Mortality of adult Cryptolestes ferrugineus (Stephens) exposed to changing CO2 concentrations

The concentration of carbon dioxide (CO₂) in a grain bin declines during a fumigation due to leakage, but mortalities of adult Cryptolestes ferrugineus (Stephens) have been obtained and reported at constant CO₂ concentrations. A procedure for predicting the mortality of adult C. ferrugineus exposed to conditions of changing CO₂ concentration was developed. Based on published data, a regression equation was obtained for mortality of adult C. ferrugineus exposed to elevated CO₂ concentrations at a temperature of 25°C. The regression equation was used to calculate a cumulative lethality index. Complete mortality should occur when the cumulative lethality index equals one. Agreement between the observed insect mortality and the corresponding cumulative lethality index was good in five experimental fumigations conducted in sealed, welded-steel hopper bins, but the cumulative lethality index over-predicted the insect mortality in the sixth experimental fumigation.     

Effects of sediment and flow regime on the aquatic insects of a high mountain stream

In 1984, a broad size range of sediment (boulder to sand) was introduced into a high elevation Rocky Mountain stream in southeastern Wyoming, U.S.A. In the spring of 1986, this stream was exposed to a high discharge of 7.5 m³ s⁻¹. From 1985 to 1987 a study was conducted to assess the impact of sediment deposition and flow regime on the aquatic insect community in context of the substrate occurrences of the insect fauna. Using a modified Surber sampler, samples were collected from June through September each year at nine stations which were rated as unimpacted, slightly-impacted, and impacted. The addition of the sediment had minimal effect on the abundance and diversity of aquatic insects. However, high water discharge severely reduced the abundance of aquatic insects and diversity was also negatively impacted. Recovery from these impacts was very rapid. The greatest insect abundance was found in samples taken in gravel and most taxa occurred predominantly on gravel or rubble substrates.     

A case for the standardization of protocols used in screening cowpea, Vigna unguiculata for resistance to Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

Cowpea cultivars Ife Brown, Maiduguri-A, Maiduguri-B and TVu 2027, were screened for resistance to Callosobruchus maculatus (F.) attack using different seed and insect densities. The number of eggs laid on the seeds and most other demographic variables increased with increase in insect density (number of females per 40 seeds). Although the same trend was observed with increase in seed density (seeds per 8 females), this was less predictable. However, the number of eggs per seed decreased significantly as seed density increased, but increased with increase in female density. Adult emergence increased significantly with increase in both insect and seed density while the growth index did not vary. Significantly more eggs were laid on the seeds of TVu 2027 (the resistant control) than on all the other cultivars when 20 or 40 seeds were available to 8 females, or at the lowest insect density (2 females per 40 seeds). However, percentage adult emergence and growth were higher on Ife Brown (susceptible control) than on TVu 2027 and the two Maiduguri cultivars. Measurements of percentage adult emergence and growth index indicated clear cultivar differences at all seed and insect densities. Also, although the loss in weight of seed increased with increase in insect density and decreased significantly with increase in seed density, meaningful differences in resistance among test cultivars were not always apparent at all densities. Based on these findings, we propose using 40 seeds and 2 pairs of adult beetles in screening cowpea for resistance. In addition, we conclude that % adult emergence, growth index and % weight loss are the most reliable indicators for resistance of cowpea to damage by this insect. The need to standardize experimental procedures used for host plant resistance work on storage pests of cowpea is emphasized.     

Correlation of retention times on liquid crystal capillary column with reported vapor pressures and half-lives of compounds used in pheromone formulations

A method has been developed to determine by capillary gas chromatography on liquid crystal stationary phases the relative vapor pressures and half-lives of many compounds used as insect pheromones. This study demonstrated that the retention time of seven acetates on a liquid crystal column (cholesteryl-p-chlorocinnamate) could be correlated closely to the reported vapor pressures of the compounds. For 13 additional pheromonal acetates and alcohols, reported half-lives showed a high degree of correlation with their retention times on the liquid crystal column. Thus chromatography on capillary liquid crystal gas Chromatographie columns appears to be a useful method for determining the relative volatilities of many pheromones to facilitate the development of more precise formulations.     

Changes in Volatile Production During the Course of Fungal Mycelial Interactions Between <Emphasis Type="Italic">Hypholoma fasciculare</Emphasis> and <Emphasis Type="Italic">Resinicium bicolor</Emphasis>

The mycelia of two wood decay basidiomycete fungi were grown opposing each other across a 1-μm pore membrane supported on the surface of malt broth, contained within a sealable reaction vessel. Production of volatiles during the time course of interaction was followed by collecting head space samples by solid phase microextraction (100 μm polydimethylsiloxane fiber) on five occasions over 25 d following coinoculation of the fungi: 1, 3 (i.e., immediately prior to mycelial contact), 9 (1–2 d after initiation of pigment production by Resinicium bicolor), 17, and 25 d. Ten volatiles were produced during interactions that were not detected in single species controls. In general, most (18) fungal volatiles were sesquiterpenes eluted between 12.5 and 21 min, with a further two eluted at 29.1 and 33.9 min; a benzoic acid methyl ester, a benzyl alcohol, and a quinolinium type compound with a distinctive fragmentation pattern at m/z 203, 204, 206, and 207 were also identified; three volatiles with m/z maxima of 163, 159, and 206–208, respectively, remained unidentified. The results are discussed in relation to possible ecological roles of volatiles.     

Formation of Simple Nitriles upon Glucosinolate Hydrolysis Affects Direct and Indirect Defense Against the Specialist Herbivore, <Emphasis Type="Italic">Pieris rapae</Emphasis>

The glucosinolate-myrosinase system, found in plants of the order Brassicales, has long been considered an effective defense system against herbivores. The defensive potential of glucosinolates is mainly due to the products formed after myrosinase-catalyzed hydrolysis upon tissue damage. The most prominent hydrolysis products, the isothiocyanates, are toxic to a wide range of organisms, including herbivorous lepidopterans. In contrast, little is known about the biological activities of alternative hydrolysis products such as simple nitriles and epithionitriles that are formed at the expense of isothiocyanates in the presence of epithiospecifier proteins (ESPs). Here, we used transgenic Arabidopsis thaliana (Brassicaceae) plants overexpressing ESP (35S:ESP plants) to investigate the effects of simple nitriles on direct and indirect defense against the specialist cabbage white butterfly Pieris rapae L. (Lepidoptera, Pieridae). In the 35S:ESP plants, glucosinolates are hydrolyzed mainly to simple nitriles upon tissue disruption, while isothiocyanates are the predominant hydrolysis products in Columbia-0 (Col-0) wild-type plants. The parasitoid Cotesia rubecula (Hymenoptera, Braconidae), a specialist on P. rapae larvae, was significantly more attracted to P. rapae-infested 35S:ESP plants than to P. rapae-infested Col-0 wild-type plants in a wind tunnel setup. Furthermore, female P. rapae butterflies laid more eggs on Col-0 wild-type plants than on 35S:ESP plants when the plants had been damaged previously. However, when given a choice to feed on 35S:ESP or Col-0 plants, caterpillars did not discriminate between the two genotypes. Growth rate and developmental time were not significantly different between caterpillars that were reared on 35S:ESP or Col-0 plants. Thus, the production of simple nitriles instead of isothiocyanates, as catalyzed by ESP, can promote both direct and indirect defense against the specialist herbivore P. rapae.     

Influence of surface characteristics on insect residue adhesion to aircraft leading edge surfaces

Leading edge contamination caused by insects is problematic for modern aircraft utilizing laminar flow aerofoils. The residue of crushed insect bodies adhering to aircraft leading edge surfaces can cause transition of the boundary layer, from laminar to turbulent, resulting in a significant increase in drag and therefore causing an increase in fuel consumption. Consequently, current research is focused on the evaluation of novel low surface energy coatings that will reduce or prevent insect adhesion. Insect residue adhesion tests were conducted on a range of surfaces, from superhydrophobic to hydrophilic. Surface free energy of the investigated substrates was obtained from measured dynamic contact angle values and surface roughness was measured using profilometry. Live insect testing with Drosophila melanogaster and Drosophila hydei was conducted using an insect delivery device inserted into a medium-speed wind tunnel. Tests were conducted at speeds ranging from 90 to 100 m/s (speeds representative of those on take-off and landing of a commercial passenger aircraft). Topography of insect residues was characterized using scanning electron microscopy and confocal laser scanning microscopy. Results obtained indicate that coatings with high surface roughness values and low wettability exhibit good anti-contamination properties.     

Male-Produced Aggregation Pheromones of the Cerambycid Beetles <Emphasis Type="Italic">Xylotrechus colonus</Emphasis> and <Emphasis Type="Italic">Sarosesthes fulminans</Emphasis>

Adults of both sexes of the cerambycid beetles Xylotrechus colonus (F.) and Sarosesthes fulminans (F.) were attracted to odors produced by male conspecifics in olfactometer bioassays. Analyses of headspace volatiles from adults revealed that male X. colonus produced a blend of (R)- and (S)-3-hydroxyhexan-2-one and (2 S,3 S)- and (2R,3R)-2,3-hexanediol, whereas male S. fulminans produced (R)-3-hydroxyhexan-2-one and (2 S,3R)-2,3-hexanediol. All of these compounds were absent in the headspace of females. Two field bioassays were conducted to confirm the biological activity of the synthesized pheromones: (1) enantiomerically enriched pheromone components were tested singly and in species-specific blends and (2) four-component mixture of racemic 3-hydroxyhexan-2-one plus racemic 2-hydroxyhexan-3-one and the four-component blend of the stereoisomers of 2,3-hexanediols were tested separately and as a combined eight-component blend. In these experiments, adult male and female X. colonus were captured in greatest numbers in traps baited with the reconstructed blend of components produced by males, although significant numbers were also captured in traps baited with (R)-3-hydroxyhexan-2-one alone or in blends with other compounds. Too few adult S. fulminans were captured for a statistical comparison among treatments, but all were caught in traps baited with lures containing (R)-3-hydroxyhexan-2-one. In addition to these two species, adults of two other species of cerambycid beetles, for which pheromones had previously been identified, were caught: Neoclytus a. acuminatus (F.) and its congener Neoclytus m. mucronatus (F.). Cross-attraction of beetles to pheromone blends of other species, and to individual pheromone components that are shared by two or more sympatric species, may facilitate location of larval hosts by species that compete for the same host species.     

HarpinEa促进烟草和蕃茄生长和诱导抗虫的信号通路

用HarpinEa对野生型烟草进行了处理,结果发现,HarpinEa能够促进植株的生长(Enhanced Plant Growth,EPG),提高内源SA和乙烯的水平,诱导对烟蚜的抗性(Insect Resistance,IR)。相应地,半定量RT-PCR方法检测表明,harpinEa诱导野生型烟草中水杨酸(salicylic acid,SA)信号传导重要调控基因NPR1、效应基因PR-1a、PR-1b以及乙烯信号通路中的ACS6、ETR1、EIN2等基因的表达。在不积累SA的NahG烟草上,harpinEa诱导EPG和IR的能力不受影响,但RP-1a、PR-1b基因的表达水平显著降低。这些结果说明,harpinEa诱导EPG和IR过程与SA信号通路无关,而可能受乙烯信号调节。