Residues and dissipation kinetics of two imidacloprid nanoformulations on bean (Phaseolus vulgaris L.) under field conditions

The current study investigates the dissipation kinetics of two imidacloprid (IMI) nanoformulations (entitled: Nano-IMI and Nano-IMI/TiO2) on common bean (Phaseolus vulgaris) seeds under field conditions and compares them with 35% Suspension Concentrate (SC) commercial formulation. To do so, it sprays P. vulgaris plants at 30 and 60 g/ha within green bean stage, sampling them during the 14-day period after the treatment. Following extraction and quantification of IMI residues, dissipation data have been fitted to simple-first order kinetic model (SFOK) and to first-order double-exponential decay (FODED) models, with 50% and 90% dissipation times (DT50 and DT90, respectively) assessed along the pre-harvest interval (PHI). With the exception of Nano-IMI at 60 g/ha, other decline curves are best fitted to the FODED model. In general, dissipation is faster for Nano-IMI (at 30 g/ha: DT50 = 1.09 days, DT90 = 4.30 days, PHI = 1.23 days; at 60 g/ha: DT50 = 1.29 days, DT90 = 4.29 days, PHI = 2.95 days) and Nano-IMI/TiO2 (at 30 g/ha: DT50 = 1.15 days, DT90 = 4.40 days, PHI = 1.08 days; at 60 g/ha: DT50 = 0.86 days, DT90 = 4.92 days, PHI = 3.02 days), compared to 35% SC (at 30 g/ha: DT50 = 1.58, DT90 = 6.45, PHI = 1.93; at 60 g/ha: DT50 = 1.58 days, DT90 = 14.50 days, PHI = 5.37 days). These results suggest the suitability of Nano-IMI and Nano-IMI/TiO2 application at both rates in terms of their residues on P. vulgaris seeds

Effects of amitraz, buprofezin and propargite on some fitness parameters of the parasitoid Encarsia formosa (Hym.: Aphelinidae), using life table and IOBC methods

The side-effects of amitraz, buprofezin and propargite were studied on Encarsia formosa (Gahan)in the laboratory, using a life table response experiment and the IOBC system for their toxicity. Bioassayswere conducted by dipping bean leaves containing third instar nymphs of the whitefly Trialeurodesvaporariorum (Westwood), parasitized by E. formosa, in insecticide solutions or caging adult parasitoidsin treated petri dishes. The insecticide buprofezin caused 19.87% and 11.87% mortality in adults andpupae respectively. Amitraz showed the highest level of toxicity for the adults (100% mortality) and thepupae of parasitoids (83.3% mortality). Both buprofezin and propargite caused no adverse effect on thefecundity and longevity of parasitoids, but amitraz significantly reduced the fecundity and longevity ofadults. Life table assay indicated that buprofezin and propargite have no major impact on the intrinsic rateof natural increase (rm), while amitraz lowered the rm value by 7.03%. According to the IOBCclassification of toxicity, buprofezin was found to be harmless for the pupae and adults and amitrazproved to be harmful for adults. Based on both the life table and IOBC methodology, buprofezin andpropargite are found to be relatively safe for E. formosa and can be used in integrated pest managementprograms where this parasitoid is involved

Efficacy of biorational insecticides against Dubas bug, Ommatissus lybicus (Hem.: Tropiduchidae) in a date palm orchard and evaluation of kaolin and mineral oil in the laboratory

In this study, mineral oil and kaolin as alternatives to conventional pesticide (diazinon) were evaluated to manage Dubas bug, Ommatissus lybicus de Bergevin, in the field and laboratory. In the field experiment, effect of four treatments was evaluated against population density (first and second nymphal stages) and honeydew production (as main damage) of Dubas bug. A single application of each product was applied at the recommended rates. Results showed that kaolin, mineral oil and diazinon were statistically similar in decreasing the population density and damage of Dubas bug. This result makes kaolin and mineral oil as potential alternatives to conventional insecticides in date palm orchards. In the laboratory, mineral oil was effective on egg mortality. In settling choice test, the ability of Dubas bug to discriminate between kaolin-treated and kaolin-untreated leaflets increased significantly over the time and females laid more eggs on untreated leaflets than kaolin-treated leaflets. Results of no-choice test revealed that the leafhoppers could lay eggs on treated leaflets as many as on untreated leaflets

Cellular energy allocation of Glyphodes pyloalis (Lep.: Pyralidae): changes related to exposure to TiO2 nanoparticles

In order to study the pollution potential of TiO2 nanoparticles (TiO2-NPs) on ecological health, this research was carried out on the cellular energy allocation (CEA) of Glyphodes pyloalis Walker exposed to TiO2-NPs. The newly ecdysed fifth instar larvae of G. pyloalis were treated with LC10, LC20, LC30, LC40 and LC50 concentrations of TiO2-NPs and the amount of energy available (Ea), energy consumption (Ec) and cellular energy allocation were compared. The resulting calculated energy reserves (lipid, carbohydrate, glycogen and protein) showed that increasing the time of exposure, the total lipid and carbohydrate amounts significantly decreased, when the LC30, LC40 and LC50 concentrations were applied. The amounts of glycogen in the larvae treated with LC10, LC20 and LC30 concentrations of TiO2-NPs were increased, whereas the LC40 and LC50 concentrations led to decrease in the amount of glycogen. The significant reduction in the amount of total protein compared to the control and over all three days of treatment was observed for LC50 concentration of TiO2-NPs; however, the LC10 concentration lead to a significant increase of the total protein after three days. Ea decreased in a dose-response related manner and over all time points, but it significantly increased in treated larvae by LC10 and LC20 concentrations after two days. Ec increased as concentrations grew to LC30 and then started to decrease. The results showed that CEA was not affected by LC10 concentration, but significantly decreased when the concentration increased and at all time points probably as a cost to deal with TiO2-NPs detoxification. Therefore, it will be possible to use the CEA as an appropriate early biomarker for the impacts of TiO2-NPs

Biochemical characterization of α-amylases from gut and hemolymph of Rhynchophorus ferrugineus Olivieri (Col.: Curculionidae) and their inhibition by extracts from the legumes Vigna radiata L. and Phaseolus vulgaris L.

α-amylase inhibitors represent an important tool in engineering crop plants against insect pests. For achieving this goal, it is necessary to find the nature of α-amylases and their properties for possible use in a pest management procedure. Because Rhynchophorus ferrugineus Olivieri is a devastating pest of palm trees in the southeast of Iran, we attempted to characterize α-amylases from larval gut and hemolymph, and to study their interaction with inhibitors extracted from the common bean and the green mung bean. The optimal pHs for gut and hemolymph α-amylases were 4 - 5 and 5 - 6, respectively. Also, high gut amylolytic activity was found at temperatures of 40 – 50 °C. The highest and lowest specific α-amylase activities were detected in the guts of last instar and adult males, and in the hemolymph of last instar, respectively. As calculated from Lineweaver-Burk plots, the Km values for gut and hemolymph α-amylases of the last instar were 0.54 and 2.15 %, respectively, when glycogen was used as the substrate. Also, when starch was used as the substrate, the Km values for gut and hemolymph α-amylases were 1.37 and 0.15 %, respectively. Zymogram pattern in the native gel revealed that R. ferrugineus gut and hemolymph α-amylases had two isoforms. α-amylase inhibitors partially purified from Vigna radiata L. and Phaseolus vulgaris L. by ionic exchange DEAE cellulose column, inhibited the R. ferrugineus gut α-amylase activity by 19 ± 0.64 % and 11.56 ± 0.69 %, respectively

Biochemical biomarkers of Glyphodes pyloalis Walker (Lepidoptera: Pyralidae) in exposure to TiO2 nanoparticles

Biochemical biomarkers and bioassays, due to their assumed immediate response after acute exposure of the organism to the stressor, are useful tools to gauging anthropogenic impacts. The toxicity of TiO2-nanoparticles (TiO2-NPs) on the Glyphodes pyloalis Walker was assessed and the LC50 value obtained as 660.85 mg/L. The in vivo responses of G. pyloalis to sub-lethal concentrations of TiO2-NPs were surveyed by monitoring the activity of general esterases (EST), peroxidase (POD) and glutathione S-transferase (GST), as biochemical biomarkers. Activity of these biomarkers affected by exposure to TiO2-NPs and this could lead to the mortality or sub-lethal impacts. The effect of TiO2-NPs concentrations on the activity of these enzymes was correlated to the exposure time. The activity of EST and GST was significantly decreased compared to the control, after 24 h of treatments. By increasing exposure time, the expression of EST and GST was significantly increased. More POD expression was occurred at low concentrations (i.e. LC20 and LC30); however, at high concentrations, less POD activity obtained. It can be concluded that these enzymes are good early indicator of toxicity and in conjunction with acute toxicity studies allow adverse effects of TiO2-NPs to be predicted and managed

The Ser431Phe substitution in acetylcholinesterase associated with pirimicarb and organophosphorous insecticide resistance in the peach-potato aphid, Myzus persicae (Hem.: Aphididae)

The peach-potato aphid, Myzus pesicae Sulzer, is a globally distributed, economically important pest of a wide range of field crops and ornamentals. Due to extensive and repeated use of insecticide, this species has developed many different resistance mechanisms to insecticides. The enzyme acetylcholinesterase (EC 3.1.1.7) (AChE) occurs widely in both vertebrate and invertebrate nervous systems and is the target of organophosphate (OP) and carbamate insecticides. One of resistance mechanisms to OP and carbamate insecticides is the insensitivity of AChE to these insecticides. In this study the possibility of mutation in insensitive AChE was surveyed. The complete coding sequences of acetylcholinesterases (MpAChE2) from susceptible and resistant populations were identified and sequences from resistant and two susceptible populations were compared. Consequently, one amino acid substitution (Ser431Phe) was detected within the resistant population at MpAChE2 gene. The Ser431Phe substitution is located in acyl pocket of acetylcholinesterase. Therefore, it seems that MpAChE2 is important as a target of pirimicarb. This substitution makes the acyl pocket narrower and pirimicarb can not have any access to this site. cDNA was obtained from individual aphids randomly and sequence of MpAChE2 indicated that MpAChE2 of the resistant population was heterozygous

Effects of Inhibitors on Haemolymph Phenoloxidase from Rosaceous Branch Borer, Ospheranteria Coerulescens (Coleoptera: Cerambycidae)

The rosaceous branch borer, Ospheranteria coerulescens, is an important pest of rosaceous trees. This insect feeds on the twigs and branches of living trees and causes their death. The characterization of the insect phenoloxidase (PO) is of interest when doing comparative investigations, and so that we may be able to understand its biochemical properties. When designing new methods of insect control such as the use of PO inhibitors, an understanding of the biochemical properties is fundamental. In this study, PO from hemolymph of the rosaceous branch borer was purified using ammonium sulfate precipitation, gel-filtration, and ion-exchange chromatography. The biochemical properties were characterized using l-dihydroxyphenylalanine (L-DOPA) as the specific substrate. The apparent molecular weights of the three isoforms of PO were determined by SDS-PAGE to be 85.23, 79.45, and 66.06 kDa. Optimal pH for PO activity was pH 8, and the optimal temperature was 45°C. Phenoloxidase lost less than 50% of its relative activity after a 60 min incubation at the optimal temperature. The effects of ions and chemical materials such as K+, Ba2+, Zn2+ and EDTA on PO showed that PO activity was strongly inhibited by Zn2+. The Michaelis constant (Km) and maximum velocity (Vmax) were 88.61 mM and 0.14 μmol/min, respectively. The inhibitory effects of kojic acid, 4-hexylresorsinol, and quercetin on PO were determined, and the IC50s (inhibitory concentration) were estimated as 23.31 for kojic acid, 35.75 for 4-hexylresorcinol, and 60.8 μM for quercetin. The inhibitory potency of kojic acid was 1.54 times higher than that of 4-hexylresorcinol and 2.58 times higher than that of quercetin. Phenoloxidase was effectively inhibited by 4-hexylresorcinol, and the inhibition type was competitive. The inhibition types of PO by kojic acid and quercetin were found to be mixed

Protease Inhibitor from the Crude Extract of Plant Seeds Affects the Digestive Proteases in Hyphantria Cunea (Lep.: Arctiidae)

Proteases are one of the most important digestive enzymes in the midgut of Hyphantria cunea Drury. Proteases are responsible for protein digestion. In the present study, we evaluated the efficiency of some plant inhibitors on proteases in the gut of the H. cunea. Last instar larvae were collected from mulberry trees. The digestive system of the larvae was used as an enzyme source. The total proteolytic and trypsin activity were assessed by the hemoglobin and BApNA, respectively, as the substrate. The evaluation of the total proteolytic and trypsin activities in various pHs showed the highest relative activity at a pH of 11. Also, the inhibitory effect of inhibitors extracted from Alhagi maurorum Medik., Lathyrus sativus L., Vicia faba L., Prosopis farcta (Banks & Sol.) Eig., and Panicum miliaceum L. on the digestive protease of the fall webworm was measured. Protease inhibitors extracted from A. maurorum, P. farcta and P. miliaceum showed negligible inhibition but L. sativus was able to inhibit 34.72% and 100% of the total activity of proteolytic and trypsin, respectively. Also, the total proteolytic and trypsin activities were inhibited by the inhibitor from V. faba, at 22.27% and 100%, respectively. The zymogram pattern of trypsin with nitro-cellulose membranes showed 2 isoforms in the gut of H. cunea. The inhibitor from L. sativus completely inhibited both isoforms. Gel electrophoresis of proteolitytic activity revealed at least 6 isoforms the inhibitor extracted from L. sativus; completely inhibiting some of them. The inhibitor from L. sativus was purified by ammonium sulfate precipitation and gel-filtration. The molecular mass of the inhibitor was determined as 45 kDa. The highest inhibition of trypsin activity by the inhibitor from L. sativus occurred at a pH of 10. The stability of the inhibitor from L. sativus was evaluated at different pHs and temperatures. The results showed that the inhibitor from L. sativus was stable at a pH of 11.0, and showed 45% inhibition on trypsin activity at a pH of 11. Also, this inhibitor revealed stability up to 50°C