A greenhouse experiment was conducted to study the indirect effects of soil salinity on a caterpillar that induces gall formation on a non-halophilic plant. Larvae of Epiblema scudderiana (Clemens) were allowed to feed on potted goldenrods (Solidago altissima L.) treated with 3 concentrations of NaCl (0, 8,000, 16,000 PPM). Experiments were also carried out with the larvae of two species of leaf beetles, Trirhabda borealis Blake, a leaf-chewer, and Microrhopala vittata F., a leaf-miner, to determine the influence of feeding guild. Adding salt to the soil affected both the plant and insect herbivores. The biomass of roots and shoots as well as root/shoot ratios of salt-stressed plants were lower, relative to controls. The biomass of the fully grown larvae and galls were decreased for the plants treated with the highest salt concentration. The percentage of biomass allocated to the gall was increased by soil salinity. All gall-inducing larvae completed their development (from second to final instar) even though their biomass was significantly reduced in the 16,000 PPM treatment. Soil salinity increased nitrogen concentrations in both gall and stem (normal) tissues but the levels were always higher in the gall. The salt treatments also increased sodium and potassium concentrations in galls and stems. Interestingly, sodium concentrations as well as the ratio of sodium ions to potassium ions increased more rapidly in the stem compared with the gall. Responses of folivorous insects to salt-stressed plants varied. Leaf-chewing larvae ate smaller amounts of plant tissue with high salt content compared with control, which also resulted in shorter feeding periods. The performance of the leaf-mining insect was not affected. However, it was able to complete its larval development within a smaller portion of the leaves. This study showed that soil salinity has a strong negative effect on S. altissima, especially on root development. Conversely, salt stress effects seemed to be progressively decreasing from the stem to the gall to the gall-inducer, which suggests that the gall tissue might act as a buffer against drastic changes in the mineral balance of the host plant. Nevertheless, it seems that unless the host plant dies, larvae of E. scudderiana can always produce a gall in which they can complete their development. On the other hand, leaf-chewing insects appeared to be sensitive to salt-rich tissues since they were deterred by them. Leaf-miners could complete their development with fewer food without any effect on their growth, suggesting that the peculiar tissues on which they feed within leaves became more abundant or nutritious in salt-treated plants.
The factors that affect oviposition and consequently spatial distribution of the galls of many gall makers are poorly understood. Knowledge of these factors could result in a better understanding of the mechanisms that initiate and regulate the development of galls. We tested the hypotheses that, regardless of tree height, galls of Cynips quercusfolii L. produced agamically are distributed randomly in the crowns and on the veins of leaves of oak trees. This study was done in Poland on 15 pedunculate oak (Quercus robur) trees of various heights. We measured the areas of 1659 leaves, including 192 leaves with galls, and the distances along a vein from a gall to the petiole and from gall to leaf edge. The number of galls did not depend on tree height but depended on the position of the leaf within the crown (upper or lower). Regardless of the position in the crown, leaves with galls were significantly larger than those without galls. We conclude that galls were located at a fixed distance from the edge of leaves irrespective of leaf size, but the distance from the gall to the leaf petiole depended significantly on leaf size. We conclude that agamic females of C. quercusfolii prefer large leaves and choose the site on a leaf on which to deposit their eggs. This probably ensures that the developing gall obtains the required amount of nutrients and assimilates., Marian J. Giertych, Andrzej M. Jagodzinski, Piotr Karolevski., and Obsahuje seznam literatury
Despite their wide distribution and frequent occurrence, the spatial distribution patterns of the well-known gall-inducing insects Mikiola fagi (Hartig) and Neuroterus quercusbaccarum (L.) in the canopies of mature trees are poorly described. We made use of the Swiss Canopy Crane (SCC) near Basel, Switzerland, to gain access to the canopy of a mixed temperate forest up to a height of 35 m. Within one and a half days we scanned 6,750 beech leaves and 6,000 oak leaves. M.fagi showed a distinct vertical zonation with highest abundance in the top-most parts of the canopy as well as a significant aggregation on particular trees. N. quercusbaccarum showed an even more pronounced preference for particular trees and a general preference for Quercus robur over Q. petraea. In contrast to M. fagi, no vertical zonation could be detected. We think that both gall-inducing species have greater powers of dispersal than formerly assumed since they overwinter on the forest floor and yet are able to 1) gain access to the entire canopy, 2) show preference for certain host trees. We found little evidence for the phenological synchrony hypothesis proposed to explain the intertree distribution of N. quercusbaccarum. The highest density of M. fagi galls was in those parts of the canopy exposed to high solar radiation; their host choice is probably determined by micro-climatological factors. The consequences of the distribution patterns of N. quercusbaccarum and M. fagi for their ecological interactions with the host-plant, inquilines and parasitoids (e.g., canopy-layer specific performance linked to plant chemistry, density-dependent parasitism) need now to be subjected to further scientific investigation.