Abstract: In the study of insect pests of soybean (Glycine max L. Merrill,) in Peshawar, the insects found or feeding on soybean plants were white fly Bemisia tabaci (Gen), Thrips flavus Schr, jassids Amrasca biguttula (Gen)., painted bug Piezodorus sp., hairy catterpiller Euproctus sp., chrysomellids Systena sp. and different species of grasshoppers including Acrida exalta Walk., Truxalix nasuta (Lin.), Euprepocnemis alacris alacris (Ser.) and Attractomorpha acutipennis (Guer). Also the relative abundance of each of these species on different cultivars of soybean was recorded from August to November. Cultivar GS-50277-266-9-21 attracted significantly large number of all the recorded insects showing its least resistance or maximum susceptibility. Not a single cultivar was fount to be resistant to all the insect pests. However, cultivar WILL was relatively more resistant to white files, cultivar GC-81090-72-7 was relatively more resistant to painted bug and hairy caterpillar and cultivar GC-81083-83 was relatively more resistant to jassids and thrips than the other cultivars.
Introduction
Soybean (Glycine max L. Merrill,) is believed to be among the oldest plants cultivated by man. Most of the scientists agree that the origin of soybean was in Eastern Asia, possibly in China (Metcalfe and Elkins, 1980). It is one of the non-conventional crops which contains 18-22 percent oil containing 85 percent unsaturated fatty acid and is cholesterol free so its is highly desirable in the diet. Soybean has 22-40 percent protein. It is used in the food industry in cookies, biscuits, candy, vegetable milk, cheese, lecithin and many other products including infant milk in which it is an important ingredient (Anonymous, 1991).
In NWFP the total area under this crop during 1996-97 was 5520 hectare. Besides other problems in the successful cultivation of soybean many diseases and insect pests have been reported to attack the crop in different soybean growing parts of this province. In Pashawar hairy caterpillar, stink bug, jassids and white flies have been recorded by Imran (1979).
Ali (1988) found Aphis spp., Attractomorpha spp., Spilosoma oblique, Monolepta signata, Nizara viradula, Myllocerus sp., Riptorus sp., Aphanus sordidus and Amrasca biguttula the most common pest species of soybean in Bangladesh. Usman et al. (1984) observed that stem borer, cut worm, hairy caterpillar, field crickets, grass hopper, white flies, white ants and jassids were attacking soybean. Therefore, this project was designed to studies the insect pests and their infestation on different cultivars of soybean.
Materials and Methods
Ten cultivars of soybean were sown during kharif 1991 season at the NWFP Agricultural University, Peshawar for the study of different insects attacking the crop. All the insects found or feeding on soybean plants were collected for identification.
For this purpose sowing was done in rows. Row to row and plant to plant distance was 50 cm and 20 cm respectively. Size of plot for each cultivar was 3 × 4 sq. meter. The experiment was replicated 4 times in randomized complete block design. For the study of population density of each species attacking soybean, density of major insect species was recorded at weekly interval.
For the population density of white flies, jassids and thrips, 4 plants from each plot were randomly selected. On each of these plants 2 leaves each from top, middle and bottom were tagged and the population of insects on the both sides of these 6 leaves was counted and recorded. For the population density of hairy caterpiller, stink bug and chrysomellid beetles, population per plant on the same 4 plants was counted. The density of grasshoppers was counted and recorded on plants per plot. The data were analyzed statistically. The insect species were identified through the Commonwealth Institute of Biological Control, Rawalpindi.
Ten cultivars for the study of insect pests of soybean were as follows:
| 1. | GC-50227-22-6-9-21 |
| 2. | GC-B-4007 |
| 3. | GC-81085049NL |
| 4. | WILL |
| 5. | GC-81090-72-7 |
| 6. | GC-81080-36 |
| 7. | AGC-242 |
| 8. | GC-81084-37 |
| 9. | GC-81084-41 |
| 10. | GC-81083-83 |
Results and Discussion
The different insects and their population density as recorded in the present study are given in Table 1. These included white flies (Bemisia tabaci (Gen), Thrips (Thrips flavus Schr.), jassids (Amrasca biguttula (Inshida)), painted bug (Piezodorus sp.), hairy caterpillar (Euproctus sp.), chrysomellid (Systena sp.), hairy caterpillar (Euproctus sp.), chrysomellid (Systena sp.) and different species of grasshoppers, including Acrida exalta Walk, Truxalis nasuta L., Euprespocnemis alacris alacris (Ser.) and Attractomorpha acutipennis (Guer.).
Workers of the past like Sagar (1986) also found Thrips flavus quildinnii on soybean in Brazil. Imran (1979) found Bemisia tabaci (Gen) as a serious pest of soybean in Pakistan. Mundhe (1980) identified 16 insect species in India and the most abundant and injurious species were Aproaerema modicella (Deventer), Heliothus armigera (Hb.), Spodoptera litura ad Caliothrips indicus (Bagn). Ramiro et al. (1986) found Euschistusheros sp., Nezara viridula and Piezodorus quilidinnii the most abundant pest in Brazil.
The insect pests of soybean recorded in the present study were almost the same as reported by the other workers from Pakistan, India Bangladesh, Brazil etc.
For the relative abundance of different insect pests attacking soybean, ten newly introduced cultivars were studied. Results showed that all the cultivars had attracted greater or lesser number of different insect pests.
In general cultivar GC-50227-22-6-9-21 attracted significantly large number of Bemisia tabaci (10.42 per 6 leaves), Thrips flavus (5.73 per 6 leaves), Piezodorus sp. (2.89 per plant), Euproctus sp (5.02 per plant), showing its least resistance of maximum susceptibility (Table 1).
| Table 1: | Population density of insect pest of soybean on different cultivars |
| Means not followed by the same letter are statistically significant at 5% level of probability | |
Cultivar GC-81090-72-7 attracted significantly large number of Amrasca biguttula (4.29 per 6 leaves), showing its least resistance or maximum susceptibility. This cultivar showed relatively more resistance to piezodorus sp. and Euprocutus sp. For other insects, it was intermediate.
Cultivar WILL was relatively more resistant to Bemisia tabaci as compared to other cultivars and carried significantly least infestation (6.57 per 6 leaves). For other insect pests it was also intermediate. Cultivar GC-81083-83 carried significantly least infestation and was relatively more resistant. For other insect pests it was also intermediate. From these results it was concluded that cultivar GC-50277-226-9-21 was relatively more susceptible or least resistant to different insect pests attacking soybean. No cultivar of soybean was found to be resistant to all the insects attacking soybean. However, cultivar GC-81090-72-1 was relatively more resistant to Pieszsodorus sp. ad Euproctus sp., while cultivars WILL and GC-81083-83 were relatively more resistant to Bemisia tabaci and Amrasca biguttula respectively.
All the cultivars attracted about same population of grasshoppers and were, therefore, uniform in their resistance or susceptibility. These results can not be strictly compared with the findings of the previous worker because no work has been done on resistance/susceptibility of these cultivars, specially because the cultivars under test in the present study were newly introduced.
The cultivars which were relatively more resistant to white flies, thrips and jassids had large number of dense hair on their stems and leaves which made them less attractive for such small insects.