Altered susceptibility of granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae) populations to insecticides after selection with pirimiphos-methyl and deltamethrin

Toxicity of the contact insecticides dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin and cypermethrin to granary weevil Sitophilus granarius (L.) adults from five populations previously selected with deltamethrin and pirimiphos-methyl, and two populations that had no contact with pesticides over an interval of 12 generations, was investigated in the laboratory by application to filter paper. The populations originated from storage facilities situated in different parts of the former Yugoslavia.A population originating from Apatin and one from Belgrade Port were selected three times each at the LD₅₀ level with deltamethrin and pirimiphos-methyl, respectively. In separate experiments, weevils from Belgrade Port were selected once at the pirimiphos-methyl LD₇₀ level and Bijeljina and Kikinda populations both once at the deltamethrin LD₇₀ level. All selection doses were at a level obtained from determining weevil mortality after 24 h of exposure to treated filter paper.Compared with the toxicity to laboratory weevils, the weevils from Apatin after the third selection were found to be 32.1 and 51.9 times less susceptible to deltamethrin at the LD₅₀ and LD₉₅ levels, respectively, while those from Belgrade Port were 2.7 and 3.2 times less susceptible to pirimiphos-methyl. Selection of Belgrade Port weevils at the pirimiphos-methyl LD₇₀ did not significantly affect their susceptibility to that insecticide but it caused a significant decrease in deltamethrin toxicity, which is indicative of a cross-resistance between the two compounds. Selection of Bijeljina weevils caused an increased resistance to deltamethrin, while selection of Kikinda weevils had little effect on their susceptibility to dichlorvos, but it caused a significant decrease in malathion and cypermethrin toxicity, and resistance to deltamethrin markedly increased (RR=238.8 at LD₅₀ and 660.8 at LD₉₅ levels, compared with laboratory weevils). Chlorpyrifos-methyl was the most toxic insecticide to all populations, while cypermethrin was the least toxic compound.     

Evaluation of edible film-forming ability of pumpkin oil cake; effect of pH and temperature

This study was conducted to evaluate the feasibility of pumpkin oil cake (PuOC) to form biodegradable films. The effect of heating treatment and pH of film solutions on films properties was determined. Film with the highest tensile strength (TS) (68.08 MPa) and elongation to break (EB) (36.62%) was produced when pH was 12 and heating T 90 °C. The same showed the best permeability properties. The total soluble matter and soluble protein reached the highest value, when the film was prepared at pH = 12 and T = 50 °C. ABTS test indicated that the film produced at pH = 10 and T = 60 °C was the best regarding the radical scavenging activity. Moisture content had not been significantly affected by the pH and heating temperature, whereas swelling capacity could be measured only for film prepared at T = 80 and 90 °C. To affirm and explain the influence of pH and T, scanning electron microscopy (SEM) was used.