Sublethal concentration and high frequency of insecticide applications is one trigger of brown rice straw planthopper (Nilaparvata lugens) pest population explosion after insecticide spraying (resurgence). Deltamethrine is known as the most active chemical to cause brown rice straw planthopper resurgence, which until now is still widely used for rice bug pest control.
Yuni Ratna, SP., MP., lecturer of the Faculty of Agriculture, Jambi University, reveals the results of research that has been done shows that there is no interaction between sublethal concentration and frequency of deltamethrin application on mortality and nymph populations, the number of offspring, as well as the number of descendants ratio of brown rice straw planthopper. The results are obtained by giving sublethal concentration (LC50 and LC25) of deltamethrin toward the brown rice straw planthopper, each by 225 and 50 ppm.
The one-time application sublethal deltamethrin increases mortality, thus subsequently decreases nymph populations significantly. However, the number of offspring showed no significant difference compared with the offspring quantity of nymphs exposed to deltramethrin. While an increase in the application frequency of deltamethrin by as much as 2-3 times will increase the population of nymphs, the number of offspring, and the ratio of the offspring quantity significantly. "The ratio of female’s offspring quantity that receives three times applications of deltamethrin at a concentration of 50 ppm is higher 2.65 times than females that do not receive deltamethrin applications," said Yuni during an open examination of Doctoral Program in Agricultural Science, Tuesday (18/10) in UGM Faculty of Agriculture.
In her dissertation entitled Resurgence Mechanisms of Brown Rice Straw Planthopper After Application of Deltamethrin Subletal Concentration, Yuni mentioned that deltamethrin application does not lead to changes in nutrition, growth, and yield of rice plants. In semi-field testing, deltamethrin and burpofezin concentrations used are 50 and 100 ppm respectively with two-stage testing. The first test is by giving one time deltamethrin/buprofezin application on the plant age of 26 HST. Furthermore, the second testing is by providing one-time application of deltamethrin/buprofezin at plant age of 50 HST and twice deltamethrin/buprofezin application at plant age of 26 and 50 HST. "The result shows that deltamethrin application does not result in total changes of chlorophyll, photosynthetic rate and part of rice plant nutrients significantly than buprofezin application and without the application of insecticides, except for the significant increase of asparagine levels compared to levels of asparagine without insecticide application. The same is applied on the plant height, number of tillers has no much difference after application of deltamethrin, buprofezin, or without the application of insecticides," said the lady born in Jambi, June 11, 1970.
Other research results showed that application of deltamethrin and buprofezin with concentrations respectively at 50 and 100 ppm at plant age 32 HST did not influence the eating rate of planthopper’s imago, but significantly decreased the eating rate than without the application of insectiside at plant age on 45 HST. Furthermore, the application of deltamethrin on plant age 31 HST resulted in higher actual quantity and viability of Brown Rice Straw Planthopper‘s eggs and significantly differs from buprofezin applications.
"From the test results, it is also known that administration of deltamethrin application of 50 ppm with three times applications will shorten the preoviposition period, making the oviposition period longer and the age of the female imago, and increasing the actual quantity (number of eggs capable to produce by female imago) significantly compared to the one-time application and without the application of deltamethrin," added the wife of Muhammad Wahyudin, A. Ma and mother of Alvita Khanza Khairunnisa.
Furthermore, Yuni described that the resurgence mechanisms of Brown Rice Straw Planthopper may occur through increased asparagine of the plant and direct stimulation of Brown Rice Straw Planthopper reproduction. "Asparagine is linked to the eating rate of Brown Rice Straw Planthopper, therefore, increased levels of plant’s asparagine concentration after deltamethrin subletal applied is presumed to be one of the factors involved in the resurgence mechanism of Brown Rice Straw Planthopper," said the 1,465th UGM doctor who passed cum laude.