Larvae and adults of T. castaneum and T. confusum reared under laboratory conditions (26 ± 2 °C and 70–80% R.H. with 16-h light and 8-h dark) on semi-artificial diet consisting of fine wheat with some adherent endosperm with 20% glycine and 5% yeast powder.
Four essential oils were used in the bioassay tests: coriander, oil, Janesville, caraway, and black seed (habat al Baraka). They were obtained by steam distillation of dried plants (Guenther 1961).
Oil emulsions were prepared as follows: 5 drops of Triton X-100 as emulsifier were mixed thoroughly with 5 ml of each tested oil, and then water was added to obtain the desired concentrations (2%) in percent of v/v. The emulsifier was mixed at the corresponding concentrations and used as a check. To evaluate the insecticidal activity of tested oils during sequential times (24, 48, 96, and 168 h), foam granules (1 cm in diameter) were treated at zero time with 2% of the tested oils dried and provided with heat sterilized rice 100 g seeds each) fastened each with a string. Then all treatments were used immediately as non-choice test. The foam particles were treated with the natural oils, which were mixed with stored seeds (2g foam/100g seeds) according to (Abd El-Aziz, 2001). Oil emulsions were prepared as follows: 5 drops of Triton X-100 as emulsifier were mixed thoroughly with 5 ml of each tested oil, and then water was added to obtain the desired concentrations (2%) in percent of (v/v). The emulsifier was mixed at the corresponding concentrations and used as a check. To evaluate the insecticidal activity of tested oils during sequential times (24, 48, 96, and 168 h), foam granules (1 cm in diameter) were treated at zero time with 2% of the tested oils dried and provided with heat-sterilized rice 100 g seeds each, fastened each with a string. Then all treatments were used immediately as non-choice test. The foam particles were treated with the natural oils, which were mixed with stored seeds (2 g foam/100 g seeds) according to Sabbour and Abd El-Aziz (2016).
A pair of newly emerged weevils were placed with treated or untreated rice seeds in glass jars (250 ml capacity) covered with muslin. The number of dead weevils in each jar was counted every day and percentages of mortality were corrected using Abbottʼs formula (Abbott 1925). The LC50 was calculated through the probit analysis (Finney 1971). The experiments were conducted under the National Research Centre laboratories conditions of 27 ± 2 °C and 60–65% R. H. The experiment was replicated four times.
It is a process through which a chemical is slowly but efficiently released to the particular host for insect pests control. “Release mechanisms include dissolution, biodegradation, diffusion, and osmotic pressure with specific (pH, 4.4)”. The nanoencapsulation process was carried out by polymerization technology. The tested oils were used as a core material and urea (U) and formaldehyde (F) as shell materials. Sulfuric acid solution (10% w/w) was prepared in our laboratory to control the pH (4.4) of emulsion, and tween 80 (polysorbate 80) was used as an emulsifier (Merck, Germany). The suspension obtained of nanocapsules was cooled down to ambient temperature, rinsed with deionized water, filtered, and finally dehydrated by freeze-drying using a LIO-5P, which is a Freeze Dryers for Laboratory Use. (Apparatus CinquePascal, Trezzano SN, Milan, Italy). Nano-emulsion is prepared by high-pressure homogenization of 2.5% surfactant and 100% glycerol, to create stable droplets which that increase the retention of the oil and cause as low release of the nanomaterials. The release rate depends upon the protection time; consequently, a decrease in release rate can prolong insect pests protection time (Quintela and McCoy 1998). For each tested bulk essential oils, four concentrations were prepared (3, 1.5, 0.5, and 0.2%). While in the case of nano-essential oils, the tested concentrations were 0.1, 0.5, 0.05, and 0.005%. Three drops of emulsifier (Triton X-100) were mixed with water and used as a check. The tested oils (Bulk & Nano) were experimented at concentrations tested for their insecticidal activities against the 3rd instar larvae of target pests. According to Abd El-Aziz (2001), the foam granules were sprayed with the tested oils (Bulk &Nano) and were mixed with wheat (2 g foam/100 g wheat). For each tested concentration, four glass jars as replicates were used. Thereafter, ten third instar larvae were introduced into each glass jar and covered with muslin for suitable ventilation. In the case of untreated control, twelve replicates were kept under the same conditions without any treatments. After 7 days of exposure, mortality percentages were calculated in the treated and untreated control experiments. All tests were carried at 27 ± 2oC and 65 ± 5% relative humidity (RH). The dead larvae numbers were estimated in each jar was used and the mortality percentage was determined. Each experiment was replicated four times. The tested oils (Bulk &Nano) were sprayed to the foam granules and were mixed with wheat (2 g foam/100 g wheat) for testing the oviposition inhibitory effects of tested oils (Abd El-Aziz 2001). In no-choice test, two pairs of mixed-sex of target moth adults (2–3 days old) were placed with treated or untreated wheat grains with foam particles in glass jars (250 cc capacity) covered with muslin. Adults female moths were left to lay their eggs, then the deposited egg numbers treated or untreated the grains/female were estimated in each of the tested jars. Four glass jars as replicates for each tested concentration were used and the test was repeated three times. The persistence effect of tested oils (Bulk and Nano) on foam as surface protectant was evaluated after storage interval 120 days (4 months) against target pests moths’ emergence. Hundred grams of heat sterilized wheat grains were introduced to gunny sacks (10 × 10 cm each) closed each with a string. The foam granules (about 1 cm in diameter) were sprayed with treatments, dried, and provided as a layer between sacks. Then, two pairs of newly emerged moths were placed in a jar (2 l capacity with two gunny sacks) and then removed the moths which died after lying egg. The count of the newly emerged adult moths after 120 days is about 4 months.
Data were statistically analyzed by F test; LSD value was estimated, using SPSS statistical program software.