Role of galeal sensilla in host recognition and feeding behaviour of the Colorado potato beetle

Abstract. Close-range interactions with plants and the early stages of feeding behaviour of adult Colorado potato beetles, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), were studied using beetles with and without various mouthpart sensilla. Representative host, potato (Solarium tuberosum) , and non-host, tomato (Lycopersicon esculentum) , leaves were treated very differently by beetles with and without their galeal or palpal sensilla. Galeal sensilla were particularly important for beetles interacting with these two plants. Compared with normal beetles, fewer beetles without galeae fed on potato leaves, and those that did feed spent more time assessing the plant and took more bites before feeding. On tomtato, more beetles without galeae fed, spent less time assessing the plant and took fewer bites before feeding. Beetles without galeae also had lower consumption rates on potato and higher consumption rates on tomato. Beetles were very reluctant to feed on tomato if the galeae were present so removal of maxillary sensilla was studied only on potato. Without the sensilla on the maxillary palpi only the time between first touch and first bite was affected (lengthened). The importance of galeal sensilla in host recognition by this species and the implications for chemosensory studies are discussed here and in a companion paper.     

A comparison of the correcting behaviour exhibited by two milkweed bugs, Oncopeltus fasciatus and Lygaeus kalmii

ABSTRACT. Adults and nymphs of two species of milkweed bugs, Oncopeltus fasciatus and Lygaeus kalmii , were studied with respect to their optomotor responses, as exhibited by the laboratory phenomenon of correcting behaviour on mazes. It was found that the O.fasciatus nymphs failed to correct while the other three groups all exhibited correcting behaviour. The differences in correcting behaviour were attributed to differences in such ecological variables as degree of socialness, nature of food source, and foraging strategies.     

Components of tomato leaf homogenate suppress responses from galeal chemoreceptors of the adult Colorado potato beetle

Abstract. Effects of both potato and tomato residues (obtained following vacuum distillation of leaf homogenate) on responses to galeal chemosensilla of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to trans- 2-hexenol, one of the leaf alcohols that stimulate a highly uniform gustatory response in this system, are described. Tomato residue suppressed the response to hexenol in a dose-dependent manner whereas potato residue had no effect. Suppression was detectable 0.3 s after the first application began and the normal response to hexenol recovered within 2 min. Alkaloids from potato (solanine) and tomato (tomarine) also suppressed the response to hexenol but the characteristic actions of these compounds could not fully explain the activity of the tomato residue. Constituents of tomato residue, in addition to tomatine, are probably responsible for its significant effect on galeal chemosensory responses and these probably comprise a complex set of active compounds that allow the Colorado potato beetle to distinguish potato and tomato leaves.     

An Ultrastructural Comparison of Euglena gracilis Klebs, Bleached Euglena and Astasia longa Pringsheim

SYNOPSIS. Some of the cytologic features of Euglena gracilis Klebs, Euglena gracilis var. bacillaris Gross (colorless), and Astasia longa Pringsheim were compared in an electron-microscope study. E. gracilis was readily differentiated from the colorless forms by the presence of chloroplasts. The 2 colorless forms were structurally similar; however, it was possible to differentiate bleached Euglena from Astasia longa by the presence of irregular plate-like aggregates of paramylum in the former; similar forms of paramylum were not seen in chloroplast-containing E. gracilis or in A. longa .     

Embryo nutrition in parthenogenetic viviparous aphids

Abstract The reproductive potential of aphids is well known and is the basis for their considerable economic importance. Reproductive output is ultimately fuelled by nutrients derived from the maternal haemolymph but mechanisms of embryo provisioning are poorly understood. Here, the morphological features of the reproductive system that have a critical role in nutrient transfer are reviewed, and the contribution of the symbiotic bacteria Buchnera to embryo nutrition is considered. In particular, the importance of the ovariole sheath as the selective barrier for nutrient exchange between the maternal haemolymph and the embryo tissue is highlighted, along with the division of the bacterial population into distinct embryo and maternal compartments. Three models are proposed to explain the relative contribution of the symbiotic compartments to embryo nutrition and the review concludes by highlighting experimental studies that have directly examined nutrient transfer from the maternal haemolymph to the developing embryos.     

Genetic structure and population dynamics of a heteroecious plant pathogen Melampsora larici-epitea in short-rotation coppice willow plantations

Complex life strategies are common among plant pathogens belonging to rust fungi ( Uredinales ). The heteroecious willow rust Melampsora larici-epitea produces five spore stages and alternates on larch ( Larix ). To shed light on the epidemiology of this pathogen, amplified fragment length polymorphisms (AFLPs) were used to determine the genetic diversity and genetic structure of rust samples collected from coppice willow ( Salix ) plantations at three UK sites (LA, CA and MC) over three sampling dates (September 2000, July 2001 and September 2001). Of the total of 819 isolates, 465 were unique AFLP phenotypes and there was a shift in genotype diversity between the two seasons (0.67 in 2000 and 0.87–0.89 in 2001). No phenotypes were common between the two seasons within a site, suggesting that the rust did not overwinter as an asexual stage within plantations. A temporal analysis detected large amounts of genetic drift ( F _S = 0.15–0.26) between the two seasons and very small effective population sizes ( N _e  =  2–3) within sites. These results all point to a new colonization of the plantations by the rust in the second season (2001). The F _ST-analogue values were Φ_CT = 0.121, Weir and Cockerham's θ = 0.086 and the Bayesian estimate θ^B = 0.087–0.096. The results suggest that the sources of inoculum were somewhat localized and the same sources were mainly responsible for disease epidemics in LA and CA over the two seasons. The relatively low F _ST-values among sites (0.055–0.13) suggest the existence of significant gene flow among the three sampled sites.     

A novel parasitoid and a declining butterfly: cause or coincidence?

1. The small tortoiseshell butterfly (Aglais urticae L.) is considered to be a widespread and abundant generalist species in Northern Europe. However, it declined sharply in the U.K. between 2003 and 2008, coinciding with the arrival and spread of a parasitoid, Sturmia bella Meig. (Diptera: Tachinidae), which specialises on nymphalid butterflies. 2. Whether the decline in A. urticae is associated with the arrival of S. bella was investigated using data from a large‐scale butterfly monitoring scheme, and by collecting larvae to assess parasitoid incidence and parasitism frequency. Similar data were compiled for a related butterfly (Inachis io) which is also parasitised by S. bella but which is not declining. 3. Sturmia bella was recorded as far north as north Lincolnshire (53.53°N). Aglais urticae has declined significantly to the south of this latitude, but not to the north. 4. Sturmia bella was present in 26% and 15% of the larval groups of A. urticae and I. io, respectively, and now kills more individuals of A. urticae (but not I. io) than any native parasitoid. 5. Survival was 25–48% lower in batches of A. urticae larvae where S. bella was present, indicating that S. bella causes host mortality in addition to that caused by native parasitoids. 6. Our results suggest that S. bella may be playing a role in the recent decline of A. urticae. However, further research is needed to establish its effects relative to other potential drivers of trends in the abundance of this butterfly.