Alberto T. Barrion

A food web approach to evaluating the effect of insecticide spraying on insect pest population dynamics in a Philippine irrigated rice ecosystem

Summary 1. Data from a 645-taxa Philippines-wide food web and multiple regression models were used to predict population fluctuations of insect pests in a rice field. Independent variables of pest models included the biomass of rice plants in the field, the abundance of each pest, and the abundances of five highly correlated enemies of the pest, all as functions of time. 2. To test the ability of the models to reveal effects of insecticide spraying, a rice field at the International Rice Research Institute (IRRI) in the Philippines was divided into deltamethrin-sprayed and unsprayed plots. Data on the abundance of seven pest species (Nephotettix virescens, Recilia dorsalis, Sogatella furcifera, Nilaparvata lugens, Hydrellia philippina, Ne. nigropictus and Cofana spectra) and their natural enemies (predators and parasitoids) were collected during the dry season of 1990. 3. Spraying insecticide disorganized the population dynamics of insect species feeding in the IRRI field. Multiple regression models were less able in the sprayed plot than in the unsprayed plot to forecast the population fluctuations of pest species on the basis of various numbers and combinations of independent variables. For example, current pest abundance, by itself, was a significant predictor of future pest abundance for four of the seven pests (Ne. virescens, R. dorsalis, S. furcifera, H. philippina) in the unsprayed plot, but significant fits were found for only two pests (R. dorsalis, H. philippina) in the insecticide-sprayed plot. 4. In the unsprayed plot, independent variables were significant predictors of future pest abundance in four of seven initial models compared to one of seven models in the sprayed plot. Step-wise removal of independent variables in the models enhanced their forecasting power in both the sprayed and unsprayed plots, but significant models in the unsprayed plot nearly always outnumbered those in the sprayed plot. 5. In the unsprayed plot, Ne. virescens retained five of seven independent variables as significant predictors, compared to four for S. furcifera, three for C. spectra, and one for the remaining four pests. Classical models that contain one or two species as independent variables may not be sufficient to forecast future abundances of some Philippine rice pests in unsprayed and sprayed plots. 6. In general, models that included interaction terms and either the presence or absence of sprays among the independent variables did not improve the forecasting power of models in either the sprayed or unsprayed plot. 7. The methods developed here for studying the impact of spraying on the organization of arthropod communities in rice fields could be applied to other interventions

Arthropod community structures of rice ecosystems in the Philippines

The arthropod community associated with irrigated rice grown in five sites in Luzon Island, Philippines, was analysed using guild categories. Phytophages and predators were predominant in all sites. The phytophage species were mainly Homoptera and dominated by Nephotettix virescens (Distant), N. nigropictus (Stal) (Cicadellidae), and Nilaparvata lugens (Stal) and Sogatella furcifera (Horvath) (Delphacidae). Predators were mainly Heteroptera with Microvelia douglasi atrolineata Bergoth (Veliidae), Mesovelia vittigera (Horvath) (Mesoveliidae), and Cyrtorhinus lividipennis Reuter (Miridae) as the most abundant species. Spiders were the next dominant group with Pardosa pseudoannulata (Boesenberg & Strand) and three species of Tetragnatha the most common. Differences in species diversity between the sites were easily differentiated using diversity indices. The relative differences in arthropod abundance, species richness and diversity may be attributed to the median temperatures, cropping patterns, and diversity in crop stages and germplasm in the sites. Predator-Homoptera correlations were significant in all cases. High positive correlations were obtained for veliids, spiders and Cyrtorhinus lividipennis , in most sites.

Jumping spiders (Araneae: Salticidae) that feed on nectar

Nectivory was studied in 90 species from the spider family Salticidae. Observations of 31 of these species feeding on nectar from flowers in nature was the impetus for laboratory tests in which all 90 species fed from flowers. That sugar, not just water, is relevant to salticids was implied by choice tests where salticids spent more time drinking from a simulated nectar source (30% sucrose solution) than from distilled water. Our findings suggest that nectar feeding may be widespread, if not routine, in salticid spiders.

Population dynamics of plant- and leafhoppers and their natural enemies in rice ecosystems in the Philippines

Abstract The population dynamics of plant- and leafhoppers and associated predators and parasitoids at five rice sites in the Philippines, are compared. Twelve species of Auchenorrhyncha, nine Cicadellidae and three Delphacidae, were found in the samples. The order of abundance was Nephotettix virescens > Sogatella fucifera > Nephotettix nigropictus > Nilaparvata lugens. The dominant predators were mostly Heteroptera [Microvelia douglasi atrolineata (Veliidae) and Cyrtorhinus lividipennis (Miridae)] followed by spiders [Pardosa pseudoannulata (Lycosidae) and Callitrichia formosana (Linyphiidae)]. The delphacid and cicadellid populations were characterized by high initial densities, which reached a peak and were followed by a decline with low growth rates. Populations of heteropteran predators were similar, except that the peaks were at a later state and growth rates were higher. Predator diversity and evenness were significantly lower in Los Banos and Cabanatuan. The results are discussed in relation to implications to plant- and leafhopper management.

Prey‐capture techniques and prey preferences of nine species of ant‐eating jumping spiders (Araneae: Salticidae) from the Philippines

Abstract Siler sp., Euophrys sp. 1 and 2, and six species of Chalcotropis feed on ants in nature. Capture techniques and preferences of each species were studied in the laboratory using a wide variety of ants and other insects. Siler sp. usually attacked ants, but not other insects, from directly behind. Euophrys sp. 1 and 2 consistently attacked ants, but not other insects, head on. Chalcotropis attacked large ants head on, but there was no particular orientation of attacks on small ants or on other prey regardless of size. All species tended to stab ants, but not other prey, several times before holding on. In three types of prey‐preference tests, each of the nine salticid species took dolichoderine, formicine, myrmicine, ponerine, and pseudomyrmecine ants in preference to a variety of other insects (aphids, bugs, caterpillars, cockroaches, crickets, flies, gnats, lacewings, mantises, may flies, midges, mosquitoes, moths, plant and leafhoppers, plant lice, and termites). Testing with laboratory‐reared s...

Food web dynamics of irrigated rice fields at five elevations in Luzon, Philippines

The above-water food webs of arthropod communities in irrigated rice fields on Luzon Island, Philippines, were studied over the growing season at five sites (Los Banos, Cabanatuan, Bayombong, Kiangan, Banaue) ranging in elevation from 22 m to 1524 m. Arthropod populations were vacuum-sampled at roughly weekly intervals from the date after seedlings were transplanted to flowering at each site. Site- and time-specific webs were constructed from a 687-taxa cumulative Philippines web and time-series of species present. Taxonomic composition, food web structure, and arthropod phenology were broadly similar across different sites. Arthropod abundance was inversely associated with altitude across the five sites, but numbers of taxa and links and six food web statistics showed no obvious increasing or decreasing trend with altitude. The rise of taxa, links and mean food chain length over the growing season at each site reflected an increase in plant size with age and, at some sites, an orderly accumulation of newly arriving herbivore, predator, parasitoid and omnivore species. At each site, herbivores built up faster than predators and parasitoids, and predators arrived faster than parasitoids; the difference between the latest and earliest sampling dates of first arrivals, averaged over the five sites, was 38, 63 and 73 days for herbivores, predators and parasitoids, respectively. Site-to-site consistencies in food web properties and first arrivals suggest that such patterns may be influenced more by crop age than by geography or altitude. Sampled predator, parasitoid and omnivore taxa potentially encountered only a subset of their lifetime prey and predator species at any particular time in the rice field. Prey lists cumulated over time may underestimate the temporal specificity of predation by potential biological control agents. Research opportunities linking rice food webs and integrated pest management with East Indies biogeography are proposed.

Prey preferences of Portia labiata, P. africana, and P. schultzi, araneophagic jumping spiders (Araneae: Salticidae) from the Philippines, Sri Lanka, Kenya, and Uganda

Abstract Prey‐preference behaviour of three species of araneophagic salticid (P. labiata from the Philippines and Sri Lanka, P. africana from Kenya and Uganda, and P. schultzi from Kenya) is studied in the laboratory for the first time. “Well‐fed” (7 day fast) and “starved” (14 day fast) males and females of each species have a pronounced preference for web‐building spiders over insects, and a less pronounced preference for salticid spiders over insects. Also, well‐fed and starved males and females of these species prefer web‐building spiders to salticids. Preferences for taxonomic type of prey are the same regardless of whether living, active prey or dead, motionless lures are used, suggesting that all these araneophagic salticids can distinguish between the different taxonomic categories of prey without reference to their different movement patterns. For each species, females—relative to males—preferred larger prey. When extra‐starved (21 day fast), males and females of all species appeared to take prey...

Predation by ants on jumping spiders (Araneae: Salticidae) in the Philippines

Abstract Using a tropical fauna from the Philippines as a case study, ant‐salticid predator‐prey relationships were investigated. In the field, 41 observations of ant predation on salticids were made, and the actual attack on the salticid was seen in four. In the laboratory, five of the ant genera observed in the field were tested with four categories of salticids: (1) four myrmecophagic (i.e., ant‐eating) species, (2) six myrmecomorphic (i.e., ant‐like) species, (3) an ant‐associate species (i.e., a species that is neither myrmecophagic nor myrmecomorphic, but known to associate with ants), and (4) 14 ordinary species (i.e., species that are neither ant‐eating nor ant‐like, and are not known to associate with ants). In these tests the highest survival rates were observed in the myrmecophagic salticids, followed by the myrmecomorphic salticids, the ant‐associate species, and finally the ordinary species.

LIVING WITH THE ENEMY: JUMPING SPIDERS THAT MIMIC WEAVER ANTS

Abstract Ants prey on salticids, and encounters with weaver ants (Oecophylla smaragdina (Fabricius 1775)) appear to be especially dangerous for many salticids. In the Philippines, Myrmarachne assimilis Banks 1930 is a salticid that mimics Oecophylla smaragdina. We tested for the abilities of four categories of salticids, plus M. assimilis, to survive in the proximity of weaver ants. The four categories were: (1) myrmecomorphic (ant-like species other than M. assimilis); (2) myrmecophagic (ant-eating species); (3) myrmecophilic (a species that is either myrmecophagic nor myrmecophagic, but is known to associate with ants) and (4) ordinary (species that are neither ant-like nor ant-eating, and are not known to associate with ants). The hypothesis investigated here is that M. assimilis has, compared with other salticids, especially pronounced ability to survive in close proximity with this particular ant species. The individual salticids used in our experiments had not had previous contact with weaver ants or any other ants. When confined with groups of 10 weaver ants, the myrmecomorphic, myrmecophagic and myrmecophilic species survived significantly more often than ordinary salticids, but Myrmarachne assimilis survived significantly more often than all other categories. When kept with groups of 20 ants, there was a proportional decrease in the number of salticids that survived within each salticid category. However, few salticids survived when confined with groups of 40 ants, regardless of category.

A Bibliography of Rice Leaffolders (Lepidoptera: Pyralidae)

This bibliography on rice leaffolders contains 886 published and unpublished references for the period 1854 to June 1987. References are arranged alphabetically by the name of author and also classified by subjects. A distribution map, tables of alternate host plants, outbreaks, resistant rice varieties, resistant wild rices, natural enemies and developmental stages, and a brief description of current status of the leaffolders are also provided.RésuméCette bibliographique sur la chenille tordeuse des feuille du riz (rice leaffolders) contient 886 références, publiées et non publiées, couvrant la période de 1854 à Juin 1987. Les références sont classées par ordre alphabétique suivant le nom des auteurs et également par sujet. Une carte de la distribution du ravageur, des tableaux sur l’apparition des hautes densités de population du ravageur, sur les varietés résistantes de riz cultivées et sauvages, sur les ennemis naturels et les tables de vie plantes hôtes ainsi qu’une description à jour du statut de la chenille tordeuse des feuilles sont également presenteés.