Culture of A. ipsilon was reared on castor bean leaves in Department of Insect Population Toxicology, Central Agricultural Pesticides Laboratory, Agriculture Research Center, Dokki, Giza, Egypt, for several generations under reared chamber environments were (25 ± 2 °C and 65 ± 5% R.H) without any insecticidal contamination and light–dark period was 12 h. Larvae reared in a big glass container with sawdust in the bottom. For adult emergence and oviposition, pupae were put in a ventilated cage. Adults were fed on a 10% sucrose solution soaked in a piece of cotton; laid eggs were collected and kept in glass containers for hatching to be used for the study.
Commercial formulations of chlorantraniliprole (Coragen®, 20% SC), and indoxacarb (Steward®, 15% EC) were supplied by Du Pont Co., and emamectin benzoate (Proclaim®, 5% S.G) was provided by Syngenta Co.
Emamectin benzoate, indoxacarb and chlorantraniliprole against A. ipsilon egg mass were determined. The upper layers of each egg mass (0–24 h old) were removed gently with a fine hairbrush. The lower layer in each egg mass was counted by the binocular. The counted egg samples were dipped (5 s) in different aqueous concentrations of the tested formulations, or distilled water as a control. After drying for 2 h at room temperature, the treated eggs were stored in Petri dishes (9 cm in diameter). Three days later, untreated castor bean leaves were added to the Petri dishes for larvae to feeding. Egg hatchability % and larval survival were monitored daily, and the mortality percentages were calculated. Results are based on four replicates of each treatment.
In other assays, 1st-, 3rd- and 5th-instars larvae (10 per each replicate) were exposed to castor bean leaves (Ricinus communis L.) treated with a series of aqueous concentrations of the test formulations, or with distilled water as a control. Leaves were dipped for 10 s. in different concentrations of tested compounds, held vertically to allow the excess solution to drip off and dried for 2 h, then offered to larvae for 42 h. After these time intervals, the treated leaves were replaced by untreated ones. Ten 1st-instar larvae were kept in Petri dishes, 3rd- and 5th-instars were held in ventilated wood boxes. The boxes contained sawdust to reduce moisture. Larval mortality recorded after 24 h. Larvae were weighed before exposure to treated leaves and again six days (3rd-instar) or (5th-instar) after exposure. Control 3rd- and 5th-instar larvae, fed untreated leaves, were weighed after similar time intervals. Weight gains of the 3rd- and 5th-instar larvae were determined 24 h, after feeding on treated leaves. Pupation and adult formation of 5th-instars were evaluated after the start of the assay.
Effects of ingestion of the tested formulations by adults were studied by allowing adults to fed on a 10% sucrose solution containing 50 or 100 mg L−1 of each test compound, or 10% sucrose solution as a control. Male and female moths were kept in a glass jar containing five individuals each. Mortality was checked daily for five days. Solutions were changed every second day to prevent fungal growth. Results are based on four replicates.
Field experiment and sampling
Application of the tested insecticides was conducted during the cotton-summer season in El-Dakahlia Governorate, Egypt, at Aga district, whereas an area of 2000 m2 was selected to be sown on 4th April 2019 with cottonseed var. “Giza 86.” The experiments were laid out in Randomized Complete Block Design (RCBD) (four replications). This area was divided into plots size each of 50 m2. Four treatments, the three tested insecticides and the check were designed in this area. Application of tested insecticides was done on 26th of June 2019 under field conditions. Irrigation water was used in diluting of the tested insecticides at their field recommended rates/200 L per feddan. Knapsack sprayer (CP3) equipped with one nozzle was used. Unplanted belts (3 m width) were left as barriers between plots to avoid contamination with drifts. Plots received all good recommended agricultural practices without any insecticidal treatments applied during the season. Samples of treated cotton leaves were collected randomly from each treatment immediately after one h from spray (zero time) and then 3, 6, 9, 12 and 14 days’ post-spray and transferred directly to the laboratory for feeding A. ipsilon by treated leaves with tested insecticides, (100 larvae/treatment/interval) for one day of each interval. Alive larvae were fed for another two days on untreated leaves. Cumulative mortalities were calculated at the end of each interval (three days) and corrected according to Abbott’s formula (1925). The cumulative mortalities of the first intervals (samples collected after spraying directly) was considered as initial kill, while the total mean of the cumulative mortality of the other intervals (3, 6, 9, 12 and 14 days from spraying) were considered as residual effects.
Data were corrected for control mortality according to Abbott’s formula (Abbott 1925). Also, mortality values were analyzed by Probit analysis (LPD line) to determine the LC values and slope for each compound according to a method adopted by Finney (1971). The results were analyzed using one-way ANOVA, significant differences between treatments were determined using Tukey’s HSD test in JMP 11.1.1. (SAS Institute Inc. 2013, Cary, NC, USA).