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Artificial infestation methods were employed to generate damage function graphs for guilds of three rice insect pests. In the vegetative stage, infestation of whorl maggot (Hydrellia philippina Ferino) and defoliators (a mixed population of Naranga aenescens Moore and Rivula atimeta [Swinhoe]) was applied as a combined or single pest attack. Infestation of yellow stemborer (Scirpophaga incertulas [Walker]) and leaffolder (Cnaphalocrocis medinalis [Guenee]) each were infested in one or two crop growth stages. Combinations of three stresses (four N application rates, solar radiation from the wet or dry season, and/or the presence or absence of weeds) were applied to each guild to develop more holistic economic injury levels (EILs). Slopes on the linear portion of damage curves of each pest guild became steeper with each additional stress applied, whether from multiple insect pest attack, low N, low solar radiation, or weeds. EILs can be developed by pest managers from the graphs of the damage functions for the variables quantified in this study. [ABSTRACT FROM AUTHOR]

Single and multiple species infestations of common insect pests were compared in terms of yield loss involving crop stresses that included weeds, sheath blight (Rhizoctonia solani Kunh.), drought, and deficiencies of N and solar radiation in addition to insect pest infestations. Losses from the various combinations of stresses were found to be additive, antagonistic, or synergistic. Most combinations of insect pests produced additive losses, with the balance being antagonistic, so implying that compensation occurred. Combinations of insect damage with other biotic and abiotic stresses produced mostly synergistic crop losses, which were significantly greater than additive ones. Among insect pests, additive losses resulted from yellow stemborer (Scirpophaga incertulas [Walker]) attacking two rice growth stages while the same was true for leaffolder (Cnaphalocrocis medinalis [Guenee]). Only the combination of whorl maggot (Hydrellia philippina Ferino) and defoliators (a mixture of Naranga aenescens Moore and Rivula atimeta [Swinhoe]) produced synergistic losses. Knowing the mode of yield loss from combinations of different plant stresses will aid the farmer in making decisions regarding which ones should be corrected and which the crop can tolerate. [ABSTRACT FROM AUTHOR]

Rainfed wetland rice (RWR) had more species in common with irrigated wetland than dryland rice agroecosystems. Across ecosystems, higher pest densities and losses were recorded in RWR sites. We hypothesise that under low pressure from natural enemies, vegetative stage losses became particularly high due the combination of whorl maggot and caseworm damage combined with the physiological stress of transplanting shock. Both of these pest groups benefited from an expanded vegetative period common in RWR agroecosystems. Losses in older rice were probably due to stemborers. RWR is more prone to an array of physiological stresses than irrigated rice that we believe minimises crop compensation to accentuate insect losses. Chemical control is uneconomical mainly due to the low yield potential of RWR and the poor efficacy of applied insecticide. [ABSTRACT FROM AUTHOR]

In the Philippines most of the dryland rice pests are distinct from those of wetland culture. Partitioned-growth-stage yield loss studies revealed the highest losses in dryland rice were due to sown-seed and seedling pests (ants, field crickets, mole crickets, and termites) as well as root feeders (white grubs and root aphids) and early seedling pests (seedling maggot and flea beetle) more than the common foliar wetland pests. Losses (5-71%) were highest in the sites with the smallest rice area in which pests were concentrated and the poorest soils (which constrain yield compensation) along a continuum of dryland rice habitats. Crop management practices such as overseeding and fertility management can mitigate potential losses to a large degree. Therefore integrated crop management plays a central role in integrated pest management in dryland rice cultivation where the use of insecticides should be minimized for economic and environmental reasons. [ABSTRACT FROM AUTHOR]

Monthly plantings conducted over 4 years in a rainfed triple maize cropping system in southern Mindanao, Philippines, revealed the Asian corn borer (ACB) Ostrinia furnacalis (Guenée) as the most important insect pest. Of minor importance and being restricted to one crop stage were rice seedling maggot Atherigona oryzae Malloch, thrips Thrips palmi Karny and Megalurothrips usitatus (Bagnall), corn leafhopper Cicadulina bimaculata (Evans), corn earworm Helicoverpa armigera (Hübner), and corn leaf aphid Rhopalosiphum maidis (Fitch). Farmers escape damage from ACB, seedling maggot, and thrips by planting the first crop in April. Planting of the second crop should be shifted from August to September to avoid ACB damage. Pest damage was low during the third crop, thus planting time is not an important consideration. Additional information on ACB bionomics was revealed in the study. Mean egg mass size was 36 eggs (range 1 - 169). Oviposition was found to be positively correlated with cumulative rainfall over the previous 3 - 8 weeks indicating that females seek healthy crops. Most (70%) oviposition occurred over a 4-week period in the 39 crops studied as a single peak between late-whorl through mid-tasseling stages when developing larvae would be more assured of feeding on the more nutritious pollen. The strong attraction of maize at early tasseling along with heavy parasitism in older maize become population synchronizing agents in the year round cropping study area, although less perfect than winters in temperate regions. Yield loss in southern Mindanao ranged from 20 to 49% which was more closely correlated with larval tunnels than moth exit holes. Correlations were significant only when damage was related to yield loss but not yield. [ABSTRACT FROM AUTHOR]

Beneficial arthropods were monitored in monthly plantings over 4 years in a rainfed, triple-maize cropping system in southern Mindanao, Philippines. Generalist predators and two egg parasitoids of the Asian corn borer Ostrinia furnacalis (Guenée) (ACB) did not show significant differences in abundance with respect to calendar month of planting over 39 crops. Two species of Trichogramma (T. evanescens Westwood and T. chilonis Ishii) collectively parasitized 67% of ACB egg masses and 58% eggs over the study becoming more abundant as the crop aged. The closeness of the two parasitism rates suggests that to increase parasitoid efficacy, particularly early in the crop, the best strategy would be augmentation and to increase longevity of wasps by providing carbohydrate sources to extend their searching time. Unparasitized egg masses tended to be smaller showing they were more likely to be overlooked. The ratio between the two parasitoids was 56:44 in favour of the former. Trichogramma evanescens had been introduced 2 years earlier by a government project, whereas T. chilonis probably was introduced by sugarcane estates. Prior to their introduction there were no ACB egg parasitoids in the Philippines and both are firmly established as annual parasitism levels did not continue to rise during the study. Parasitoid activity caused significant reductions in neonate ACB larval numbers beginning 7 weeks after crop emergence in an average crop. Egg parasitism rates were positively and linearly correlated with ACB egg mass density. A quadratic regression model was established between mean egg parasitism rates and egg masses size with peak parasitism rates occurring at 25 eggs per mass. Collectively 32 species of generalist predators averaged 0.9 - 1.5 individuals per plant based on weekly samplings. If ants were excluded, the average dropped to 0.1 - 0.3 per plant. Ants, dominated by Solenopsis geminata (F.), fed on ACB eggs and larvae. Coccinellids as the next most numerous were represented by three species where Micraspis crocea (Mulsant) in particular tracked ACB egg masses and probably the corn leaf aphid Rhopalosiphum maidis (Fitch) as well. Four species of orthropterans also tracked ACB egg masses. The third most abundant guild was 17 spiders with the oxyopid Oxyopes javanus Thorell and the araneid Araneus inustus (C.L. Koch) highly correlated with ACB egg mass densities. Other spiders targeted ACB moths and Atherigona oryzae Malloch adults. The predatory mirid Cyrtorhinus lividipennis Reuter probably targeted the corn leafhopper Cicadulina bimaculata (Evans) and possibly thrips Thrips palmi Karny and Megalurothrips usitatus (Bagnall). The lacewing Chrysopa sp. was abundant late in the crop when aphids were present on tassels. [ABSTRACT FROM AUTHOR]

Action thresholds as insecticide decision tools were developed and evaluated against chronic vegetative stage insect pests of irrigated transplanted rice in the Philippines: whorl maggot Hydrellia philippina Ferino (Diptera: Ephydridae( and two lepidopterous defoliators, Naranga aenescens Moore and Rivula atimeta (Swinhoe( (Lepidoptera: Noctuidae(. Through an iterative process, new threshold characters and insecticide technologies were evaluated at four sites (categorized as high and low pest density sites( over a 13-year period with the objectives of minimizing insecticide usage and maximizing farmer adoption. Characters were evaluated as to their ability to predict significant pest densities and yield loss. Significant differences occurred between high and low pest density sites among the best characters and monitoring methods for both pests. Earlier-planted fields were used as a forecasting tool, showing best results in the high pest density sites. Overall, most threshold characters performed well but the insecticide response was poor. Insecticide control was better with some threshold characters than others due to better timing. Seedling root soak with isofenphos was more effective than granules or foliar sprays against whorl maggot but required a decision before planting. Foliar sprays were most effective if applied twice (2 and 7 days after transplanting(. The best performing characters for whorl maggot were 1 – 2 eggs/hill for the low pest density sites and 15 – 30% damaged leaves in earlier planted fields in high density sites. The best performing characters for defoliators were 10% damaged leaves monitored in earlier planted fields for high density sites and 10% damaged leaves in low density sites. Carbaryl was the most effective insecticide spray against defoliators that combined performance and relative safety. [ABSTRACT FROM AUTHOR]

Action thresholds (ATs) as insecticide application decision tools were developed and tested against mainly yellow Scirpophaga incertulas (Walker) and white S. innotata (Walker) rice stemborers in four sites in the Philippines over 68 crops. Damage incidence was low with a mean over all crops and sites of 2% deadhearts (DH) and 3% whiteheads (WH) based on weekly sampling. Highest incidence reached 19% WH as a mean of one crop and 31% WH in an individual field in 1 week. AT characters were based on deadhearts, egg masses, or flushed moths. A mean of 9% fields exceeded ATs in the vegetative, 5% in the reproductive, and 4% in the ripening stages. The most effective AT character in each of the three growth stages was percentage DH with 5% being optimal in the vegetative, 25% in the reproductive, and 10% in the ripening stages. These ATs resulted in 96 – 99% correct decisions based on criteria involving DH and yield loss benchmarks set from earlier studies on economic loss. Insecticide response to the highly accurate ATs was a disappointing [ABSTRACT FROM AUTHOR]

Action thresholds (AT) as insecticide application decision tools were developed and tested against rice leaffolders Cnaphalocrocis medinalis (Guenée) and Marasmia patnalis Bradley (Lepidoptera: Pyralidae) in four sites and 68 crops over a 13-year period in the Philippines. Leaffolder damage levels were generally low with a mean over all sites and crops of 2 – 3% damaged leaves (DL) and 6 – 9% in a given site as a per-crop average based on weekly samplings, with highest incidence per field on a given sampling date of 48%DL. The damage incidence over a typical crop cycle formed a bell-shaped curve with maximum numbers in the late reproductive and early ripening stages. Continuous population buildup over the planting cycle did not occur in any one site over the season, thus a strategy of monitoring earlier planted fields to forewarn against impending economic damage had no basis. ATs were based on different levels of percentage DL, number of larvae per hill (L), and density of flushed moths. Collectively ATs were surpassed in 1, 12, and 4% of fields in each of the three main growth stages. A scoring system was based on benchmark criteria including both leaffolder damage and yield loss. The 15%DL threshold performed best in all growth stages, only equaled by 1L in the vegetative stage, scoring 93 – 99% correct decisions in each of the growth stages. Flushed moths produced the most false positive decisions and the lowest performance scores. The best insecticide response gave only a disappointing 53% control and therefore was a significant weakness in using AT technology. BPMC, endosulfan, and monocrotophos performed the best and azinphos-ethyl and Bt the least. Sites with the highest densities had the most rapid rise in damage levels, thus requiring more frequent monitoring. Low leaffolder damage levels were most likely due to the activity of natural enemies. Given the ability of high tillering varieties to compensate from pest damage, farmers would be better off embracing integrated crop management as a preventative measure to bolster inherent tolerance levels combined with crop monitoring based on historical population levels. In sites with a record of high damage levels, monitoring should start 4 weeks after transplanting (WT) on a weekly basis and more risk averse farmers may increase the interval to twice a week during flag leaf stage. In sites with lower observed levels, monitoring can begin 6 WT on a weekly basis and continue through the flag leaf stage. Significant yield increases were recorded with the best AT characters despite evidence of modern rices to tolerate high damage levels. Reasons for this apparent paradox are discussed. [ABSTRACT FROM AUTHOR]

The rice white stemborer (WSB) Scirpophaga innotata (Walker) supplanted the closely related rice yellow stemborer (YSB) S. incertulas (Walker) in irrigated, double-rice culture in both Koronadal, South Cotabato, Philippines and Java, Indonesia. In Java, WSB became a serious pest but not in Koronadal where damage levels remained unchanged. The species shift and subsequent outbreaks are seen as independent events. The former occurred just after the El Niño droughts in 1982 – 1983 which suggests that climatic factors triggered the demise of YSB which does not aestivate. A contributing factor may have also been the crop failures from pest outbreaks that occurred during the same period creating long fallows which would have allowed WSB larvae selectively to survive. WSB larvae have been known to diapause for up to 10 – 12 months and consequently is able to survive climatically driven long fallows. Diapause is terminated by rainfall >10 mm after larvae have rested for a minimum of 4 months. Supportive evidence in favour of climate as the causal agent of change is that the distribution of WSB in Asia and Oceania overlaps that of the Intertropical Convergence Zone of the Southern Oscillation. YSB on the other hand is more adapted to a monsoon climate. It is also hypothesised that WSB, normally associated with single-crop, rainfed-rice culture, was able to adapt to double-cropped, irrigated culture due to the introduction of early maturing rices. From what is known about rice stemborer ecology, five cultural practices and natural events were postulated as the reasons keeping WSB densities in check in Koronadal: (1) medium maturing varieties to reduce the dry season fallow, (2) low inorganic N levels, (3) natural enemies, (4) destruction of crop residue harbouring larvae and pupae during land preparation, and (5) rainfall in the dry season causing suicide flights. Control strategies for areas where WSB is a pest should be based on: (1) reducing the fallow period by growing longer maturing varieties and (2) undertaking early ploughing for the wet season crop. [ABSTRACT FROM AUTHOR]

Although the rice white stemborer (WSB) Scirpophaga innotata (Walker) has been an epidemic pest in other locations in the Philippines and Indonesia, its population has remained at chronic pest levels in Koronadal, southern Mindanao, Philippines. Field studies were undertaken to determine the role of egg parasitoids and general predators in suppressing WSB numbers. The results revealed greater mortality levels on WSB than in any other location where beneficials have been assessed. Four hymenopteran parasitoids ( Tetrasticus schoenobii Ferriere [Eulophidae], Telenomus rowani (Gahan) [Scelionidae], Telenomus dignus (Gahan), and Trichogramma japonicum Ashmead [Trichogrammatidae]) combined to parasitise 65% of eggs in the second 1990 – 1991 rice crop. Multiple parasitism occurred in 61% of parasitised egg masses. Egg predation averaged 44% principally by the tettigoniids Conocephalus longipennis (de Haan) and C. maculatus (Leth.). Generalist predators steadily built up over the rice crop. A contributing factor to the high success of natural enemies could be related to the special situation of two irrigation systems interspersed among each other. Communal systems fed by artesian wells resulted in asynchronous planting areas where farmers can plant five crops in 2 years juxtaposed to a larger river diversion system typified by highly synchronous double rice cropping. The heterogeneous habitat created by the two irrigation systems could favour the density-dependent T. schoenobii , the keystone parasitoid in the rice ecosystem, which acts as both a parasitoid and predator. [ABSTRACT FROM AUTHOR]

Rice seedling maggot Atherigona oryzae Malloch is a minor pest of upland rice Oryza sativa L. and maize Zea mays L. in the Philippines. Two cultural control methods, early planting and overseeding, were evaluated separately on upland rice in an eroded, high rainfall area in Northern Mindanao. Farmers plant maize ahead of upland rice in separate fields with the onset of the rainy season. Regression analysis from data over six seasons showed on average the first 50% of farmers who planted ahead of their neighbours suffered damage significantly below the 5% deadheart action threshold. When early rice planting relative to one's neighbours was combined with earliness with regard to sowing maize, damage was further reduced. Useful methods for forecasting deadhead incidence 1-2 months ahead of rice planting were developed. The deadheart incidence rate was highly correlated with the amount of rain that fell in February and March as well as with the number of adults collected from bait traps in March or April. Six seeding rates were compared in 20-kg increments from 50 to 150 kg/ha with and without insecticide seed treatment. There was no significant yield response over the seeding rates tested when protected by insecticide, but when untreated, the highest yield occurred at 120 kg seed/ha and the greatest return at 90 kg/ha. Yields declined above the 120 kg/ha level from interplant competition Rice seedling maggot egg density decreased but the deadheart incidence rate increased with increasing plant densities, both linearly. Perhaps higher plant densities led to greater larval survival and dispersal. Planting rice early is dependent on early maize planting. Planting maize early and following maize within the generation period of rice seedling maggot with rice sown from 90 to 120 kg/ha would be particularly beneficial in years when the rice seedling maggot is predicted to be a high risk. [ABSTRACT FROM AUTHOR]

Evaluates the effects of insecticide spraying on insect pest population dynamics in a rice ecosystem in the Philippines. Cofana spectra; Sogatella furcifera; Recilia dorsalis; Natural enemies; Population fluctuations.