Summary 1 We tested four hypotheses concerning the variation in species richness of gall-inducing insects (GII) in plant communities. We sampled deciduous and riparian habitats in a tropical dry forest at Chamela-Cuixmala Biosphere Reserve in western Mexico, that differ in phenology and moisture availability. 2 GII species richness might be expected to increase with the richness of host plant species, with life-form complexity of host plants (trees to shrubs, herbs and climbers), with host age or with host plant density. 3 We found 172 plant species, of which more were present in deciduous than in riparian habitats, but 34 (19.8%) occurred in both. A different GII species colonized each of 39 host species. Most GII species (69.2%) were gall midges (Cecidomyiidae). 4 We found a significant positive correlation between GII species richness and plant species richness in both deciduous and riparian habitats, suggesting that radiation of GII species may be associated with plant species richness. 5 Most of the GII species occurred on trees or shrubs rather than herbs or climbers, consistent with structural complexity providing more colonization sites. 6 The frequency of GII was greater on saplings, which may have more undifferentiated meristems susceptible to gall induction. 7 Both the frequency and intensity of damage by galls were greater in deciduous than riparian habitats, indicating a preference of GII species for plants in the more xeric habitat. 8 The frequency of GII increased with host plant density in only 18 (46.2%) of GII species. 9 Richness of GII depends on all proposed factors, although density is often the least important. The effects of host richness and host age are similar to those seen in many specialist folivorous insects, although the unique association of a single insect with a single host is only seen for GII.

http://ww2.oikos.unam.mx/CIEco/polinizacion/files/Cuevas,Quesada,Hanson,Dirzo&Oyama2004(1).pdf

Diversity of gall-inducing insects in a Mexican tropical dry forest: the importance of plant species richness, life-forms, host plant age and plant density

Five hypotheses were tested to explain the pattern of galling insect species richness in four neotropical savanna physiognomies, 'canga ', 'campo sujo', 'cerrado' s. st., and 'cerradao', that occur in Minas Gerais, southeastern Brazil. We found 125 species of galling insects on 80 host plant species. The increase of plant species richness explained 35% of the variation in galling insect richness, corroborating the plant species richness hypothesis. Most of the galling species occurred on trees, followed by shrubs, and herbs. However, the difference in mean number of galls was only statistically significant between herbs and trees, corroborating partially the plant structural complexity hypothesis. A significant relationship was observed between galling species richness and density of herbs, and shrubs, corroborating partially the resource concentration hypothesis. Galling insect richness showed a negative correlation with magnesium, potassium, and zinc on soil, corroborating the soil fertility hypothesis. The content of magnesium, potassium, iron and CTC (T) explained 72% of the variation in galling insect richness. Plant family size positively influenced galling insect richness, corroborating the plant family size hypothesis. Overall, the results corroborate the hypothesis that predicts that habitat stress is the main factor generating the patterns of galling insect richness in Brazilian savannas.

http://labs.icb.ufmg.br/leeb/publicacoes/2001_alvim_&_fernandes.pdf

Biodiversity of galling insects: historical, community and habitat effects in four neotropical savannas

Despite the speciose fauna of gall-inducing insects in the Neotropical region, little is known about their taxonomy. On the other hand, gall morphotypes associated with host species have been extensively used as a surrogate of the inducer species worldwide. This study reviewed the described gall midges and their galls to test the generalization on the use of gall morphotypes as surrogates of gall midge species in the Brazilian fauna. We compiled taxonomic and biological data for 196 gall midge species recorded on 128 host plant species. Ninety two percent of those species were monophagous, inducing galls on a single host plant species, whereas only 5.6% species were oligophagous, inducing galls on more than one congeneric host plant species. Only four species induced galls on more than one host plant genus. We conclude that gall morphotypes associated with information on the host plant species and attacked organs are reliable surrogates of the gall-inducing species.

https://www.scielo.br/pdf/rbent/v53n3/10.pdf

Are gall midge species (Diptera, Cecidomyiidae) host-plant specialists?

One hundred thirty-seven morphotypes of insect galls were found on 73 plant species (47 genera and 30 families) in Serra de Sao Jose, in Tiradentes, MG, Brazil. Fabaceae, Myrtaceae, Asteraceae, and Melastomataceae were the plant families that supported most of the galls (49.6% of the total). Galls were mostly found on leaves and stems (66.4% and 25.5%, respectively). Galls were induced by Diptera, Lepidoptera, Coleoptera, Hemiptera (Sternorrhyncha), Hymenoptera, and Thysanoptera. The majority of them (73.7%) were induced by gall midges (Cecidomyiidae: Diptera). Besides the gall inducers, other insects found associated with the galls were parasitoids (Hymenoptera), inquilines (Coleoptera, Lepidoptera, Diptera, and Hemiptera), and predators (Diptera).

/pdf/insect-galls-from-serra-de-sao-jose-tiradentes-mg-brazil-4y9zjtiiuq.pdf

Insect galls from Serra de São José (Tiradentes, MG, Brazil)

1. Hypersensitive reaction is an important type of induced defence by which the plant elicits a defence response to pathogens and insects. Hypersensitive reaction has been argued to be the most common plant resistance mechanism against insect herbivores that have intimate associations with their host plants. 2. The work reported here attempted to establish how important and widespread hypersensitive reaction might be against gall-forming species across host taxa. 3. Hypersensitive reaction was the most important mortality factor against gall formation across host plant taxa in seven out of eight cases. 4. The number of insect galls correlated with the size of the leaves but module (leaf) size was a weak factor influencing the incidence of plant hypersensitive reaction to galling. 5. Insect galls and hypersensitive reactions occurred in genetically distant as well as geographically widespread host plant taxa.

The occurrence and effectiveness of hypersensitive reaction against galling herbivores across host taxa

During the past decade many studies have been carried out on the distribution of gall- forming insects along gradients of temperature, humidity, elevation, and latitude. Over 300 localities have already been sampled around the world representing numerous vegetation types such as shrubland, desert, chaparral, cerrado, savanna, tropical rain forest, taiga, tundra, and pine forest using sound and field-tested methods. The peak of species richness has been found at low and dry elevations, in areas of sclerophyllous vegetation. Nevertheless, gallers are most species rich and abundant in dl'\ kbitats. Among alI habitats studied, the Brazilian cerrado has the richest fauna of galling insects. At 900 m altitude in a cerrado area at the base of the Serra do Cipo in south-east Brazil, we found the richest galling insect fauna (forty- six species in a census of forty-five trees, 100 shrubs and 1000 herbs per site). At this elevation, the soil is rocky and sandy, nutrient-poor, and the vegetation is dominated by woody, sclerophyllous plants, with few herbs. The plant most attacked was Baccharis concinna (Asteraceae) which supported fifteen galling species.

https://www.jstor.org/stable/info/2999724

Anoela Christina F. Lara

Papers

The highest diversity of galling insects: Serra do Cipo,