The prospect of using sub-lethal imidacloprid or pirimicarb and a parasitoid wasp, Lysiphlebus fabarum, simultaneously,to control Aphis gossypii on cucumber plants

The broad-spectrum insecticides greatly influence the control of cotton aphids; however, due to frequent chemical control, Aphis gossypii (Hemiptera: Aphididae) has developed resistance against several classes of synthetic insecticides. In this study, we explored the sub-lethal effects of imidacloprid and pirimicarb, two commonly used insecticides for aphid control, on a parasitoid wasp, Lysiphlebus fabarum (Marshall) (Braconidae: Aphidiinae), when simultaneously used to control melon aphid on cucumber plants, as part of a comprehensive study for integrated pest management. Bioassays of imidacloprid and pirimicarb were performed to calculate LC₅₀ with third instars of A. gossypii. The LC₅₀ of these insecticides (110.55 and 250.89 μg/lit, respectively) were used to expose the wasp larvae, pupae, and adult parasitoids on a cucumber leaf. The percent mortality, percent adult emergence, and sex ratio were calculated during each exposure test. Moreover, the body size, egg load, and mature egg size of wasps surviving the insecticide treatments, as well as the sex ratio of the second generation was evaluated. Regardless of the host aphid mortality, none of the insecticides caused mortality of larval stage of the parasitoid. The insecticide application on pupal stage revealed that the percentage of mortality, sex ratio, body size, and egg load of surviving wasps, as well as the sex ratio of their offspring was adversely affected by imidacloprid, but not by pirimicarb. The present study suggests pirimicarb as a preferred insecticide, with less harmful effects on the fitness components of L. fabarum, for integrated pest management of cotton aphids.     

Genetics of resistance to parathion and demeton-S-methyl inTetranychus urticae Koch (Acarina)

Out of a strain, resistant to organophosphorous insecticides, a dominant factor has been isolated by repeated backcrossings with a susceptible strain under selection pressure. This factor, calledOP, gives a large resistance to parathion and a much smaller resistance to demeton-S-methyl. Modifiers toOP increase the demeton-S-methyl resistance to a high level. Evidence is given that the resistance to the mentioned insecticides of the well known Leverkusen resistant strain has a similar inheritance.Abbreviations used OP organophosphorus - R resistant - S susceptible     

Side effects of flonicamide and pymetrozine on five aphid natural enemy species

The effects of flonicamide and pymetrozine, on inert and natural substrates, on the rove beetle Aleochara bilineata (Gyll.), the parasitic wasp Aphidius rhopalosiphi (DeStefani-Perez), the ladybird Adalia bipunctata (L.), the carabid beetle Bembidion lampros (Herbst), and the hoverfly Episyrphus balteatus (DeGeer) were assessed in the laboratory. Deltamethrin and pirimicarb were also tested as toxic reference compounds. The results indicated high selectivity of flonicamide and pymetrozine for all the species tested. No significant effects on B. lampros and A. bilineata were recorded for sand or on E. balteatus for plants. Pymetrozine on inert substrates had no effects on A. bipunctata larvae, whereas flonicamid was slightly toxic on glass plates but harmless on plants. Both compounds were toxic to adult A. rhopalosiphi on glass plates and on plants in the laboratory, but no effects were observed on plants treated in the field. In comparison, the toxic reference products were always more toxic. Compared with classical insecticides tested on the same species using similar methods, flonicamide and pymetrozine seem to be promising insecticides for aphid control in terms of selectivity for aphid antagonists.     

Alarm pheromone secretion by insecticide-susceptible and -resistant Myzus persicae treated with demeton-S-methyl; aphid dispersal and transfer of plant viruses

The insecticides demeton-S-methyl and pirimicarb induced cornicle secretion, and thereby alarm pheromone release, in Myzus persicae. Secretion was earliest in young and insecticide-susceptible aphids. In laboratory experiments to assess the behavioural significance of this effect, demeton-S-methyl applied to colonies of R₁ (moderately resistant) aphids killed the majority, but caused the remainder to disperse. The timing and degree of dispersal depended on the size and composition of the colonies. Beet yellows virus was transferred by dispersed aphids, but less frequently when recipient indicator seedlings were treated with demeton-S-methyl. R₂ (strongly resistant) aphids soon dispersed from colonies containing susceptible nymphs (which secrete alarm pheromone early) and transmitted readily even to treated seedlings. The non-persistent potato virus Y was transferred by dispersed R_: aphids and no protection was afforded by treatment of the seedlings.     

Susceptibility of the woolly apple aphid parasitoid,Aphelinus mali (Hym.: Aphelinidae), to common pesticides used in apple orchards in Israel

The effects of one acaricide (cyhexatin), two fungicides (penconazole and sulfur), and six insecticides (azinphos-methyl, chlorpyrifos, imidacloprid, pirimicarb, triazamate and vamidothion) on the adult stage of the parasitoidAphelinus mali (Haldeman), a parasite of the woolly apple aphidEriosoma lanigerum (Hausmann), were investigated under laboratory conditions. Chlorpyrifos (an organophosphorus insecticide-OP) was found to be highly toxic to the adult wasps. Vamidothion (OP) was more toxic to the parasitoid than azinphos-methyl (OP). On the other hand, both chlorpyrifos and azinphos-methyl were found to be harmless to the immature stages of the parasitoid in a test conducted under semi-field conditions. Of the other insecticides, imidacloprid was more toxic to the adult parasitoid than pirimicarb and triazamate. Neither cyhexatin nor penconazole had a considerable toxic effect upon the parasitoid. In contrast, sulfur was found to be moderately toxic to the parasitoid under laboratory conditions, as well as in a field survey in which we followed populations ofE. lanigerum andA. mali parasitization in sulfur-treated plots, and in a plot treated withAmpelomyces quisqualis Ces., a fungus antagonist to powdery mildew. The implications of these results to IPM programs of apple orchards in Israel are discussed     

Effects of 45 insecticides,acaricides and molluscicides on the rove beetleAleochara bilineata (Col.: Staphylinidae) in the laboratory

Effects of 45 insecticides, acaricides and molluscicides on adult females of the rove beetleAleochara bilineata were investigated in the laboratory. The pesticides were tested in concentrations equivalent to the highest recommended dosages for practical use. Mortality, egg production and hatch of the eggs were measured. The reproducibility of the test and the suitability of the strain ofA. bilineata used are discussed. The toxicity of the cholinesterase inhibitors tested was varying, but in general high. Only pirimicarb and acephate showed low toxicity. The pyrethroids tested were highly toxic, even though fluvalinate allowed a few eggs to be laid. The test did not give conclusive results for insect growth regulators. The ecological relevance of laboratory results is discussed, and it is concluded that only for pesticides with no or low toxicity can the results be used for prediction of effects in the field.     

Toxicity of field-weathered insecticide residues to Anaphes iole (Hymenoptera: Mymaridae), an egg parasitoid of Lygus lineolaris (Heteroptera: Miridae), and implications for inundative biological control in cotton

Anaphes iole Girault is an egg parasitoid that has potential as an inundative biological control agent for the tarnished plant bug Lygus lineolaris (Palisot de Beauvois) in cotton in the midsouth USA. Our research addressed survival of A. iole wasps exposed to field-weathered residues of insecticides important to cotton production in the region. Our objectives were to identify insecticides with decay profiles that might be compatible with augmentative releases of A. iole in cotton. Survival of female wasps exposed to field-weathered residues on cotton leaves was determined at 0, 2, 4, 8, 16, 23, and 30 days after treatment with field rates of nine compounds. Immediately after treatment, residues of most insecticides (acephate, cyfluthrin, λ-cyhalothrin, imidacloprid, thiamethoxam, spinosad, fipronil, and oxamyl) resulted in <3% survival. Indoxacarb was the exception with about 30% survival at this time. Survival of wasps exposed to oxamyl, imidacloprid, indoxacarb, and acephate increased considerably during the first week after treatment. Upper limits of 95% CI values for ST₅₀ estimates (days for 50% survival) were ⩽5 days for these insecticides. Survivorship of wasps exposed to λ-cyhalothrin and thiamethoxam was intermediate (95% CI values between 5 and 11 days). Of the insecticides tested, residues of cyfluthrin, fipronil, and spinosad were most deleterious to A. iole (95% CI values > 11 days). Precipitation and wind speed during the study period were less than 30-year averages; thus, under typical weather conditions insecticides might decay more rapidly than observed in this study. Our results suggest that while most insecticides tested exhibited high acute toxicity to A. iole wasps, residues of several compounds decayed rapidly enough to show promise in an augmentative release program.     

Inhibition of erythrocyte membrane (Ca2+ + Mg2+)-ATPase by the organophosphorus insecticides parathion and methylparathion

Organophosphorus insecticides parathion and methylparathion non-competitively inhibited the activity of (Ca²⁺ + Mg²⁺)-ATPase bound to and solubilized from pig erythrocyte membrane. Both enzyme preparations exhibited biphasic substrate curves displaying the existence of two functional active sites with low and high affinity to ATP. Also, the relationship between the activity of bound enzyme and Ca²⁺ concentration was biphasic. The activity reached maximum at 20 μM then dropped progressively as the Ca²⁺ concentration was raised. The inhibition of the activity was more pronounced for parathion than for methylparathion and the solubilized enzyme preparation was more affected than the bound one. The inhibition constants (K_i) for parathion for bound enzyme were 55 and 158 μM for high- and low-affinity active sites, respectively; for methylparathion these values equalled 74 and 263 μM, respectively. K_i values for parathion were 36 and 118 μM for solubilized enzyme (high- and low-affinity sites, respectively), for methylparathion −62 and 166 μM, respectively. The magnitude of the effect was greater for a low Ca²⁺ concentration, which could arise from different conformational states of the enzyme at different calcium concentrations. The results of the experiment suggest that the insecticides inhibited the ATPase by binding to a site on the enzyme rather than by the interaction with associated lipids, although lipids could weaken the action of the compounds due to the strong affinity of organophosphorus insecticides to lipids.     

Side-effects of insecticides on two erigonid spider species

The current rearing technique forErigone atra (Blackwall) andOedothorax apicatus (Blackwall) (Araneae, Erigonidae) was improved. To reduce time spent rearing on live fruit flies the spiders were kept on a culture of the Collembola speciesLepidocyrtus lanuginosus (Gmelin) (Entomobryidae). Side-effects on spiders of two pyrethroid insecticides (fenvalerate and lambda-cyhalothrin) and one carbamate insecticide (pirimicarb) were tested. Sensitivity of adults of both sexes and juveniles to insecticides and their influence on the rate of emergence of spiderlings from cocoons were investigated using topical application, spraying or residual contact. LD₅₀ values for adults ranged from 0.49 to 2.52 ng a.i./spider for lambda-cyhalothrin and from 5.75 to 98.20 ng a.i./spider for fenvalerate. Topical application also resulted in up to a week's delay of web-building. A moving laboratory spraying equipment was used to spray spiders with different insecticide dosages and water volumes. Pyrethroids sprayed onto adults in webs had stronger effects than pyrethroids sprayed onto sitting or walking spiders on the soil surface. Residual contamination caused higher mortality of spiders after contact with lambda-cyhalothrin than fenvalerate. In all tests, males were more susceptible to pyrethroids than females; this difference was related to body weight. Mortality rate was higher forE. atra than forO. apicatus. Both pyrethroids were also toxic to spiderlings. Lambda-cyhalothrin inhibited emergence ofE. atra spiderlings from cocoons. Pirimicarb was harmless to both spider species.     

Studies on the toxicity of insecticidal drift to the first instar larvae of the Large White butterfly Pieris brassicae (Lepidoptera: Pieridae)

The toxicity (LD,) of eight insecticides to 2–day-old first instar larvae of Pieris brassicue was determined by topical application. On this basis, the insecticides could be ranked in ascending order viz. dimethoate > pirimicarb > phosalone > endosulfan > fenitrothion > pirimiphos-methyl > fenvalerate > diflubenzuron. Relative to endosulfan, dimethoate and pirimicarb were 30–25 times less toxic while at the other extreme, fenvalerate (x 12) and diflubenzuron (x 26) were much more toxic to the larvae of P. brassicae. A methodology was developed for examining the effects of spray drift through bioassay using these 2–day-old larvae. Six field trials with commercial formulations were carried out in which variables other than the insecticide and wind speed were held constant as far as possible. Phosalone (700 g active ingredient ha) produced no effect beyond 1 m downwind at low wind speed (2 m s); at high wind speed (4 m s-¹). larval mortality (5.3%) was recorded up to 2m. Fenitrothion (1050 g a.i. ha^-1) at moderate wind speed (3 m s-^l) caused mortality up to 4 m while fenvalerate (30 g a.i. ha-^l) at the same wind speed affected larvae up to a distance of 8 m. Diflubenzuron at a very low dosage (6.5 g a.i. ha-¹) also produced effects up to 8 m. At the maximum approved dosage (100 g a.i. ha^-1), and at high wind speed (4.25 m s-^l), diflubenzuron killed 8.4% of the larvae at 16 m distance. At wind speeds of 2 - 3.5 m s^-1, spray deposits on the upper surfaces of water sensitive papers were high at 0 m and declined exponentially with distance. At higher wind speeds (4 - 4.25 m s^-I) turbulence produced irregular deposits. Deposition on lower surfaces was much lower than on upper surfaces but the trends with distance and wind speed were the same. The exponential relationships between mortality and distance, and drift deposition and distance, were examined. The results are discussed with respect to laboratory toxicities, application rates, wind speeds and ecological factors.     

Behavioural consequences of cold exposure on males and females of <Emphasis Type="Italic">Aphidius rhopalosiphi</Emphasis> De Stephani Perez (Hymenoptera: Braconidae)

Cold storage of insect parasitoids is currently used before mass release in the field in biological control programmes. The physiological consequences of constant cold storage are known in various species of parasitic wasps, but there are few reports on the behaviour of survivors and even fewer reports where both sexes were tested. In this study, we observed the consequences of a long storage of Aphidius rhopalosiphi De Stephani Perez (Hymenoptera: Braconidae), a parasitoid of the cereal aphid Sitobion avenae Fabricius (Hemiptera: Aphididae), at low temperature on some key behavioural decisions that both sexes will make when released in the field. Males are less tolerant than females and both sexes suffer from a long exposure (28 days or more) at 4°C during the pupal stage: alteration of olfactory responses, decrease in mating capacity and decrease in the efficiency of patch exploitation by females.     

Resistance to organophosphates in red spider mite, Tetranychus urticae, from English hop gardens

Two strains of Tetranychus urticae, collected in 1969 from hops in Kent (strain RK) and Wisbech, Cambridgeshire (RW), showed a similar pattern of resistance to organophosphates, high to parathion (> 100 ×), low to azinphos-ethyl (7 ×) and intermediate to demeton-S-methyl (21–27 ×); they were both fully susceptible to tetradifon, dicofol and formetanate. RK showed greatei than 50 × resistance to fourteen other organophosphates; exceptions were azinphos-methyl (11 ×), phosphamidon (21 ×) and methidathion (31 ×). Resistance in RK was shown to be controlled by a single major gene, incompletely dominant with parathion but nearer to intermediate in expression to demeton-S-methyl and azinphos-ethyl. A test for allelism showed that the major genes for O.P. resistance in RK and the Dutch strain Baardse reside at the same locus or are closely linked. The results are compared with other work on T. urticae and on Panonychus ulmi.     

Lethal and sublethal effects of two new insecticides spirotetramat and flupyradifurone in comparison to conventional insecticide deltamethrin on Trichogramma evanescens (Hymenoptera: Trichogrammatidae)

The effects of three insecticides including deltamethrin, spirotetramat and flupyradifurone on pre-imaginal stages of Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) were investigated using dipping method. The mean emergence rate of T. evanescens when exposed to the recommended field concentrations of deltamethrin, spirotetramat and flupyradifurone were 62.8, 84 and 86.1%, respectively while 94.3% of the wasps emerged in the control group. According to the concentration–response experiments, the LC₅₀ values of deltamethrin, spirotetramat and flupyradifurone were 262.9, 274.8 and 334.8 ppm, respectively. The results indicated that lethal (LC₅₀) and sublethal (LC₃₀) concentrations of three tested insecticides significantly reduced the fecundity and longevity of T. evanescens. However, LC₃₀ of spirotetramat and flupyradifurone didn’t influence the oviposition duration of the wasps when compared with the control group. The gross reproductive rate (GRR), intrinsic rates of increases (r), net reproductive rate (R₀), and finite rate of increase (λ) were significantly lower in all the treated wasps in comparison with control. However, the mean generation time (T) was not affected by the sublethal concentrations of tested insecticides. According to our findings, all insecticidal treatments have adverse effects on the population of T. evanescens, notwithstanding sublethal concentration of flupyradifurone followed by spirotetramat were more compatible with adults T. evanescens in comparison with deltamethrin. However, further studies under the field conditions are required to confirm the results.     

Sublethal effects of chlorantraniliprole and thiamethoxam seed treatments when Lysiphlebus testaceipes feed on sunflower extrafloral nectar

The extrafloral nectar (EFN) of sunflower, Helianthus annuus L., is an important summer resource for many insects and represents a potential route of exposure to systemic insecticides applied as seed treatments to cultivated varieties. Among the many parasitoids that utilize sunflower EFN, Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae) is an important generalist parasitoid of cereal aphids in North America. This study evaluated the performance of adult wasps fed EFN of sunflower plants grown from seed treated with chlorantraniliprole and thiamethoxam. Consumption of EFN from treated sunflower seedings caused no lethal effects, but reduced the numbers of greenbug nymphs, Schizaphis graminum Rondani, attacked and parasitized when wasps foraged in Petri dish arenas. Whereas control females self-superparasitized every fourth host, those exposed to chlorantraniliprole did not. Offspring developmental time and adult emergence were unaffected by either treatment, but thiamethoxam greatly reduced the proportion of female offspring.     

The effect of insecticides on the distribution of foracing parasitoids,Diaeretiella rapae [Hym.: Braconidae] on plants

Foraging aphid parasitoids,Diaeretiella rapae M'Intosh, were exposed to sublethal doses of the insecticides pirimicarb, permethrin and malathion on brusslls sprouts plants. Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and, while on these plants, tended to concentrate activity on unsprayed surfaces. For permethrin and malathion, pesticide residues reversed the stereotypic upward foraging pattern of the wasp. Negative consequences of sublethal pesticide doses for parasitoid foraging efficiency are discussed.      

BIOCHEMICAL ASPECTS OF INSECTICIDE RESISTANCE IN COTTON BOLLWORM FROM HANDAN OF HEBEI PROVINCE*

Abstract The cotton bollworms, Helicoverpa armigera Hübner, collected from Handan of Hebei Province, have evolved high resistance to pyrethroid, organophosphate and carbamate insecticides, The sensitivity of acetylcholinesterase (AChEs) to paraoxon and methomyl varied with the development stages of the cotton bollworm. After the treatments with LD₅ and LD₅₀ of parathion and methomyl to the cotton bollworms, the affinity of AChE to acetylthiocholine (ATCh) and acetyl-β-bmethyl-thio choline (MeTCh) increased significantly except the treatment of parathion using LD₅₀ dosage while the sensitivity of AChEs to paraoxon significantly decreased. The sensitivity of AChEs to methomyl strongly increased in the treatment of parathion using LD₅₀ dosages while strongly decreased in other treatments. The affinity of carboxylesterase to β-naphthyl acetate (β-NA) was higher in groups of treatment with insecticides than in group of control. The glutathione-s-transferase (GST) activity significantly decreased in the induced groups using LD₅ dosages, while increased in the selection groups using LD₅₀ dosages. The effects of parathion and methomyl on the phosphatases of cotton bollworm were related to the dosages of application and the time after treatment and the effect on the alkaline phosphatase was stronger than on acid phosphatase.     

The toxicity of some soil-applied systemic insecticides to Aphis gossypii (Horn. Aphididae) and Phytoseiulus persimilis (Acarina: Phytoseiidae) on cucumbers

Tests with potted cucumber plants confirmed that granular or soil drench treatments applied against Aphis gossypii Glover may limit the performance of a predaceous species introduced to control another pest. Soil applications of thionazin, methomyl, demeton-S-methyl and aldicarb in equal amounts caused deaths, in descending order of toxicity, of the predatory mite Phytoseiulus persimilis Athias-Henriot. This effect was not demonstrated for pirimicarb, menazon or isolan on whole plants at rates up to 10 mg a.i. nor in laboratory tests on detached plant portions. Methomyl and thionazin, but not aldicarb, were relatively more toxic to P. persimilis than to its prey, Tetranychus urticae Koch. Some survival of P. persimilis occurred on plants treated with demeton-S-methyl, but this material was inferior to pirimicarb in both selectivity and persistence. Pirimicarb offers practical control of A. gossypii on cropping cucumbers, without phytoxicity or residues, when applied at 125 mg a.i./plant. It is therefore preferable to other aphicides for use on cucumbers during propagation or cropping, especially where the favoured means of control of T. urticae is by introductions of P. persimilis. Qualitative evidence of in vitro tests suggested that those systemic materials which affect P. persimilis do so by ‘food-chain’ toxicity, but that vaporization from the leaf may also be a factor.     

Monitoring for insecticide resistance in field-collected populations of Blattella germanica (Blattaria: Blattellidae)

Seven field-collected populations of German cockroach, Blattella germanica (L.) (ICN, DNH, CHN, DGU, BSN, GSN, and GWJ), were tested for susceptibility to eight different insecticides by a topical application method, and were compared to an insecticide-susceptible KSS strain. Marked regional variations of insecticide susceptibility were observed. Extremely high to high levels of resistance were observed in bifenthrin [resistance ratio (RR), 46–159], deltamethrin (RR, 61–160), and esfenvalerate [RR, 70–270; except for BSN females (RR, 20) and GSN females (RR, 24)]. Low to moderate levels of resistance were observed in cypermethrin [RR, 16–29; except for DGU females (RR, 88) and BSN females (RR, 41)], permethrin [RR, 11–39; except for DNH females (RR, 110) and BSN females (RR, 44)], chlorpyrifos [RR, 2–13; except for GSN and GWJ females (RR, ca. 140)], chlorpyrifos-methyl (RR, 2–8), and fenthion (RR, 8–17). All of the colonies were susceptible to one or more of the insecticides examined. These results indicate that careful selection and rotational use of these insecticides should result in continued satisfactory control against field populations of German cockroach.     

Parathion and methyl parathion toxicity and metabolism in piperonyl butoxide and diethyl maleate pretreated mice

Pretreatment of male mice with piperonyl butoxide, 400 mg/kg 1 h before challenge with insecticides, resulted in a 40-fold antagonism of the acute i.p. toxicity of methyl parathion but potentiated the toxicity of parathion two-fold. Piperonyl butoxide had no effect on the toxicity of the oxygen analogs of these insecticides, methyl paraoxon and paraoxon. Diethyl maleate (1 ml/kg) depleted liver glutathione by 80% after one hour, potentiated the toxicity of both methyl parathion and methyl paraoxon, and partially counteracted the protective effect of piperonyl butoxide on methyl parathion toxicity. Piperonyl butoxide delayed the onset of brain cholinesterase inhibition by parathion. Studies of the metabolism of the insecticides by liver homogenates in vitro demonstrated that piperonyl butoxide inhibited both the oxidative formation of the oxygen analogs (activation) and oxidative cleavage to p-nitrophenol and dialkylphosphorothioic acid (detoxification). While parathion metabolism was mostly oxidative, methyl parathion metabolism appeared to be predominantly via glutathione-dependent enzymes. Studies of in vitro distribution of the insecticides demonstrated that piperonyl butoxide pretreatment resulted in elevated tissue concentrations of parathion and methyl parathion; however, the rate constant for elimination from plasma for both insecticides was unaffected by piperonyl butoxide. The overall rate of metabolism of methyl parathion in vivo was approximately twice that of parathion. These results suggest that during piperonyl butoxide inhibition of oxidative activation and cleavage, methyl parathion detoxification continues through uninhibited glutathione-dependent pathways of metabolism. The net result is a reduction in the acute toxicity of methyl parathion. Lack of an effective alternate pathway of detoxification may explain the delayed but greater toxicity of parathion in piperonyl butoxide pretreated mice.     

Assessment of Sublethal and Transgenerational Effects of Pirimicarb on the Wheat Aphids Rhopalosiphum padi and Sitobion avenae

The wheat aphids, Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius), are key pests on wheat crops worldwide. Management practices rely primarily on insecticides. The pirimicarb (carbamate) is used extensively as an effective insecticide to control these two aphids. In addition to the mortality caused by pirimicarb, various sublethal effects may occur in aphids when exposed to low lethal or sublethal doses. Understanding the general effect of pirimicarb on aphids could help increasing rational use of this insecticide. Under laboratory conditions, we assessed the sublethal effects of a low lethal concentration of pirimicarb (LC₂₅) on biological traits and acetylcholinesterase (AChE) activity of R. padi and S. avenae. Both direct and transgenerational effects, i.e. on parent and the F1 generations were assessed, respectively. We found that R. padi and S. avenae responded differentially to the LC₂₅ of pirimicarb. The parent generation of R. padi showed a 39% decrease in fecundity and multiple transgenerational effects were observed in the F1 generation; overall juvenile development, reproductive period, adult longevity and lifespan were longer than those of the control group. By contrast, LC₂₅ of pirimicarb showed almost no effects on S. avenae biological traits in both the parent and F1 generations; only the pre-reproductive duration was reduced in F1 generations. Demographic parameter estimates (e.g. r_m) showed similar trend, i.e. significant negative effect on R. padi population growth and no effect on S. avenae. However, AChE activity decreased in both R. padi and S. avenae treated by the LC₂₅ of pirimicarb. We demonstrated sublethal and transgenerational effects of pirimicarb in the two wheat aphid species; it hinted at the importance of considering sublethal effects (including hormesis) of pirimicarb for optimizing Integrated Pest Management (IPM) of wheat aphids.