Some properties of a mechanism delaying penetration of insecticides into houseflies

The penetration of insecticides into houseflies, with and without the factor that delays penetration, was studied by measuring the amounts of the insecticides on the surface of the flies at intervals after treatment. The factor slowed the entry of all the insecticides tested, but its effect depended on the dose, and had little or no effect when the dose applied was big (20 μmUg/fiy). Penetration in all strains, susceptible and resistant, increased but not proportionally to the size of the dose. The rate insecticide was lost from the surface slowed with time and increasing age of the insects. It was faster in males than females, and was always faster in flies without the penetration factor. The differences in penetration between the flies with and without the factor was less with n-dodecane as solvent than with acetone. With all strains, rate of loss from the surface was slowest with dieldrin. Diazinon, parathion and chlorthion-ethyl were lost at about the same rate; diazoxon penetrated fastest.     

Mechanism of resistance to dichlorvos in adult houseflies

Houseflies (Musca domestica) originating from agricultural buildings in Jalasjarvi (Vaasa province of Finland) were found to be resistant to contact with a variety of organophosphorus insecticides, including dichlorvos. Tolerance to topical application of bromophos, crotoxyphos, and trichlorfon was fairly high, to dimethoate and dichlorvos it was moderate, and to tetrachlorvinphos it was very low. Much higher degrees of resistance were obtained after exposure to surface deposits.Evidence is presented to suggest that the mechanism of resistance in the Jalasjarvi flies is probably based on reduced penetration. With dichlorvos less of the absorbed chemical penetrates the central nervous system (the thoracic ganglionic complex) of the resistant fly than penetrates that of the susceptible fly. No differences were apparent between the strains in the otherwise small rates of degradation of dichlorvos.     

Development of resistance to pyrethroids in field populations of danish houseflies

Houseflies (Musca domestica) on Danish farms have developed high multiresistance to organophosphorus compounds, after successive use of several OPs, mainly dimethoate, in recent years. Topical application tests 1971–73 with flies from many farms showed that the high OP-resistance did not involve resistance to pyrethroids (± the synergist piperonyl butoxide (pb)) above a level of 3–7 x, unless field pressure with synergised pyrethrum (py/pb) or other pyrethroids was applied. In 1971–72 moderate to high, often heterogeneous, pyrethroid resistance was found on a few trial farms treated frequently with pyrethroid aerosols (mainly py/pb) and in 1973 on most of 23 trial farms treated intensively with aerosols (or space spray) containing py/pb, bioresmethrin ± pb, tetramethrin/pb or tetramethrin/resmethrin. The effect of field pressure with these different pyrethroids on development of pyrethroid resistance is summarised and discussed. Maximum resistance ratios, R/S at LD₅₀-LD₉₅, were: py/pb (1:5), 40->100; bioresmethrin, 191–770; bioresmethrin/pb (1:5), 55–133; tetramethrin/pb (1:5), 171->200; tetramethrin/resmethrin (1:5), 78->370. The intensity of selection pressure with pyrethroids is believed to be an important factor. Although py/pb has been widely used as a supplementary fly control on Danish non-trial farms, pyrethroid resistance has only been found on a few of them.     

Interaction between powdery mildew and barley with mlo5 mildew resistance

Powdery mildew infection of barley with the mlo5 barley powdery mildew resistance gene was examined, using near-isogenic barley lines, with and without mlo5 resistance, and two near-isogenic powdery mildew isolates, HL3/5 and GE3 with high (virulent) or low (avirulent) penetration efficiency on the resistant barley line. In all isolate–host combinations (except GE3 on the resistant barley line), frequency of haustorium formation increased significantly from zero at 11 h after inoculation to a maximum by 13 h, and there was no subsequent increase up to 24 h. In the susceptible barley line, 27% of appressoria from both isolates formed haustoria. Although this was significantly higher than the frequency of haustorium formation (18%) of HL3/5 on the resistant barley line, HL3/5 was much more successful than GE3 (frequency of haustorium formation less than 1%). The fact that HL3/5 did not possess a generally higher ability to penetrate successfully to form haustoria on the susceptible barley line, indicates that HL3/5 did not overcome the mlo5 resistance by being generally more vigorous. In the resistant barley line, papillae were larger than in the susceptible line; however, both isolates were associated with papillae of the same diameter at the time of penetration. We suggest that the mlo5 resistant barley line confers two different forms of resistance: isolate-specific and isolate-nonspecific.     

Association between insecticide use and greenhouse whitefly (Trialeurodes vaporariorum westwood) resistance to insecticides in hawaii

Susceptibility to acephate, methomyl, and permethrin was determined with laboratory bioassays for adults of greenhouse whitefly, Trialeurodes vaporariorum Westwood, from 12 to 14 sites in Hawaii. Comparisons at LC₅₀ showed up to 42-fold resistance to acephate, 36-fold resistance to methomyl, and 8-fold resistance to permethrin. Higher levels of resistance to acephate and methomyl than to permethrin are consistent with greater use of organophosphates and carbamates than pyrethroids by growers. Insecticide use varied from 1 to 98 insecticide sprays per site per season. Significant positive associations between LC₅₀ for each insecticide and frequency of application of the same insecticide were found across sites. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.     

Insecticide resistance in houseflies from the middle east and North Africa with notes on the use of various bioassay techniques

The susceptibility to pyrethroid, organochlorine, organophosphorus and carbamate insecticides, of 20 strains of houseflies (Musca domestica L.) collected in the Middle East and North Africa, was assessed by topical application. No resistance to pyrethroids was found but most flies were resistant to DDT, gamma-HCH, organophosphorus and carbamate insecticides. Numerical factors of resistance for a susceptible and two different resistant strains, obtained using different bioassay techniques, were compared. High mortality (≥95%) was achieved with ‘resisted’ insecticides in tests with space sprays, but only low, variable mortality resulted from deposit tests. If this occurs under practical field conditions, moderately resistant populations of flies could be controlled by using space sprays containing comparatively high concentrations of active ingredient, but increased levels of deposit would be ineffective.     

Effect of insecticides on the short-circuit current and resistance of isolated frog skin

The effects of aldrin, carbaryl, α- and γ-chlordane, dichlorodiphenyldichloroethane (DDD), dichlorodiphenyltrichloroethane (DDT), dieldrin, endrin, heptachlor, lindane, methoxychlor, and nonachlor on the short-circuit current and resistance of the isolated intact frog skin were studied. The short-circuit current is approximately equivalent to the rate of active transport of sodium, while the resistance indicates the summed ionic permeability of the skin. At a concentration of 2 × 10^?4M, only carbaryl, DDD, dieldrin, and lindane produced significant (P<0.05, paired t test) changes in the short-circuit current. Nonachlor produced a decrease (P=0.12) in the short-circuit current and also increased the resistance (P=0.07). DDD, dieldrin, and carbaryl caused significant increases in short-circuit current while at the same time the resistance was significantly decreased. Lindane increased both the short-circuit current and the resistance. It was concluded that the frog skin probably contains effective permeability barriers that prevent externally applied insecticides from reaching the site of active sodium transport. It appeared likely that most of the insecticides produced the observed effects on the frog skin by altering the sodium permeability of the outer barrier.     

Development of resistance to pyrethroids in insects resistant to other insecticides

Resistance to pyrethroids in insects is rare, but its recent rapid development in the field suggests that this resistance may be facilitated by previous exposure to or by resistance to insecticides of unrelated groups. To test this houseflies of strain 49_r2b, originally resistant to dimethoate in the field, were selected eight times during ten generations with either pyrethrum extract or bioresmethrin with or without piperonyl butoxide or with dimethoate. Selecting with any of the pyrethroids led to resistance to these insecticides and in particular to pyrethrum/piperonyl butoxide. Selecting with pyrethrum/piperonyl butoxide resulted in strongest resistance to the pyrethroids tested, whereas selecting with bioresmethrin/piperonyl butoxide resulted in least resistance. These results show that dimethoate-resistant flies selected with pyrethroids can readily develop resistance to these insecticides, but development of resistance can be minimised by using bioresmethrin/piperonyl butoxide. The implications of these findings on the sequential use of insecticides are discussed.     

Delta-aminolevulinic acid synthetase in the house fly and its possible role in oxidative resistance to insecticides

δ-Aminolevulinic acid synthetase (ALA synthetase EC 2.3.1.37) is the initial and rate-limiting enzyme in the biosynthetic pathway leading to heme and cytochrome formation in animals. The occurrence of ALA synthetase in house fly mitochondria was established and its possible relationship to oxidative resistance to insecticides was investigated.Levels of ALA synthetase in five house fly strains were measured and compared with levels of microsomal oxidases and cytochrome P-450 in the same strains. ALA synthetase was elevated in those strains with elevated levels of microsomal oxidases and cytochrome P-450 and was highest in the strain with the highest levels of microsomal oxidases and P-450. A possible regulatory role for ALA synthetase in relation to oxidative resistance to insecticides in the house fly is discussed.     

Genetics of Heliothis and Helicoverpa resistance to chemical insecticides and to Bacillus thuringiensis

Genetic linkage maps of Heliothis virescens and Helicoverpa armigera are being used to identify and characterize resistance-conferring genes. The insensitive acetylcholinesterase conferring resistance to organophosphorus insecticides and the insensitive sodium channel conferring resistance to pyrethroids have both been mapped in H. virescens. The linkage mapping approach permits a genetic dissection of resistance, even when the mode of action and lethal target are not precisely known, such as for the insecticidal toxins from the bacterium Bacillus thuringiensis (Bt). We have identified and mapped a major Bt-resistance locus in a strain of H. virescens exhibiting up to 10000-fold resistance to Cry1Ac toxin and are currently developing a linkage map for H. armigera with a set of ‘anchor’ loci to facilitate comparison with H. virescens. Both species are currently experiencing their first significant selective pressure in the field by transgenic cotton expressing Cry1Ac, and timely identification of resistance mechanisms and their underlying genetic basis will be essential in successfully managing the Bt resistance that will eventually appear. ©1997 SCI     

Phenobarbital induction of detoxifying enzymes in resistant and susceptible houseflies

Houseflies, Musca domestica, L., were treated with the drugs phenobarbital and 3-methylcholanthrene to study the effects of these compounds as inducing agents of the microsomal oxidases, heptachlor epoxidase, and p-nitroanisole O-demethylase, and of DDT-dehydrochlorinase. Phenobarbital was active when applied by injection or as part of the diet but inactive when topically applied. The resulting increases in heptachlor epoxidase activity were as much as 25-fold that of the untreated controls. The net increase in enzyme activity after phenobarbital treatment was greater in an insecticide-susceptible strain, WHO-SRS strain, than in a carbamate-resistant strain. However, the phenobarbital induced increases in DDT-dehydrochlorinase were greater, about 2-fold, in the resistant strains than in the susceptible strain.The optimum dose for phenobarbital was 1% in the diet for a period of 3 days. None of the treatments with 3-MC, feeding, injection, exposure to residues, or topical, were effective in induction.     

Cytochrome P-based resistance mechanism and pyrethroid resistance in the field Anopheles albimanus resistance management trial

The relative rates of cytochrome P⁴⁵⁰ selection in southern Mexican Anopheles albimanus populations were investigated during a 3 years indoor residual house spraying intervention with a pyrethroid (PYR) or DDT, a mosaic of organophosphate (OP)-PYR, and the annual rotation of OP-PYR-carbamate (CARB). This insecticide resistance mechanism, initially evenly spread in the mosquito population, correlated with PYR resistance during the second treated year, when cytochrome P⁴⁵⁰ contents increased in most villages of the PYR, rotation and mosaic schemes. However, by the third year, mean cytochrome P⁴⁵⁰ contents declined to susceptible levels in mosquitoes of the rotation and one mosaic group but not in the PYR-treated villages. In DDT-treated villages, a continuous decrement of cytochrome P⁴⁵⁰ levels occurred since the first treatment year, and susceptible levels were observed at the end of the intervention. Most correlations of cytochrome P⁴⁵⁰ levels and PYR resistance were lost during the third year, indicating that another mechanism evolved in resistant mosquito populations.     

Interaction of insecticides with the Ca2+-pump activity of sarcoplasmic reticulum

The organophosphorus insecticides, parathion and azinphos (10^?5-10^?4M), significantly stimulate the Ca²⁺-pump activity of sarcoplasmic reticulum, while malathion has a limited effect. The rates of Ca²⁺ translocation and ATP hydrolysis are both stimulated and, apparently, the $\text{Ca}{}^{\mathrm{2+}}\text{ATP}$ ratio is improved. Parathion and azinphos maximally increase this ratio by 26 and 14%, respectively. The organochlorine compounds, DDT and aldrin, also stimulate the Ca²⁺ pump, and lindane has a reduced effect. These effects are smaller than those observed for parathion and azinphos. The order of effectiveness is similar to the toxicity of the compounds to mammals and can be described as follows: parathion > azinphos > DDT ≈ aldrin > malathion ≈ lindane.     

Patterns of resistance to organophosphate insecticides in field populations of Helicoverpa armigera in Pakistan

The pattern of organophosphate resistance in field populations of Helicoverpa armigera (Hübner) was monitored in Pakistan from 1994 through 1997 using an IRAC leaf-dip method. Generally, moderate to high resistance was found to an orthophosphorate, monocrotophos and to a dithiophosphorate, ethion. Resistance to the commonly used thiophosphorates, chlorpyrifos and profenofos, was very low during 1994 and 1995 but showed an upward trend during 1996 and 1997. Resistance factors to the other thiophosphorates such as quinalphos, parathion-methyl, methamidophos and triazophos remained very low. Baseline lethal concentrations for ethion, methamidophos and triazophos were at least four to five times higher than those for the other organophosphates tested, suggesting their low intrinsic efficacy against H armigera. © 1999 Society of Chemical Industry     

Comparative measurements of resistance to insecticides in three closely-related old and new world bollworm species

Toxicity measurements were made with three closely-related Bollworm species, Heliothis virescens F., Helicoverpa zea (Boddie), and Helicoverpa armigera (Huebner) using insecticides of 3 different chemical classes. Tests were carried out by a leaf-dip method using neonate larval stages, a topical application test on 3rd larvae, and a topical test with imagines. H. armigera populations from Ivory Coast, Turkey, Thailand, and India were obtained and investigated. H. virescens originated from the USA and Colombia, and H. zea from Guatemala and Nicaragua. Resistance was expressed in all species, the sensitive reference strains having similar LC₅₀s in tests with monocrotophos, profenofos, thiodicarb, and methomyl. Since resistance appeared not to be a quality related to species but rather a feature common to all of the samples investigated, its origin must be connected with the type of cotton culture and the selection pressure they were subjected to in their respective agro-ecosystem. Resistance was highest for monocrotophos and cypermethrin in Central American countries, differences in the treatment regime being reflected by the resistance levels attained. In all stages tested, resistance was sufficiently well expressed to make a monitoring system based on neonate larvae, the 3rd larval stage, or imagines of the species possible. The final decision as to which should be used for a general, comparative monitoring system, therefore, should be governed by the technical parameters of the testing process.     

An evaluation of the role of oxidative enzymes in Colorado potato beetle resistance to carbamate insecticides

Carbofuran and carbaryl LD₅₀ values were determined with and without piperonyl butoxide pretreatment for a resistant (New Jersey) and two susceptible (Utah and Netherland) populations of Colorado potato beetle larvae. Similar bioassays were conducted with carbofuran for resistant (Rutgers) and susceptible (NAIDM) adult house flies. The degree of resistance development by New Jersey Colorado potato beetles (RR = 848) was greater than that of the laboratory-selected colony of Rutgers house flies (RR = 583). Comparisons of synergist difference calculations including “percentage synergism” (%S), “log percentage synergism” (L%S), and “relative percentage synergism (R%S) for the resistant (R) and the susceptible (S) populations indicated the possibility that monooxygenases and other resistance mechanisms may be involved in Colorado potato beetle resistance to these carbamates. Monooxygenase involvement in resistance of Rutgers house flies was demonstrated in vitro by a 4-fold enhancement of p-nitroanisole O-demethylation over that of NAIDM house flies. O-demethylation of p-nitroanisole could not be demonstrated for potato beetle larvae. Colorado potato beetle resistance was associated with increases in microsomal levels of NADPH-cytochrome c reductase (ca. 2-fold) and NADPH oxidation (1.2-fold). The inability to measure O-demethylation in Colorado potato beetles may have been due to the solubilization of NADPH-cytochrome c reductase during microsomal preparation. Significant differences between resistant and susceptible Colorado potato beetle larvae were not observed in the penetration of [¹⁴C]carbaryl. Excretion of the radiocarbon may have been significantly greater in the resistant New Jersey population, but some of the insecticide may have also rubbed off the cuticle. This increased capacity for excretion, combined with increased levels of monooxygenase enzymes, could account for the high resistance level of this population.     

The role of GABA and glutamate receptors in susceptibility and resistance to chloride channel blocker insecticides

Despite a point mutation in the pore-forming segment of the Rdl GABA receptor subunit that is widespread and persistent in insect populations and confers high levels of resistance to dieldrin and other polychlorocycloalkane (PCCA) insecticides, the phenylpyrazole insecticide fipronil, which binds at same site, has proven to be effective in controlling many insects, including dieldrin-resistant populations. Fipronil and its major sulfone metabolite are unique among chloride channel blocking insecticides in that they also potently block GluCls. We present here a patch clamp study of the action of fipronil sulfone on native GABA receptors and GluCl receptors from susceptible and dieldrin-resistant German cockroaches, to provide a better understanding of the effect of the Rdl mutation on the function and insecticide sensitivity of these two targets, and its role in resistance. Dieldrin blocked GABA currents with an IC₅₀ of 3 nM in wild-type cockroaches, and 383 nM in resistant insects, yielding a resistance ratio of 128. Fipronil sulfone blocked GABA currents with an IC₅₀ of 0.8 nM in susceptible insects and 12.1 nM, or 15-fold higher, in resistant insects. While both GluClD (desensitizing) and GluClN (non-desensitizing) receptors were found in German cockroach neurons, GluClN receptors were rare and could not be included in this study. GluClD receptors from resistant insects had reduced sensitivity to glutamate and a lower rate of desensitization than those from susceptible insects, but their sensitivity to block by fipronil sulfone was not significantly changed, with an IC₅₀ of 38.5 ± 2.4 nM (n = 8) in the susceptible strain and 40.3 ± 1.0 nM (n = 7) in the resistant strain. Fipronil sulfone also slowed the decay time course of GluClD currents. These results suggest that GluClD receptors contain the Rdl subunit, but their sensitivity to fipronil sulfone is not altered in resistant insects.     

Assessing the performance against houseflies of indoor aerosol space sprays. Part I. Factors examined during tests with houseflies in free flight

The development of a mathematical model which, by quantifying the interaction of a population of houseflies with an ageing spray cloud, is capable of predicting the knockdown and kill performance of insecticidal aerosol formulations shown against houseflies, Musca domestica L., will be presented in a series of four separate papers. In this first paper, measurements were made of insecticide collected by houseflies during free flight using a standard room-spray technique. With pressure-packed aerosol formulations where the solvent is the principal change, it was shown that both knockdown and mortality responses of the insects were directly related to dose collected. The process of droplet collection was most significantly influenced by their size and availability, dependent upon the time after spraying, the position of insect release and the activity of individual adult M. domestica. The knockdown or mortality response of the insect to given amounts of insecticide was largely unaffected by the remaining solvent, although, with mineral oil, some inhibition was noted at low mortality levels. The amount of insecticide accumulated by houseflies in their initial flight was of prime importance in determining the overall effect. Flies remaining not knocked down at the end of the exposure period were shown to be so because they had accumulated less toxicant and not necessarily because they were more tolerant of the insecticide. The establishment of a relationship between the number of flies in flight and time after release has provided a key function for incorporation into the model.     

Monitoring of resistance of insecticides in house fly (Musca domestica) populations in hungary

Samples of 24 house fly (Musca domestica L.) populations were collected from animal farms in Hungary in 1990 and kept in the laboratory to determine their susceptibility to different types of insecticide: organochlorines, organophosphates, carbamates, pyrethroids, macrocyclic lactone and insect growth regulators. The adulticides were tested with topical bioassay in all 24 populations, the larvicides were studied with treated larval medium in 16 populations. The data were expressed as LD₅₀ and LC₅₀ values (ng fly ?1 and mg kg ?1 larval medium respectively). The percentages of populations which had resistance ratios > 10 at LD₅₀ or LC₅₀ were: 63% to DDT, 50% to methoxychlor, 13% to lindane, 83% to malathion, 63% to trichlorfon, 4% to propetamphos, 96% to dioxacarb, 46% to propoxur, 4% to methomyl, 13% to pyrethrum, 96% to bioresmethrin, 63% to permethrin, 58% to cypermethrin, 79% to SK-80, 79% to deltamethrin, 38% to invermectin, 0% to diflubenzuron, 0% to cyromazine. Correlation analysis showed a high degree of positive correlation among the adulticides except for ivermectin, bioresmethrin and SK-80. No cross-resistance was found between the larvicides and the conventional adulticides. Differences of insecticide resistance levels among the populations surveyed were studied by principal component and factor analysis. A fairly good relationship between resistance status and control practices used on farms was revealed. The populations originating from those farms where the application of adulticides had been frequent or regular and where high resistance was shown to most chemicals could be separated from the others.