Bottom-up trophic cascades caused by moose browsing on a natural enemy of a galling insect on balsam fir

To elucidate the impact of browsing by moose on the indigenous insect community, we investigated the abundance of a specialist insect herbivore (galler; Paradiplosis tumifex) and its natural enemy (inquiline; Dasineura balsamicola) on balsam fir saplings in the field using exclosures in Newfoundland, Canada. The number of current-year shoots on each sapling, but not the density of balsam fir saplings, was significantly higher inside exclosures, where moose had been excluded for 9–12 years, than outside exclosures. Current-year shoots were longer and contained more, but smaller, needles inside than outside exclosures. Moose browsing had a negative impact on the abundance of both the galler and its natural enemy. Gall density was 85.6% and 60.4% lower in 2006 and 2007, respectively, outside than inside exclosures. Similarly, the attack rate of D. balsamicola was 76.5% lower outside than inside exclosures in 2007. The apparent survival rate of P. tumifex larvae was similar outside and inside exclosures due to higher rates of unexplained mortality in galls outside exclosures. Survival of P. tumifex larvae was positively related to shoot length and inversely related to gall density. Only gall density was negatively related to D. balsamicola survival. Our results demonstrate that a large mammal can cause strong bottom-up trophic cascades.     

Competition and niche relationships among Eriosoma aphids occurring on the Japanese elm

Summary Galls of more than one species of Eriosoma (Aphidoidea) are found sympatrically even on single trees. Incipient galls are frequently invaded by conspecific and/or allospecific fundatrices. Eriosoma yangi, a component of Eriosoma communities, does not form its own galls but obligatorily usurps those of other species. There were interspecific differences in the timing of gall formation and the spatial distribution of galls. Nevertheless E. yangi fundatrices randomly invaded galls of any Eriosoma species and occupied 33%–41% of galls of each species. When more than one E. yangi fundatrix invaded one gall, mortal fights sometimes occurred. Fundatrices of gall-forming species also seemed to take part in such fights. Fundatrices of gall-forming species had a significant tendency to invade galls of a particular species. However, taking account of niche differences among species, invaders apparently entered available galls at random. Apparently E. yangi fundatrices search an extensive range within a branch for galls, while invaders of gall-forming species search a restricted speciesspecific range. The niche relation of gall-forming species in a northern community containing E. yangi were compared with those in a southern community lacking E. yangi. No obvious difference was found between them, suggesting that parasitism by E. yangi has not influenced niche divergence within the Eriosoma community.     

The role of olfactory cues in the sequential radiation of a gall‐boring beetle,Mordellistena convicta

1. Herbivorous insects often have close associations with specific host plants, and their preferences for mating and ovipositing on a specific host‐plant species can reproductively isolate populations, facilitating ecological speciation. Volatile emissions from host plants can play a major role in assisting herbivores to locate their natal host plants and thus facilitate assortative mating and host‐specific oviposition. 2. The present study investigated the role of host‐plant volatiles in host fidelity and oviposition preference of the gall‐boring, inquiline beetle, Mordellistena convicta LeConte (Coleoptera: Mordellidae), using Y‐tube olfactometers. Previous studies suggest that the gall‐boring beetle is undergoing sequential host‐associated divergence by utilising the resources that are created by the diverging populations of the gall fly, Eurosta solidaginis Fitch (Diptera: Tephritidae), which induces galls on the stems of goldenrods including Solidago altissima L. (Asteraceae) and Solidago gigantea Ait. 3. Our results show that M. convicta adults are attracted to galls on their natal host plant, avoid the alternate host galls, and do not respond to volatile emissions from their host‐plant stems. 4. These findings suggest that the gall‐boring beetles can orient to the volatile chemicals from host galls, and that beetles can use them to identify suitable sites for mating and/or oviposition. Host‐associated mating and oviposition likely play a role in the sequential radiation of the gall‐boring beetle.     

Trichopsomyia ochrozona (Stackelberg, 1952) (Diptera: Syrphidae) recorded from Iran for the first time with a key to the West Palaearctic Trichopsomyia Williston, 1888 species

The hoverfly Trichopsomyia ochrozona (Stackelberg, 1952) (Diptera: Syrphidae) is recorded for the first time from Iran. An illustrated key to the West Palaearctic species of Trichopsomyia is presented. Illustrations of the puparium of Trichopsomyia joratensis Goeldin, 1997 and the larva and puparium of T. ochrozona are given and their larval and adult habitats are described. A short discussion is given on the known larval habitat of other West Palaearctic Trichopsomyia species. Some of the synonyms have been evaluated and Pipiza melancholica Meigen, 1822 is withdrawn from synonymy of Trichopsomyia flavitarsis (Meigen, 1822) and is considered as a junior synonym of Musca viduata Linnaeus, 1758 syn. nov.     

Intra-specific phenotypic variations in Lantana camara leaves affect host selection by the gall maker Aceria lantanae

Leaf galls induced by Aceria lantanae occur in distinct populations of Lantana camara, exclusively on individuals with red flowers. Anatomical, histochemical and phytochemical analyses of leaves were performed to determine characteristics related to host selection among individuals with red (RF), pink (PF) and white flowers (WF). The host plants (RF) presented amphistomatic leaves, higher stomatal index value, and non-glandular trichomes significantly longer and less dense when compared to non host plants. Morphological features of RF indicated a more propitious micro-habitat for A. lantanae, with physical protection against its natural enemies. The monoterpenes limonene and eucalyptol, and the sesquiterpene α-caryophyllene were detected only in non host plants. These differences in volatiles composition might be related to the selection of RF as host plants, and chemical repellence in PF and WF. Our analysis revealed intra-specific morphological and chemical variations possibly related to host selection by A. lantanae.     

Identification of the bona fide DHDPS from a common plant pathogen

Agrobacterium tumefaciens is a Gram‐negative soil‐borne bacterium that causes Crown Gall disease in many economically important crops. The absence of a suitable chemical treatment means there is a need to discover new anti‐Crown Gall agents and also characterize bona fide drug targets. One such target is dihydrodipicolinate synthase (DHDPS), a homo‐tetrameric enzyme that catalyzes the committed step in the metabolic pathway yielding meso‐diaminopimelate and lysine. Interestingly, there are 10 putative DHDPS genes annotated in the A. tumefaciens genome, including three whose structures have recently been determined (PDB IDs: 3B4U, 2HMC, and 2R8W). However, we show using quantitative enzyme kinetic assays that nine of the 10 dapA gene products, including 3B4U, 2HMC, and 2R8W, lack DHDPS function in vitro. A sequence alignment showed that the product of the dapA7 gene contains all of the conserved residues known to be important for DHDPS catalysis and allostery. This gene was cloned and the recombinant product expressed and purified. Our studies show that the purified enzyme (i) possesses DHDPS enzyme activity, (ii) is allosterically inhibited by lysine, and (iii) adopts the canonical homo‐tetrameric structure in both solution and the crystal state. This study describes for the first time the structure, function and allostery of the bona fide DHDPS from A. tumefaciens, which offers insight into the rational design of pesticide agents for combating Crown Gall disease. Proteins 2014; 82:1869–1883. © 2014 Wiley Periodicals, Inc.