Thesis Abstract of AGS Students

Effect of intercropping corn with soybean on the aphid (Aphis glycines Matsumura) population and its potential natural enemies

Jirawan Puttacharoen (1988)

Studies on the effect of intercropping corn with soybean on the aphid (Aphis glycines Matsumura) population and its potential natural enemies were conducted at the Multiple Cropping Centre, Chiang Mai University in the wet season (July - October 1985) and dry season (December 1985 - April 1986). The experiment was consisted of nine planting arrangements as follows : sole crop of soybean, soybean-corn intercropped in 2:2, 4:2 and 6:2 rows with soybean in treatments planted at the same time as corn and at two weeks after corn emergence. Sole crop of corn was also included. The experiment was designed in a Randomized Complete Block with three replications.

The aphid population within soybean canopy in the wet season by direct count was four times higher than that in the dry season averaging 3,100 and 767 per 24 plants, respectively. The aphid population at the top of soybean canopy counted from yellow pan trap indicated that the number of insects was higher in the dry season than in the wet season, 771 compared with 231. The population of coccinellids in both seasons was nearly the same averaging 25.6 per 24 plants. The spider population was 12.6 and 2.2 per 24 plants in the wet and dry seasons, respectively. It was also found that the aphids were parasitized by Aphidius sp. 25.5 percent in the dry season and 4.8 percent in the wet season.

In the wet season, the aphid population by direct count was lowest in the 4:2 arrangement with soybean planted two weeks after corn emergence (1,618 per 24 plants). In the dry season, the lowest population was found in the 2:2 arrangement with soybean planted at the same time as corn (470 per 24 plants). The aphid population from the trap was lowest in the 2:2 arrangement in the wet season averaging 148 per trap, and in the 6:2 arrangement in the dry season when soybean was planted at the same time as corn with 594 per trap.

The aphid parasite (Aphidius sp.) was highest in the 4:2 arrangement in the wet season when soybean was planted at the same time as corn at 8.4 percent and in 4:2 arrangement in the dry season when soybean planted two weeks after corn emergence at 38.8 percent. The highest population of coccinellids was found in the wet season in the 2:2 arrangement where soybean was planted at the same time as corn with 41.3 per 24 plants and 54.2 per 24 plants in the same arrangement but with soybean grown after corn emergence for two weeks. The spider population was found more in the 6:2 arrangement where soybean was planted at the same time as corn in the wet season with 21.2 per 24 plants and in 4:2 arrangement in the dry season with 4.7 per 24 plants. The population of big-eyed bug was found greater in sole crop than in intercrop in the wet season with 16.3 per 24 plants when soybean was planted at the same time as corn and 2.7 per 24 plants when soybean was planted two weeks after corn emergence. The land use efficiency of various intercropping arrangements as described by the Land Equivalent Ratio (LER) was highest in the 2:2 and 4:2 arrangements where soybean was planted at the same time as corn in the wet season with the values of 1.29 and 1.26, respectively. The LER values for the dry season revealed that there was no significant difference among the treatments.

Back to Thesis Topics