Induced resistance in mountain birch: defence against leaf-chewing insect guild and herbivore competition

Summary The effect of leaf damage simulating the feeding of early season insect herbivore species, e.g. Epirrita autumnata, to mountain birch, Betula pubescens ssp. tortuosa, on the performance of insect larvae was studied with eleven leaf-chewing sawfly species. I found variation in the results that was due to short- and long-term inducible responses and to the phenology of herbivore species. In general, early and mid-season species were more strongly affected by induced reactions than late-season species. This finding is in accordance with earlier results but I could show that the persistance of induced reactions rather than the influence of timing of damage is responsible for the result. The growth of the larvae of mid-season sawfly species was affected by both short- and long-term induced reactions. This result shows that early season species may escape short-term induced reactions of mountain birch in current year but may not avoid long-term effects. It is supposed that seasonal deterioration of leaf quality either masks the effects of induced defences or late-season species are better adapted to low-quality leaves. Some species show variation in their response to induced defence in different years. This may be due to yearly differences in induced reactions as well as to species-specific responses. Induced defence reactions may play a role in competitive interactions between herbivore species in leaf-chewing guild of mountain birch.     

Patterns of intra- and interspecific association of gall-forming sawflies in relation to shoot size on their willow host plant

Summary Four species of gall-forming sawflies were each frequently found to have clumped distributions among shoots within their willow host plant across four sites and three years. When all species were considered together by clone, year, and site, species showed independence of distribution among shoots two thirds of the time and showed positive covariance one third of the time. When pairs of species were considered separately, but clones were combined within sites and years, 60% of the chi-square tests of association were significant. All but one of the significant tests showed positive associations between pairs of species. The stem galler was positively associated with the leaf folder at all sites in all years, and the petiole galler was positively associated with the stem galler and leaf folder for most year by site combinations. When species paris co-occurred on shoots they were usually found at the same or higher density as when found alone on shoots. Only 2 of 100 tests showed a depressed density of a species when co-occurring on shoots with heterospecifics.All sawfly species were found on shoots that were significantly larger (mean node number) than on shoots without sawflies, and species responded to shoot size variation similarly. Sizes of shoots occupied by heterospecific species combinations were usually significantly larger than shoots with only conspecifics, for all species. These data supported the hypothesis that similar species' responses to within-plant variation would lead to positive rather than negative or random species associations. The data do not support the hypothesis that interspecific competition was important in determining shoot choice or species density.     

Size and shape analysis of mineral resources in arroyo willow and their relation to sawfly densities

The association between host-plant mineral nutrients and insect herbivory is complex, idiosyncratic, and dynamic. Because of this we employed an unusual statistical method to evaluate the relationship between tenthredinid sawfly herbivory and concentrations of foliar nutrients in arroyo willow,Salix lasiolepis. We discovered that among 20 willow clones and between two years arroyo willow varied in the size (absolute concentrations) and shape (relative concentrations) of five mineral nutrients (Ca, Mg, N, P, and K). Similarly, the densities of five sawfly species varied in size and shape among clones and between years. In 1984, relative densities, or shape, of the sawfly community was associated with relative concentrations, or shape, of foliar nutrients in 20 willow clones. In contrast, in 1985 absolute densities, or size, was associated with absolute concentrations, or size, of foliar nutrients. This shift from a shape to a size association between herbivory and foliar mineral nutrients may reflect the large difference in winter precipitation and sawfly densities between years: precipitation and sawfly densities were much greater in 1985 than in 1984.     

Influence of watering and trenching ponderosa pine on a pine sawfly

Summary Neodiprion autumnalis (Smith) larvae were caged for two successive years on root-trenched, watered, and untreated ponderosa pine (Pinus ponderosa Doug. ex Laws.) to determine effects of host moisture stress on larval feeding. Levels of moisture stress (as measured by the Scholander pressure chamber) differed significantly among treatment levels during 1984 and 1985 larval feeding periods. Differences in larval feeding success were not detected in 1984. In 1985, however, larvae on trenched (stressed) trees clipped and rejected more foliage, consumed more needles, had lower pupal weights, lower survival, and a longer feeding period than larvae on watered or untreated trees. Frass production did not differ among treatment levels. The length of the feeding period was shorter for larvae on watered trees than for larvae on untreated trees, but other measures of feeding success did not significantly differ between watered and untreated trees.     

Review of the sawfly genus Empria (Hymenoptera, Tenthredinidae) in Japan

The following eleven Empria species are reported from Japan: Empria candidata (Fallén, 1808), Empria japonica Heidemaa & Prous, 2011, Empria liturata (Gmelin, 1790), Empria loktini Ermolenko, 1971, Empria plana (Jakowlew, 1891), Empria quadrimaculata Takeuchi, 1952, Empria rubicola Ermolenko, 1971, Empria tridens (Konow, 1896), Empria tridentis Lee & Ryu, 1996, Empria honshuana Prous & Heidemaa, sp. n., and Empria takeuchii Prous & Heidemaa, sp. n. The lectotypes of Poecilosoma pallipes Matsumura, 1912, Empria itelmena Malaise, 1931, Tenthredo candidata Fallén, 1808, and Tenthredo (Poecilostoma) hybrida Erichson, 1851 are designated. Empria itelmena Malaise, 1931, syn. n. is synonymized with Empria plana (Jakowlew, 1891). Poecilosoma pallipes Matsumura, 1912, previously assigned to Empria, is transferred to Monsoma, creating Monsoma pallipes (Matsumura, 1912), comb. n. Results of phylogenetic analyses using mitochondrial (COI) and nuclear (ITS1 and ITS2) sequences are also provided.