1.  The effects of rice varieties and nitrogen fertilizer rates on nymphal performance of black bug, Scotinophara coarctata
Buyung A.R. Hadi, Bryce Blackman, and Sylvia Villareal
International Rice Research Institute, Los Baños, Laguna, Philippines
Introduction
Rice black bug (Scotinophara coarctata, Hemiptera: Pentatomidae, Figure 1) was first detected in the southern part of the Philippines in Since then, rice black bug has been reported in the northern islands and provinces of the country (Cuaterno 2007). Feeding injuries between seedling and panicle development stages may cause plant death or yield reduction (Morill et al 1995). We investigated rice the black bug’s responses toward nitrogen fertilizer levels to obtain insight on how fertilizer management may affect black bug population dynamics on rice.
Fig. 1. Female rice black bug, Scotinophara coarcatata, guarding the eggs on a rice leaf. a ab b
Fig. 2. Effects of nitrogen fertilizer rates on nymphal performance of black bug, Scotinophara coarctata. Bars with different letters are statistically different at p<0.05.
Methodology
The experiment was conducted in a greenhouse with black bug colonies originally collected from rice fields in Laguna, Philippines. The treatments consisted of a combination of three N rates (~30, 75, and 150 kg/ha) and three rice varieties selected on the basis of their popularity among Filipino farmers (IR64, Rc18, and Rc222). Each treatment combination was replicated nine times. Fifteen 1–2-day-old eggs of S. coarctata were used in each replicate. After six weeks, the number of surviving black bugs, their developmental stages, and individual weights were recorded. Three variables were calculated: (1) survivorship (calculated as the percentage between the number of surviving individuals after 6 weeks and the number of original eggs); (2) development rate (calculated as the percentage between the number of individuals reaching adulthood and the number of surviving individuals); and (3) average weight of survivors. Analyses were performed in SAS 9.3 (SAS Institute, Cary NC).
Results and discussion
We found no statistical difference in black bug nymphal performance among the three rice varieties. The data were collated across varieties and analyzed for the effect of fertilizer rates on the measured performance variables. There was a significant difference between low and high fertilizer rates in terms of average survivorship (Fig. 2a). We found no significant difference in the average weight of the survivors and developmental rate among treatments (Figs. 2b and 2c).
High N leaf content has been shown to increase the ecological performance of brown planthopper, another hemipteran pest of rice (Lu et al 2004). Thus, good agricultural practices are needed to manage nitrogen fertilizer rates and optimize yield without stimulating brown planthopper populations. While we showed that the black bug’s nymphal development and weight gain were not affected by the three tested fertilizer rates, survivorship was, surprisingly, negatively affected (i.e., a lower fertilizer rate was associated with higher survivorship) within the range of tested fertilizer rates. We are working to repeat this experiment to ascertain the relationship between fertilizer rate and the black bug’s nymphal survivorship.
While most heteropterans respond positively to supplemental nitrogen fertilizer, neutral response has been reported from the azalea and azalea lace bug system (Casey and Raupp 1999).
Conclusion
Our work thus far showed no difference in black bug nymphal performance among three popular rice varieties in the Philippines. The increasing potential for black bug as a damaging pest across the country signals the need for host plant resistance breeding against black bugs.
More work is needed to elucidate the relationship between N fertilizer rate and black bug performance and preference. This will provide information for optimization of fertilizer management in areas where black bug threats are on the rise.
References
Casey CA, Raupp MJ Supplemental Nitrogen Fertilization of Containerized Azalea Does Not Affect Performance of Azalea Lace Bug (Heteroptera: Tingidae). J. Env. Entomol. 28:
Cuaterno WR Current status of rice black bug and its management in the Philippines. In: Joshi RC, Barrion AT, Sebastian LS, editors. Rice black bugs: Taxonomy, Ecology, and Management of Invasive Species. Muñoz, Nueva Ecija (Philippines): PhilRice.
Lu Z-X, Heong KL, Ye X-P, Hu C Effects of plant nitrogen on ecological fitness of the brown planthopper, Nilaparvata lugens Stal. In rice. J. Asia-Pacific Entomol. 7:
Morrill WL, Shepard BM, Arida GS, Parducho M Damage by the Malayan black bug in rice. J. Econ. Entomol. 88: