Abstract: The impact of gall-inducing aphids on shoot development was analyzed in 900 shoots from 20 pistachio trees, Pistacia atlantica Desf. (Anacardiaceae): 600 in which the axillary - lateral - buds were galled by Slavum wertheimae HRL during the previous growth season, and 300 ungalled shoots. Although P. atlantica is a compensating tree, and the aphids do not attack the apical buds, further development of shoots from the apical buds was stopped in 62% of the galled shoots, while only 8.7% of non-galled shoots stopped their growth. Further development was stopped more often on shoots carrying two galls or more than on shoots supporting only one gall. To assess the hypothesis that bud destruction by the aphids explains this pattern, I conducted a field experiment in 140 shoots, distributed across seven trees. I removed one, two or three axillary buds from five shoots of each tree for each treatment, and marked five other shoots as controls. I found that only 14 shoots (10%) of the 140 did not develop. The growth of the other shoots was not very different among the treatments. I monitored the colonization of the apical shoots, which developed on previously treated shoots, by three other galling aphid species. Removing lateral buds reduced considerably the establishment of Geoica sp. galls (70% of them colonized control shoots), but weakly influenced Forda riccobonii (Stefani). It also contributed only five percent of the total variance of the distribution of Smynthurodes betae West. The different results of the survey and the experiment show that the impact of S. wertheimae galls on the future growth of shoots from apical buds is more complex than the simple physical destruction of the axillary buds.
Abstract: Sampling along roadsides is convenient and is widely practiced in insect population researches. Ecological conditions in road verges are very different than those prevailing in natural habitats and they affect the annual growth of plants in semi-arid and arid regions. This in turn may improve development, survival and abundance of insects feeding on plants growing in roadsides. These trends may bias the results of sampling. To verify this assertion, we quantified the effects of growing in roadside on annual growth of Pistacia atlantica trees and Pistacia palaestina shrubs and compare 2 demographic indexes of nine gall-inducing aphid species on trees growing along roads with trees in the open landscape, in Israel.
The annual growth of the two host plants was significantly more vigorous in roadsides than away from roads. Tests of Combined Probabilities showed that the likelihood of P. atlantica and P. palaestina to be parasitized by more galls of Fordini species is higher in roadsides than away from roads. Moreover, in the semi-dry regions of Israel, three aphid species on P. atlantica and five species on P. palaestina induced more galls in plants growing along roads than away from roads, while in the rainy Northern region, the difference was not significant between the two habitats.
These results indicate a biased evaluation of population size in roadside habitat, which has to be accounted in insect-plant relation researches.
Abstract: Mutualistic ants efciently protecting myrmecophilic plants from herbivores are often rewarded
with nectar provided by extra-oral nectaries (EFN). Ants may serve as biocontrol agents in coffee,
citrus and cacao plantations. The goals of the present study were to examine the ant fauna and their
antiherbivores role in two orchards: cherries (Prunus avium – a myrmecophilic plant with EFN) and
olives (Olea europaea – a non-myrmecophilic plant) in Kibbutz Bar-Am (northern region of Israel).
Six ant species were observed on 13% and 30% of the cherry and olive trees, respectively. Ants
were not attracted to the EFNs on the cherry trees. In the spring, ant activity was experimentally
excluded from isolated shoots with a sticky Tanglefootâring. In the autumn, shoot length and foliar
damage were examined on isolated and intact shoots (control). Isolated shoots were shorter and
suffered from signicantly greater leaf damage. We placed articial EFN (50 ml test tubes with 30%
sucrose solution) on the trees for 2 weeks in the summer. Trees with articial EFN were more often
visited and patrolled by ants than control trees, but the proportion of control trees occupied by ants
diminished during the experiment. At the end of the experiment, cherry trees with articial EFN were
also less often visited. We detected higher predation rates of patrolling ants on insect and insect eggs
that were placed on trees with articial EFNs. These preliminary results show a potential role for
ants in biological control of leaf pests in cherry and olive trees. [L]
Abstract: For weak flying insects feeding on two different host plants during their life cycle, such as gall-inducing aphids, patch and matrix characteristics may play a critical role in patch occupancy and population size in occupied patches. The aims of the present study were to define the basic patch size of Baizongia pistaciae (L) (Aphididae, Fordini), an aphid inducing galls on Pistacia palaestina Boiss (Anacardiaceae) using a genetic approach, and to estimate the impact of landscape structure and patch quality on patch occupancy and gall density on occupied trees of this aphid and four other closely related species. Using 42 genetic markers detected by RAPD-PCR in 117 clones of the galling aphid Baizongia pistaciae, we calculated Wright’s F statistics and estimated the number of winged migrants between demes. We found that host trees at least 150 m apart supported genetically differentiated demes of B. pistaciae, and formed distinct patches. Since the annual cycle of this aphid involves alternation between two different hosts, P. palaestina trees and Poaceae roots, patch – the smallest area that sustains a deme – is a relatively small area that must be composed of at least a single P. palaestina tree and nearby secondary hosts. To assess the impact of landscape structure and patch quality on patch occupancy and gall abundance in occupied patches, two field surveys of P. palaestina trees in natural Mediterranean maquis were performed. Among the five species
of gall-inducing aphids found, B. pistaciae was the most abundant of those surveyed. Host trees were occupied more often in the ecotone, the transition zone between Mediterranean closed maquis and open bata, than in the maquis. Mature and old trees were more often occupied than young ones, and shrubs more often than tree-like plants. There was no difference in the proportion of occupied trees between isolated host trees or those growing in groups. Species richness showed similar trends. We also found no
significant differences in gall abundance in occupied trees among tree quality categories, except that trees growing in the ecotone tended to carry more galls than those growing in the maquis. In conclusion, the best patch of gall-inducing aphids seems to be a small area, composed of an old shrub of P. palaestina standing in an open landscape with nearby secondary hosts, grass roots, available for colonization by winged migrants.
Abstract: The effects of long term browsing on growth and morphology of P. atlantica trees and P. palaestina shrubs, and on the colonization of these hosts by their respective gall-inducing aphid guilds, were studied in natural vegetation pastures in Israel. To simulate apical dominance release by browsing, trees and shrubs were pruned and observed one year later. P. atlantica responded strongly to browsing, producing a crown of dense and sharp dry branches and thorn-like shoots, and pruning, compensating or overcompensating for the lost biomass in the studied morphological variables. Morphological responses of P. palaestina were less evident: we found no compensation in most variables. Three species of aphids produced more galls on browsed than on control shoots of P. atlantica. Two species induced more galls on pruned shoots. The five aphid species on P. palaestina colonized browsed and unbrowsed shoots equally, and produced fewer galls on pruned shoots. The role of apical dominance in architectural responses of trees and shrubs to browsing and pruning, as related to resource availability and timing, is discussed.
