Hypothesis-testing methods for multivariate data are needed to make rigorous probability statements about the effects of factors and their interactions in experiments. Analysis of variance is particularly powerful for the analysis of univariate data. The traditional multivariate analogues, however, are too stringent in their assumptions for most ecological multivariate data sets. Non-parametric methods, based on permutation tests, are preferable. This paper describes a new non-parametric method for multivariate analysis of variance, after McArdle and Anderson (in press). It is given here, with several applications in ecology, to provide an alternative and perhaps more intuitive formulation for ANOVA (based on sums of squared distances) to complement the description pro- vided by McArdle and Anderson (in press) for the analysis of any linear model. It is an improvement on previous non-parametric methods because it allows a direct additive partitioning of variation for complex models. It does this while maintaining the flexibility and lack of formal assumptions of other non-parametric methods. The test- statistic is a multivariate analogue to Fisher's F-ratio and is calculated directly from any symmetric distance or dissimilarity matrix. P-values are then obtained using permutations. Some examples of the method are given for tests involving several factors, including factorial and hierarchical (nested) designs and tests of interactions.

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A new method for non-parametric multivariate analysis of variance

Spinosad® (Dow Agrosciences) is a neurotoxic insecticide produced by fermentation of an actinomycete. Spinosad is classified as an environmentally and toxicologically reduced risk material and has been embraced by IPM practitioners as a biorational pesticide. We examined the available information on the impact of spinosad on natural enemies and classified mortality responses to spinosad using the IOBC laboratory and field scales that run from 1 (harmless) to 4 (harmful). In total, there were 228 observations on 52 species of natural enemies, of which 162 involved predators (27 species) and 66 involved parasitoids (25 species). Overall, 71% (42/59) of laboratory studies and 79% (81/103) of field-type studies on predators gave a class 1 result (not harmful). Hymenopteran parasitoids are significantly more susceptible to spinosad than predatory insects with 78% (35/45) of laboratory studies and 86% (18/21) of field-type studies returning a moderately harmful or harmful result. Predators generally suffer insi...

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Is the Naturally Derived Insecticide Spinosad® Compatible with Insect Natural Enemies?

Phloem feeding involves unique biological interactions between the herbivore and its host plant. The economic importance of aphids, whiteflies, and other phloem-feeding insects as pests has prompted research to isolate sources of resistance to piercing-sucking insects in crops. However, little information exists about the molecular nature of plant sensitivity to phloem feeding. Recent discoveries involving elicitation by plant pathogens and chewing insects and limited studies on phloem feeders suggest that aphids are capable of inducing responses in plants broadly similar to those associated with pathogen infection and wounding. Our past work showed that compatible aphid feeding on leaves of Arabidopsis thaliana induces localized changes in levels of transcripts of genes that are also associated with infection, mechanical damage, chewing herbivory, or resource allocation shifts. We used microarray and macroarray gene expression analyses of infested plants to better define the response profile of A. thaliana to M. persicae feeding. The results suggest that genes involved in oxidative stress, calcium-dependent signaling, pathogenesis-related responses, and signaling are key components of this profile in plants infested for 72 or 96 h. The use of plant resistance to aphids in crops will benefit from a better understanding of induced responses. The establishment of links between insect elicitation, plant signaling associated with phloem feeding, and proximal resistance mechanisms is critical to further research progress in this area. Arch. Insect Biochem. Physiol. 51:182-203, 2002. Published 2002 Wiley-Liss, Inc. †

Gene expression profiling of Arabidopsis thaliana in compatible plant‐aphid interactions

Under herbivore attack plants mount a defence response characterized by the accumulation of secondary metabolites and inhibitory proteins. Significant changes are observed in the transcriptional profiles of genes encoding enzymes of primary metabolism. Such changes have often been interpreted in terms of a requirement for an increased investment of resources to 'fuel' the synthesis of secondary metabolites. While enhanced secondary metabolism undoubtedly exerts an influence on primary metabolism, accumulating evidence suggests that rather than stimulating photosynthesis insect herbivory reduces photosynthetic carbon fixation and this response occurs by a re-programming of gene expression. Within this context, reactive oxygen species (ROS) and reductant/oxidant (redox) signalling play a central role. Accumulating evidence suggests that ROS signalling pathways are closely interwoven with hormone-signalling pathways in plant-insect interactions. Here we consider how insect infestation impacts on the stress signalling network through effects on ROS and cellular redox metabolism with particular emphasis on the roles of ROS in the plant responses to phloem-feeding insects.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2011.02399.x

Plant responses to insect herbivory: interactions between photosynthesis, reactive oxygen species and hormonal signalling pathways

BACKGROUND

The common cutworm, Spodoptera litura (Fabricus), is the most serious pest of peanuts in Taiwan. In order to devise an ecology-based and cost-effective control program, we collected life table data and consumption rates from larvae reared indoors at a constant temperature of 25°C, or outdoors at ambient temperatures during the spring and fall of 2010. A computer simulation was then used to project the population growth and damage potential of S. litura on peanuts.



RESULTS

Laboratory-reared S. litura individuals produced 3548 eggs/female, whereas those reared outdoors produced 3452 and 3072 eggs/female in the spring and fall, respectively. The intrinsic rate of increase was 0.1828, 0.1308 and 0.1545 day−1 , and the net consumption rate was 194.0, 132.2 and 166.6 cm2 larva−1 at 25°C, in spring and fall, respectively. Population projection showed a faster growth and higher damage potential of S. litura in the fall.



CONCLUSION

Population projections based on life tables and stage-specific consumption rates can reveal the stage structure and damage potential of the pest population. Our results showed that monitoring data obtained by using pheromone traps were not in concordance with the damage potential of the pest population. This approach offers a promising tool for pest management. © 2013 Society of Chemical Industry

Population and damage projection of Spodoptera litura (F.) on peanuts (Arachis hypogaea L.) under different conditions using the age‐stage, two‐sex life table

Plant tolerance to injury from insect herbivores has several advantages as a pest management approach. However, its use is limited because mechanisms conferring plant tolerance are not well understood. We hypothesize that plant physiological responses, specifically photosynthesis, substantially contribute to plant tolerance to arthropod injury. This hypothesis was tested on 3 wheat ( Triticum eastivum L.) lines that differed in their mode of resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko). The lines were ‘Arapahoe’ (a susceptible line), PI 137739 (an antibiotic line), and PI 262660 (a tolerant line). These lines were grown in a greenhouse, aphids were maintained on plants for 1 wk, and physiological responses of these lines were determined. Light curve and fluorescence data indicated that the primary mechanism for photosynthetic rate reduction in aphid-injured leaves is via interference of the photochemical efficiency at the initial stage of photosynthesis. Aphid-injured seedlings had lower light-saturation points, which suggested less efficient use of light energy compared with control seedlings. Immediately after aphid removal, aphid injury reduced chlorophyll fluorescence and photosynthetic rates in all lines, but PI 137739 (with antibiosis) had significantly greater photosynthetic rate reduction. Photosynthetic rates of the tolerant line, PI 262660, began recovering 3 d after aphid removal with complete photosynthetic recovery 7 d after aphid removal. This gradual photosynthetic compensation did not occur in the other 2 lines. PI 262660 also had greater leaf area and more dry matter when compared with the other cultivars. This study demonstrates that photosynthetic adjustments can significantly contribute to plant tolerance resulting from arthropod injury. Moreover, evidence here indicates that an active plant defense through antibiosis comes at the cost of reduced capacity for physiological tolerance and compensation.

Physiological and Growth Tolerance in Wheat to Russian Wheat Aphid (Homoptera: Aphididae) Injury

Understanding the response of soybean [Glycine mas (L.) Merr.] cultivars to insect defoliation is important for identifying differences in insect tolerance and compensation among soybean genotypes, for assessing yield loss differences among cultivars, and for determining if a single economic injury level (EIL) can be used for all cultivars. Therefore, this study was conducted to evaluate the relative tolerance of selected soybean cultivars to insect defoliation. Field experiments were conducted in 1994 and 1995 on three indeterminate soybean cultivars: Dunbar, Corsica, and Clark. Sequential defoliation (46-66%) was imposed manually at the R2 stage (reproductive development of soybean at full flowering), guided by an insect consumption model. Leaf area index, percent light interception, growth, and yield data were determined. Because of ample rainfall during the soybean growing period in 1994, defoliation did not affect soybean yield; all cultivars compensated for all levels of defoliation via delayed leaf senescence and compensatory regrowth, which enhanced the light interception capacity of defoliated soybean canopies. In 1995, however, defoliation caused a significant yield reduction (15-70%) in all cultivars; this yield reduction was greater for Dunbar than the other two cultivars. In both years, yields were directly related to the light interception capacity of soybean canopies after defoliation. There were significant EIL differences among soybean cultivars. Large differences in EILs among cultivars suggest a need to revise existing EILs for defoliating pest species.

Soybean cultivars and insect defoliation : Yield loss and economic injury levels

Plant tolerance to pest injury is an ideal component of integrated pest management (IPM) programs, because it places no selection pressure on pest populations, but tolerance is little understood and its use in pest management is limited. In field experiments in 1994, 1995, and 1996, we characterized tolerance to defoliation in 'Clark' soybean [Glycine max (L.) Merr.] isolines differing in leaf morphology : 3- and 5-leaflet, narrow and wide leaflet. Sequential defoliation was imposed manually at the R2 stage (full flowering), based on an insect consumption model. In 1994 and 1996, with ample rainfall, all isolines expressed yield compensation or overcompensation for defoliation as high as 75%, due to compensatory regrowth and delayed leaf senescence; in 1995, however, when rainfall was marginal, defoliation caused significant yield reduction. Equal amounts of leaf tissue removed resulted in different leaf area indices (LAIs). Wide-leaflet isolines had higher LAI than narrow-leaflet isolines, but the narrow-leaflet isolines, particularly Clark-3N, had greater light interception capacity for a given LAI level and had a higher light extinction coefficient in 1995. This shows that light was available to leaves in the lower canopy in the narrow-leaflet isoline. Both low and high defoliation treatments caused significant yield reductions in all isolines, except that low defoliation did not significantly affect the yield of Clark-3N in 1995. The narrow-leaflet isolines apparently tolerated defoliation better than the wide-leaflet isolines because the narrow-leaflet isolines had greater light interception and maintained equal or better yields, despite similar defoliation. In addition to LAI, both canopy light interception and light extinction coefficient are important criteria for selecting cultivars tolerant to defoliation.

Soybean Leaf Morphology and Defoliation Tolerance

Field experiments were conducted in 1997 and 1998 to understand the physiological responses of soybean, Glycine max (L.) Merrill, to injury from two-spotted spider mite, Tetranychus urticae Koch, and to examine the contribution of soil moisture toward soybean tolerance to spider mite injury. A split-plot treatment design was used consisting of moisture stress as the main plot and spider mite injury as the sub-plot treatments in a randomized complete block design with eight replications. Soybeans were moisture-stressed beginning approximately at V10 growth stage, and spider mites were maintained on soybeans for 10 d, and then physiological responses of soybean were determined. Moisture-stressed soybeans had lower leaf water potentials, photosynthetic rates, stomatal conductances, and transpiration rates. Spider mite injury also caused a significant reduction in photosynthesis, stomatal conductance, transpiration, and chlorophyll content. The lack of a significant impact of spider mite injury on chlorophyll fluorescence and similar light curves, at low light intensities, of soybean leaves with and without spider mite injury, suggest that spider mite injury does not interfere with the light reaction center at the initial stage of photosynthesis. Despite measurable reductions in total chlorophyll content from mite injury, fluorescence data and light curves strongly indicate photosynthetic rate reductions from mite injury were not immediately associated with chlorophyll loss or effects on photosynthetic electron transport. There were significant interactions between moisture stress and spider mite injury for some gas-exchange parameters. Photosynthetic rate reductions by spider mites were greater in moisture-unstressed than stressed soybeans. Superimposing spider mite injury did not reduce photosynthetic rates greatly in moisture-stressed soybeans because of an initially low photosynthetic rate from moisture stress. However, comparison of absolute photosynthetic rates of spider mite-injured soybean leaves with and without moisture stress suggested that soil moisture improved soybean tolerance to spider mite injury.

Changes in soybean gas-exchange after moisture stress and spider mite injury

Based on previous photosynthesis studies, adult Mexican bean beetles, Epilachna varivestis Mulsant, produce a different physiological response to injury in soybean than other insect defoliators. In 1993 and 1994, we conducted experiments to determine the nature and extent of photosynthetic rate reductions in soybean, Glycine max (L.) Merrill, and dry bean, Phaseolus vulgaris L. We used a randomized complete block design for all experiments. In most experiments, treatments were an uncaged, uninjured leaflet; a caged, uninjured leaflet; and a caged, injured leaflet. Treatments were replicated >5 times. Experimental units were individual trifoliolate leaflets. Four to 8 larvae or adults were placed in each leaflet cage and allowed to feed for 6–18 h. After feeding, the insects and leaf cages were removed and gas exchange properties were determined. Both adults and larvae reduced photosynthetic rates of the remaining tissue of the injured leaflet on both soybean and dry bean. A significant linear relationship between photosynthetic rate and percentage injury was observed for both adult and larval injury. Injury reduced photosynthetic rates in all 6 soybean and dry bean cultivars used in the experiments. There was no recovery of photosynthetic rates after injury of an individual leaflet. Stomatal conductance rates were not consistently different between injured and uninjured leaflets. Intercellular CO2 concentrations were similar or higher in injured leaflets. Consequently, reductions in photosynthesis do not seem to be attributable to stomatal limitations. Quantum efficiency was not affected by injury, indicating that light-harvesting structures were not perturbed. Therefore, our results suggest that the limitations to photosynthesis are attributable to the utilization of CO2 or the supply or utilization of phosphate. Our findings suggest that the limitation is associated with RuBPcase, RuBP regeneration, or phosphate utilization.

Fikru J. Haile

Papers

Physiological and Growth Tolerance in Wheat to Russian Wheat Aphid (Homoptera: Aphididae) Injury

Soybean cultivars and insect defoliation : Yield loss and economic injury levels

Soybean Leaf Morphology and Defoliation Tolerance

Changes in soybean gas-exchange after moisture stress and spider mite injury

Mexican Bean Beetle (Coleoptera: Coccinellidae) Injury Affects Photosynthesis of Glycine max and Phaseolus vulgaris