The experiments were conducted in the Research Laboratory, College of Agricultural Studies (Shambat), Sudan University of Science and Technology (SUST), during February - March, 2021. The average temperature is between 25-32°C.

Larval instars of H. armigerawere collected from unsprayed tomato plants grown in Gamouaia Scheme Southern Khartoum and brought to the laboratory for mass rearing. Early instar were reared in groups of 100 larvae in plastic cages 19 cm in diameter covered with muslin cloth and fed on okra fruits, whereas 4^th instars were reared separately in plastic cubs 5 cm in diameter and 7 cm in height to avoid cannibalism and the bottom of each cubs was filled with sand for pupations. Upon emergence the adults were transferred to plastic cages 31x20x19 cm covered with muslin cloth and fed on 10% sugar solution 19, cotton stripes were hung on the margins of the cages for eggs laying and were replaced daily with new stripes while newly hatching larvae were transferred to the larval rearing cages. The rearing process continued until a sufficient number of homogenous populations of larvae was collected for the experiments.

Seeds of R. communis and C. occidentalis were collected from river bank, Omdurman area and brought to the laboratory for shade-drying. After complete dryness the plant samples were crushed by an electronic blender to obtain the powder. 120g of prepared seeds powder were extracted with absolute ethanol using Soxhlet apparatus for six hours, and rotary evaporator was used to remove the solvent20.

Biotect® 9.4 % WPcommercialformulation containing Bacillus thuringiensiskurstakifrom( Organic Biotechnology Co., First industrial zone , El Noubareya, El Beheira, Egypt ) were used in 5 concentrations (0.62, 1.25, 2.5, 5, and 10 mg/ml). For plant extracts also 5 concentrations (4%, 6%, 8%, 10% and 12%) were used.

Second larval instar was used in this study. Fruits dipping method 21 was followed, small pieces of fresh okra fruits were dipped for 30 seconds in different concentrations and left to dry under room conditions for 10 minutes. Ten pre starved larvae (one hour) were used for each treatment and each treatment was replicated three times. Three replicates were also used as a control set. All treated larvae were kept in Petri-dishes 9 cm in diameter at temperature of 25±1 °c. Treated larvae were provided with fresh okra pieces till the end of experiment. The mortality % was recorded 24, 48, 72 and 96 hrs after application.

To evaluate the joint action of tested plant extracts and Bt the method of Mansour et al. 22 was adopted with some modifications. In which paired mixtures of plant extracts were prepared at concentration levels of their respective LC₂₅ values at 1:1 ratio. Each mixture was tested in three replicates along with controls. Mortality percentages were determined after 24to 48 hrs and the combined action of the different mixtures was expressed as Co-toxicity factor. The following formula were used to determine potentiation, antagonism and additive effect:

Co - toxicity factor = (O - E) x 100/E; where:

O : is observed % mortality and E : is expected % mortality.

The co-toxicity factor differentiates the results into three categories. A positive factor of ≥ 20 indicates potentiation, a negative factor of ≤ -20 indicates antagonism, and the intermediate values of >-20 to < 20 indicates an additive effect 22. The LC₂₅ values of each extract and Bt were tested again against 2^nd larval instar in order to determine the accurate expected mortality. The expected mortality of the combined pair is the sum of the mortalities of single compound at recorded LC₂₅ and the observed mortality is the recorded mortality obtained after 24 - 48 hrs of exposure to the mixture.

The obtained data were statistically analyzed according to analysis of variance (ANOVA); Duncan's Multiple Range Test was used for means separation using genstat version 12.1 Also the data were subjected to Probit analysis using SPSS 16.0 software.

The results presented in (Table 1) clearly proved that all concentrations of the seeds ethanolic extract of R. communis L. And C. occidentalis gave significantly higher mortality percentage than the control throughout the experimental period. Additionally, the lethal effect of these extracts were dose and time dependant. The highest concentration (12 %) of R. communis induced 80% after 96 hrs which were significantly different and higher that caused by the same concentration of C. occidental which cause 70% larval mortality after the same period. Its observed from the results exhibited in (Table 2) that the seeds ethanolic extract of R. communis are significantly more toxic than its counterpart of C. occidental where the LC₅₀ values were 6.4 % for R. communis and 8.1% for C. occidental.

The results shown in (Figure 1) proved that all Bt concentrations generated a significantly (p < .001) higher mortality percentage than the control throughout the experimental period. It should be noted that the percent mortality increases with the increase of both concentration and exposure period. LC₅₀ value of Bt was 0.41 mg/ml as shown in (Table 2).

Paired mixtures of plant extracts and Bt were tested against 2^nd larval instar of H. armigera as described in material and method section. The results shown in (Table 3) illustrated that the binary mixture of R. communis and C. occidental have an additive effect after 24 hrs whereas, after 48 hrs of application a potentiation effect (CTF = +23.5) was recorded. Regarding the binary mixture of Bt and plant extracts the results revealed that the R. communis and Bt mixture induced a potentiation effect (CTF = +26.7), meanwhile, C. occidental and Bt mixture induced a an additive effect (CTF = +14.9).

Botanicals have long been proposed as smart alternatives to synthetic insecticides for pest management because they are safe to the environment and human health. More than thousands species of plants have been reported to have chemicals in its various parts which have insecticidal properties. However, a few of them were used for insect control on a commercial scale 23. The study findings clearly proved the efficacy of R. communis against 2^nd larval instar o H. armigera. In fact its highest concentration (12%) gave 80% mortality of tested larvae after 96 hrs of application. Kodjo et al. 24 found that 5% oil emulsion of R. communis caused 89.58% mortality of the diamondback moth Plutellaxylostella in ingestion toxicity test. Parajapati et al. 25 also recorded that the seed extracts of R. communis showed better insecticidal activity than the leaf extracts against S. Frugiper due to the active compounds such as castor oil and ricinine.

The mortality percent recorded after 48 hours of exposure by the lowest and highest concentrations (4% and 12%) of seeds ethanolic extract of C. occidentalis does not changed even after 72 hrs post treatment. This may indicate to an acute action of this plant extract. Similar results were recorded by Elnour 20 who found that the percent mortality caused by various concentrations of seeds ethanolic extract of C. occidentalis against African melon ladybird Henosepilachnaelaterii after 24 hrs dose not changed after 48 hrs of exposure. Also Vashishta et al. 26 found that C. occidentalis generate an acute toxic effects in vertebrates and its toxins do not accumulate in body tissues.

The results also revealed that all Bt concentrations caused a significantly higher mortality percentage (p<.001) than control throughout the experimental period. The estimated LC₅₀ value of Bt was 0.41 mg/ml in this study. Plata-Rueda et al. 27 found that LC₅₀ of Btkon nettle caterpillar Euprosternaelaeasa was 1.25 mg/ ml.

The use of extract mixtures may increase the spectrum of activity of extract mixtures against target pests. In addition, if the extract mixture show synergistic effect, then low concentration is needed to control target pests. Further, low extract application rates might minimize the risk to non-target organisms as well as to the environment. Also the use of synergistic extract mixtures might delay the development of insecticide resistance 28.

Study findings illustrated that the binary mixture of R. communis and C. occidental have an additive effect after 24 hrs, whereas after 48 hrs of application a potentiation effect (CTF = +23.5) was recorded. Regarding the binary mixture of Bt and plant extracts the results revealed that the R. communis and Bt mixture induced a potentiation effect (CTF = +26.7), meanwhile, C. occidental and Bt mixture generated a an additive effect.

Reddy and Chowdary 29 noted that the compatibility of a plant extract for combination with microbial insecticides depends on qualitative and quantitative variations of secondary metabolites, which may affect the microbes. Many plants extract such as Annona squamosa L., Datura stramonium L., Eucalyptus globules Labile, Ipomea carnea Jacq., Lantana camara L., Nicotiana tabacum L., and Pongamia pinnata L. Showed a synergistic effect when mixed with Btk.