David F. Cook

Effect of diet on the excretion profile of ivermectin in cattle faeces

Two groups of 26 cattle (cross-bred, 3-8 years old, weight 450-650 kg) were placed onto 2 feed regimens, pasture-fed and grain-fed. The pasture-fed cattle were kept on irrigated pasture with hay supplement ad libitum, whereas the grain-fed cattle were kept in a feedlot and fed hay and lupin grain in a 40:60 ratio. Half the cattle within each feed group (n = 13) were given a subcutaneous injection of ivermectin (Ivomec) at the dose rate of 200 micrograms/kg liveweight. Over 5 times higher levels of ivermectin were excreted in the faeces of grain-fed cattle compared with pasture-fed (grazing) cattle. Peak excretion levels of 0.36 mg/kg (grain-fed) and 0.09 mg/kg (pasture-fed) of ivermectin were recorded at 6 and 8 days post-injection (dpi), respectively. Ivermectin was detected in faeces for up to 13 dpi (grain-fed) and 14 dpi (pasture-fed). Faecal pH in grain-fed cattle was more acidic (6.43) compared with pasture-fed cattle (7.28) and the levels of nitrogen in faeces from grain-fed cattle were higher (0.42%) compared with pasture-fed cattle (0.20%). Treatment with ivermectin had no influence on either the pH or nitrogen levels of faeces from either feed regimen. The impact of diet on the excretion profile of ivermectin is discussed in the context of studies attempting to demonstrate ecotoxic effects of ivermectin residues in cattle faeces on dung beetles.

Forensic entomology: application, education and research in Western Australia.

Forensic entomology as a science and a tool for investigation has had slow beginnings in Australia. A number of small animal decomposition trials have been recorded in the literature but mostly from an ecological rather than a forensic entomology perspective. In the last 20 years, a number of more forensically orientated field trials on small pigs and some fly developmental trials in the laboratory have been conducted but lack any replication. The following article was presented at an international seminar to detail the current research in forensic entomology, the applications of forensic entomology in scene of crime (SOC) and homicide investigations and the education of police and judiciary in the discipline of forensic entomology in Western Australia over the last 10 years.

Rate of development of Hydrotaea rostrata under summer and winter (cyclic and constant) temperature regimes

The black carrion fly Hydrotaea rostrata Robineau‐Desvoidy (Diptera: Muscidae) is a muscid, which occurs on approximately one‐third of decomposing human corpses involved in homicide cases in south‐western Australia. Work to date on its development rates is scant with only one published source available. The current study measured the precise developmental rates of this species using high repetition and sampling rates. A comparison was made of the developmental rates between constant and cyclic temperatures in winter and summer temperature regimes in south‐western Australia. Developmental times for 90% of first stage larvae to emerge as adult flies are: summer constant, 21.6 days, summer cyclic, 23.5 days, winter constant 64.5 days and winter cyclic, 48.3 days. These data will allow forensic entomologists to make more accurate determinations of post‐mortem intervals in cases where H. rostrata life history stages are present.

Addition of alarm pheromone to insecticides and the possible improvement of the control of the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)

This study represents the first attempt to improve insecticide contact using the dodecyl acetate component of the alarm pheromone of the western flower thrips ( Frankliniella occidentalis Pergande ). Dodecyl acetate dissolved in ethanol was added to both fipronil and maldison and used in three spray applications (7 days apart) against field infestations of F. occidentalis on strawberries in two separate trials. Fipronil alone was highly effective against larvae and to a lesser extent against adults; however, the addition of dodecyl acetate did not significantly enhance thrips mortality. Although maldison was significantly less effective against adults and larvae, the larval mortality rate was significantly increased with the addition of dodecyl acetate. In one trial, dodecyl acetate applied on its own caused a significant reduction in larval numbers. Frequent insecticide applications are recommended for control of F. occidentalis in Australia because of the short-term effectiveness of most insecticides. This may hasten the development of insecticide resistance, which is already evident in F. occidentalis populations across the continent. Hence, either cultural methods, biological control agents or more effective chemicals need to be identified. This study has shown that there is potential for dodecyl acetate to enhance insecticide control of F. occidentalis .

Management of stable fly and other nuisance flies breeding in rotting vegetable matter associated with horticultural crop production

Stable-fly (Stomoxys calcitrans L., Diptera: Muscidae) and other nuisance flies breeding in horticultural substrates around the Perth metropolitan area of Western Australia were investigated with regard to their larval habitats and relative abundances. Substrates were found to comprise either crop residue (i.e. stalks, leaves and fruit) left in or on the ground after harvesting, or harvested crop waste (i.e. reject produce or processing scraps dumped into open pits or fed to livestock). Stable-flies were the predominant species (>85%) developing from a wide variety of trashed vegetable crop residues. Other flies developing from these materials included house-fly, lesser house-fly, false stable-fly, blue-bodied blow-fly, black carrion-fly and flesh-flies. Stable-fly development was reduced by >90% when crop residues were sprayed with diazinon or chlorpyrifos, either prior to or immediately after incorporation of the residue into soil. Untreated crop residues yielded several hundred to >1,000 stable flies/m2 of production. Insecticides applied several weeks after crop residue incorporation into soil did not significantly reduce stable-fly emergence.

The laying of live larvae by the blowfly Calliphora varifrons (Diptera: Calliphoridae)

This study examined larviposition in Calliphora varifrons Malloch (Diptera: Calliphoridae), an ovoviviparous blowfly of forensic importance in Western Australia. Females took 1.5 min (mean 89±10.0s, n=42) to deposit their live, first instar larvae (average body length 2.5 mm) on fresh liver in the laboratory. Females laid an average of 30 live larvae (mean of 29.9±1.2, n=50) at a rate of 1 larva every 2 s (mean of 0.46±0.05 larvae/s, n=42). Most females (66%) laid live larvae only, but 18% laid fully developed eggs (half of the egg masses laid by individual females were viable) and 16% laid live larvae and some eggs at the same time. Females laying only eggs laid a mean of 24.1±3.0, n=10 eggs on each occasion. Field females carried between 20 and 44 live larvae (mean of 33.4±1.0, n=49) with a strong linear relationship between female size and number of live larvae. In the laboratory, females typically laid larvae in multiple locations. Very few females (<8%) retained some larvae in their ovisacs, retaining on average, half of their complement of developed larvae. Those larvae retained had begun to be resorbed by the female with necrosis evident on the posterior segments.