Effects of Ferula assa-foetida L. and Aloysia citriodora Palau ethanolic extracts on mortality and some physiological characteristics of Ephestia kuehniella (Lepidoptera: Pyralidae) larvae

The lethal and physiological effects of plant secondary metabolites on a wide range of pest insects have been proved. These compounds, while having a direct effect on the target pest, are low risk to humans and the environment, and this has led to their advantage over chemicals. In this study, the lethal effect of Ferula assa-foetida L. and Aloysia citriodora Palau ethanolic extracts was determined on the third instar larvae of Ephestia kuehniella. The larval mortality was directly related to increasing the extracts concentration. The activity of some digestive enzymes in the gastrointestinal tract and the changes in hemocytes were also studied in the third instar larvae treated with the extracts. First, sublethal concentration of plant ethanolic extracts was calculated. The larvae then fed the diet contaminated by the lethal concentration of 25% (LC25) of the extracts (40 and 30 ppm for F. assa-foetida and A. citriodora,respectively). The control group consisted of larvae that fed the diet contaminated with diluted ethanol. The results indicated that both extracts significantly reduced the activity of trypsin and chymotrypsin enzymes. F. assa-foetida extract significantly reduced the activity of lipase and beta-glucosidase enzymes compared to the control, but the effect of A. citriodora extract on the activity of these two enzymes was in a statistical group with the control. The extracts had no significant effects on the alpha-glucosidase enzyme activity. The immune activity of larvae was also stimulated by changes in the number of blood cells affected by both extracts. The total number of cells and granulocytes of hemolymph showed a significant increase after 12 hours of feeding in the both extracts treatments, but gradually decreased until 24 hours that was still higher than the control group. The plasmatocytes showed a significant increase in the A. citriodora extract treatment after 12 hours,but in the F. assa-foetida extract treatment, this increase was significant after 24 hours. Understanding the intractions of plant extracts with the insect physiological characteristics such as the physiology of digestive and blood circulatory systems can lead to the possibility of appropriate use of these factors in the target pest control and be used in the pests management programs.