Dispersal ecology of rice bug Leptocorisa oratorius F. (Hemiptera: Alydidae) in Nueva Ecija [Philippines]

Field survey at Carranglan, Nueva Ecija [Philippines] resulted in the identification of two weed host plants of Leptocorisa oratorius F. namely, Echinochloa colona L. and E. crusgalli L., of the family Poaceae. Monthly monitoring revealed a relatively low rice bug (all developmental stages) population. During the off-season, they were commonly seen on weed host plants near the rice fields suggesting that rice bugs move from one area to another in response to food availability. The local dispersal pattern or behavior of the bug under field conditions varied. The rice bug nymphs in the non-rice habitat or no-food cage tend to move farther in search for available food than the nymphs in the rice habitat or food-available cage. This indicates that food stimulates/triggers their movement. Farthest mean distances after 7 days observation from non-rice and rice habitats were recorded at 20.87 cm and 5.82 cm, respectively. L. oratorius F. breeding was observed mainly on weed host plants and rice in the study sites at Carranglan and Munoz and Talavera, respectively. The development of the bugs reared on the different weed species under screenhouse condition varied. E. colona L. and E. crusgalli L. - reared bugs took 35.25 and 38.56 days to complete its development period. The female bug reared on E. colona L. and E. crusgalli L. deposited 11.50 and 12.25 eggs/egg mass, respectively. The presence of rice bug on the ratooned rice in Munoz and Talavera site suggests that there was a small breeding population supported by the ratooned rice. In both study sites, peak in adult population occurred soon after the peak in nymphal numbers indicating that adult populations were mainly generated locally. The extremely low population of rice bug in Munoz and Talavera can be possibly attributed to the management strategies employed by the farmer-respondents. The combination of cultural practices, biological and chemical control were the most popular strategies in managing rice bug in the two study areas in Nueva Ecija. However, these management strategies must be carefully evaluated for efficacy. The extremely low rice bug population may also indicate that bugs may not be a pest problem. Further studies to establish yield loss due to rice bugs under different condition are suggested. In summary, the research has demonstrated the need for a basic understanding of L. oratorius F. ecology and for the development of alternative control strategy