Effect of Bermuda Grass Cynodon dactylon Extracts on Cotton Leaf Worm, Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae)

Bermuda grass, Cynodon dactylon (L.) extracts were tested on cotton leaf worm, Spodoptera littorals (Boisd.). Five solvents were used in preparing of these extracts, (i.e., methanol, petroleum ether, acetone, diethyl ether and distilled water). Distilled water was used as polar solvent. The results showed that extracts of non polar solvents were more effective than water. Methanol extract resulted in highest number of giant larvae. Methanol and diethyl ether extracts resulted in the highest number of deformed pupae. Acetone extract caused highest number of mortalities, followed by diethyl ether and methanol extracts. Methanol extract proved to be the most efficient on fertility of S. littorals. All extracts had a slight effect on the larval and pupal stages duration compared with control. Larval and pupal weights were affected in the same manner also. It was concluded that all extracts caused a disturbance in hormonal balance in the larvae.

Effect of this grass on fall army worm larvae and the relationship of its quality to the larval developmental parameters was studied by Lynche et al. (1983 and1986).
Cynodon plant was also used to investigate host associated genetic differentiation and developmental and reproductive traits in fall armyworm strains (Pashly, 1986;and Pashly et al., 1995).Excellent work was experimentally done on consumption, utilization, biology and economic injury levels of fall army worm on Bermuda grasses by Jamjanya (1987) and Jamjanya and Quisenberry (1988).This grass was also used as host plant for Spodoptera exempta (Walker) in biological control studies using highly effective strains of Bacillus thuringiensis (Broza et al., 1991) The present paper is concerned with demonstrating the effect of five extracts of Bermuda grass using different non polar and polar solvents on morphogenetic and fertility of Spodoptera littoralis Boisd.

Experimental animals:
Larvae of the cotton leaf worm S. littoralis were obtained from culture bred and constantly maintained for several years under laboratory conditions according to Noeman B. AREF 172 the procedure of El-Ibrashy and Chenouda (1970).They were fed on fresh castor-oil leaves and kept at 30-+1 о C and 65 ± 5% RH.The tested larvae were individually placed in glass vials (10x2.7 cm each).Tightly covered with muslin mesh for daily inspections and weightings.

Preparation of plant extracts:
Bermuda grass, C. dactylon (Fam.Geramineae) was planted in clay soil in the experimental plots at National Research Center.After one month, grass was collected and the leaves were separated from roots.Plant leaves were allowed to dry for ten days at room temperature.Dried leaves were separated manually and crashed by house hold grinder.Hundred grams crashed plant leaves were soaked in 200 ml of each solvent as methanol, petroleum ether (60-80), acetone, diethyl ether and distillated water for 48 hours, with continuous stirring.Filtration was then carried out through very fine gauze.All extracts were kept in a dry cold place.

Treatments:
Castor-oil leaves discs (2 cm diameter) were prepared using cork corer and each was weighted.By micro pipette one (µl) of each extract was applied to each caster oil disc.A new moulted 4 th instar larva was located on each disc.The experimental discs were then placed individually in cups (120 ml) and each was weighted before and after introducing the larvae, during the first 24 th hour.(El-Gammal et al., 1988).After 24 th the larvae were fed on untreated castor leaves.The percents of mortalities were calculated in the end of the experiment.

Statistical analysis
Data were analyzed by analysis of variance (one way classification ANOVA) and followed by a least significant difference (L.S.D at 5%) (SAS Institute Inc., 2003).

RESULTS
The obtained data showed that the highest number of mortalities occurred when acetone (7), methanol (5), diethyl ether (5) followed by water (3) and petroleum ether extracts were used (Table 1).Data also proved that non polar extracts affected the hormonal balance of treated larvae resulted in occurrence of deformed and giant larvae.The highest numbers of giant larvae were when methanol extract (12) was used.The highest number of deformed larvae was obtained when methanol and diethyl ether extracts (3) were used.On the other hand, the lowest number of giant larvae was found after using water, acetone and petroleum ether extract.
The number of laid eggs were highest when water was used followed by diethyl ether, petroleum ether, acetone.

Effect of Bermuda Grass Extracts on Cotton Leaf Worm
173 Statistical analysis (Table 2) revealed that both methanol and water reduced the time of 4 th instar larvae compared with control.These durations were 4.933 and 4.850 compared with 5.450 days, respectively.The fifth instar larvae durations by three non polar extracts (i.e., methanol, petroleum ether and diethyl ether) were not significantly different from the control.As far as the sixth instar and the prepupal stages, data revealed that all extracts had significantly reduced durations compared with the control.The longevity of the pupal stage was similar among affected by methanol, petroleum ether and acetone extracts resembling the control.
Results presented in data in Table 3 shows also that the weight of the different stages of S. littorals had been variously affected by the C. dactylon extracts.All non polar and water extracts have equal effect on the weight of the fourth instar resembling the control.As far as the fifth instar is concerned water and diethyl ether had equal low effect.Petroleum ether and acetone had intermediate effect resembling the untreated insects.However, methanol had rather high effect on the weight of this instar.The weight of the sixth instar was equally affected by water and diethyl ether.
Petroleum ether and methanol have the highest effect on the weight of the pupa, while water caused low effect resembling the control.However methanol had high effect on the prepupal weight.

Table ( 1
): Biological parameters of Bermuda grass, C. dactylon (L.) extracts with different solvents on 4 th instar larvae of S. littoralis * 20 larvae were used in each extract treatments.**Mortality was calculated when larvae reached at adult emergence.

Table 2 :
Effect of Cynodon dactylon extracts on the duration of different stages of Spodoptera littoralis

Table 3 :
Effect of Cynodon dactylon extracts on the weight (g ± SE) of different stages of Spodoptera littoralis.Means under each variety sharing the same letter in a column are not significantly different at P<0.05 *