Insecticide susceptibility of the dengue vector Aedes aegypti (Diptera: culicidae) in Makkah City, Saudi Arabia

Objective To examine the insecticide susceptibility of Aedes aegypti (Ae. aegypti) from various sites in Makkah City, Saudi Arabia. Methods This was examined based on WHO standard procedures. Results The larvae of Ae. aegypti were susceptible to all larvicides examined, but this susceptibility was more pronounced in wild populations, which tended to show tolerance to icon. Icon was the most effective larvicide with LC50 values of 0.007 ppm and 0.012 ppm for the laboratory and field strains, respectively. Ae. aegypti adults exposed to lambda-cyhalothrin showed a low mortality rate in comparison with those exposed to deltamethrin and cyfluthrin. Conclusions The results of the present study indicate differential susceptibility between field and laboratory larval populations. Wild larvae are less susceptible to insecticide treatments than their laboratory-bred counterparts. Taken together, these results suggest that tolerance and the tendency toward resistance to commonly used insecticides are present in Ae. aegypti populations throughout Makkah City, Saudi Arabia

Ecological variations and role of heat shock protein in Artemisia judaica L. in response to temperature regimes of Tabuk, Saudi Arabia

Artemisia judaica L. (Compositae) are shrubby herbs growing wildly in Tabuk region and distributed in the desert regions. This region is characterized by extremely variable environmental conditions where the temperature varies from extreme low to extreme high. These temperature regimes have a profound effect on morphology, growth physiology and biochemistry of the plants. The plant samples were collected from Tabuk–Jordan road (760 m above sea level) in the month of January, April, July and October 2013 to evaluate the effect of temperature dynamics on A. judaica L. in four different seasons. Physiological, biochemical alterations and heat shock proteins (HSPs) were studied during these seasons in order to evaluate the environmental adaptation and stress tolerance in response to temperature variations. Plant growth parameters showed a significant increase in height, fresh and dry matter accumulation, total chlorophyll, nitrogen, phosphorus, potassium, artemisinin and leaf relative water contents investigated in the month of April and October. Growth of plant was suppressed and an active role of carbonic anhydrase (CA), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) was observed to cope with the extreme low temperature in January and extreme high temperature in July 2013. However, the plants collected in October and April did not show a statistical difference. Inductions in the expression of HSP90 were recorded in all the plants collected during April and October 2013 with no statistically significant difference. Therefore, based on the results it is recommended that during April and October the environmental conditions are best suitable for growth, development and medicinal use of Artemisia. Keywords: Antioxidants, Climate change, Growth, Heat shock proteins, Medicinal plant

Peroxidase Activity after Viral Infection and Whitefly Infestation in Juvenile and Mature Leaves of Solanum lycopersicum

Whitefly infestation and the begomoviruses that they transmit have been shown to affect the activities of plant defence proteins, but with no relation to heterophylly, a process of great importance underlying the overall biology of plants. Here, we have assessed the effects of Tomato yellow leaf curl virus (TYLCV) infection on Solanum lycopersicum peroxidase (POD) activity and have examined whether leaves of different ages exhibit differential POD activity in response to infection and infestation with Bemisia tabaci B biotype. We used leaf discs of two ages (juvenile and mature) with two different infection statuses (infected and healthy) to examine the activity of the tomato plant peroxidase using guaiacol as a substrate and taking exposure time into account. S. lycopersicum showed increased POD activity in the presence of TYLCV. The activity of the enzyme was higher in mature than in juvenile leaves. In general, both infected and healthy leaves exhibited greater POD activity during whitefly infestation. In the infested juvenile leaves, POD activity was much lower in the healthy leaves and increased gradually with period of exposure to B. tabaci B infestation. In contrast, the activity of the enzyme remained low in infested mature leaves in both the presence and absence of the virus even with increased exposure time. Determination of the distribution of an insect pest is critical for sampling and management. Leaf age is presumed to be associated with the within-host distribution of the geminivirus vector B. tabaci. Juvenile leaves will usually attract more insects due to increased nutritional value and weaker defences. Our results highlight the importance of leaf age/position on the whitefly – host plant – geminivirus interactions and have important implications for sampling and control strategies

Fern-synthesized silver nanocrystals: Towards a new class of mosquito oviposition deterrents?

Mosquitoes act as vectors of devastating pathogens and parasites, representing a key threat for millions of humans and animals worldwide. Eco-friendly control tools are urgently required. We proposed a novel method of fern-mediated biosynthesis of silver nanoparticles (AgNP) using Dicranopteris linearis, acting as a reducing and capping agent. AgNP were characterized by UV–vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), zeta potential and particle size analysis. In mosquitocidal assays, the LC50 of D. linearis extract against Aedes aegypti ranged from 165.213 (larva I) to 255.055 ppm (pupa). LC50 of D. linearis-synthesized AgNP ranged from 18.905 (larva I) to 29.328 ppm (pupa). In the field, the application of D. linearis extract and AgNP (10 × LC50) led to 100% larval reduction after 72 h. Smoke toxicity experiments conducted against A. aegypti adults showed that D. linearis leaf-, stem- and root-based coils evoked mortality rates comparable to the permethrin-based positive control (58%, 47%, 34%, and 48% respectively). In ovicidal experiments, egg hatchability was reduced by 100% after treatment with 25 ppm of AgNP and 300 ppm of D. linearis extract. Interestingly, oviposition deterrent assays highlighted that 100 ppm of fern extract reduced oviposition rates of more than 65%, while 10 ppm of fern-fabricated AgNP reduced oviposition rates of more than 70% in A. aegypti (OAI were − 0.52 and − 0.55, respectively). Overall, our results highlighted that D. linearis-synthesized AgNP could be useful candidates to develop nano-formulated oviposition deterrents effective against dengue vectors

Slow release formulations of Bacillus thuringiensis israelensis (AM 65-52) and spinosyns: effectiveness against the West Nile vector Culex pipiens in Saudi Arabia

Objective: To investigate the effectiveness of slow release formulations of Bacillus thuringiensis israelensis (AM 65-52) (B. thuringiensis israelensis) and spinosyns against the West Nile vector Culex pipiens (Cx. pipiens) in Saudi Arabia. Methods: We tested slow release insecticide formulations of Natular DT, Tap 60 and VectoBac granule against II instars of Cx. pipiens larvae in 50 L laboratory arenas. Results: Slow release formulations of B. thuringiensis israelensis and spinosyns gave continuous control against Cx. pipiens for several weeks. Natular DT was more effective over Tap 60 and VectoBac granule of about 1.3 and 5.8 times, respectively. Variations in the durations of effective control among the tested slow release formulations may reflect differences in their active ingredients and the mode of action. Conclusions: Our results highlighted the effectiveness of B. thuringiensis israelensis and spinosyns against an important West Nile vector, providing baseline data to develop ecofriendly mosquito control programs in Saudi Arabia