The activity of a wettable powder formulation of Bacillus thuringrensis serovar isruelensis against I st and 4th instar larvae of Chironomus tepperi was assessed by bioassay in the laboratory. The LC,, for 4th instar larvae was 0.79 ppm which was about 4 times that for 1st instar larvae.Chironomus re peri (Skuse) is a serious pest of rice crops in New South Wales. The larvae damage establishing crops &y feeding on the roots of young seedlings (Hely 1958: Jones 1968. Currently. larval infestations are controlled by treating rice bays with organophosphorus insecticides. Most of these have broad spectrums of activity but as an alternative, narrow-spectrum insecticides are being considered.Bacillus rhuringiensis serovar isruelensis (BTl) is a bacterial entomopathogen known to be highly toxic to mosquitoes (Goldberg and Margalit 1977; Garcia e/ a/. 1980) and blackflies (Undeen and Colbo 1980). BTl has also produced mortality in North American chironomids under both field and laboratory conditions (Ali 1980; Ali et a/. 1981).The potential of BTI for control of C . lepperi was investigated using Bactimos (R! a wettable powder formulation of B. thuringiensis serovar israelensis (Biochem Products. Batch No. LRB-687-688. specified activity vs. Aedes aegypti. of 6.000 i.u./mg). A fresh stock suspension was prepared for each test; Martin's Salt Solution (Martin et a/. 1980). pre-aerated for 24 h was used as the diluting solution. Suspensions of Bactimos' Rl were maintained by continuous stirring.Larvae of C. tepperi were hatched from egg masses collected either in the field or from adults reared in the laboratory for 1 generation. In the laboratory they were reared in glass aquaria (Martin ef a/. 1980) at 25 + I ' C and a 12 h photophase. First and fourth (final) instar larvae were tested to represent the 2 stages most commonly treated in the field.Bioassays were performed by placinggroups of20 instar 1V larvae in 25 mi of BactimoslRIsuspension in 100 x 25 mm glass tubes capped and held at 25 f I C for 48 h (when mortality was complete) belhre mortality was assessed. Larvae which did not move when subjected to a jet of water were classified as dead.Untreated controls were included in each series. Two replicates. each of 5 doses were tested and the procedure was carried out 3 times. The corrected mortality against concentration of formulation was analysed after the method of Finney (1952).Preliminary experiments indicated that instar 1 C. repperi were not amenable to the handling procedures used above, sufering high control mortality, presumably due to mechanical damage. The approximate LC,, for this instar was obtained by allowing field-collected egg masses to hatch into the test suspensions of Bactimos'R! Mortality was recorded ca 24 h after hatching was complete in the control treatment. The percentage mortality was scored, then each egg mass was examined with a binocular microscope to determine the percentage hatch. There were 4 replicates of each dose and the test was repeated.
SummaryApplications of Steinemema carpocapsae All strain in water thickener into cuts or holes made in residual rhizomes of bananas gave significant mortality of Cosmopolites sordidus larvae in the rhizomes. The methods proved suitable for field application and two large scale field trials using S. carpocapsae All and S. carpocapsae NC513 gave acceptable levels of control as measured by Vilardebo's (1973) Co‐efficient of Infestation. Mortality of adult C. sordidus attracted to the application sites on treated rhizomes was observed during these field trials.
Factors affecting the probability of detecting infestations of Boophilus microplus when herds of cattle are examined were studied. The probability of detecting a tick depends on the number of infested cattle in the herd, the probability of ticks being present on the areas of the beast examined, the efficiency of the examination and the proportion of the herd examined. A mathematical expression relating these factors was derived, and a range of values calculated to demonstrate the relative importance of each factor. It was evident that the efficiency of the examination should be kept better than 75%, and that it is necessary to employ a high sampling rate, preferably 100% of the herd. The probabilities of ticks being present on 6 predilection sites and 4 combinations of sites of an infested animal were determined experimentally. The tail butt, esutcheon, belly, dewlap and to a lesser degree neck and ear were all very suitable sites on which to find cattle ticks. A combination of tail butt, escutcheon and neck produced probabilities (0.58 and above) considered adequate to form the basis of an examination system. Examination systems used in New South Wales, Queensland, Argentina and at the United States-Mexico border are described. As a result of this study a new standardised system has been adopted by the Board of Tick Control for use by all New South Wales inspectors.
The presence of an aggregation pheromone has been demonstrated for the first time in indigenous Australian ticks. Filter paper discs exposed to either Australian paralysis ticks Ixodes holocyclus or echidna ticks Aponomma concolor showed inter-sex or intra-sex attraction for ticks of their own species. Nymphal exuviae of Ap, concolor were highly attractive to adult ticks. Discs were significantly attractive to I. holocyclus at distances up to 80 cm.
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