Title: Resistance risk assessment of two insect development inhibitors, diflubenzuron and cyromazine, for control of the housefly Musca domestica L. Part II: Effect of selection pressure in laboratory and field populations Keiding J, El-Khodary AS, Jespersen JB Ref: Pest Sci, 35:27, 1992 : PubMed
Laboratory selection with diflubenzuron (DFB) and cyromazine (CYR) was carried out with strains of houseflies collected on Danish farms. The adult flies were multiresistant to organophosphorus, carbamate and pyrethroid insecticides. Susceptibility to the larvicidal effect of DFB or CYR was monitored on Danish farms where fly control with DFB or CYR had been carried out for one to nine years. On these farms the fly population continued during the winter, but at a low level.
Four strains were selected with DFB in seven out of 13-18 laboratory generations. The selections varied from 56% to 94% mortality. The strains showed 1-5 times increase of LC50 and LC95 to DFB. The larvicidal effect of DFB was monitored on five farms where treatment of fly breeding sources in manure (1 g DFB m-2) was carried out regularly for one to nine fly seasons. On none of the farms was any general increase of tolerance to DFB found. Resistance ratios (R/S) compared to the WHO Standard Reference Strain ranged from 0.8 to 2.0 at LC50 and from 1-0 to 2-9 at LC95.
Two strains were selected with CYR in five or six out of 13 laboratory generations. The selections varied from 62 to 97% mortality. The strains showed no increase of LC50 or LC95. The larvicidal effect of CYR was monitored on three farms where housefly breeding places in the animal houses were treated with CYR (0.5 g m-2) for two fly seasons. No reduction of susceptibility to CYR was found and the R/S was 0.7 to 0.9.
The effect of DFB or CYR selection pressure is compared with other investigations and discussed. Moderate to high resistance to DFB or CYR can develop in housefly populations if the selection pressure is strong, especially when used as feed-through applications on poultry farms where all feed contains DFB or CYR. If the treatment of fly breeding sources is less complete, resistance problems may not develop.
Title: Resistance risk assessment of two insect development inhibitors, diflubenzuron and cyromazine, for control of the housefly Musca domestica. part i: Larvicidal tests with insecticide-resistant laboratory and danish field populations Keiding J, Jespersen JB, El-Khodary AS Ref: Pest Sci, 32:187, 1991 : PubMed
Larvicide tests with diflubenzuron (DFB) and cyromazine (CYR) were carried out against 15 laboratory housefly strains and 89 field strains collected from 87 Danish and 2 Swedish farms, 1975-89. The strains represented a wide range of adult insecticide resistance and R-mechanisms.
The larvicide tests were done by treating larval medium with serial or discriminating dosages of the larvicide, seeding it with eggs and calculating the mortality during development to adults. The WHO susceptible strain (S) was used as a reference.
Dose-response tests with DFB gave resistance ratios (R/S) from 1.1 to 4.1 at LC50 and 0.3 to 3.4 at LC95 and, with CYR, R/S from 0.6 to 1.8 at LC50 and 0.6 to 2.9 at LC95.
It was concluded that the relatively small variation in susceptibility between strains was not generally correlated with resistance in adult flies to organophosphorus, pyrethroid or other conventional insecticides (neurotoxins).
Tests with discriminating dosages of DFB (59 farms) and CYR (63 farms) showed no indication of resistance to either product.
The results of investigations by other workers on the relation between resistance to DFB or CYR and resistance to conventional insecticides are discussed.
Title: Factors affecting the sequential acquisition by Danish houseflies (musca domestica L.) of resistance to organophosphorus insecticides Sawicki RM, Keiding J Ref: Pest Sci, 12:587, 1981 : PubMed
The prolonged use of dimethoate, introduced into Denmark to control houseflies (Musca domestica L.) that had become resistant to parathion and diazinon, resulted ultimately in dimethoate resistance. Selection with dimethoate led to the disappearance of the hydrolytic phosphatase, a major mechanism of resistance to parathion and diazinon, and its replacement by the acetylcholinesterase AChER with somewhat decreased sensitivity to inhibition by organophosphorus (OP) insecticides. The hydrolytic phosphatase probably disappeared because low substrate turn-over made it ineffective against dimethoxon (O, O-dimethyl S-methylcarbamoylmethyl phosphorothioate, also known as omethoate). which accumulates at higher concentrations than paraoxon (diethyl4-nitrophenyl phosphate) in the haemolymph. Dimethoate selected AChER preferentially because it improved the chances of houseflies surviving against the relatively poor AChE inhibitor dimethoxon, whereas its relatively small insensitivity to OP insecticides, unimportant against good inhibitors such as paraoxon, prevented its selection by parathion.
Resistance to fenitrothion was investigated in housefly populations in Danish farms 1964--72 in connection with trials of fenitrothion, dimethoate and other organophosphorus compounds for fly control. Resistance was tested by topical application and expressed as resistance ratios, R/S, relative to normal susceptible strains. In 1964--70 fly populations on farms sprayed with fenitrothion (one year each) only developed mode-rate fenitrothion-resistance, R/S at LD 95 below 21 and fly control was generally satisfactory. However, in 1972 high fenitrothion-resistance, R/S 100--400 at LD 95, was found in several fly populations, both on farms treated with fenitrothion and on farms treated with dimethoate, fenitrothion, or bromophos. In all cases the high fenitrothion-resistance was associated with high resistance to dimethoate. Some characteristics of this, apparently complex, resistance are discussed including the effect of certain synergists. Resistance to fenitrothion in Danish flies is only partly reduced by pretreatment with high dosages of sesamex, which inhibits microsomal detoxication, and very little by TBTP (S, S, S tributyl phosphorotrithioate), which inhibits other types of break-down of organophosphorus compounds, e.g. by ali-esterases. The occurrence of fenitrothion- resistance in field populations of houseflied in other regions is briefly reviewed. Widespread, partly very high, resistance has recently been reported from Japan.
Title: Problems of housefly (Musca domestica) control due to multiresistance to insesticides Keiding J Ref: J Hyg Epidemiol Microbiol Immunol, 19:340, 1975 : PubMed
The development of chemical control of Musca domestica on Danish farms 1945--72 is outlined. It has been strongly influenced by successive development of resistance and failure of control by one insecticide after another. The chlorinated hydrocarbons used as residual sprays failed 1947--51. Organophosphorus compounds (OPC) were widely used from 1953, first as strips impregnated with parathion and residual sprays with diazinon. Resistance to OPC was first found in 1955, diazinon was given up in 1957--59 and parathion strips failed in the early '60's. Trichlorfon paint-on baits were widelyused 1958--64 and serious resistance did not appear until 1967, induced by selective pressure of fenthion and dimethoate used as residual sprays. High resistance to the contact effect of trichlorfon now occurs everywhere in Denmark. However, trichlorfon baits are still able to kill many flies. Residual sprays with fenthion, ronnel and fenitrothion were used to some extent 1960--70, but increased resistance reducing the residual effect developed in 2--3 years. Dimethoate was used on the majority of farms 1965--72. It was very effective the first years and resistance increased slowly until 1971--72, when high to extreme dimethoate-resistance became general on Danish farms. This was associated with high resistance to other OPC for fly control, e.g. fenthion, fenitrothion, bromophos, and tetrachlorvinphos, and to carbamates, with the result that no generally effective residual sprays were available. In 1971--72 frequent treatments with synergized pyrethroids have been tried. However, the method is often expensive, and serious resistance problems have appeared on a few farms. In this situation preventive, sanitary measures to eliminate or reduce fly breeding in manure are becoming decisive again, but difficult to practise due to lack of farm labour. The extreme Danish situation is compared with those in other areas, and probable reasons for differences in resistance and control problems are discussed, as well as possibilities for strategies to reduce resistance development.
