Gall Species Research Articles

The adaptive significance of insect gall distribution: survivorship of species in xeric and mesic habitats.

We studied the relationship between habitat moisture and gall-forming insect populations. Population sizes for most galling taxa were significantly larger in xeric habitats compared with mesic habitats. Our results indicate that the differential abundance of galling insects in these habitats is due primarily to differential mortality and survivorship. Mortality factors acting upon eight insect galling species (belonging to eight genera and four families) were measured on six species (five genera and five families) of host plants. Survival was significantly higher for galling populations inhabiting xeric habitats compared with mesic habitats. Parasitism was higher in mesic habitats in seven of eight habitats and fungus-induced diseases were higher in five of seven habitats. Mortality due to predation and other (unknown) factors showed no clear trends. Overall, there was a tendency towards lower mortality and consequently higher survival for populations inhabiting xeric habitats. We hypothesize that reduced mortality caused by natural enemies and endophytic fungi has contributed to the speciation and radiation of galling insects in apparently harsh environments.

Host-Plant Manipulation by Gall-Insects: A Test of the Nutrition Hypothesis

1. Nitrogen is generally regarded as a crucial, limiting nutrient for phytophagous insects. Nitrogen levels in two species of cynipid galls (Neuroterus quercus-baccarum L. and Andricus lignicola Hartig) on oak (Quercus robur L.) were monitored after experimental enhancement of host-plant nitrogen levels over 2 years. 2. The nitrogen content of gall-tissue was unaffected by fertilization of the hostplant, although the nitrogen content of leaf-tissue was elevated. Furthermore, fertilization did not improve gall-insect performance. These results superficially run counter to the predictions of the nutrition theory for the adaptive nature of plant galls. 3. However, in one of the two species (Neuroterus) survivorship was highly variable across individual oak trees, and was negatively correlated with gall nitrogen content. Between-tree differences persisted across years, irrespective of fertilization treatment. 4. Consistent with these results, experimental reduction in number of Neuroterus galls per leaf did not lead to an increase in nitrogen levels in the remaining galls, or to an improvement in insect performance. Thus, there was no relationship between gall density and gall nitrogen content, nor between density and insect performance. 5. We conclude that cynipid gall-formers may be able to manipulate host nitrogen levels to their own advantage, by preventing an increase in gall nitrogen levels on fertilized trees; such an increase would reduce insect survival rates. Our results are therefore consistent with the nutrition hypothesis to explain the evolution of insect galls.

Ecological Recovery of a Gall Midge and its Parasite Guild Following Disturbance

Density and population structure of a native cecidomyiid gall midge, Rhopalomyia californica Felt, and the spatial structure of its parasite guild have returned to normal at Woodside, Calif., several years after ecological disruption caused by repeated applications of malathion bait for eradication of Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Midge larvae develop in terminal galls on Baccharis pilularis DC; galls are multichambered and can contain >50 larvae per gall (one larva per chamber). Samples taken during the summer–fall of 1989 and April 1990 (7–8 yr after the disruption) revealed that the number of larvae per 100 terminals, number of larvae per gall, and number of galls per 100 terminals were comparable at Woodside and the Jasper Ridge Biological Preserve, an adjacent nontreated area. The parasite guild consists of seven solitary species. Analysis of spatial structure of the guild in April 1990 revealed no significant differences (Woodside versus Jasper Ridge) for the following six parameters: parasitization by individual species, total parasitization, number of parasite species per gall (relative frequency), parasite species per gall as a function of gall size, total percent parasitization as a function of number of parasite species per gall (species dependence), and total percent parasitization as a function of gall size (spatial density dependence). The evidence obtained also illustrates how host population structure can influence parasite guild structure (i.e., direct relationship between number of host larvae per gall and number of parasite species per gall), and supports the view that there is a relationship between parasite guild structure and effect on the host population (i.e., direct relationship between number of parasite species per gall and total percent parasitization per gall). Some additional aspects of structure of parasite guilds are discussed.

Biogeographical gradients in galling species richness : Tests of hypotheses.

Five hypotheses were invoked to account for variation in galling species number per location on plants of different structural complexity, namely herbs, shrubs, and trees, both in Brazil and USA. The hypotheses were: 1) the altitudinal/latitudinal gradient hypothesis; 2) the harsh environment hypothesis; 3) the plant species richness hypothesis; 4) the host plant area hypothesis; 5) the plant structural complexity hypothesis. The altitudinal and the harsh environment hypotheses were correlated and supported with sample data in both localities, with increasing gall species number as altitude/latitude declined and as sites became hotter and drier. The two hypotheses were separated by studying riparian sites and dry hillside sites at the same elevation in Arizona. Galling species frequency was higher in dry sites than in riparian sites, supporting the harsh environment hypothesis. Of the five hypotheses tested only the harsh environment hypothesis predicted that galling insect species number should vary in response to environmental variables such as moisture and temperature. Temperate shrubs supported more galling species than did other plant types, both in dry and mesic sites. The overall difference between galling species richness for tropical and temperate latitudes was not statistically significant. Free-feeding insect herbivore species exhibited the opposite pattern of species richness to gallers, being more speciose in riparian sites. The present study corroborates the hypothesis that the gall forming habit is an adaptation to harsh or stressful environments, and we describe for the first time broad scale geographical patterns in galling insect species richness.

Parasitoids, Patches, and Phenology: Their Possible Role in the Local Extinction of a Cynipid Gall Wasp Population

The cynipid gall wasp Xanthoteras politum (Bassett) and its associated chalcid and inquiline parasitoid community were studied from 1976 to 1978 at a postfire site near Lake Oswego in the New Jersey Pine Barrens. X. politum and two other cynipid species selectively attacked new sucker shoots growing from larger fire—damaged trees. Chalcid and inquiline parasitoid attack was the major mortality factor in the population in all 3 yr. In each successive year a higher frequency of the host population was killed by parasitoid attack, and by 1978 on 76 host galls occurred at the site. Inquiline cynpids were minor parasitoid elements the 1st yr of the gall outbreak, but dominated the parasitoid guild in subsequent seasons. Their dominance is attributed to two major factors. First, they attack galls earlier than other parasitoids, and those galls attacked remained at a smaller size and were not chosen for oviposition by later arriving chalcids. Secondly, inquilines did not emerge in spring and infest other gall species as did the chalcid parasitoids. These inquilines remained in the leaf litter and reinfested the next asexual generation of X. politum which appeared on trees in mid—July. The parastioid community displayed neither strong stability nor consistent composition. The apparent overexploitation of the host population by parasitoids may be to their selective advantage as phenological changes in host plants eventually eliminate X. politum from postfire sites anyway.

CHALCID PARASITOID ATTACK ON A GALL WASP POPULATION (ACRASPIS HIRTA (HYMENOPTERA: CYNIPIDAE)) ON QUERCUS PRINUS (FAGACEAE)

AbstractThe developmental sequence of the asexual generation of the gall wasp Acraspis hirta Bassett (Hymenoptera: Cynipidae) on its host plant Quercus prinus (Fagaceae) is described from a site in New Jersey. Chalcid attack was the key mortality factor in the gall population. Parasitoids concentrated their attack on host galls before galls matured and hardened. Hardening of gall walls appears to be the most important deterrent to later attack by inhibiting oviposition. Parasitoids which emerged from A. hirta galls did not reinfest the surviving hosts but probably shifted to other gall species. The parasitoids of Cynips divisa, a similar Old World gall species, became progressively more generalized in their feeding preferences as the season progressed. No such temporal sequencing wau observed in A. hirta.Spacing out of A. hirta galls among leaves is an important strategy for increasing individual fitness in response to parasitoid attack. Most trees were sparsely infested, and few leaves supported more than one gall. Parasitoid mortality was significantly higher on multiply infected leaves than on leaves with one gall. Galls which were parasitized had a significantly smaller average distance to the nearest neighboring gall than those that escaped parasitism suggesting a slight resource concentration effect.

A new vine Thrips (Thysanoptera) from Cyprus

I have been asked by the Director of the Imperial Bureau of Entomology to report upon, and, if necessary, describe a thrips which has been discovered to be distinctly injurious to vines in Cyprus. Two curious species of the suborder Terebrantia have been described from vines, viz., Retithrips aegypticus, Marchal, from Egypt and Rhipiphorothrips bicolor (Bagnall) from Ceylon, and Karny and Doctor van Leeuwen Reijnvaan record the following gall-thrips of the suborder Tubulifera from vines in Java; Dolerothrips picticornis, Karny, with an inquiline (Cryptothrips pachypus, Karny) from Vitis papillosa, Gynaikothrips viticola, Karny, from V. lanceolaria anda gall (species unknown) from V. mutabilis.

Observations on an astringent vegetable substance from China

The substance described in this communication was sent to Sir Joseph Banks as a species of galls, used by the Chinese in dyeing black. They have the appearance of irregular vesicles, of a purely astringent flavour, and closely agree with those described by Du Halde under the name of ou poey tse , which are also employed in China as the bases of many astringent medicines. By digestion in cold distilled water, these galls yielded a pale brown infusion, of a highly astringent taste, and furnishing a copious white precipitate with solution of animal jelly: 100 parts thus yielded 78 of soluble matter, which, when obtained by evaporation, was of a brown resinous appearance; and, though only slightly sour to the taste, powerfully reddened the infusion of litmus.

VI. Observations on an astringent vegetable substance from China

The substance described in the following pages was put into my hands for examination by the President, who received it from China, with some others employed in the art of dying; and although the small quantity hitherto sent to this country, has not enabled me to extend my experiments upon its useful applications as far as I could have wished, I trust that its chemical history will be deemed of sufficient impor­tance to interest the Royal Society, and to prove its usefulness as an article of commerce, provided it can be obtained abun­dantly, and at a cheap rate, which I think admits of little doubt. The parcel containing this substance was marked “Oong poey,” a species of galls used in dying black . They have the appearance of irregular vesicles, the coats of which are about one-tenth of an inch thick, of a grey and reddish colour, smooth, and very brittle, and containing in their interior a brown powder, among which insects may be discerned by the microscope. Some of these vesicles were adhering to twigs of the tree, and they appear to be formed upon the younger branches.