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.

No abstract

No abstract

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.

Some biological aspects of Tetranychus urticae Koch on three soybean cultivars (i.e., Giza 21, Giza 35 and Giza 83) at three constant temperatures of 22, 26 and 30°C; 65% R.H. and 16:8 L: D photoperiods were studied. The results indicated that, T. urticae successfully developed on all experimental soybean cultivars at the three constant temperatures. The life cycle of T. urticae was the longest at 22°C followed by 26°C, than 30°C. The longevity of T. urticae female were 18.18, 18.88 and 19.18 days at 22°C, while the shortest periods were 13.65, 13.85 and 15.30 days on Giza21, Giza84 and Giza35, respectively. Significantly differences occurred between all stages at the three levels of temperatures. The highest fecundity and daily rate at 30°C was 95.65 eggs/female and 8.72 eggs/♀/day, while the lowest was71.58 eggs/female and 5.33 eggs/♀/day at 22ºC. Significant differences occurred between the three varieties diets as fecundity was the highest on Giza35 and the lowest on Giza21. These results indicated that, soybean Giza35 was more susceptible to the infestation by spider mite, while Giza21 was more tolerance, whereas Giza83 was in between. The lowest threshold temperature (t 0 ) to different stages of the mite, T. urticae were recorded as: 14.26, 3.44, 6.34, 11.32, 7.93, 11.32, 9.85 and 4.66 for egg, larva, protonymph, deutonymph, immature, life cycle, generation and life span for the mite females, respectively. Whereas, T. urticae female required 135.4 DDUs to complete its development (egg to adult).

Aphids, particularly Aphis gossypii Glov., is one of the most-important-pests in squash farms, caused serious losses by sucking plant sap in addition to plant viruses' transmission such as Papaya ringspot virus-W (PRSV-W). The current work conducted to study of the effect of various-systemic-insecticides and mineral-oil against melon-aphid, "Aphis gossypii" and its ability on transmissions of non-persistent-viruses under laboratory conditions. Data obtained showed that the "flonicamid" and "pymetrozine" recorded significantly-reduction in virus-acquisition and inoculations when compared-with control "also" reductions were compared-with mineral-oil applications. On-other-hand, data obtained of insecticide-residues activity and KZ-oil on "PRSV" transmission-rate by "A. gossypii" revealed that flonicamid had significantly higher persistence up to 12 days followed by pymetrozine. The mineral oil experienced a significant increase in transmission rate as its efficacy decreased dramatically on the eighth transmission and twelfth days.

The population fluctuations of Tetranychus urticae Koch and the associated phytoseiid mite, Euseius scutalis (A.-H.) on three soybean cultivars at Gharbia Governorate were studied during two successive seasons of 2015 and 2016. The results indicated significant differences in the T. urticae infestations through 2015 and 2016 seasons. Giza 35 variety harbored the highest infestation recorded 552.56 and 440.5 motile stages/10 leaflets for the two successive seasons, as compared with Giza 21 and Giza 83 varieties. Giza 21 variety was the most tolerant one recorded 130.38 and 174.88 motile stages/10 leaflets for two successive seasons. Significant positive correlations occurred between the T. urticae population and E. scutalis in all soybean varieties. The predatory mite was the main important predator for suppressing population density of T. urticae population during the two successive seasons. The insignificant positive effect of maximum and minimum temperatures on the population of T. urticae infested the three soybean varieties during 2015 and 2016. The combined effect of the tested weather factors (max temp., mini temp. and R.H. %) and the plant age together on T. urticae population were studied. The plant age and phenology were more effective on T. urticae population as compared with the weather factors.