The toxicities of four insecticides to Tribolium confusum Duv. in two sets of conditions of temperature and humidity

The toxicities to Tribolium confusum Duv. of wettable powder formulations of malathion, pirimiphos-methyl, fenitrothion and jodofenphos in constant conditions of 25°C, 70% r.h. were compared to the toxicities when exposure was in a diurnal cycle of temperature and humidity varying between 5°C, 82% r.h. and 10°C, 79% r.h. All insecticides were more effective at the higher temperature. The ED₅₀ values obtained in the two sets of environmental conditions differed by factors of less than 10 in the cases of malathion and pirimiphos-methyl, and more than 20 in the cases of fenitrothion and jodofenphos. The minimum doses required to kill all the insects tested in the colder conditions were as follows: pirimiphos-methyl 232 mg/m², fenitrothion 465 mg/m², malathion 1395 mg/m² and jodofenphos > 1395 mg/m².     

Studies on insecticide resistance in Oryzaephilus mercator (Fauv.) (Coleoptera,Silvanidae)

Strains of Oryzaephilus mercator from the Gambia, Italy, Senegal, and Swaziland were found to be resistant to malathion, and to malathion synergized by triphenyl phosphate while single strains from Botswana, England, and Spain were malathion-susceptible. Strains from Botswana, the Gambia, Italy, Senegal, and Swaziland were resistant to lindane. After 6 selections with malathion, a strain from Senegal had a 7-fold resistance to malathion, and was also resistant to malathion synergized by triphenyl phosphate (×8), bromophos (×158), jodfenphos (×28), fenitrothion (×2), diazinon (×4), tetrachlorvinphos (? × 64), and lindane (? ×89).     

Susceptibility to contact insecticides of granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae) originating from different locations in the former Yugoslavia

The insecticides dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin and cypermethrin were applied to filter paper to assess their toxicity to granary weevil Sitophilus granarius adults. Based on discriminating doses obtained from tests on a susceptible laboratory population, the susceptibility of 12 populations originating from different storage facilities (11 in Serbia and 1 in Bosnia-Herzegovina) was tested. The facilities included silos, floor stockpiles and attic stockpiles. Weevils originating from Apatin, Belgrade Port, Bijeljina and Kikinda were submitted to toxicity testing, and determination of ld-p lines, LD values and levels of susceptibility/resistance. Chlorpyrifos-methyl proved the most toxic and cypermethrin the least toxic insecticides against all populations. Dichlorvos, malathion and pirimiphos-methyl had the least toxic effect on weevils originating from Belgrade Port and Kikinda, While deltamethrin was most toxic to weevils from Belgrade Port, and least toxic to weevils from Kikinda. The resistance ratios (RR) for deltamethrin at the LD₅₀ and LD₉₅ levels 48 h after exposure to treated filter paper were 11.2 and 14.5 for Bijeljina weevils, and 20.9 and 25.5 for Kikinda weevils.     

The effect of holding adult Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) at different temperatures on their subsequent susceptibility to malathion

There is reason to believe that the temperature prior to exposure may effect the response of adult Oryzaephilus surinamensis to the recommended discriminating dose test for malathion resistance. Experiments were carried out in which four malathion resistant strains of O. surinamensis were kept at 15, 20, 25 and 30°C for two weeks prior to testing at 25 C. It was found that conditioning at the lower temperatures resulted in a significantly higher knockdown than conditioning at the higher temperatures. For each 5°C fall in conditioning temperature there was a 7.5% increase in knockdown. Chemical analysis showed that in the first hour of exposure more malathion was taken up by the beetles conditioned at lower temperatures than by those conditioned at the higher temperatures.     

Field trials to control insect pests of farm-stored maize in Zambia

Severe infestations of Sitophilus zeamais Motsch and Sitotroga cerealella Oliv. occur in maize cobs stored under farm conditions in Zambia causing up to 92% damaged grains 8 months after harvest. Shelling the maize reduced S. cerealella damage to low levels and also stabilized the moisture content of the grain providing a more suitable substrate for insecticide application and c control of S. zeamais. Malathion at 12 ppm a.i., tetrachlorvinphos (12 ppm), and jodfenphos (12 ppm), applied as dust admixtures to shelled maize in traditional mud-walled, timber and thatch storage cribs, all kept damaged grains below 10% up to 10 months after harvest. Pirimiphos-methyl (4 ppm) and fenitrothion (2 ppm) maintained these low damage levels up to 8 months after harvest, but there was evidence of continued S. cerealella infestation with these two insecticides.     

Altered susceptibility of granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae) populations to insecticides after selection with pirimiphos-methyl and deltamethrin

Toxicity of the contact insecticides dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin and cypermethrin to granary weevil Sitophilus granarius (L.) adults from five populations previously selected with deltamethrin and pirimiphos-methyl, and two populations that had no contact with pesticides over an interval of 12 generations, was investigated in the laboratory by application to filter paper. The populations originated from storage facilities situated in different parts of the former Yugoslavia.A population originating from Apatin and one from Belgrade Port were selected three times each at the LD₅₀ level with deltamethrin and pirimiphos-methyl, respectively. In separate experiments, weevils from Belgrade Port were selected once at the pirimiphos-methyl LD₇₀ level and Bijeljina and Kikinda populations both once at the deltamethrin LD₇₀ level. All selection doses were at a level obtained from determining weevil mortality after 24 h of exposure to treated filter paper.Compared with the toxicity to laboratory weevils, the weevils from Apatin after the third selection were found to be 32.1 and 51.9 times less susceptible to deltamethrin at the LD₅₀ and LD₉₅ levels, respectively, while those from Belgrade Port were 2.7 and 3.2 times less susceptible to pirimiphos-methyl. Selection of Belgrade Port weevils at the pirimiphos-methyl LD₇₀ did not significantly affect their susceptibility to that insecticide but it caused a significant decrease in deltamethrin toxicity, which is indicative of a cross-resistance between the two compounds. Selection of Bijeljina weevils caused an increased resistance to deltamethrin, while selection of Kikinda weevils had little effect on their susceptibility to dichlorvos, but it caused a significant decrease in malathion and cypermethrin toxicity, and resistance to deltamethrin markedly increased (RR=238.8 at LD₅₀ and 660.8 at LD₉₅ levels, compared with laboratory weevils). Chlorpyrifos-methyl was the most toxic insecticide to all populations, while cypermethrin was the least toxic compound.     

The cross-resistance spectrum of Sitophilus granarius (L.) (Coleoptera: Curculionidae) heterozygous for pyrethrin resistance

Dose-response data were obtained from the F₁ progeny of crosses between virgin Sitophilus granarius (L.) from pyrethrin-resistant and susceptible strains. These data were compared with data from the parental strains. The insects were tested with pyrethrins, bioresmethrin, malathion, pirimiphos-methyl, lindane, DDT and propoxur. The exposure method was confinement of the insects on filter papers impregnated with insecticide in oil. The pyrethrin-resistant strain showed resistance to all seven insecticides. The probit lines of the heterozygotes fell approximately half-way between those of the resistant and susceptible strains for all the compounds tested. R-strain males responded to lindane more slowly than did the females, whereas there was no significant difference in the rate of response of the sexes of the S-strain.     

Selective treatments,including combinations of pyrethroid and organophosphorus insecticides. For control of stored product Coleoptera at two temperatures

Selective treatments, appropriate to simulated storage conditions, reinfestation pressures and species or strains of insects present in the wheat, required less insecticide than any “blanket” or all-purpose treatment. In particular, the pyrethroids bioresmethrin, synergized bioresmethrin or synergized pyrethrins were especially effective where Rhyzopertha dominica and especially a strain resistant to organophosphorus insecticides, was the only species present. Conversly, the organophosphorus insecticides dichlorvos, malathion, fenitrothion and pirimiphos-methyl were especially effective against Tribolium and Sitophilus species. There was no antagonism between any of the pyrethroids and any of the organophosphorus insecticides when they were applied in combination, in that the period of protection given by combinations was the period of protection given by the pyrethroid component against R. dominica and the organophosphorus component against Tribolium and Sitophilus species. As an example of the data required for selective treatments, bioassays were conducted at 20 and 30°C and it was found that the net effect of the lower temperature in reducing toxicity but increasing persistence was to increase the period of protection given by insecticides in cooled storages. It is suggested that the amounts of insecticides applied to grain could be considerably reduced if more consideration was given to grain conditions, if reinfestation pressures were more carefully examined and if less attention were given to surviving adults under conditions where progeny do not develop.     

The effectiveness of various insecticides on some resistant beetle pests of stored products from Uganda

Laboratory tests were carried out using populations of Tribolium castaneum (Herbst), Tribolium confusum Jacquelin du Val, Sitophilus zeamais Motschulsky, Callosobruchus maculatus (F.), and Zabrotes subfasciatus Boheman, from Uganda, firstly to determine whether they were resistant to malathion and/or lindane and secondly to measure the effectiveness and stability of pirimiphos-methyl, fenitrothion, etrimfos, permethrin and deltamethrin dilute dusts in protecting cereals and pulses from these insect pests. All the insect populations tested were resistant to malathion or lindane and some were resistant to both. Of the insecticides tested, deltamethrin at 1 ppm was generally the most effective. The organophosphorus compounds were only effective against the Tribolium species and Sitophilus zeamais. Permethrin was the least effective, only controlling Callosobruchus maculatus.     

Residual effects of deltamethrin and malathion on different populations of Sitophilus granarius (L.) on treated wheat grains

The impact of 2-, 7-, 14-, 30-, 90-, 150- and 720-day-old deposits of deltamethrin, applied with or without the synergist piperonyl butoxide (PBO), and of malathion, on adults of different populations of granary weevil Sitophilus granarius on wheat was investigated in the laboratory. The insecticides used were commercial formulations and their application rates were as recommended: deltamethrin (dustable powder) 0.5 mg a.i./kg, deltamethrin + PBO (1:10) (emulsifiable concentrate) 0.25 mg a.i./kg, and malathion (dustable powder) 10 mg a.i./kg. The weevil populations examined were: (a) a laboratory population, (b) field populations with different susceptibility to some insecticides as established previously, and (c) populations selected in the laboratory with deltamethrin or pirimiphos-methyl.The 2-day-old deposit of malathion caused complete mortality of all weevil populations after 7 and 14 days. The corresponding deposit of deltamethrin was 100% effective only against the laboratory weevils after 7-14 days, while deltamethrin at the lower level formulated with PBO caused about 90% mortality of laboratory weevils and much lower levels of kill among field and selected weevils.Deposits of deltamethrin and malathion up to 90 days old killed all field weevils after 14 days of exposure. The 150-day-old deposit of deltamethrin was also 100% effective against field weevils exposed for 14 days, while the effectiveness against selected populations was around 50%. Malathion deposits of the same age gave 40-50% mortality of field weevils, and 4-68% mortality of selected weevils. The 720-day-old deposits of malathion were ineffective against all weevil populations, while the mortality of laboratory weevils after 14 days contact with deltamethrin deposits of the same age was 76%, and that of field and selected weevils about 50%.     

Evaluation of three compounds with insect juvenile hormone activity as grain protectants against insecticide-susceptible and resistant strains of Sitophilus species (Coleoptera: Curculionidae)

Three compunds with insect juvenile hormone activity have been tested as protectants for wheat grain against one insecticide-susceptible and two insecticide-resistant strains of Sitophilus granarius. Neither JH I nor methoprene gave complete control of S. granarius at 100 ppm whereas ethyl[2-(p-phenoxy)ethyl]carbamate was effective at only 5 ppm. There was no loss of biological activity of this last compound even after treated grain was stored at 25°C and 70% r.h. for 12 months, and it was also found to be highly active against susceptible strains of Sitophilus oryzae and Sitophilus zeamais. There was no evidence that two insecticide-resistant strains of S. granarius were cross-resistant to any of the compounds tested.     

Evaluation of chlorpyrifos and chlorpyrifos-methyl for control of Dermestes maculatus Deg. (Coleoptera: Dermestidae) on sheepskins

Chlorpyrifos and chlorpyrifos-methyl were compared to sodium arsenate for control of Dermestes maculatus Deg. on sheepskins.Laboratory experiments showed that sprays of chlorpyrifos depositing 24·5 mg/m² gave complete control of eggs whereas the standard rate of arsenate only gave 80% control. Almost complete knockdown of mixed instar larvae was obtained with sprays of chlorpyrifos depositing 49 mg/m² whereas the standard rate of arsenate only gave 60% knockdown.In laboratory experiments in which treated sheepskins were stacked to simulate bale conditions, chlorpyrifos deposits of 49 mg/m² gave more effective control of 4th–5th instar larvae at 1 day, 1, 2 and 3 months after treatment than did the standard deposit of arsenate. Chlorpyrifos and chlorpyrifos-methyl deposits of 49 mg/m² permitted less than 10% survival of 4th–5th instar larvae and adults on treated sheepskins at 2 months after treatment.     

Behavior and incidence of Vibro parahaemolyticus in Sydney rock oysters (Crassostrea commercialis)

Vibrio parahaemolyticus grew poorly or not at all during storage of unopened Sydney rock oysters (Crassostrea commercialis) at 15 and 30°C for 2 and 7 days. Although V. parahaemolyticus counts often increased at 30°C, counts above 10⁴/g were not observed. Escherichia coli counts did not usually change substantially under these conditions. V. parahaemolyticus grew more readily during storage of unopened oysters under more severe conditions, with counts approaching or exceeding 10⁶/g after continuous or intermittent storage at 37°C. Opened oysters provided a much more favourable environment than unopened oysters for growth of V. parahaemolyticus. Growth occurred at 15, 30 and 37°C, with counts > 10⁶/g after overnight storage at 30 or 37°C. A survey of 30 market samples of oysters was conducted. Sixteen samples of unopened oysters were collected at the wholesale level and 14 samples of refrigerated opened oysters were purchased from retailers. V. parahaemolyticus was present in all samples of unopened oysters (range 0.4/g?2.3 × 10⁴/g) and in 13 samples of opened oysters (range 4.3/g? > 1.1 × 10³/g).     

Studies on the toxicity of phosphine to tolerant stages of Trogoderma granarium Everts (Coleoptera: Dermestidae)

Tests were conducted at 20 and 30°C at 60% r.h. to find the dosages of phosphine needed for control of diapausing larvae and eggs of Trogoderma granarium. At 20°C, 60% r.h., some larvae from each of four recently acquired field strains of T. granarium survived a 5-day exposure period at a concentration-time (Ct) product of 164 g hr/m³. Under these conditions laboratory stock larvae were killed by a 4-day exposure period of about 120 g hr/m³, and eggs by a 3-day exposure of about 50 g hr/m³. Eggs, aged 0–1 days, proved the most tolerant stage at 30°C, 60% r.h., surviving a Ct-product of 16 g hr/m³ over a 2-day exposure period. At 30°C the diapause of larvae became unstable and their tolerance of phosphine was low. Adults emerging after fumigation of larvae appeared normal and if sufficient numbers emerged together a second generation was produced.Complete control of larvae of several stocks (about 20 weeks in diapause) was achieved within a 4-day exposure at 20°C with a mixture of methyl bromide (2.0 g/m³) and phosphine (1.4 g/m³), whereas 6 days were required for these stocks using phosphine alone. To ensure elimination of all stages of non-resistant T. granarium, exposures to phosphine should last 7 days at 20°C and 4 days at 30°C.     

The biology and control of Zabrotes subfasciatus (Boheman) (Coleoptera: Bruchidae) infesting red kidney beans

Experiments were set up to determine the pattern of development of a South American strain of Zabrotes subfasciatus infesting red kidney beans. The duration of the life cycle was 36 days from egg to adult and after a pre-oviposition period of less than one day females laid 50 eggs in their 13 day life. Most of the eggs were laid after 4 days and 90% hatched. ‘Windows’ developed in the beans after 26 days. Dilute dust insecticides were admixed with beans containing young larvae and with beans with ‘windows’. The treatments did not prevent emergence of the adults but killed them thereafter. Survivors were found on tetrachlorvinphos and bromophos treated beans but not on any others. Adults put on to treated beans at various intervals after treatment were initially killed by all insecticides. Malathion, however, lost its activity within 6 weeks and gamma-HCH was the most persistent being effective up to 24 weeks. For the period for which farmers would require to protect their beans in storage, about 8 weeks, iodofenphos or pirimiphos-methyl applied at 8 ppm would be good alternatives to gamma-HCH.     

Degradation of organophosphorus pesticides in aqueous extracts of young green barley leaves (Hordeum vulgare L)

The degradation of the organophosphorus pesticides malathion, chlorpyrifos, guthion, diazinon, methidathion and parathion in an aqueous extract of young green barley leaves (Hordeum vulgare L) was monitored by gas chromatography. Aqueous solutions of various amounts of freeze‐dried young barley leaves containing 5.75 mg l⁻¹ of malathion were incubated at 37 °C and pH 7.4 over prolonged time periods. Over 95% of the malathion degraded in 4 h in a 3% (30 g l⁻¹) solution of young green barley leaves. When the barley solution was autoclaved at 120 °C for 25 min prior to the addition of malathion, no degradation of malathion was observed. When 10 mg l⁻¹ each of the above six pesticides was incubated in a 15% (150 g l⁻¹) solution of young green barley leaves for 3 h at 37 °C and pH 7.4, malathion and chlorpyrifos degraded 100%, whereas parathion (75%), diazinon (54%), guthion (41%) and methidathion (23%) showed lesser degrees of degradation. © 1999 Society of Chemical Industry     

The effect of temperature and humidity upon the development and fecundity of Dermestes haemorrhoidalis Küster and Dermestes peruvianus Laporte de Castelnau (Coleoptera: Dermestidae)

Larvae of Dermestes haemorrhoidalis Küster and D. peruvianus Cast. were bred on a diet of fishmeal, wheat-germ, yeast and cholesterol at 15, 20, 25, 30 or 32.5°C with a constant 65% r.h. and at 25°C with 40, 50, 60, 70 or 80% r.h. Whenever possible emerging adults were paired and kept under the same conditions to determine their longevity and fecundity. Egg hatch was determined at a wider range of temperatures and humidities. Eggs of D. peruvianus hatched over the range 10–30°C and those of D. haemorrhoidalis from 12.5–35°C when the eggs were laid at 25°C. D. haemorrhoidalis completed development from 20 to 32.5°C, the period ranging from about 100 days (20°C) to about 38 days (30°C). D. peruvianus developed from 15 to 30°C taking about 300 days (15°C) to about 60 days (25°C, 80% r.h.). Both species developed at all humidities tested at 25°C. Adult D. haemorrhoidalis lived up to 240 days if provided with a weekly drink and the longest lived D. peruvianus exceeded 300 days. Adult D. haemorrhoidalis bred at 30°C laid few eggs and those bred at over 30°C were infertile. At 20 and 25°C approximately 150 eggs were found over a period of up to 220 days, most eggs being deposited in the first 100 days. Few eggs of D. peruvianus were found except at 20°C and to a lesser extent at 25°C, 80% r.h. At 20°C, the number of eggs found averaged 75 laid over up to 300 days, the rate of oviposition diminishing with age of female. It is suggested that egg-cannibalism is a probable cause of the apparent low productivity of D. peruvianus females.     

Initial efficacy of pyrethroids,inert dusts,their low-dose combinations and low temperature on Oryzaephilus surinamensis and Sitophilus granarius

In this study, initial efficacy of three pyrethroids, two inert dusts and their low-dose combinations were investigated on adults of Sitophilus granarius and Oryzaephilus surinamensis at laboratory conditions. The insects were exposed to treatments on concrete surface. The LC₂₅ values of the pyrethroids and LD₂₅ values of the inert dusts were estimated and used for determining their combination effects. Mortality of insects was recorded 48 h after treatments. The effect of a low temperature, −18 °C was also assessed on both species. Exposure times to −18 °C were 15, 18, 22, 27, 33 and 40 min for S. granarius and 10, 12, 15, 19 and 23 min for O. surinamensis in main experiments. The treated insects were kept in the laboratory conditions for 24 h after cold treatments, then the mortalities were recorded. The LC₅₀ values estimated for deltamethrin, lambda-cyhalothrin and fenvalerate on S. granarius were 45.08, 43.34 and 465.00 mg ai/L; and on O. surinamensis were 0.65, 1.83 and 81.36 mg ai/L, respectively. The LD₅₀ estimated for zeolite on S. granarius was 10.32 g/m²; and kaolin was not effective on this species. The LD₅₀ values estimated for zeolite and kaolin on O. surinamensis were 7.7 g/m² and 12.0 g/m², respectively. Mortalities caused by deltamethrin + zeolite and lambda-cyhalothrin + zeolite combinations on S. granaries were 80.0% and 63.3%, respectively. The effects of combinations of the pyrethroids and zeolite or kaolin on O. surinamensis were also significantly higher than sum of their individual effects. It means the effects of these combinations were synergistic. The LT₅₀ values estimated at −18 °C were 33 min for S. granarius and 16 min for O. surinamensis. The results obtained from this study can be used as basic and preliminary information for practical control programs of these pests in stored products.     

Some further observations on the effect of temperature on the fecundity and longevity of Dermestes lardarius L. (Coleoptera: Dermestidae)

The fecundity of Dermestes lardarius L. was determined on a diet of fish-meal, yeast and cholesterol at 65% r.h., 17.5, 20, 22.5, 25, 27.5 and 30°C. Pairs of adults were given a water drink and eggs removed twice weekly. The median life-span of adults was longest at 17.5 and 20°C (maximum of 223 days) and shortest, 56 days, at 30°C. At each temperature, except 30°C, 50% of the females lived longer than males. At temperatures ranging from 17.5 to 27.5°C some females laid much earlier than others and some individuals exhibited two periods of oviposition. The longest oviposition periods were recorded at 20°C and the shortest at 27.5°C. Temperature had a great influence on the numbers of eggs laid. The total yield of eggs reached a peak of 1261 at 20°C and then declined to 52 at 27.5°C. Fifty percent of the females failed to lay at 27°C and no eggs were laid at 30°C. Fecundity of the females was very variable (0–196). The temperature of 20°C seemed to be optimal for egg laying in this species.     

Residual toxicities and persistence of organophosphorus insecticides mixed with carbaryl as structural treatments against three liposcelidid psocid species (Psocoptera: Liposcelididae) infesting stored grain

Four organophosphorus insecticides, azamethiphos, fenitrothion, chlorpyrifos-methyl, and pirimiphos-methyl were each mixed with carbaryl and evaluated as structural treatments on concrete and galvanized steel panels (0.3×0.3 m) against adults of three liposcelidid psocids: Liposcelis bostrychophila Badonnel, L. entomophila (Enderlein), and L. paeta Pearman. Residual toxicities and persistence of these insecticide mixtures were assessed at 30±1°C, 70±2% r.h., and a photoperiod of 12:12(L:D) h from 1 day after treatment (0 week) and at weeks 1, 2, 4, 6, and 8, and then every 4 weeks up to week 40. Mortality was recorded at exposure periods of 6 h and then every 24 h until end-point was achieved. Significant enhancement in residual toxicities was observed in azamethiphos plus carbaryl against L. entomophila, and chlorpyrifos-methyl plus carbaryl and pirimiphos-methyl plus carbaryl against all three species on steel surfaces, compared with the individual effectiveness of these insecticides reported earlier. We conclude that combining carbaryl with either azamethiphos, chlorpyrifos-methyl, or pirimiphos-methyl as a structural treatment will provide long-term protection (up to 40 weeks) against infestation by all three psocid species on steel storage structures, whilst carbaryl with fenitrothion will give shorter protection (up to 8 weeks). On concrete structures, however, only azamethiphos plus carbaryl will provide long-term protection against L. bostrychophila (up to 28 weeks) and L. paeta (up to 16 weeks). None of the four insecticide mixtures studied would provide long-term protection against an L. entomophila infestation on concrete surfaces.