Identification and bioactivity of alarm pheromone in the western flower thrips,Frankliniella occidentalis.

Analysis by gas chromatography (GC) and GC-mass spectroscopy disclosed that droplets of anal fluid produced by second-instar western flower thrips,Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), contain a two-component alarm pheromone, comprised of decyl acetate and dodecyl acetate, in a molar ratio of approximately 1.5∶1. Both nymphs and adults responded to the pheromone by walking away from the source. The synthetic pheromone was active at a concentration of 1.0 ng, and the proportions of insects responding to the pheromone, but not the distances moved, increased with increasing dose. Each component was active alone, although at low doses, the response to decyl acetate was less than to either dodecyl acetate or the blend. The pheromone also induced some second instars to drop from leaves and reduced oviposition by adult females in both two-choice and nochoice experiments. Because the response of western flower thrips to the alarm pheromone is relatively weak, the potential for its use in pest management is limited, unless it is used in conjunction with other control measures.

Molecular cloning and nucleotide sequence of another variant of the Escherichia coli Shiga-like toxin II family.

Escherichia coli strain H.I.8 (O128:B12) produces low levels of a Shiga-like toxin (SLT) which we have called SLTIIva because of its close relationship with SLTIIv. The Vero cell cytotoxicity of SLTIIva is neutralized by antisera against SLTII and SLTIIv but not by antisera against SLTI. These data indicate that the SLT of strain H.I.8 is a member of the SLTII family. Since SLTIIva shares with SLTIIv the property of having low cytotoxicity to HeLa cells compared with Vero cells, it is appropriate to consider both toxins as variants of SLTII. SLTIIva differs from SLTIIv in that it is more heat-stable. Further, SLTIIv-producing strains of E. coli have only been isolated from pigs while the SLTIIva-producing E. coli strain examined in this study was isolated from a human infant with diarrhoea. The genes for this SLT were cloned from a cosmid library of total cellular DNA by screening recombinants for Vero cell toxicity and with a DNA probe derived from SLTIIv structural genes. Nucleotide sequence analysis was performed on a 2.0 kb AvaII-HincII fragment which encodes the toxin gene. The nucleotide sequence data confirm the close relationship between SLTIIva and SLTIIv: they have 98% nucleotide sequence homology in the B subunit gene and 70.6% homology in the A subunit gene. Comparison of DNA sequences indicated that SLTIIva was most closely related to SLTIIv, closely related to SLTII and less closely related to SLTI.