Soil Moisture Effects on Entomopathogenic Nematodes

The effect of soil moisture on entomopathogenic nematode virulence was examined in the laboratory. Objectives were to determine the virulence of several species and isolates of entomopathogenic nematodes at various soil moisture contents and temperatures, and after fluctuations in soil moisture. Studies included up to five isolates of entomopathogenic nematodes: Heterorhabditis bacteriophora Poinar (Oswego and Tuscarora strains), Steinernema glaseri (Steiner) (NC1 strain), S. feltiae (Filipjev) (Biosys 369 strain), and S. carpocapsae (Weiser) (NY001 strain). Nematodes were applied to sandy loam soils ranging in soil moisture content from below the permanent wilting point of plants to near saturation. In all experiments, a rainfall or irrigation event was simulated by adding water to rehydrate soils to high moisture levels (near saturation). Nematode virulence was evaluated periodically by measuring insect mortality in Galleria mellonella (L.) larval bioassays, before and after rehydration. Nematode virulence increased with soil moisture content for all species and isolates tested. Our studies demonstrated that the virulence of entomopathogenic nematodes in low moisture conditions could be restored by rehydrating the soil. Insect mortality was generally low in low-moisture, nematode-infested soils before rehydration, but increased to high levels posthydration. Moisture effects were evident from the onset of each experiment, whereas the effect of soil temperature on nematode-induced insect mortality was delayed and nonsignificant until 14 wk after the initiation of the third experimen

Effects of Soil Rehydration on the Virulence of Entomopathogenic Nematodes

The work presented examines the effects of soil moisture on the virulence of selected entomopathogenic nematode isolates in the laboratory and has broad implications for managing soil-dwelling insects in all production systems. Two species of entomopathogenic nematodes, Heterorhabditis bacteriophora (Oswego and Tuscarora strains) and Steinernema glaseri (NC1 strain), were applied to sandy loam soils ranging from below the permanent wilting point of plants to near saturation. Fluctuations in soil moisture were created by simulating a rainfall or irrigation event (i.e., rehydration), or by allowing soil to dry. Nematode virulence was evaluated by measuring insect mortality in Galleria mellonella larvae bioassays. Soils prepared at four moisture contents were inoculated with nematodes and subsequently bioassayed at their original moisture contents and after rehydration, over an 18-mo period. Insect mortality increased with soil moisture content for both H. bacteriophora isolates but was highest in relatively low moisture soils (≈−15 bar) for S. glaseri. Insect mortality was generally low in low-moisture soils before rehydration but rebounded to high levels posthydration. Both isolates of H. bacteriophora nematodes were reactivated to cause high insect mortality (≥ 98%) as long as 18 mo after infective juveniles were inoculated into very low moisture soils (≈−30 bar). The posthydration insect mortality levels in the S. glaseri treatments were significantly lower than in the H. bacteriophora treatments. For all nematode treatments, the cumulative insect mortality of prehydration and posthydration bioassays was higher in lower moisture soils compared with higher moisture soils. In an additional experiment, moisture thresholds for activation of nematodes in dry soil were determine

Environmental Influences on Soil Macroarthropod Behavior in Agricultural Systems

Many basic and applied studies in insect ecology have focused on the proximate and ultimate responses of insect populations to their physical and chemical environment (2, 15, 21, 27, 32, 74, 82, 111, 112). From an economic perspective, macro- and microclimatic factors can influence the stress that insect populations inflict on plants and the efficacy of management tactics. For above-ground insects, the mechanisms of behavioral response to environmental factors are often observable, if not always apparent to the researcher. However, this is not typically the situation with soil insects. As a result, field studies of soil insects often quantify only the consequences of behavior while the behaviors themselves remain hidden within the soil matrix (14, 103, 105). Soil ecology research has been productive at the ecosystem level on such topics as nutrient cycling (18), arthropod regulation of micro- and meso-fauna in below-ground detrital food webs (75), impact of microfauna on soil genesis and structure (87), rhizosphere dynamics (17), and energy dynamics of soil systems (79). These examples highlight the importance of multidisciplinary approaches to research programs that unite expertise in insect ecology, soil physics, chemistry, and microbiology as well as systems analysis and modeling (87). Considerable interest also exists in the relationships within soil communities, but these studies have focused primarily upon nonagricultural systems (71, 108) and on the more abundant microarthropod members of the soil fauna ( 106-109). Ecological, morphological, and physiological adaptations of nonagricultural soil arthropods have been discussed in the literature (8, 10, 26, 59); however, insects that are agricultural pests primarily in their immature soil-inhabiting stages have often been studied in detail only in their more accessible adult stage. Although the mobile adult stages of soil pests often determine initial habitat and host selection, a considerable proportion of subsequent host and habitat selection is performed by immatures in the soil, if host or habitat quality deteriorates over time. A major obstacle to the study of soil insect ecology has been the inability to follow soil insect movement and feeding behavior in situ (3, 14, 33, 34, 103, 105). It is critically important in these studies to minimize the disturbance of the soil system through experimental manipulations. R. L. Rabb (cited in 103) notes that the greatest problem with studies of soil insects is that the system is altered through its study. Also, research workers often fail to consider dominant mass and energy transport mechanisms in soil ecosystems. Differences in above- and below-ground environments may alter soil insect sensitivity (over ecological and evolutionary time) to shifting environmental conditions, the movement of chemical cues from potential food sources to soil herbivores, and the mechanisms for soil insect host-finding behavior when compared to terrestrial organisms. In this review we briefly outline several basic principles of soil physics as they relate to soil insect movement and host-finding behavior, to provide a general understanding of the environment in which soil macroarthropods exist. We then selectively review the entomological literature in light of these principles to stress the need to evaluate soil insect behavior within the soil matrix when trying to understand the underlying mechanisms that produce observable behavior. Finally we briefly discuss the importance of behavior in the management of soil insects

Environmental Influences on Soil Macroarthropod Behavior in Agricultural Systems

Many basic and applied studies in insect ecology have focused on the proximate and ultimate responses of insect populations to their physical and chemical environment (2, 15, 21, 27, 32, 74, 82, 111, 112). From an economic perspective, macro- and microclimatic factors can influence the stress that insect populations inflict on plants and the efficacy of management tactics. For above-ground insects, the mechanisms of behavioral response to environmental factors are often observable, if not always apparent to the researcher. However, this is not typically the situation with soil insects. As a result, field studies of soil insects often quantify only the consequences of behavior while the behaviors themselves remain hidden within the soil matrix (14, 103, 105). Soil ecology research has been productive at the ecosystem level on such topics as nutrient cycling (18), arthropod regulation of micro- and meso-fauna in below-ground detrital food webs (75), impact of microfauna on soil genesis and structure (87), rhizosphere dynamics (17), and energy dynamics of soil systems (79). These examples highlight the importance of multidisciplinary approaches to research programs that unite expertise in insect ecology, soil physics, chemistry, and microbiology as well as systems analysis and modeling (87). Considerable interest also exists in the relationships within soil communities, but these studies have focused primarily upon nonagricultural systems (71, 108) and on the more abundant microarthropod members of the soil fauna ( 106-109). Ecological, morphological, and physiological adaptations of nonagricultural soil arthropods have been discussed in the literature (8, 10, 26, 59); however, insects that are agricultural pests primarily in their immature soil-inhabiting stages have often been studied in detail only in their more accessible adult stage. Although the mobile adult stages of soil pests often determine initial habitat and host selection, a considerable proportion of subsequent host and habitat selection is performed by immatures in the soil, if host or habitat quality deteriorates over time. A major obstacle to the study of soil insect ecology has been the inability to follow soil insect movement and feeding behavior in situ (3, 14, 33, 34, 103, 105). It is critically important in these studies to minimize the disturbance of the soil system through experimental manipulations. R. L. Rabb (cited in 103) notes that the greatest problem with studies of soil insects is that the system is altered through its study. Also, research workers often fail to consider dominant mass and energy transport mechanisms in soil ecosystems. Differences in above- and below-ground environments may alter soil insect sensitivity (over ecological and evolutionary time) to shifting environmental conditions, the movement of chemical cues from potential food sources to soil herbivores, and the mechanisms for soil insect host-finding behavior when compared to terrestrial organisms. In this review we briefly outline several basic principles of soil physics as they relate to soil insect movement and host-finding behavior, to provide a general understanding of the environment in which soil macroarthropods exist. We then selectively review the entomological literature in light of these principles to stress the need to evaluate soil insect behavior within the soil matrix when trying to understand the underlying mechanisms that produce observable behavior. Finally we briefly discuss the importance of behavior in the management of soil insects

Submanifolds, Isoperimetric Inequalities and Optimal Transportation

The aim of this paper is to prove isoperimetric inequalities on submanifolds of the Euclidean space using mass transportation methods. We obtain a sharp ?weighted isoperimetric inequality? and a nonsharp classical inequality similar to the one obtained by J. Michael and L. Simon. The proof relies on the description of a solution of the problem of Monge when the initial measure is supported in a submanifold and the final one supported in a linear subspace of the same dimension

Emergence, Mating, and Postmating Behaviors of the Oriental Beetle (Coleoptera: Scarabaeidae)

In a previous field-trapping study of the oriental beetle, Exomala orientalis (Waterhouse), by using synthetic sex pheromone on golf course fairways, numerous males were observed and trapped during the hours of peak mating activity. However, very few beetles were observed in the same areas when synthetic pheromone was absent. To investigate the hypothesis that mating in nature occurs cryptically within vegetation at the soil surface, laboratory studies on female emergence and pheromone release, male emergence and mate-locating, and female and male mating behaviors were conducted. Mate acquisition and copulation occurred on the soil surface near the female emergence site, with both sexes engaging in pheromone-mediated behaviors after having emerged from the soil. A highly stereotyped female pheromone release, or calling, behavior was observed, consisting of insertion of the female's head into the soil and elevation of the tip of her abdomen into the air. Bioassays conducted in a wind tunnel that simulated a turf fairway environment showed that walking and flying were both important in the upwind response of males to females. Mating and copulation occurred without an obvious complex courtship, but observations of postmating behaviors suggested that mate guarding occur

Damage detection in an uncertain nonlinear beam based on stochastic Volterra series: an experimental application

International audienceThe damage detection problem becomes a more difficult task when the intrin-sically nonlinear behavior of the structures and the natural data variation are considered in the analysis because both phenomena can be confused with damage if linear and deterministic approaches are implemented. Therefore, this work aims the experimental application of a stochastic version of the Volterra series combined with a novelty detection approach to detect damage in an initially nonlinear system taking into account the measured data variation, caused by the presence of uncertainties. The experimental setup is composed by a cantilever beam operating in a nonlinear regime of motion, even in the healthy condition, induced by the presence of a magnet near to the free extremity. The damage associated with mass changes in a bolted connection (nuts loosed) is detected based on the comparison between linear and nonlinear contributions of the stochastic Volterra kernels in the total response, estimated in the reference and damaged conditions. The experimental measurements were performed on different days to add natural variation to the data measured. The results obtained through the stochastic proposed approach are compared with those obtained by the deterministic version of the Volterra series, showing the advantage of the stochastic model use when we consider the experimental data variation with the capability to detect the presence of the damage with statistical confidence. Besides, the nonlinear metric used presented a higher sensitivity to the occurrence of the damage compared with the linear one, justifying the application of a nonlinear metric when the system exhibits intrinsically nonlinear behavior

Temporal and Spatial Distribution of the Oriental Beetle (Coleoptera: Scarabaeidae) in a Golf Course Environment

The mating season of the oriental beetle, Exomala orientalis (Waterhouse), in 1994 and 1995 at Bethpage State Park, Farmingdale, NY (40° 45′ N, 73° 28′ W) began in the middle of June, peaked in the 1st wk of July, and ended in the middle of August. There were differences in the emergence schedule among fairways as well as local differences between roughs and fairway. Both sexes were most active around sunset on shorter-cut turf (i.e., fairways, greens, and tees, versus roughs), and the few individuals seen during the daylight hours were mostly males. These males were generally found perched on vegetation at the border of the fairway. Feeding was not observed, except on flowers by females devoid of mature eggs. This study confirms our observations on the pattern of activity in an earlier study conducted with the use of synthetic pheromone traps. It also explains the difficulty encountered by earlier workers in finding adults of this insect in the field. Implications of the above findings on the management of the oriental beetle are discusse

l-Leucine Methyl Ester: The Female-Produced Sex Pheromone of the Scarab Beetle, Phyllophaga lanceolata

The female-produced sex pheromone of the scarab beetle Phyllophaga lanceolata was identified as the methyl ester of an essential amino acid, l-leucine. During field testing, 239 male P. lanceolata were caught in traps baited with l-leucine methyl ester. l-Isoleucine and l-valine methyl esters, similar in structure to l-leucine methyl ester and previously identified as female-produced sex pheromone compounds employed by other Phyllophaga species, were also tested. Addition of l-valine or l-isoleucine methyl esters to the l-leucine methyl ester in 1:1 ratios completely inhibited attraction of P. lanceolata males. Males of P. squamipilosa were also captured using l-leucine methyl ester. This is the first record of P. squamipilosa from Kansa

Moisture, a Vital but Neglected Factor in the Seasonal Ecology of Insects: Hypotheses and Tests of Mechanisms

Of the major physical factors that influence insect seasonal ecology, moisture is least understood and least appreciated. It is our premise that experimental probing of insects from diverse zones and various habitats would reveal general patterns of insect responses to moisture that are as striking as those for photoperiod and temperature. Using the paradigms of photoperiod and temperature as ecophysiological determinants of insect seasonality, we hypothesize that moisture influences insect life cycles via one or more of three mechanisms—as a token stimulus for diapause, modulator of developmental or reproductive rates, or behavioral cue for vital seasonal events. For heuristic purposes, we offer each of these hypotheses in close association with approaches for testing their validity in insects that undergo dry-season dormancy. The approaches appear appropriate for examining the role of moisture in the life histories of terrestrial invertebrates other than insects, as well as plants and microbes that have a seasonal resting stage. Elucidating moisture's role in insect seasonal cycles is critical to the development of comprehensive phenological models, improved insect management systems, and identification of novel evolutionary mechanisms for adaptation to wet-dry seasons, especially in tropical, subtropical, and Mediterranean region