The inheritance of resistance to phosphine was studied in two strains of the lesser grain borer, Rhyzopertha dominica (F.), labeled 'Weak-R' and 'Strong-R'. These strains were purified versions of field-selected populations collected in Queensland, Australia. Weak-R and Strong-R were, respectively, 23.4 times (20-h exposure) and 600 times (48-h exposure) resistant to phosphine compared with a reference susceptible strain (S-strain). Each -R strain was crossed with the S-strain and the response to phosphine was measured in their respective F1, F2, and F1-backcross (F1-BC) progenies. Data from testing of reciprocal F1 progeny indicated that resistance in Weak-R was autosomal and incompletely recessive with a degree of dominance -0.96. Modified chi-square analysis and contingency analysis of the observed response to phosphine of F1-BC and F2 progenies rejected the hypothesis of single gene inheritance of resistance. Analysis of the response of the F1, F2, and F1-BC progeny from the Strong-R x S-strain cross also rejected the null hypothesis for single gene resistance. Resistance in the Strong-R strain was autosomal and incompletely recessive with a degree of dominance of -0.64. The Weak-R and Strong-R strains were then crossed. Analysis ofthe F1 and F2 progenies of this reciprocal cross revealed that the strong resistance phenotype was coded by a combination of the genes already present in the Weak-R genotype plus an extra major, incompletely recessive gene. There was also evidence of a minor dominant gene present in approximately 5% of Strong-R individuals.

No abstract

Organophosphorothioates and synergised synthetic pyrethroids were used in duplicate field trials carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays using malathion‐resistant strains of insects were carried out on samples of treated grain at intervals over 9 months. These established that all treatments were generally effective. Deltamethrin (2 mg kg−1)+ piperonyl butoxide (8 mg kg−1), fenitrothion (12 mg kg−1)+ fenvalerate (1 mg kg−1)+ piperonyl butoxide (8 mg kg−1), fenitrothion (12 mg kg−1)+ phenothrin (2 mg kg−1)+ piperonyl butoxide (8 mg kg−1) and pirimiphos‐methyl (4 mg kg−1)+ permethrin (1 mg kg−1)+ piperonyl butoxide (8 mg kg−1) controlled common field strains of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). Against a highly resistant strain of S. oryzae, deltamethrin (2 mg kg−1)+ piperonyl butoxide (8 mg kg−1) was superior to the remaining treatments. All treatment combinations completely prevented progeny production in Tribolium castaneum (Herbst), T. confusum Jacquelin du Val and in Ephestia cautella (Walker). Residues of deltamethrin, fenvalerate, permethrin and phenothrin were determined and shown to be highly persistent on stored wheat. During milling, residues accumulated in the bran fractions and were reduced in white flour. They were not significantly reduced during baking.

In the Mildura district of Victoria, Brevipalpus lewisi McGregor is responsible for 'bunch mite' symptoms on grapevines. Age-specific life and fecundity tables, compiled in the laboratory, showed that B. lewisi is capable of positive population growth over a range of temperatures at relative humidity levels commonly encountered in the field. The maximum value of rm obtained in the laboratory was 0.04/day, at 28�C and 35 % relative humidity. A field study of the seasonal abundance and intra-vine distribution of B. lewisi showed that populations increased about 60-fold during a season. The rate of population increase during summer was similar to laboratory estimates of population growth potential. Although the mites were present solely at the base of canes early in the season, later all green parts of the plant became infested. Predation and loss associated with leaf fall reduced the numbers of mites overwintering. Populations were further reduced by removal of mites during pruning.

Duplicate field trials were carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays on samples of treated grain at intervals over 9 months, using malathion‐resistant strains of insects, established that treatments were generally effective. Fenitrothion (12 mg kg−1)+ (1R)‐phenothrin (2 mg kg−1) was more effective than pirimiphos‐methyl (6 mg kg−1) + carbaryl (10 mg kg−1) against Sitophilus oryzae (L.) and Ephestia cautella (Walker); the order of effectiveness was reversed for S. granarius (L.). Against Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.), both treatments effectively prevented the production of progeny. The order of persistence was pirimiphos‐methyl> (1R)‐phenothrin>carbaryl or fenitrothion. During processing from wheat to white bread, residues were reduced by 98% for carbaryl, >44% for (1R)‐phenothrin, 98% for fenitrothion and 85% for pirimiphosmethyl.