Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an important pest of citrus. In addition, D. citri is the vector of Huanglongbing, a destructive disease in citrus, also known as citrus greening disease caused by Candidatus Liberibacter asiaticus. Huanglongbing causes huge losses for citrus industries. Insecticide application for D. citri is the major strategy to prevent disease spread. The heavy use of insecticides causes development of insecticide resistance. We used RNA interference (RNAi) to silence genes implicated in pesticide resistance in order to increase the susceptibility. The activity of dsRNA to reduce the expression of carboxyesterases including esterases FE4 (EstFE4) and acetylcholinesterases (AChe) in D. citri was investigated. The dsRNA was applied topically to the fourth and fifth instars of nymphs. We targeted several EstFE4 and AChe genes using dsRNA against a consensus sequence for each of them. Five concentrations (25, 50, 75, 100, 125 ng/μl) from both dsRNAs were used. The treatments with the dsRNA caused concentration dependent nymph mortality. The highest gene expression levels of both AChe and EstFE4 were found in the fourth and fifth nymphal instars. Gene expression analysis showed that AChe genes were downregulated in emerged adults from dsRNA-AChe-treated nymphs compared to controls. However, EstFE4 genes were not affected. In the same manner, treatment with dsRNA-EstFE4 reduced expression level of EstFE4 genes in emerged adults from treated nymphs, but did not affect the expression of AChe genes. In the era of environmentally friendly control strategies, RNAi is a new promising venue to reduce pesticide applications.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Lividae) transmits the Candidatus Liberibacter asiaticus, which causes citrus greening disease or Huanglongbing, (HLB). To date, there is no efficient cure for HLB disease and the control of D. citri using insecticides became the most important tools for the management of HLB. However, the extensive use of insecticides could increase D. citri resistance to these insecticides. The objective of this study was to investigate the effect of RNA interference of acetylcholinesterase (AChE) on the mortality and susceptibility of D. citri to the four major insecticides used in Florida. In this study, we used a consensus sequence derived from the two AChE genes and cholinesterase 2-like (ChE-2-like) gene to target all of the three genes. Treatment with dsRNA-AChE increased the mortality percentages of both nymphs and adults of D. citri. The mortality percentage increased with the increase in the concentration of applied dsRNA-AChE, and the highest mortality (> 60%) was observed at the highest applied concentration (125ng/μl). Treatments of nymphs or adults with dsRNA-AChE down-regulated the expression of the three targeted genes of D. citri. Silencing of AChE and ChE in D. citri nymphs increased the susceptibility of emerged adults to chlorpyrifos and carbaryl, which act as AChE inhibitors. However, treatment with dsRNA-AChE did not increase the susceptibility of emerged adults to imidacloprid, which acts as an agonist of nicotinic acetylcholine receptors. In the same manner, treatment of adults with dsRNA-AChE increased their susceptibility to chlorpyrifos and carbaryl, but did not affect their susceptibility to imidacloprid. The ANOVA did not show any significant increase in susceptibility of D. citri adults to fenpropathrin after treatment with dsRNA-AChE, either as nymphs or as adults. However, simple linear regression showed that treatment with dsRNA-AChE increased D. citri susceptibility to fenpropathrin, which indicated that AChE could be involved in the metabolism of fenpropathrin. Our results indicated that silencing of AChE and ChE genes in D. citri to increase its susceptibility to insecticides could be a promising tool for the control of this important vector.

A total of 22 chiral toxaphene congeners were analyzed in organ tissues and eggs of laying hens after they had been fed with food spiked with technical toxaphene. For the analysis, multidimensional high-resolution gas chromatography using a chiral column coated with randomly silylated heptakis(O-tert-butyldimethylsilyl)-beta-cyclodextrin, electron capture detection, and valveless "live column switching" technique was applied. The analytical results were additionally confirmed with mass spectral data, recorded in electron-capture negative ionization mode with selected-ion monitoring mass spectrometry. During both the feeding period of the laying hens with toxaphene-contaminated food (38 weeks, accumulation phase) and the following subsiding period without toxaphenes (another 14 weeks, decontamination phase), organs (liver, kidney, skin/fat), blood, meat, and eggs of the hens served as model matrices for toxaphene uptake. The enantiomeric ratios (ERs) of congeners 26, 31, 32, 40, 41, 42(a+b), 44, 50, and 62--known as the most important components of technical toxaphene occurring in the environment--could be analytically determined. Significant differences were observed with respect to their initial racemic ratios. On the basis of their chemical structures, the metabolic pathways of some congeners could be explained. Astonishingly, some of the toxaphenes applied as racemates could merely be found as single enantiomers at the end of the feeding program, for example, congener 32 in blood and meat samples or congener 44, especially in organ tissues, which showed ERs of zero or infinity. The findings of this study impressively emphasize that it is essential to isolate and analyze individual toxaphene enantiomers in food and biota tissues to be capable of evaluating their toxicity and metabolization more specifically.

The problem has been exacerbated by the steady increase in population density and the establishment of the Grand Ethiopian Renaissance Dam. Therefore, preserving the availability and quality of this resource is enormously important. Water quality is affected by a number of factors related to the characteristics of the watercourse and surrounding environment, like soil type, agricultural and industrial activity in the studied regions. Therefore, a comparative study was conducted on water samples collected from eight different locations at west and middle Delta regions from Beheira and Gharbia governorates. The obtained results showed that there are significant differences among the means of sample collection sites and dates, as well as the interaction between studied variables in all studied parameters. Although, most physical and chemical parameters were within standards limits except turbidity and chemical oxygen demand (COD). However, the average values of turbidity, color and pH were convergent in both governorates. While total dissolved salts (TSS) had a higher value (42.2 mg L-1) in the Beheira governorate. In the case of, the remaining studied parameters, the values recorded in Gharbia gov. were higher than the corresponding values recorded in Beheira gov. including COD and UV 245 absorbance, which are associated with organic pollution. Thus, physical and chemical approaches can be used to evaluate the water quality in relevant locations. Further studies based on biological approaches should be also carried out.

Cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae) is considered a key pest of cotton in Egypt. Hence, field and laboratory studies were conducted at Sakha Agriculture Research Station, Egypt during seasons 2016 and 2017. Efficiency of seven insecticides i.e., flonicamid, imidacloprid, thiamethoxam, emamectin-benzoate, chlorpyrifos, methomyl and deltamethrin against A. gossypii in cotton fields were evaluated. Their side effects on the associated predators, soil fauna and plant defense enzymes also were studied. Flonicamid was the most effective against A. gossypii. The efficacy of imidacloprid and thiamethoxam did not differ significantly from that of chlorpyrifos and methomyl recording from 83.28-93.27% reduction in A. gossypii infestation. Flonicamid, emamectin-benzoate, imidacloprid and thiamethoxam were the least harmful to the associated predators causing less than 50% mortality, while the others were highly toxic. Flonicamid exhibited the highest degree of safety to the soil micro-arthropods, followed by emamectin-benzoate, methomyl and deltamethrin. In contrast, chlorpyrifos and imidacloprid were the most toxic to the soil microarthropods. The conventional insecticides (chlorpyrifos, methomyl and deltamethrin) increased the activity of catalase and peroxidase causing physiological stress on the treated cotton plants, whereas the other tested insecticides recorded decreases in catalase and peroxidase activities inducing the plant defense response. Only imidacloprid and thiamethoxam increased the activity of polyphenol oxidase. Emamectin-benzoate and deltamethrin decreased the total soluble protein content, while the others tested insecticides caused increases in this criterion comparing to the control.