Impact of nitrogenous-fertilization on the population dynamics and natural control of rice leaffolders (Lep.: Pyralidae)

Abstract

The effect of nitrogenous-fertilization on the population dynamics and natural control of rice leaffolders was studied in an irrigated rice area in the Philippines. Nitrogen was applied at three levels (0, 75 and 150 kg N ha Ð 1 ), and its impact on crop growth and yield, arthropod abundance, and rates of leaffolder parasitism and survival was assessed with weekly samples. Rice plants were taller and had a higher leaf nitrogen content with increasing levels of nitrogenousfertilization, but grain yield was highest at the medium nitrogen level. Herbivores, predators, and parasitoids increased in abundance with nitrogenous-fertilization level. The average density of rice leaffolder larvae at the highest nitrogen level was eight times the density at zero nitrogen level, and the peak percentage injured leaves increased from 5 to 35%. The strong increase in larval density was due to the positive effect of nitrogenous-fertilization on egg recruitment and survival of medium-sized larvae. The percentage parasitism of eggs and larvae was not affected by nitrogenous-fertilization. The increase in survival of medium-sized larvae with nitrogen levels was associated with lower predator to leaffolder ratios. The strong effect of nitrogenous-fertilization in the present small-scale experiment was attributed mainly to allowing the moths an oviposition choice between plots with different application levels of nitrogen. Therefore it is hypothesized that the effect of increasing nitrogenous-fertilization level on leaffolder larval densities will be less pronounced when implemented over a large area.

Effects of nitrogen application on beetle communities in tea plantations

“…The non-response of beetle abundance to short-term N application contrasts with the three related conclusions from previous short-term studies on beetle and insect communities: (i) decreased beetle abundance with shortterm N deposition in an Artemisia ludoviciana monoculture (Strauss, 1987); (ii) increased beetle abundance with short-term N deposition in the San Bernadino Mountains of southern California (Jones et al, 2004); and (iii) increased insect abundance along both short-term N addition in grassland (Hurd et al, 1971;Hurd & Wolf, 1974;Kirchner, 1977;Sedlacek et al, 1988;Siemann, 1998) and rice field (de Kraker et al, 2000), and long-term N addition in grassland (Haddad et al, 2000).…”

Comparison of insect pest complexes in different Philippine dryland rice environments: population densities, yield loss, and management

“…Tanauan with highest nitrogen usage would have favoured planthoppers and leaffolders along with stemborers, as noted by studies done in wetland rice culture (Litsinger 1994). The beneficial effects of nitrogen on planthoppers have been higher fecundity, greater survivorship, and increased feeding rates while those for leaffolders were egg recruitment (ovipositing moths are attracted to the most vigorous growing fields) and survival (Kraker et al 2000). Rothschild (1970) also found leaffolders on dryland rice to be more abundant in fields of high N but least numerous if the crop were under drought stress.…”

Effect of Prey and Predator Density on Predation of Rice Leaffolder Eggs by the Cricket Metioche vittaticollis

“…Both ® ndings are suggestive of random search, but the possibilit y of undirected systematic search (no researching) cannot be ruled out with the current data. However, given the highly mobile searching behaviour observed in the ® eld, characterized by short visits and low exploitation of available prey on single plants (de Kraker et al, 2000a), systematic search seems unlikely.…”

“…Two species of predatory crickets, Metioche vittaticollis (Sta Ê l) and Anaxipha longipennis (Serville) (Orthoptera: Gryllidae), were identi® ed as the most important egg predators. During direct observation s in the ® eld they were found responsible for 90% of the observed egg predation (de Kraker et al, 2000a).…”

“…the densities of the predators and their prey, are quite variabl e in time and space, and their eVect must thus be known to understand and predict the impact of cricket population s on leaVolder egg mortality. Densities of both predatory crickets and rice leaVolder eggs per plant vary considerably during a crop season and between ® elds (de Kraker et al, 1999a(de Kraker et al, , 2000b. In the period that leaVolder eggs are present in the ® eld, the rice plant's leaf area increases ® ve-to tenfold, depending on the growing conditions.…”