Aerosolized Insecticide Spray Distributions and Relationships to Efficacy against Stored Product Pests.

Aerosol insecticides are widely used in stored product insect management programs in food facilities. Previous research has shown spatial variation in aerosol efficacy within facilities, but information on how spatial patterns of aerosol droplet concentration, size distribution, dispersal, and deposition contribute to this variation in efficacy is limited. This study involved two aerosol application systems: a high-pressure cylinder containing TurboCide Py-75® with pyriproxyfen IGR (ChemTech Ltd., Des Moines, IA, USA) and a hand-held fogger containing Pyrocide 100® (MGK, Minneapolis, MN, USA) with Diacon II which contains methoprene IGR (Wellmark, Schaumburg, IL, USA). These systems were used at single or multiple application locations. The spray trials were conducted in a small-scale flour mill, Hall Ross Flour Mill (Kansas State University, Manhattan, KS, USA). The droplet size distributions were monitored at multiple positions within the room using nine aerodynamic particle sizing (APS, TSI Incorp, Shoreview, MN, USA) instruments. The APS data collected over the treatment period were summarized into a mass concentration index (MCI), which ranged from 155 to 2549 mg/m3 for Turbocide and 235-5658 mg/m3 for Pyrocide. A second parameter called the Deposition Index (Dep.Idx) was derived to estimate potential insecticide depositions on the floor and has units of g/m2. The Dep.Idx was below 5.3 g/m2 for most Turbocide applications, while the Dep.Idx was below 8.4 g/m2 for most Pyrocide applications. The MCI and Dep.Idx values varied with APS position and spray application location, with proximity to the aerosol application location and degree of obstruction between the release point and APS position contributing to this variation. We assessed the relationship between aerosol droplet parameters and insect efficacy using Tribolium confusum Jacqueline DuVal, the confused flour beetle. The adults were treated directly, while the larvae were treated two weeks later during the residual test (previously published). For Turbocide, efficacy against adults increased with MCI and Dep.Idx values, but for residual efficacy of the IGR, efficacy was high at all aerosol droplet values, so no relationship was apparent. In contrast, the relationship between Pyrocide deposition and adult insect efficacy was highly variable. But with larval insect efficacy, residual larvae control was directly related to increases in Pyrocide MCI and Dep.Idx. Contour plots of Dep.Idx values were developed, which could be used to predict areas of the mill that are not receiving an adequate application rate, and this could be used to develop more effective application strategies for aerosol insecticides in food facilities.

Biochemical characterization of chitin synthase activity and inhibition in the African malaria mosquito, Anopheles gambiae.

Chitin synthase (CHS) is an important enzyme catalyzing the formation of chitin polymers in all chitin containing organisms and a potential target site for insect pest control. However, our understanding of biochemical properties of insect CHSs has been very limited. We here report enzymatic and inhibitory properties of CHS prepared from the African malaria mosquito, Anopheles gambiae. Our study, which represents the first time to use a nonradioactive method to assay CHS activity in an insect species, determined the optimal conditions for measuring the enzyme activity, including pH, temperature, and concentrations of the substrate uridine diphosphate N-acetyl-d-glucosamine (UDP-GlcNAc) and Mg(++) . The optimal pH was about 6.5-7.0, and the highest activity was detected at temperatures between 37°C and 44°C. Dithithreitol is required to prevent melanization of the enzyme extract. CHS activity was enhanced at low concentration of GlcNAc, but inhibited at high concentrations. Proteolytic activation of the activity is significant both in the 500 ×g supernatant and the 40 000 ×g pellet. Our study revealed only slight in vitro inhibition of A. gambiae CHS activity by diflubenzuron and nikkomycin Z at the highest concentration (2.5 µmol/L) examined. There was no in vitro inhibition by polyoxin D at any concentration examined. Furthermore, we did not observe any in vivo inhibition of CHS activity by any of these chemicals at any concentration examined. Our results suggest that the inhibition of chitin synthesis by these chemicals is not due to direct inhibition of CHS in A. gambiae.

Identification and characterisation of ten glutathione S-transferase genes from oriental migratory locust, Locusta migratoria manilensis (Meyen).

BACKGROUND: Synthetic pyrethroids are the primary insecticides that are widely used for controlling Locusta migratoria manilensis (Meyen), a major pest in eastern and southern Asia and the Pacific region. In this paper, ten cDNAs encoding glutathione S-transferases (GSTs) were sequenced and characterised in L. migratoria manilensis. The effects of deltamethrin on the ten GST gene expressions were studied. RESULTS: Phylogenetic analysis revealed nine GSTs in three different classes, including seven in sigma, one in delta and one in theta. The remaining GST (LmGSTu1) was unclassified. RT-PCR analysis showed that most GST genes were expressed in all tissues examined, including the foregut, midgut, gastric caecum, hindgut, Malpighian tubules, fat bodies, muscles, spermaries and ovaries, except that LmGSTs2, LmGSTs4, LmGSTs7 and LmGSTu1 were expressed in several tissues. LmGSTu1 appeared to be the only gene whose expressions could not be detected in eggs. Real-time quantitative PCR showed that deltamethrin at 0.08 and/or 0.12 µg mL⁻¹ increased almost all ten GST gene expressions in third-instar nymph locusts. However, deltamethrin at 0.16 and/or 0.2 µg mL⁻¹ decreased the expressions of LmGSTd1, LmGSTs1, LmGSTs5 and LmGSTs6. CONCLUSION: The increases in GST gene expressions after deltamethrin exposure in L. migratoria manilensis might result in its elevating tolerance to other insecticides and xenobiotics.

Expression patterns of three heat shock protein 70 genes among developmental stages of the red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae).

Three genes were identified encoding heat shock protein 70's in Tribolium castaneum (Herbst) and they were tentatively named as tchsp70 I, tchsc70 II, and tchsp70 III. Comparison of deduced amino acid sequences of tchsp70 I and tchsc70 II showed 99% identity. However, the amino acid sequence of tchsp70 III was only 58.5% identical to those of tchsp70 I and tchsc70 II. Stage-specific expression patterns of the tchsp70 were investigated in young larvae, old larvae, pupae, and adults of T. castaneum exposed for 1 h to 23 degrees C (control) or 40 degrees C (heat-shock). Northern blot and real-time quantitative PCR analyses were carried out to determine mRNA levels in each life stage. Transcripts of all three genes were detected by Northern blotting, and the sizes were 2.4- 2.2-, and 2.3-kb for tchsp70 I, tchsc70 II, and tchsp70 III, respectively. A 1.1- to 2.0-fold increased expression of tchsp70 I mRNA was found in heat-shocked developmental stages compared with the control. The expression of tchsc70 II mRNA among developmental stages was similar between heat-shocked and control insects, and the expression of tchsp70 III mRNA varied among developmental stages. Results suggest that the expression of tchsp70 I gene is heat-inducible, tchsc70 II is constitutive, and tchsp70 III is developmentally regulated in T. castaneum.