GENETIC DIFFERENTIATION AND HETEROZYGOSITY IN PINYON PINE ASSOCIATED WITH RESISTANCE TO HERBIVORY AND ENVIRONMENTAL STRESS

Arizona's Sunset Crater began erupting in 1064 AD and for the next 200 years buried over 2,000 km² in ash, cinders, and lava. Soil analyses indicate that pinyon pines (Pinus edulis) currently colonizing the cinder fields are faced with a highly stressful environment. Many of these pinyons suffer chronic, intense insect herbivory that reduces plant growth and eliminates female cone production. In contrast, herbivory among pinyons growing in neighboring sandy-loam soils is minimal. Furthermore, numerous trees within the heavily infested cinder field population suffer relatively low herbivory and maintain normal growth and reproduction. We used four polymorphic enzymes to examine the relationship between herbivore attack, environmental stress and genotypes of the adjacent cinder field, and sandy-loam soil pinyon populations. Our results demonstrate that 1) resistant trees display significant genetic differences and are more heterozygous for two enzymes associated with herbivory than susceptible trees; and 2) the cinder-soil pinyons exhibit significant genetic differences and are more heterozygous for an enzyme associated with environmental stress than the neighboring sandy-loam soil pinyons. We conclude that heterozygosity of specific or closely linked loci may facilitate pinyon resistance to herbivory and environmental stress, and that strong selection across narrow geographic boundaries resulted in rapid genetic differentiation of pinyon populations.     

Chronic herbivory negatively impacts cone and seed production,seed quality and seedling growth of susceptible pinyon pines

Although herbivory often reduces the reproduction of attacked trees, few studies have examined how naturally occurring insect-resistant and susceptible trees differ in their reproduction, nor have these effects been experimentally examined through long-term herbivore removals. In addition, few studies have examined the effects of herbivory on the quality of seeds produced and the implications of reduced seed quality on seedling establishment. We evaluated the impact of chronic herbivory by the stem-boring moth, Dioryctria albovittella, on cone and seed production of the pinyon pine (Pinus edulis) during two mast years. Three patterns emerged. First, moth herbivory was associated with reductions in cone production, viable seed production and seed mass. Specifically, pinyons susceptible to moth attack had 93–95% lower cone production, and surviving cones produced 31–37% fewer viable seeds, resulting in a 96–97% reduction in whole tree viable seed production. In addition, surviving seeds from susceptible trees had 18% lower mass than resistant trees. Second, long-term experimental removal of the herbivore resulted in increased rates of cone and seed production and quality, indicating that moth herbivory was the driver of these reductions. Third, seed size was positively associated with seed germination and seedling biomass and height, suggesting that trees suffering chronic herbivory produce poorer quality offspring. Thus, the resistance traits of pinyons can affect the quality of offspring, which in turn may affect subsequent seedling establishment and population dynamics.     

Seeing the trees for the leaves – oaks as mosaics for a host-specific moth

From the perspective of a specialist herbivore, how homogenous are individual tree crowns as patches of habitat? We partitioned variation in physical and chemical host leaf traits and in the abundance and performance of a specialist oak leaf miner, Tischeria ekebladella, into variation at different hierarchical levels. For the phenolic contents of the leaves, we examined variation among oak stands, among trees within stands and among branches within trees. For leaf size and water content, we assessed variation among trees within a single stand, among shoots within trees, and among leaves within shoots. For moth abundance and performance, we examined variation across all levels: among oak stands, among trees within stands, among branches within trees, among shoots within branches and among leaves and insect individuals. For measures of phenolic contents, we found little variation among stands but substantial variation among individual trees. Yet, a tree particularly rich in a given compound was often comparatively poor in another. At a finer spatial scale, the phenolic composition of individual parts of a single tree was quite consistent, whereas leaf weight and water content varied widely within individual tree crowns. Moth abundances varied more among shoots within branches than at any other spatial level, whereas moth survival showed equal levels of variation within individual shoots as among separate oak stands. Likewise, for four other measures of larval performance (assessed at the level of trees and lower), we found more variation within than between trees. In conclusion, the large variation observed in the performance of a specialist moth and in the physical traits of the leaves among different parts of single tree crowns refutes the image of an oak tree as an ‘island’ of internally homogeneous quality. Hence, we may expect little evolutionary adaptation of T. ekebladella at the scale of individual trees. The moths may instead evolve to behaviourally select their resource at a very fine scale. Large variation within trees also calls for extensive replication within trees in ecological sampling designs and/or the sampling of maximally similar leaves.     

Deadly combination of genes and drought: increased mortality of herbivore-resistant trees in a foundation species

Current climate models predict a shift to warmer, drier conditions in the southwestern US. While major shifts in plant distribution are expected to follow these climate changes, interactions among species and intraspecific genetic variation rarely have been incorporated into models of future plant distributions. We examined the drought‐related mortality of pinyon pine (Pinus edulis) in northern Arizona focusing on trees that showed genetically‐based resistance or susceptibility to a nonlethal herbivore, the shoot‐boring moth, Dioryctria albovittella. Because moth resistant trees have outperformed susceptible trees during 20 years of study, and herbivory has been shown to increase drought related mortality, we expected higher mortality rates in susceptible trees. However, our field observations and greenhouse experiments showed several unexpected patterns relevant to understanding the consequences of climate change: (1) The mortality of adult P. edulis resistant to the moth was three times higher than the mortality of trees susceptible to the moth. (2) Over a few years, differential mortality caused a shift in stand structure from resistant dominated to equality (3 : 1 resistant : susceptible to 1 : 1). (3) Adult moth resistant trees suffered significantly greater water stress than adult moth susceptible trees, suggesting that variation among the two groups in drought tolerance may be a mechanism for differential mortality. (4) When grown under drought conditions in the greenhouse, seedlings from resistant mothers died sooner than seedlings from susceptible mothers. These data support the hypothesis that drought can act as an agent of balancing selection and that drought resistance is a heritable trait. Taken together, our findings suggest that genetic variation in a population can be an important factor in determining its response to future climate change, and argue for the inclusion of genetics into models developed to understand the consequences of climate change.     

Relative Importance of Environmental Stress and Herbivory in Reducing Litter Fall in a Semiarid Woodland

We examined the impact of soil stress (low water and nutrient availabilities) and two keystone insect herbivores on pinyon pine (Pinus edulis) needle litterfall. We compared trees growing on two distinct soil types: volcanic cinders, which exhibit pronounced water and nutrient limitation, and sandy-loam soils, which have higher water-storage capacity and nutrient availability. Using two long-term herbivore removal experiments (15 and 18 years, respectively), we also examined the effects of the pinyon needle scale (Matsucoccus acalyptus, which attacks juvenile trees) and the stem-boring moth (Dioryctria albovittella, which attacks mature trees) on pinyon litterfall. These herbivores reach high densities on cinder soils but are absent or occur at much lower levels on sandy-loam soils. Four years of litterfall measurements showed four major patterns. First, independent of herbivory, needle litterfall was 20% lower under trees on high-stress cinder soils than on sandy-loam soils. Second, in agreement with the negative impact of scales on tree growth (that is, a 30% decline in stem growth), trees with scale infestations had 25% lower litterfall rates than trees resistant to scale; however, 15 years of scale-insect removal did not significantly increase needle litterfall. This implies possible intrinsic differences in litter production between scale-resistant and scale-susceptible trees. Third, in contrast with significant negative effects of moth herbivory on tree growth (that is, a 27% decline in stem growth), moth herbivory had no effect on needle litterfall. This, along with increased stem density in moth-susceptible trees, may be evidence of compensatory production. Fourth, there were strong year by soil type and year by scale herbivory interactions, such that in some years the effect on litterfall can be obscured or reversed by some other factor. In summary, soil stress has a strong and predictable effect on needle litterfall, whereas the relationship between insect herbivory and needle litterfall is weaker and depends on the individual herbivore. These effects, however, are mediated by other environmental factors that have considerable annual variation.     

Effect of body size and larval experience on mate preference in Helicoverpa armigera (Hübner) (Lep., Noctuidae)

Abstract:  We studied the mating selection in the cotton bollworm, Helicoverpa armigera (Hübner), in relation to body size and larval diet in the laboratory. When provided with an artificial diet at larval stage, weight, body and forewing length did not affect the probability of a male/female moth being selected for mating, but the abdominal width of selected female moths was significantly wider than that of non-selected female moths. 30 female moths were dissected and number of eggs was counted after mating, and there was a correlation between the abdominal width and egg number. There was also significant difference of weight loss between selected and non-selected male/female moths after the mating. The effect of operational sex ratio on mating latency and copulation duration were tested, and the result indicated that mating latency of male selection was significantly longer than that of female selection, but the difference of copulation duration was not significant. Cotton, corn and peanut plants were provided to larvae to test the effect of larval host plant experience on mate choice. When cotton- and peanut-fed moth severed as potential partners, both female and male of cotton-fed moths significantly preferred cotton- to peanut-fed moths for mating. The possible reasons for mate preference based on larval host plant experience may account for host plants attributes on sex pheromone variation and sexual maturity. These findings may impact Bacillus thuringiensis resistance management.     

Season mediates herbivore effects on litter and soil microbial abundance and activity in a semi-arid woodland

Herbivores can directly impact ecosystem function by altering litter quality of an ecosystem or indirectly by shifting the composition of microbial communities that mediate nutrient processes. We examined the effects of tree susceptibility and resistance to herbivory on litter microarthropod and soil microbial communities to test the general hypothesis that herbivore driven changes in litter inputs and soil microclimate will feedback to the microbial community. Our study population consisted of individual piñon pine trees that were either susceptible or resistant to the stem-boring moth (Dioryctria albovittella) and susceptible piñon pine trees from which the moth herbivores have been manually removed since 1982. Moth herbivory increased piñon litter nitrogen concentrations (16%) and decreased canopy precipitation interception (28%), both potentially significant factors influencing litter and soil microbial communities. Our research resulted in three major findings: (1) In spite of an apparent increase in litter quality, herbivory did not change litter microarthropod abundance or species richness. (2) However, susceptibility to herbivores strongly influenced bulk soil microbial communities (i.e., 52% greater abundance beneath herbivore-resistant and herbivore-removal trees than susceptible trees) and alkaline phosphatase activity (i.e., 412% increase beneath susceptible trees relative to other groups). (3) Season had a strong influence on microbial communities (i.e., microbial biomass and alkaline phosphatase activity increased after the summer rains), and their response to herbivore inputs, in this semi-arid ecosystem. Thus, during the dry season plant resistance and susceptibility to a common insect herbivore had little or no observable effects on the belowground organisms and processes we studied, but after the rains, some pronounced effects emerged.     

An endemic population of western poplar clearwing moths (Lepidoptera: Sesiidae) invades a monoculture of hybrid poplar

Western poplar clearwing, Paranthrene robiniae (Hy. Edwards) (Lepidoptera: Sesiidae), is endemic in Pacific Northwest riparian habitats at low population densities. These moths have colonized commercial hybrid poplar (Populus spp.) plantings. Moth populations increased rapidly and became a major pest. Trap catches of male moths in mid-season surveys increased 190-fold from 95 in 2001 to >18,500 in 2002 across 6597 ha of poplars monitored. The outbreak of western poplar clearwings was widespread in 2002. Pheromone-baited traps placed one trap per 81.75 ha over 13,274 ha of commercial poplars captured >108,000 male moths in 2002. Damage to commercial poplars included girdling of saplings and burrows in limbs and trunks of trees. Repeated applications of chlorpyrifos failed to reduce the abundance of moths in 2002. Two management strategies over two separate plantations of approximately 6500 ha each were contrasted. Future control strategies recommend a halt to the use of contact insecticides that target adult moths. Short-term (3-5 yr) control should involve a pheromone-based mating disruption strategy followed eventually by selection of a clone that is less susceptible to P. robiniae attack.     

Comparisons of ectomycorrhizae on pinyon pines (Pinus edulis; Pinaceae) across extremes of soil type and herbivory

Using field and greenhouse studies, we examined the relationships among pinyon pines (Pinus edulis), their ectomycorrhizal mutualists, and their moth herbivores as a function of soil fertility. We studied two soil types—the ash and cinder soils of the San Francisco volcanic field and nearby sandy loam soils. In the field, pinyons growing in cinders suffered from reduced moisture, negative nitrogen mineralization rates, low phosphate levels, reduced growth, and high moth herbivory relative to pinyons growing in sandy loam. Pinyons growing in cinders also had twofold higher levels of ectomycorrhizal colonization than their noncinder counterparts. Similarly, in the greenhouse, seedlings grown in cinders had higher levels of ectomycorrhizal colonization and greater numbers of ectomycorrhizae than seedlings grown in sandy loam. Seedling shoot growth was significantly enhanced by ectomycorrhizae in both soils. These patterns support three conclusions. First, field and greenhouse studies demonstrated that trees growing in nutrient-poor soils had higher levels of ectomycorrhizal colonization than trees growing in better soils. Second, across soil types, variation in ectomycorrhizal colonization was better predicted by soil fertility than by herbivory. However, herbivory negatively affected ectomycorrhizae in the stressful cinder environment. Third, although mycorrhizae can be parasitic under some conditions, ectomycorrhizae had mutualistic impacts on pinyon seedlings across the environmental extremes we studied.     

Competition between the gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis: interactions mediated by host plant chemistry, pathogens, and parasitoids

The gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis, overlap geographically as well as in their host ranges. Adult female swallowtails are incapable of distinguishing between damaged and undamaged leaves, and the opportunities for competition between these two species are numerous. We designed field and laboratory experiments to look for evidence of indirect competition between P. canadensis and L. dispar larvae. Swallowtail caterpillars were reared in the laboratory on leaves from gypsy-moth-defoliated and undefoliated trees to explore host-plant effects. We tested for pathogen-mediated interactions by rearing swallowtail larvae on both sterilized and unsterilized leaves from defoliated and undefoliated sources. In addition, we measured the effects of known gypsy moth pathogens, as well as gypsy moth body fluids, on the growth and survival of swallowtail larvae. Field experiments were designed to detect the presence of parasitoid-mediated competition, as well: we recorded parasitism of swallowtail caterpillars placed in the field either where there were no gypsy moth larvae present, or where we had artificially created dense gypsy moth populations. We found evidence that swallowtails were negatively affected by gypsy moths in several ways: defoliation by gypsy moths depressed swallowtail growth rate and survival, whether leaves were sterilized or not; sterilization significantly reduced the effect of defoliation, and gypsy moth body fluids proved lethal; and swallowtail caterpillars suffered significantly increased rates of parasitism when they were placed in the field near gypsy moth infestations.     

Increased moth herbivory associated with environmental stress of pinyon pine at local and regional levels

 Using 6 years of observational and experimental data, we examined the hypothesis that water and nutrient stress increase the susceptibility of pinyon pine (Pinus edulis) to the stem- and cone-boring moth (Dioryctria albovittella). At two geographic levels, a local scale of 550 km² and a regional scale of 10,000 km², moth herbivory was strongly correlated with an edaphic stress gradient. At a local scale, from the cinder soils of Sunset Crater to nearby sandy-loam soils, nine of ten soil macro- and micronutrients, and soil water content were lowest in cinder-dominated soils. Herbivore damage was six times greater on trees growing in the most water and nutrient deficient site at Sunset Crater compared to sites with well-developed soils. Percentage silt-clay content of soil, which was highly positively correlated with soil nutrient and soil moisture at a local scale, accounted for 56% of the variation in herbivory at a regional scale among 22 sites. Within and across sites, increased stem resin flow was positively associated with reduced moth attack. On the basis of moth distribution across a stress gradient, we predicted that pinyons growing in highly stressful environments would show increased resistance to herbivores if supplemented with water and/or nutrients. We conducted a 6-year experiment at a high-stress site where individual trees received water only, fertilizer only, and water + fertilizer. Relative to control trees, stem growth and resin flow increased in all three treatments, but only significantly in the water + fertilizer treatment. Although there was no significant difference in herbivore damage among these three treatments, there was an overall reduction in herbivore damage on all treatment trees combined, compared to control trees. This experiment suggests that release from stress leads to increased resistance to insect attack and is consistent with our observational data. While other studies have predicted that short-term stress will result in herbivore outbreaks, our studies extend this prediction to chronically stressed host populations. Finally, while flush-feeders are not predicted to respond positively to stressed host plants, we found a positive association between herbivore attack and stressed pinyon populations. Received: 25 December 1995 / Accepted: 15 August 1996     

蛾类昆虫性信息素受体及其作用机理

蛾类昆虫性信息素受体首先从烟芽夜蛾Heliothis virescens和家蚕Bombyx mori中鉴定出来, 到目前为止已经克隆得到了19种蛾类昆虫的几十种性信息素受体基因, 并且这些基因在系统发育树中聚成一个亚群。性信息素受体从蛾类蛹期开始表达, 主要表达在雄性触角的毛形感器中, 少部分受体在雌性触角、 雄性触角其他感器以及身体其他部位中也有表达。大部分蛾类性信息素受体的配体并不是单一的, 而是能够对多种性信息素组分有反应, 部分性信息素受体还能够识别性信息素以外的其他物质, 还有一部分性信息素受体的识别配体目前尚不清楚。另外发现在雌性蛾类触角中也存在一些嗅觉受体能够识别雄性分泌的性信息素。在蛾类性信息素受体与性信息素识别的过程中, 性信息素结合蛋白不仅能够特异性地运送配体到嗅觉神经元树状突上, 还能够提高性信息素与性信息素受体之间的结合效率。另外, OrCo类受体与性信息素受体共表达在嗅觉神经元中, 在蛾类性信息素受体与配体的识别过程中扮演了重要角色。但是蛾类信息素对神经元刺激的终止并非由性信息素受体控制, 而是由细胞中的气味降解酶等其他因子调控。蛾类性信息素受体研究中还有很多疑问需要解答, 其过程可能比我们想象的更为复杂。     

Sexual differences in flower defense and correlated male‐biased florivory in a plant–florivore system

Male‐biased florivory is a prominent phenomenon in the interaction between plants and florivores, and is potentially related to the evolution of flower traits and sex expression; however, its adaptive significance is not well understood. We studied florivory in the geometrid moth Chloroclystis excisa utilizing flower buds of a sexually polymorphic shrub, Eurya japonica, to reveal relationships between flower sex and moth oviposition preference, moth larval performance, and plant phenolics composition. In the field, C. excisa exploited flower buds on male and hermaphrodite trees but never those on female trees. In the laboratory, moths showed a strong oviposition preference for male over female flower buds, and larvae did not survive on female buds. Mortality was caused solely by feeding on the calyx covering the female bud. Female calyces contained higher concentrations of total phenolics and condensed tannins than did male calyces. These results suggest that substantial sexual differences in defense against florivory may have evolved in association with the differentiation of flower sexes and that a strong preference for the weakly defended flower sex may have evolved in florivores as a counter‐adaptation.     

Induced defences in the neotropical tree Bauhinia brevipes (Vog.) to herbivory: effects of damage-induced changes on leaf quality and insect attack

Induced defences to herbivory are physical, nutritional, and allelochemical traits that change in plants following damage or stress, and that reduce the performance and/or preference of herbivores. The aim of this study was to verify the occurrence and effect of induced responses in Bauhinia brevipes (Vog.) (Leguminosae) which defend it against herbivores, through the manipulation of its leaves, and their effects on herbivore foraging behaviour. We selected 15 plants in the field, and three shoots per plant were subjected to one of three treatments: (1) damaged shoots (simulation of the main types of foliar herbivory and insect exclusion); (2) damaged control shoots (insect exclusion); and (3) control shoots (not manipulated). Water and nitrogen content, tannin concentration, levels of herbivory, and shoot growth rates were compared among treatments. Leaf quality varied among treatments. Damaged leaves showed higher tannin concentration, and lower water and nitrogen content compared to undamaged leaves. On the other hand, they experienced higher rates of herbivory than leaves on control shoots. Moreover, shoots that were experimentally induced showed a higher increase in final shoot length. These results suggest that simulated herbivory on B. brevipes reduced the nutritional quality of its leaves and increased the amount of secondary compounds, therefore altering insect herbivore attack and increasing shoot performance.     

Herbivory and tree mortality across a pinyon pine hybrid zone

We examined the abundances of three common insect herbivores on pure and hybrid pinyon pines along a 250-km transect in west-central Arizona, United States. Using six morphological traits, we developed a hybrid index to classify trees as pure Pinus californiarum, hybrid, or pure Pinus edulis. The insects (the stem-boring moth, Dioryctria albovittella, the scale insect, Matsucoccus acalyptus, and several species of pitch moths that produce wounds on the trunk and branches) exhibited different distributional patterns across tree types. Stem-boring moths were significantly more abundant on trees at hybrid sites compared to trees at pure sites. In addition, within hybrid sites, hybrids supported significantly more moth larvae than pure trees of either species. These two patterns support the hybrid susceptibility hypothesis in which hybrid breakdown results in increased susceptibility to herbivory. In contrast to stem-borers, there were significantly more pitch moth wounds on trees at pure P. californiarum sites than at hybrid and pure P. edulis sites. Within the hybrid zone, pitch moth abundance was equal on pure P. californiarum and hybrids, and both were significantly greater than on pure P. edulis. These within-site comparisons support the dominance hypothesis where hybrid resistance differs from one tree species, but not the other. Scale insects exhibited the most restricted distribution; over the 250 km transect they were found only in the hybrid zone. This supports the hybrid susceptibility and/or the stress hypothesis (i.e., species at the edge of their range suffer greater stress and are more susceptible to herbivory). We summed the mean numbers of these three common herbivores across sites and found that hybrid sites supported 2.1 and 3.9 times more herbivores than pure P. californiarum and P. edulis sites, respectively. Furthermore, tree mortality was on average, 35 times greater within the hybrid zone compared to pure zones of each species and was associated with the cumulative abundance of herbivores (r ²=0.646). Regardless of whether this mortality is due to insect infestation, stress or a combination of both, these results suggest that hybrid zones are important arenas of natural selection.     

Saproxylic moths reveal complex within-group and group-environment patterns

We investigated saproxylic moths of the family Tineidae, a neglected group inhabiting wood-decaying fungi and dead wood, within the Bia?owie?a Primeval Forest in Poland. Study data were obtained from the collection of 280 fruiting bodies of wood-decaying fungi and the subsequent rearing of adults. Spatial and statistical distribution of saproxylic moths, relationship among species and the influence of environment reflected by interaction with tree and fungal species together with tree and stand level characteristics were studied. Fifteen species and 533 individuals of saproxylic moths were reared. The fungal species, number of fruiting bodies and standing position of a tree influenced species richness. Moth abundance was influenced by fungal species, coniferous trees, increasing tree diameter, number of fruiting bodies and brown rot. Moth abundance was also enhanced by standing dead trees located in managed forests with higher canopy closure. Analyses indicate that several moth species favor a particular rot type and that some fungi host a richer fauna than others. Furthermore, our results indicate mutually independent fungal colonization events by saproxylic moth species, and thus a possible mechanism exists for competition avoidance with other saproxylic moths. Saproxylic moths revealed complex within-group patterns that responded differently to environmental variables. Thus, potential conservation of these organisms requires various approaches including ecosystem management, especially in the context of addressing their diverse habitat requirements.     

Influence of within-orchard trap placement on catch of codling moth (Lepidoptera: Tortricidae) in sex pheromone-treated orchards

The influence of trap placement on catches of codling moth, Cydia pomonella L., was examined in a series of studies conducted in orchards treated with Isomate-C Plus sex pheromone dispensers. Mark-recapture tests with sterilized moths released along the interface of pairs of treated and untreated apple and pear plots found that significantly more male but not female moths were recaptured on interception traps placed in the treated plots. In a second test, significantly higher numbers of wild male and female moths were caught on interception traps placed in treated versus untreated plots within a heavily infested orchard. The highest numbers of male moths were caught on traps placed along the interior edge of the treated plots. Trap position had no influence on the captures of female moths. In a third test, north-south transects of sex pheromone-baited traps were placed through adjacent treated and untreated plots that received a uniform release of sterilized moths. Traps on the upwind edge of the treated plots caught similar numbers of moths as traps upwind from the treated plots. Moth catch was significantly reduced at all other locations inside versus outside of the treated plots, including traps placed on the downwind edge of the treated plot. In a fourth test, five apple orchards were monitored with groups of sex pheromone-baited traps placed either on the border or at three distances inside the orchards. The highest moth counts were in traps placed at the border, and the lowest moth counts were in traps placed 30 and 50 m from the border. In a fifth test, the proportion of traps failing to catch any moths despite the occurrence of local fruit injury was significantly higher in traps placed 50 versus 25 m from the border. The implications provided by these data for designing an effective monitoring program for codling moth in sex pheromone-treated orchards are discussed.     

Geographic variation in oviposition preference for male and female host plants in a geometrid moth: implications for evolution of host choice

Several dioecious plant species exhibit sexual dimorphisms in defensive traits. However, the effects of sexual dimorphism on defense against herbivores remain poorly understood. Eurya japonica (Thunb.) (Theaceae) is a dioecious shrub that shows sexual dimorphism in the chemical defense of flower buds. Female calyces contain higher concentrations of total phenolics and condensed tannins than do male calyces. Male flower buds are edible for a florivore moth, Chloroclystis excisa (Butler) (Lepidoptera: Geometridae), whereas the female flower buds are lethal to the moth larvae. The moths prefer to oviposit on male over female E. japonica flower buds. As the moths also occur in areas lacking E. japonica, we tested whether the oviposition preference for E. japonica flower sex differed between moths sympatric and allopatric with E. japonica. The moths sympatric with E. japonica showed a stronger preference for male E. japonica than the moths allopatric with E. japonica. Our phylogeographic study using mitochondrial cytochrome oxidase subunit I gene sequences revealed little genetic differentiation between moth populations sympatric and allopatric with E. japonica. These results suggest that the adaptive oviposition preference for flower sex of E. japonica has evolved rapidly in C. excisa.     

Influence of intra-tree variation in time of budburst of white spruce on herbivory and the behaviour and survivorship of Zeiraphera canadensis

Abstract.

• 1 Field studies were carried out to determine the effects of intra-tree variation in the time of budburst of white spruce, Picea glauca Moench (Voss.), on the behaviour and survivorship of, and herbivory by, the spruce bud moth, Zeiraphera canadensis Mutt. & Free.
• 2 There was significant variation in the time of budburst among whorls, shoots and buds. Budburst was acropetal, with buds in the interior of the lower crown bursting first and terminal buds on terminal shoots in the upper crown bursting last.
• 3 Bud moths laid the greatest proportion of their eggs in the middle of the crown and egg hatch was usually best synchronized to budburst in this region. Many eggs hatched before terminal buds on terminal shoots in the upper crown had burst and thus intra-tree variation in budburst decreased the probability that first-instar larvae would colonize the most important plant parts for growth.
• 4 However, many later instars dispersed upwards and outwards in the crown and colonized the late bursting buds in the upper crown. Such dispersal reduces the effectiveness of intra-plant variation in budburst to reduce herbivory and permits Z.canadensis to eat young nutritious buds for a longer period of time.
• 5 Intra-tree variance in the date of budburst was greater than that between trees but there were no consistent differences between the intra-tree variance of trees in half-sib families with high or low susceptibility to Z.canadensis. Differences between trees in herbivory, bud moth density and survivorship were not related to the amount of intra-tree variation in budburst.

     

The Pinyon Rhizosphere,Plant Stress,and Herbivory Affect the Abundance of Microbial Decomposers in Soils

In terrestrial ecosystems, changes in environmental conditions that affect plant performance cause a cascade of effects through many trophic levels. In a 2-year field study, seasonal abundance measurements were conducted for fast-growing bacterial heterotrophs, humate-degrading actinomycetes, fungal heterotrophs, and fluorescent pseudomonads that represent the decomposers in soil. Links between plant health and soil microbiota abundance in pinyon rhizospheres were documented across two soil types: a dry, nutrient-poor volcanic cinder field and a sandy-loam soil. On the stressful cinder fields, we identified relationships between soil decomposer abundance, pinyon age, and stress due to insect herbivory. Across seasonal variation, consistent differences in microbial decomposer abundance were identified between the cinders and sandy-loam soil. Abundance of bacterial heterotrophs and humate-degrading actinomycetes was affected by both soil nutritional status and the pinyon rhizosphere. In contrast, abundance of the fungal heterotrophs and fluorescent pseudomonads was affected primarily by the pinyon rhizosphere. On the cinder field, the three bacterial groups were more abundant on 150-year-old trees than on 60-year-old trees, whereas fungal heterotrophs were unaffected by tree age. Fungal heterotrophs and actinomycetes were more abundant on insect-resistant trees than on susceptible trees, but the opposite was true for the fluorescent pseudomonads. Although all four groups were present in all the environments, the four microbial groups were affected differently by the pinyon rhizosphere, by tree age, and by tree stress caused by the cinder soil and insect herbivory.