Essential oils: effects of application rate and modality on potential for combating northern fowl mite infestations.

The northern fowl mite (NFM), Ornithonyssus sylviarum (Mesostigmata: Macronyssidae), is the primary blood-feeding ectoparasite found on poultry in the U.S.A. Three experiments were conducted in vitro to test the acaricidal properties of cade, garlic, lavender, lemongrass, pine and thyme essential oils against NFM, and to evaluate whether these effects are altered by adjusting oil application rates and application modality (direct vs. vapour contact). Applied at the rate of 0.21 mg/cm2 , the essential oils of cade, thyme, lemongrass and garlic resulted in higher NFM mortality at 24 h post-application than lavender and pine oils, and the untreated and ethanol-treated controls. Cade and thyme were the most consistent and fast-acting of the essential oils in terms of toxicity to NFM. Cade applied at 0.21 mg/cm2 and 0.11 mg/cm2 and thyme applied at 0.21 mg/cm2 were effective in eliminating NFM within 2 h through direct contact. The modality of application did not affect the efficacy of cade and thyme essential oils. The results suggest that essential oils may be utilized as alternatives to chemical pesticides and could be used as fumigants for the control of NFM.

The effects of colony structure and resource abundance on food dispersal in Tapinoma sessile (Hymenoptera: Formicidae).

The odorous house ant, Tapinoma sessile (Say) (Hymenoptera: Formicidae), exhibits a high degree of variation in colony spatial structure, which may have direct and indirect effects on foraging. Protein marking and mark-release-recapture techniques were utilized to examine the effect of colony spatial structure on food dispersal. Sucrose water spiked with rabbit IgG protein was presented to colonies with varying spatial configurations in laboratory and field experiments. In monodomous laboratory colonies, the rate and extent of food dispersal was rapid due to a decrease in foraging area. In polydomous colonies, food dispersal was slower because conspecifics were forced to forage and share food over longer distances. However, over time, food was present in all extremities of the colony. Experiments conducted in the field produced similar results, with nests in close proximity to food yielding higher percentages of workers scoring positive for the marker. However, the percentage of workers possessing the marker decreased over time. Results from this study provide experimental data on mechanisms of food dispersal in monodomous and polydomous colonies of ants and may be important for increasing the efficacy of management strategies against T. sessile and other pest ant species.

The effects of colony structure and resource abundance on food dispersal in Tapinoma sessile (Hymenoptera: Formicidae).

The odorous house ant, Tapinoma sessile (Say) (Hymenoptera: Formicidae), exhibits a high degree of variation in colony spatial structure which may have direct and indirect effects on foraging. Protein marking and mark-release-recapture techniques were utilized to examine the effect of colony spatial structure on food dispersal. Sucrose water spiked with rabbit IgG protein was presented to colonies with varying spatial configurations in laboratory and field experiments. In monodomous lab colonies, the rate and extent of food dispersal was rapid due to a decrease in foraging area. In polydomous colonies, food dispersal was slower because conspecifics were forced to forage and share food over longer distances. However, over time, food was present in all extremities of the colony. Experiments conducted in the field produced similar results, with nests in close proximity to food yielding higher percentages of workers scoring positive for the marker. However, the percentage of workers possessing the marker decreased over time. Results from this study provide experimental data on mechanisms of food dispersal in monodomous and polydomous colonies of ants, and may be important for increasing the efficacy of management strategies against T. sessile and other pest ant species.

Transcriptomic profiles of Drosophila melanogaster third instar larval midgut and responses to oxidative stress.

Oligoarray analysis was used to determine the number and nature of genes expressed in third instar Drosophila melanogaster larval midguts. The majority of transcripts were associated with protein synthesis and metabolism. Serine proteases were the main proteolytic enzymes detected. Some 40% of the cytochrome P450 genes and 74% of the glutathione S transferases (GSTs) in the genome of D. melanogaster were observed to be expressed in the midgut by oligoarray analysis. We also identified potential transcription factor binding motifs (TFBMs) of P450s, GSTs and carboxylesterases. Many of the midgut-expressed GST genes contained candidate TFBMs homologous to TFBMs in mammals that have been associated with responses to oxidative stress. We also investigated the response of GSTs in the midgut to dietary H2O2, which showed a dosage-based differential response.

Genome-wide analysis of phenobarbital-inducible genes in Drosophila melanogaster.

An oligoarray analysis was conducted to determine the differential expression of genes due to phenobarbital exposure in Drosophila melanogaster (w(1118) strain) third instar larvae. Seventeen genes were observed to be induced with increased expression by a statistical analysis of microarrays approach with a q < or = 0.05. At q < or = 0.12, four more genes (Cyp12d1, DmGstd4, and two genes with unknown function) were found to be up-regulated, and 11 genes with unknown function were found to be down-regulated. Fifteen of these genes, Cyp4d14, Cyp6a2, Cyp6a8, Cyp12d1, Cyp6d5, Cyp6w1, CG2065, DmGstd6, DmGstd7, Amy-p/Amy-d, Ugt86Dd, GC5724, Jheh1, Jheh2 and CG11893, were verified using quantitative real time polymerase chain reaction. Some of these genes have been shown to be over-transcribed in metabolically DDT-resistant Drosophila strains.

Transfer of ingested insecticides among cockroaches: effects of active ingredient, bait formulation, and assay procedures.

Foraging cockroaches ingest insecticide baits, translocate them, and can cause mortality in untreated cockroaches that contact the foragers or ingest their excretions. Translocation of eight ingested baits by adult male Blattella germanica (L.) was examined in relation to the type of the active ingredient, formulation, and foraging area. Ingested boric acid, chlorpyrifos, fipronil, and hydramethylnon that were excreted by adults in small dishes killed 100% of first instars within 10 d and >50% of second instars within 14 d. Residues from these ingested baits were also highly effective on nymphs in larger arenas and killed 16-100% of the adults. However, when the baits and dead cockroaches were removed from the large arenas and replaced with new cockroaches, only residues of the slow-acting hydramethylnon killed most of the nymphs and adults, whereas residues of fast acting insecticides (chlorpyrifos and fipronil) killed fewer nymphs and adults. Excretions from cockroaches that ingested abamectin baits failed to cause significant mortality in cockroaches that contacted the residues. These results suggest that hydramethylnon is highly effective in these assays because cockroaches that feed on the bait have ample time to return to their shelter and defecate insecticide-laden feces. The relatively high concentration of hydramethylnon in the bait (2.15%) and its apparent stability in the digestive tract and feces probably contribute to the efficacy of hydramethylnon. To control for differences among baits in inert ingredients and the amount of active ingredient, we compared 1% chlorpyrifos with 1% hydramethylnon in identical baits. Again, hydramethylnon residues provided greater secondary kill, but the results highlighted the importance of the inert ingredients. We conclude that, in the absence of cannibalism and necrophagy, translocation of baits and secondary kill are most effective with slow acting insecticides in palatable baits that can traverse the digestive tract and be deposited within and around the cockroach aggregation.

Method of insecticide delivery affects horizontal transfer of fipronil in the German cockroach (Dictyoptera: Blattellidae).

Horizontal transmission of insecticide occurs when foragers contact or ingest an insecticide, return to the aggregation or nest, and translocate the insecticide to the shelter and its vicinity. Relatively more sedentary members of the population then contact or eat the translocated insecticide and die. We evaluated three different methods of delivering fipronil to adult male German cockroaches, Blattella germanica (L.), for their potential to cause such secondary mortality in various developmental stages of the cockroach. Adult males topically treated with 5 ng of fipronil (approximately LD99) caused low mortality in untreated nymphs and no mortality in untreated adults within the same aggregation. Males exposed to residual fipronil on a glass surface translocated more insecticide, resulting in higher mortality of cockroaches they contacted, but only early instars were affected and no adult mortality was observed. Ingested fipronil bait, however, was most effectively translocated, and caused high mortality of untreated adults and nymphs. Ingestion of fipronil also caused greater secondary kill compared with a topical application of 25 ng, approximately the same amount recovered from the exterior of males that ingested 1 mg of 0.05% fipronil bait. Secondary mortality in the untreated population was significantly affected by the duration of contact between the treated and untreated cockroaches, the quantity and freshness of excretions from the treated insects, and the accessibility of the secretions to untreated cockroaches. The mechanisms that cause secondary kill may include ingestion of excreted fipronil residues, cannibalism of bait-fed cockroaches, as well as contact with fipronil-contaminated substrates.