Responses of insect herbivores to sharing a host plant with a hemiparasite: impacts on preference and performance differ with feeding guild

1. Root hemiparasites are common components of many ecosystems and can affect both the biomass and the nutritional quality of the plants they infect. The consequences of these modifications for the preference and performance of three herbivore feeding guilds sharing a host with the hemi‐parasite were examined. 2. It was predicted that as the hemiparasite increased in biomass its impact on the host would increase, as would the indirect impacts on the herbivores. It was also predicted that herbivores from different feeding guilds would respond differently to the presence of the hemiparasite, reflecting the extent to which they utilise resources disrupted by the parasite and hence are in competition with it. 3. The preference and performance of phloem‐feeding aphids, xylem‐feeding spittle bugs, and leaf‐feeding grasshoppers were measured on the host grass species, Holcus lanatus L. (Poaceae), with and without attachment from the hemi‐parasite, Rhinanthus minor L. (Orobanchaceae). 4. The effects of R. minor on the host were dependent on the hemiparasite's stage of growth, being most pronounced when it was at peak biomass. At this stage it caused a significant reduction in the biomass, water content, and total nitrogen content of the host plants. 5. Overall, herbivores benefited from, or preferred, shared host plants more than uninfected plants. The aphid benefited from sharing a host with R. minor, showing increased population growth on, and preference for, parasitised plants. The spittle bug also showed a preference for parasitised plants. The grasshopper, Chorthippus brunneus Thunberg (Orthoptera: Acrididae), did not show a preference for, or a performance response to, parasitised hosts, but it consumed significantly more plant material when caged on parasitised plants. 6. These data support the prediction that invertebrate herbivores responded to changes in host plant traits driven by the hemiparasite, and strongly suggest that these indirect interactions could impact on population and community processes within natural communities.     

Relationship between reflectance spectra of host plant surfaces and visual detection of host fruit by Rhagoletis pomonella flies

ABSTRACT. Within host trees, male and female Rhagoletis pomonella (Walsh) flies locate visually individual fruit of apple and hawthorn, which are sites of mating and oviposition. By measuring the diffuse reflectance spectra of both fruit and foliage and by using artificially pigmented natural fruit and artificial fruit mimics, we show that fruit hue is not as important in R. pomonella fruit detection as is intensity contrast of dark fruit against a bright background of light transmitted through foliage or skylight. In discussing the fruit detection system of R. pomonella , we compare it to that of vertebrate fruit consumers and seed dispersers.     

Purification and serology of the W strain of cucumber mosaic virus

During studies on the purification of cucumber mosaic virus (strain W) it was found that preparations were most infective and stable when made from tobacco leaves (10–12 days after inoculation) homogenized in phosphate buffer containing EDTA and thioglycollic acid and clarified with diethyl ether. The preparations were further purified by centrifugation in sucrose density gradients containing EDTA at pH 9.0 and were then stable at 2 °C for > 100 days. When mounted in neutralized ammonium molybdate they were shown to consist of predominantly intact particles. In tube and ring precipitin tests and in agar gel-diffusion tests, specific precipitation with homologous antiserum occurred only in media containing alkaline adjusted solutions (ammonium molybdate and dipotassium hydrogen phosphate).     

Regeneration of Rapid Escape Reflex Pathways in Earthworms

SYNOPSIS. The medial and lateral giant nerve fibers in the earthworm,Eisenia foetida, regenerate cell-specific connections and recoverthrough-conduction capabilities in as little as 1–2 daysafter ventral nerve cord (VNC) transection Similar cell-specificreconnections between giant fibers occur approximately 4–10days after grafting together two posterior pieces of worms ortransplanting lengths of VNC from donor to recipient worms fromwhich a comparable length of VNC has been removed In the lattercase, touch-sensory and giant motor neurons within the transplantedVNC also regenerate, leading to restoration of escape reflexfunction in segments receiving the transplant Results from heterotopicallytransplanted VNC indicate that both central and peripheral regenerationis cell-specific, but specificity is sufficiently broad to includesegmentally homologous target cells from body regions otherthan those of the transplant origin E. foetida and related speciesmay be useful for studying the extent to which differentiatednervous systems, composed of serially homologous neuronal networks,can be remodelled by experimental manipulations such as graftsand transplants.     

THE BIOLOGY AND FUNCTIONAL MORPHOLOGY OF MYOCHAMA ANOMIOIDES STUTCHBURY, 1830 (BIVALVIA: ANOMALODESMATA: PANDOROIDEA), WITH REFERENCE TO CEMENTATION

The small, exclusively Australasian, anomalodesmatan familyMychamidae comprises only two genera; the shallow-burrowingMyadora and the cementing Myochama. This paper describes theanatomy ad cementing behaviour of Myochama anomioides and drawscomparisons with Myadora. The anatomy of Myochama anomioides is little different fromthat previously described for Myadora, except that they aremirror images. Valve inequality is not reflected in the organsof the mantle cavity in either taxon. Such differences whichare present, for example the reduction of the foot in Myochama,mostly relate to the adoption of a sessile habit. There arefew idfferences in mantle folds of the cementing and non-cementinggenus, except that in M. anomioides the right mantle fold, whichsecretes the cemented valve, is thicker and less well-developedthan the left. During the cementation process, the periostracumsecreted by the right fold is thinner and has a quilted appearance. Individuals of Myochama anomioides cement by their right valveonce they have recahed a size of 1.2—3.9 mm. They appear tohave a preference for attaching to the posterior portions ofa diversity of living, shallow infaunal bivalves. The pronounced stereotypicorientation they adopt suggests that these hosts are most oftenalive at the time of colonization and that the mychamids benefit fromthe relationship. The relationship, however, is not obligate. Theyare capable of attaching to other shelly or rock debris, butdo so at a lager size, presumaby whe the preferred substrataare not available. The thin layer of extra-periostracal cementlacks the calcereous crystalline nature of oyster cement, insteadof being largely composed of organic material. This cement ispresumably secreted by glands within the mantle, but these havenot been identified. Indeed, the mantle lacks arenophilic glandswhich might have been thought a suitable candidate for supplyingcement. (Received 14 December 1999; accepted 4 February 2000)     

Why Grow Cash Crops? Subsistence Farming and Crop Commercialization in the Kolli Hills, South India

In this article, I provide an analysis of local decision making surrounding crop commercialization in the Kolli Hills, South India. I argue that in the context of changes in the physical environment, cultivating tapioca (cassava) as a cash crop is a conscious decision made by small farmers based on their perceptions of environmental insecurity. Farmers understand market integration as key to coping with external, uncontrollable changes and to fulfilling household and community aspirations. Decisions to cultivate tapioca have contributed to aspects of community development and increasing political agency on the part of villagers.     

Acetone Production as a Result of Sodium Bisulfate Preservation of Soil Samples

The use of sodium bisulfate for field preservation of soil samples collected for the analysis of volatile organics (VOCs) can result in the formation of acetone. The work was performed at Camp Edwards, Massachusetts, as part of a multi-year investigation of the effects of training activities on the local environment. Preservation with sodium bisulfate was initiated in 1999 under regulatory mandate. The frequency of acetone detection and the quantities reported increased immediately thereafter. Correlation of duplicate sample results and a side-by-side comparison of six sample handling methods involving two analytical laboratories suggest the interaction of sodium bisulfate with naturally occurring organic matter in samples from Camp Edwards cause the formation of acetone. The data also indicate that a higher content of natural organic matter results in a greater production of acetone, and more acetone is formed the longer the sodium bisulfate is in contact with the soil.     

The incidence of gangrene of potatoes caused by Photna exigua in relation to handling and storage

Damage to potatoes during harvesting and grading increases the incidence of gangrene. Among the factors involved, the condition of the soil and the type of damage caused by the implements may be of importance. Gangrene is most evident in tubers which have been stored cold or moved when cold; warmer storage at some stage usually reduces its incidence and severity. Seasonal incidence is not directly related to rainfall but is determined by factors affecting ripening and destruction of haulm, moisture status of soils at harvest, susceptibility to damage, and exposure during storage and in transit.