patterns. Chlorpyrifos altered 72 proteins, mostly in nervous tissue, and carbaryl 35, distributed evenly between organs. Several specific spots were selected as specific protein expression signatures for chlorpyrifos or carbaryl exposure in gills and nervous tissue, respectively.     

Analytical methods for detecting pesticide switches with evolution of pesticide resistance

After a pest develops resistance to a pesticide, switching between different unrelated pesticides is a common management option, but this raises the following questions: (1) What is the optimal frequency of pesticide use? (2) How do the frequencies of pesticide applications affect the evolution of pesticide resistance? (3) How can the time when the pest population reaches the economic injury level (EIL) be estimated and (4) how can the most efficient frequency of pesticide applications be determined? To address these questions, we have developed a novel pest population growth model incorporating the evolution of pesticide resistance and pulse spraying of pesticides. Moreover, three pesticide switching methods, threshold condition-guided, density-guided and EIL-guided, are modelled, to determine the best choice under different conditions with the overall aim of eradicating the pest or maintaining its population density below the EIL. Furthermore, the pest control outcomes based on those three pesticide switching methods are discussed. Our results suggest that either the density-guided or EIL-guided method is the optimal pesticide switching strategy, depending on the frequency (or period) of pesticide applications.     

Effect of pesticide exposure on the cholinesterase activity of the occupationally exposed tea garden workers of northern part of West Bengal,India

Context: Pesticide poisoning and related deaths are a global concern, but there is little information about its effect on the occupationally exposed tea garden workers of North Bengal.

Objective: This study investigates the level of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the blood of the tea garden workers at risk of exposure to a mixture of pesticides.

Materials and methods: The study sample consisted of pesticide exposed workers, non-exposed (control), smokers and alcoholics. AChE and BuChE activity was measured and tested for significance.

Results: Results showed that AChE activity was half in the pesticide exposed individuals than controls (p≤ 0.001). BuChE activity was also significantly decreased in the pesticide exposed individuals than controls (p≤ 0.001), while AChE and BuChE activity in smokers and alcoholics were not different from that of controls. However, significantly decreased AChE and BuChE activities were recorded in pesticide exposed workers compared to smokers and alcoholics.

Conclusions: The results indicated that the decrease in enzyme activities in tea garden workers was due to mixed pesticides (containing organophosphates) exposure. Age was not found to influence the enzyme activities. However, the gender had little effect on the enzyme activities but the effect was not so prominent.     

Identification of factors responsible for insecticide resistance in Helicoverpa armigera

Moth larvae (Helicoverpa armigera Hübner) collected from field crops were tested for resistance to cypermethrin, fenvalerate, endosulfan, monocrotophos and quinolphos. Larvae were treated with a dose of the pesticide that would kill 99% of the susceptible insects. The percent survival of the resistant strains was determined. Highest seasonal average percentage survival was recorded by fenvalerate (65.0%) followed by cypermethrin (62.4%). Acetylcholinesterase of resistant larvae was less sensitive to monocrotophos and methyl paraoxon. Resistant larvae showed higher activities of esterases, phosphatases and methyl paraoxon hydrolase compared with susceptible larvae. The presence of high activity of esterases was attributed to appearance of extra bands of esterases in native PAGE. The presence of P-glycoprotein expression was detected in resistant larvae using P-gp antibodies; this was not detected in the susceptible larvae. Our results indicate that the high level of resistance detected in the field pests could be because of a combined effect of decreased sensitivity to AChE, higher levels of esterases, phosphatases and the expression of P-gp.