Bromine residues in potato and wheat crops grown in soil fumigated with methyl bromide

The bromine content of potato tubers grown in soil fumigated with methyl bromide at 487 and 975 kg/ha (1 lb and 2 lb/100 ft2) averaged 170 and 280 mg/kg of dry weight. Most of the bromine was in the outer layers of the tubers; peeled tubers has less than 100 mg/kg, which remained after boiling. Potato haulm contained 4000 or 6700 mg/kg bromine respectively for the two rates of application. The bromine content of wheat grain grown after potatoes depended on the rate of application of methyl bromide and the time interval between treatment and wheat crop. Wheat grain harvested 31/2 21/2 and 11/2 years after fumigation with methyl bromide at 975 kg/ha had mean bromine contents of 4.5, 15 and 44 mg/kg. but the amounts in grain from plots having the same treatments varied more than two-fold; wheat grain harvested 11/2 years after fumigation at 487 kg/ha contained 23 mg bromine/kg. Wheat yields were unaffected by fumigation.     

Cross-resistance to pyrethroids and other insecticides in Aedes aegypti

Two substrains of Aedes aegypti, already resistant to DDT and pyrethroids, were further selected using either DDT or permethrin by mass exposure of the females only. DDT selection over 14 generations raised the resistance to DDT so far that no accurate LC₅₀ values could be determined. Selection with permethrin raised the tolerance to an irregular plateau 7–10 times the original. DDT selection in the adults raised the DDT resistance of the larvae, but this could be partly overcome using a dehydrochlorinase inhibitor. The resistance to pyrethroids was increased but tolerance of dieldrin, malathion and propoxur compounds was little changed. Permethrin selection of the adults raised resistance to pyrethroids more than DDT selection but also increased DDT resistance. Similar patterns were found for the larval insects. A strain from Demerara in Guyana showed both DDT and pyrethroid resistance, including strong resistance to pyrethrins together with dieldrin and propoxur. It was concluded that two major independent resistance mechanisms existed in the selected strains, a dehydrochlorinase affecting DDT alone, and an unknown mechanism, probably nerve insensitivity (kdr) affecting both DDT and pyrethroids.     

Occurrence and distribution of <Emphasis Type="Italic">Phytophthora</Emphasis> species in European chestnut stands,and their association with Ink Disease and crown decline

The Phytophthora complex associated with Castanea sativa Mill. was investigated in five European countries in 35 regions and with respect to various domestication levels. Annual precipitation and length of drought season were the main parameters that regulated the presence of Phytophthora species in the chestnut stands. Seven species of Phytophthora were detected; three of these, P. megasperma, P. cryptogea and P. syringae had not been previously reported on sweet chestnut. P. cinnamomi. P. cambivora and P. citricola were most frequently isolated. P. cinnamomi and P. cambivora were the species significantly associated with declining trees with symptoms of Ink Disease. P. cinnamomirequired distinct ecological conditions compared to the other species. P. cinnamomi was never detected in sites characterized by minimum temperatures below 1.4 °C, maximum temperature above 28 °C, or soil pH below 5.4. The results obtained provide useful information for modeling the probability of Ink Disease, crown decline and associated Phytophthora species in chestnut groves in global climatic change scenarios.     

Efficacy of a collar impregnated with amitraz and pyriproxyfen for prevention of experimental tick infestations by Rhipicephalus sanguineus, Ixodes ricinus, and Ixodes scapularis in dogs

OBJECTIVE: To compare the efficacy of collars impregnated with 9% amitraz or 9% amitraz and 0.5% pyriproxyfen (PPF) for control of newly established tick infestations by Rhipicephalus sanguineus, Ixodes ricinus, and Ixodes scapularis in dogs and determine whether egg production by surviving female ticks was decreased. DESIGN: Prospective study. ANIMALS: 72 dogs. PROCEDURE: Dogs were fitted with 1 of 3 test collars impregnated with amitraz, amitraz and PPF, or only excipients (untreated controls). In 3 trials corresponding to each of the 3 tick species, dogs were infested with 150 unfed adult ticks on days 8, 10, 13, and 18. The number of feeding female ticks was recorded on days 10, 13, 18, and 28. Surviving females were weighed and permitted to oviposit under controlled conditions. RESULTS: Collars impregnated with amitraz and PPF decreased tick loads as efficiently as collars containing amitraz alone. Inclusion of PPF into the collar did not significantly decrease the efficacy of amitraz. The few female ticks that survived after feeding on dogs treated with collars containing PPF were unable to oviposit. CONCLUSIONS AND CLINICAL RELEVANCE: Collars impregnated with amitraz were efficient in preventing tick infestations in dogs but did not inhibit oviposition in the few surviving female ticks. Incorporation of PPF into the amitraz-impregnated collar resulted in impairment of the reproductive ability of ticks.     

A case study of capture-recapture methodology using scrapie surveillance data in Great Britain

We applied capture–recapture methodology (CRC) to data from three surveillance sources (statutory notification, abattoir survey (AS) and fallen stock (FS) survey) to estimate the number of holdings infected with scrapie in Great Britain and to assess the sensitivity of the surveillance network. Between January 1, 2002 and March 31, 2003, 144 holdings were identified by the three sources. Using CRC modelling techniques, we estimated a minimum lower bound for the total number of holdings infected as 642. A biologically plausible positive dependence between the statutory reporting and the fallen stock survey was found statistically significant. The sensitivity of the three sources combined was very low. The integration of the three overlapping sources provided a better understanding of the interactions within the surveillance network. However, the scarcity of the data and reduced overlapping among sources only allowed for very cautious inferences to be drawn about the true proportion of scrapie affected holdings in the national population. Future surveys and surveillance activities should be planned such that the resulting data can be used more effectively as part of CRC modelling approaches.