J. P. Bandong

Rice crop loss from insect pests in wetland and dryland environments of Asia with emphasis on the Philippines

Yield losses from insect pests were determined by the insecticide check method in 60 crops in the Philippines from 1976–1986 in three rice environments with traditional and modern cultivars in 10 sites. Plot size of 100 m2 minimized interplot interference from insecticide protection on untreated plots. Low and high crop losses were recorded across sites in drylands (2-39%, -X = 25%), rainfed wetlands (13-24%, -X = 21%), and irrigated wetlands (5-40%, -X = 18%). Weighted crop loss for the Philippines based on production by environment and cultivar type averaged 18.3% or 0.57 t/ha per crop. Consistently greater yield loss occurred in the vegetative (50%) than reproductive (30%) or ripening (20%) stages across environments and cultivars. No epidemics affected the trials therefore crop losses were those from chronic pests. The major chronic pests in the wetlands were stem borers, leaffolders, whorl maggot, and rice bug; and in the drylands were ants, seedling maggots, white grubs, leaffolders, stem borers and rice bug. Yield loss variability was greater between fields than crops or sites, therefore a control strategy based on corrective actions when pest numbers reach threshold levels is more efficient than prophylactic actions. Yield loss was more in early maturing cultivars stressing the importance of compensation in tolerating insect damage. Insect stresses perhaps can be compensated by total crop management to increase the plant’s ability to tolerate insect damage.RésuméLes pertes de rendement de cultivars modernes et traditionnels, dues aux ravageurs, ont été évaluées de 1976 à 1986 aux Philippines, par comparaison avec des traitements insecticides, lors de 60 cycles culturaux dans dix sites correspondant à trois situations agroécologiques rizicoles. L’utilisation de parcelles de 100 m2 a permis de minimiser l’interférence entre parcelles traitées et non traitées. Les pertes de rendement observées ont varié de 2 à 39% (moyenne: 25%) en riziculture sèche, de 13 à 24% (moyenne: 21%) en riziculture aquatique et de 5 à 40% (moyenne: 18%) en riziculture aquatique irriguée. Les pertes de rendement observées pour les différentes situations agroécologiques et cultivars se sont réparties autour d’une moyenne de 18% correspondant à 0.57 t/ha. Les pertes au cours de la phase végétative (50%) ont été régulièrement plus élevées que lors de la phase reproductive (30%) ou de maturation (20%). Etant donné qu’aucune épidémie de ravageurs n’a été observée au cours de l’étude, les pertes de rendements sont attribuables aux ravageurs endémiques. Les plus importants sont: (1) la chenille foreuse des tiges, la chenille tordeuse des feuilles, la mouche des feuilles, et la punaise coreide en riziculture aquatique; (2) les fourmis, la mouche des plantules, les larves blanches (white grubs), la chenille tordeuse des feuilles et la punaise coreide en riziculture sèche. La variabilité des pertes de rendement observée entre les différents champs d’essai a été supérieure à celle observée entre les types de cultures et les situations agroécologiques évaluées. Une stratégie de contrôle des ravageurs fondée sur la détermination des seuils critiques des populations est plus efficace que des actions prophylactiques. Les pertes de rendement plus élevés observées avec les cultivars précoces mettent en évidence l’importance de l’aptitude de la plante à compenser les dommages des ravageurs. Les pratiques culturales qui augmentent la tolérance de la plante aux ravageurs pourraient compenser la pression de ces derniers.

Rice crop stage susceptibility to the rice yellow stemborer Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae)

From field trials with artificial infestation of rice yellow stemborer Scirpophaga incertulas (Walker) (YSB) egg masses over the post-transplanted crop cycle and reports in the literature, it was concluded that rice passes through three stages of general morphological resistance interceded by two stages of susceptibility. Resistance occurs on very young rice, at mid-growth, and after panicle exsertion. The resistant period at mid-growth varied by plant maturity. On an early maturing rice variety (IR72), resistance occurred from panicle initiation (PI) to pre-booting, while on the medium maturing IR70, resistance was extended from the late vegetative stage to booting. High deadheart (severed tiller) densities occurred post transplanting because, being small, up to three tillers are damaged by a single larva. Whiteheads (severed panicles) were formed from infestations from booting onwards and were relatively higher than deadhearts on the early maturing variety but relatively less on the medium maturing variety. Zinc deficiency delayed maturity of IR72, and the period of naturally high resistance of seedlings was extended throughout most of the vegetative stage as well as after PI through pre-booting. Resistance at mid-growth and after panicle exsertion could be from: (1) lignin and cellulose deposits on the cell walls, (2) tight wrapping of the leaf sheath, and (3) deposition of silica. All three trials produced similar quadratic models of the yield response to crop age when infested. Deadheart damage was compensated to a large degree, but lowest yields occurred from whitehead damage when infested at or just after the pre-booting stage.

Insecticide decision protocols: a case study of untrained Filipino rice farmers

Abstract Surveys in four irrigated rice sites in the Philippines over a span of eight years (1984–91) focused on farmers’ insecticide decision making protocol before formalized farmer field school training programmes. Despite past extension campaigns to the contrary, farmers based their decisions more on crop monitoring than prophylaxis. Farmers were deficient in pest identification skills using terms such as worms, moths, and hoppers while some farmers targeted beneficials. Farmers mostly based decisions on planthoppers, leafhoppers, and moths by seeing the insect pest, on whorl maggot, defoliators, and leaffolders by noting damage, and on rice bug and seedbed pests by prophylaxis. Decision protocols were largely site specific based on different pest complexes and outbreak histories as well as being highly farmer specific. A large proportion of prophylactic applications during the early crop stages was timed with fertilizer application. Farmers’ frequency of field visitation was as recommended for pests, but reasons to visit the field at the time of a spray decision were predominantly water management. A generalized pattern emerged with monitoring starting on the way to the farmers field. Some decisions were prompted upon seeing infestation in an earlier planted field or a neighbour spraying. A number of farmers sought lower lying more flooded parcels or downwind sides of parcels to visit first as these microhabitats favour greater pest densities. Most decisions were made while walking along the field border observing patches of damage or flushed moths with the unit of measure being the parcel. The field was entered only as a last resort. Farmers’ action thresholds were lower than those of researchers and sampling was less rigorous. A minority of farmers, however, expressed insect pest abundance in quantitative terms using sampling units of several rice hills, distance of rice rows, and per panicle. Some of the more innovative farmers’ pest assessment methods were tested later by researchers.

Insect pests of rainfed wetland rice in the Philippines: population densities, yield loss, and insecticide management

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.

Mass rearing, larval behaviour and effects of plant age on the rice caseworm, Nymphula depunctalis (Guenée) (Lepidoptera: Pyralidae)

Abstract The mass-rearing method for efficient production of rice caseworm Nymphula depunctalis (Guenee) was improved. Moths oviposit most in ventilated cages on the undersides of floating cut rice leaves aged 4–8 weeks after transplanting (WT). There was no effect of leaf width on oviposition. Greatest egg production occurs with a 12 h scotophase. Moths are highly tolerant of crowding in oviposition cages, as up to 40 females averaged 86–115 eggs per female in 0.14 m 3 cages. Honey as a carbohydrate energy source increases the rate of oviposition but not total oviposition. Larvae require standing water to fill their cases as respiration occurs with tracheal gills. Larval survival was equal when reared in distilled water, pesticide-free ricefield water, or chlorinated tap water, whether aerated or not. Larvae survive better, grow larger, mature more rapidly, and become more fecund adults when reared on plants 2–6 WT. Pupae are non-aquatic. The caseworms inability to develop satisfactorily on post-vegetative rice may be attributed to poor nutrition and less favourable oviposition substrates. Females prefer to oviposit on dropping leaves floating on the water surface. As the crop matures, fewer leaves touch or float on the water surface. Eggs desiccate if laid on aerial portions of plants and are more exposed to natural enemies.

Effect of multiple infestations from insect pests and other stresses to irrigated rice in the Philippines: II. Damage and yield loss

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 Künh.), 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 [Guenée]). 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.

Natural Enemies of the Rice Caseworm Nymphula Depunctalis (Guenée) (Lepidoptera: Pyralidae)

Larval and adult predators comprise the largest component of the natural enemy fauna which attack the semi-aquatic rice caseworm Nymphula depunctalis (Guenée). Spiders, birds, and adult dragonflies/damselflies were the dominant predators of caseworm adults, while aquatic beetle larvae, aquatic bug nymphs and adults, and ants preyed on caseworm larvae. Egg parasitolds are unknown in nature and larval/pupal parasitoids are rare. A nuclear polyhedrosis virus, the only recorded pathogen, occurs but rarely. A ricefield pulmonate snail Lymnaea quadrasi (Mollendorff), which forages on algae, causes limited caseworm egg mortality in a passive and fortuitous manner. Water beetles—the dytiscid Cybister tripunctatus orientalis Gschwendtner and hydrophilid Sternolophus rufipes Fabricius—are voracious larval predators. Prey consumption by these water beetles is higher on older caseworm larvae whose larger size creates more movement while the larvae are crossing the water surface. Also, older caseworms are more prone to leave the protection of their cases while under attack. Younger caseworm larvae, however, tend to retract and remain motionless when attacked. The last instar dytiscid preyed on an average of 11.4 caseworm larvae per day while that of the hydrophilid preyed on 6.7 larvae per day.RésuméLes predateurs de larves et d’adultes constituent la composante principale des ennemies naturels de Nymphula (Nymphula depunctalis Guenée). Les araignées, les oiseaux et les libellules sont les principaux prédateurs d’adultes, tandis que les Coléopters aquatiques, les punaises d’eau, et les fourmis attaquent les larves. II n’y a pas de parasites d’oeufs connus dans la nature, et les parasites de larves/pupes sont rares. Une polyèdrose nucléaire virulante existe, mais est rarement trouvée. Un escargot pulmoné de rizière (Lymnaea quadrasi Mollendorf), qui se nourrit d’algues constitue indirectement une cause mineure et fortuite de mortalité pour les oeufs. Les Coléopters aquatiques(le dysticide Cybistes tripunctatus orientalis Gschwendtner et l’hydrophilide Sternolophus rufipes Fabricius) sont des prédateurs de larves particulièrement actifs. La predation par ces Coléopters aquatiques est plus importante sur les larves âgées, qui par leur taille provoquent des turbulences plus importantes lors de leurs mouvements sur la surface le l’eau, et qui ont tendance a quitter facilement leurs abris. Les larve plus jeunes ont tendance à s’y retirer et à rester immobiles lorsqu’elles sont attaquées. C. tripunctatus orientalis au dernier stade larvaire a une activité prédatrice plus élevée que celle des S. rufipes.

Evaluation of action thresholds for chronic rice insect pests in the Philippines: II. Whorl maggot and defoliators

Abstract 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.

Effect of multiple infestations from insect pests and other stresses on irrigated rice in the Philippines: I. Damage functions

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 [Guenée]) 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.