Specialisation of bacterial endosymbionts that protect aphids from parasitoids

1. Infection by the bacterial endosymbiont Hamiltonella defensa is capable of protecting the pea aphid from parasitism by Aphidius ervi and the black bean aphid from parasitism by Lysiphlebus fabarum. Here we investigate protection of a third aphid species, the cowpea aphid, Aphis craccivora, from four parasitoid species: Binodoxys communis, B. koreanus, Lysiphlebus orientalis, and Aphidius colemani. 2. We compared parasitism of A. craccivora lines that were either infected with, or cured of H. defensa separately for the four parasitoid species. Infection by H. defensa almost completely eliminated parasitism of A. craccivora by B. communis and B. koreanus, but had no effect on parasitism by L. orientalis and A. colemani. 3. This indicates at least genus‐level specificity of protective effects by H. defensa and we discuss implications of our findings on the known world‐wide distribution of this host/symbiont interaction.     

On the use of DNA sequences for determining the species limits of a polymorphic new species in the stink bug genus Halys (Heteroptera: Pentatomidae) from Pakistan

Abstract.  We describe a new species of Halys Fabricius (Pentatomidae: Pentatominae: Halyini) based on morphological and DNA sequence data, and demonstrate the value of DNA sequences for taxonomic problems that are difficult to resolve on the basis of morphology alone. Halys sindillus Memon, Meier & Manan, sp.n. varies with regard to characters that are usually constant within the genus (spermathecal bulb of females; blade of male clasper; ratio between the second and third antennomeres; length of labium). The surprising levels of variation raised the question as to how many species were represented in three series of specimens from Pakistan. Because the morphological variability was largely continuous, we hypothesized the presence of one new species, and confirm this result here using sequence data from two mitochondrial markers. The data reveal very little molecular variation within the newly described species (COI: 730 bp: 0–0.16%; COI/tRNA_Leu/COII: 563 bp: 0–0.36%), that is, morphology and DNA sequences show very different patterns of variability. The new species is compared with the closely related Halys sulcatus (Thunberg) whose sequences are distinctly different and whose spermathecal bulbs are largely invariable (I: 2.87–3.28%; II: 2.13–2.49%). We discuss the shortcomings of mitochondrial data in taxonomy and compare the genetic distances in Halys with frequency distributions of intra- and interspecific distances obtained for all 878 Hemiptera COI sequences in GenBank. We conclude that the observed distances for Halys are consistent with our taxonomic conclusions, thus demonstrating the usefulness of DNA sequences for Halys taxonomy. However, the observed overlap between intra- and interspecific sequence variability in Hemiptera is so wide that it questions the feasibility of approaches to taxonomy based predominantly on DNA sequences (e.g. DNA taxonomy, DNA barcoding).     

Efficacy of carboxin and heat treatment for controlling the growth of Sclerotium rolfsii during culture of the mushroom Pleurotus flabellatus

Soaking paddy straw for 18 h in a carboxin suspension in water (5 mg a.i./l) effectively controlled the growth of Sclerotium rolfsii occurring as a natural contaminant in paddy straw, during culture of the mushroom Pleurotus flabellatus. Carboxin at this concentration delayed sporophore formation by 2–3 days, but did not affect total yield. No detectable carboxin residues were found in the mushrooms grown on the treated paddy straw. Treatment of the paddy straw with hot water at 60°C for 10 min completely controlled the contaminant without affecting mushroom growth and yield; but 20 mm treatments with hot air at 60°C or heating with the steam to 75–80°C did not control S. rolfsii.