Fumigation with carbonyl sulfide: a model for the interaction of concentration, time and temperature.

The new fumigant carbonyl sulfide offers an alternative to both methyl bromide and phosphine as a grain fumigant. Separate mathematical models for levels of kill, based on quantitative toxicological studies were developed for adults and eggs of the rice weevil Sitophilus oryzae (L.). These models suggest that fumigation exposure times for carbonyl sulfide will be a compromise between those of methyl bromide (typically 24h) and phosphine (7-10d) to achieve a very high kill of all developmental stages. S. oryzae eggs were more difficult to kill with carbonyl sulfide fumigation than the adults. At 30 degrees C, a 25gm(-3) fumigation killed 99.9% of adults in less than 1d, but took 4d to kill the same percentage of eggs. Models were generated to describe the mortality of adults at 10, 15, 20, 25 and 30 degrees C. From these models it is predicted that fumigation with carbonyl sulfide for 1-2d at 30gm(-3) will kill 99.9% of adults. Furthermore the models illustrate that fumigations with concentrations below 10gm(-3) are unlikely to kill all adult S. oryzae. Significant variation was observed in the response of eggs to the fumigant over the temperature range of 10 to 30 degrees C. Models were generated to describe the mortality of eggs at 10, 15, 20, 25 and 30 degrees C. As the temperature was reduced below 25 degrees C, the time taken to achieve an effective fumigation increased. Extrapolating from the models, a 25gm(-3) fumigation to control 99.9% of S. oryzae eggs will take 95h (4d) at 30 degrees C, 77h (3.2d) at 25 degrees C, 120h (5d) at 20 degrees C, 174h (7.5d) at 15 degrees C and about 290h (11d) at 10 degrees C. The role of temperature in the time taken to kill eggs with carbonyl sulfide cannot be ignored. In order to achieve the desired level of kill of all developmental stages, the fumigation rates need to be set according to the most difficult life stage to kill, in this instance, the egg stage.

Genetic maps of the sheep blowfly Lucilia cuprina: linkage-group correlations with other dipteran genera.

Linkage data and revised genetic maps for 72 autosomal loci in Lucilia cuprina are presented. Comparison of the linkage relationships of biochemically and morphologically similar mutations in Ceratitis capitata, Drosophila melanogaster, and Musca domestica supports the hypothesis that the major linkage elements have survived relatively intact during evolution of the higher Diptera. The relationship of the linkage groups of the mosquito Aedes aegypti to these species is less clear.

Male crossing over and genetic sexing systems in the Australian sheep blowfly Lucilia cuprina.

Field-female killing (FK) systems based on deleterious mutations and Y-autosome translocations are being evaluated for genetic control of the Australian sheep blowfly, Lucilia cuprina. Experience during field trials has shown that mass-reared colonies of FK strains are subject to genetic deterioration, caused mainly by genetic recombination in males. A previous study found higher male recombination frequencies in two Y-linked translocation strains than in chromosomally normal males. However, the results of the present study indicate that breakage of the Y chromosome is neither sufficient nor necessary for increased levels of male recombination. The frequency of male recombination appears to be unrelated to the presence of specific chromosome rearrangements.

Homozygous-viable pericentric inversions for genetic control of Lucilia Cuprina.

The isolation of homozygous-viable pericentric inversions for inclusion in field-female killing (FK) systems in Lucilia cuprina is described. From 7,236 irradiated chromosomes screened, 16 pericentric inversions were isolated. Four of these were viable as homozygotes. One of these, In (3LR) 14, possesses the properties required for inclusion in FK systems (tight linkage of one inversion break-point to the white-eye gene and substantial genetic exchange within the inversion in heterozygous females).