Efficacy of pesticides on the functional response on larval ectoparasitoid,Habrobracon hebetor Say (Hymenoptera: Braconidae)

Exposing to sub-lethal and low lethal doses of pesticides may cause changes in natural enemy behavioural, such as functional, response. In this study, the effects of chlorpyrifos, carbaryl, abamectin and spinosad were evaluated on the functional response of the Habrobracon hebetor to different densities of last instar larvae of Anagasta kuehniella Zeller. Young adult females of the parasitoid were exposed to LC₃₀ of chlorpyrifos, carbaryl, abamectin and spinosad that were 0.32, 4.03, 3.05 and 17.51?mg a.i./l for 24?h, respectively. Host densities of 2, 4, 8, 16, 32 and 64 were offered to treated young females for 2?h in 10-cm Petri dishes and then the parasitism data were recorded. Experiments were conducted in eight replications. Functional response type was determined using logistic regression and the parameters were appraised by non-linear regression using statistical analysis software. Functional response was type Ш in control and insecticide treatments. Searching efficiency in control, chlorpyrifos-, carbaryl-, abamectin- and spinosad-treated wasps were 0.008?±?0.002, 0.002?±?0.0009, 0.0034?±?0.0013, 0.0076?±?0.002 and 0.0073?±?0.002?h^?1and handling times were 1.38?±?0.1, 7.64?±?1.01, 3.3?±?0.315, 1.55?±?0.1 and 1.46?±?0.11?h, respectively. Chlorpyrifos and carbaryl had the highest effect on searching efficiency of H. hebetor. Spinosad and abamectin showed less adverse effect on the functional response parameters. Finally, after conducting the advanced field studies, spinosad and abamectin may be used as a compatible chemical material with biological control agent in integrated pest management programmes.     

Effects of pupal treatment with Proteus® and Metarhizium anisopliae sensu lato on functional response of Habrobracon hebetor parasitising Helicoverpa armigera in an enclosed experiment system

The ectoparasitoid wasp, Habrobracon hebetor Say (Hymenoptera: Braconidae) is a valuable biocontrol agent attacking larval stages of many lepidopteran pests including Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). The possibility of combined application of this parasitoid wasp with other biological control agents and chemical insecticides is necessary for the success of an Integrated Pest Management (IPM) programme. One of the most important behaviours of a parasitoid refers to the number of hosts attacked by per parasitoid as a function of host density. In this research, the single and joint effects of the insecticide, Proteus® and the entomopathogenic fungus, Metarhizium anisopliae sensu lato (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) (isolate M14) were studied on the functional response of H. hebetor. Newly mated females (<24?h) from treated pupae of H. hebetor were used to study the functional response of this parasitoid wasp to different densities of H. armigera larvae. A type II functional response was observed in all treatments. The results revealed that control and Proteus® treatments developed the lowest (0.5599?±?0.0373?h) and the highest (0.5709?±?0.0443?h) handling time, respectively. The most and the least values of attack rate were observed in control (0.0996?±?0.0164?h^?1) and Proteus® (0.0776?±?0.0119?h^?1) treatments, respectively. The maximum theoretical parasitism rate (T/T_h) was estimated to be 42.86 for female control wasps. After conducting field experiments on functional response along with life table parameters, M. anisopliae sensu lato (isolate M14) may be used as a compatible biocontrol agent with H. hebetor in IPM programmes of H. armigera.     

Comparative study of the population level effects of carbaryl and abamectin on larval ectoparasitoid <Emphasis Type="Italic">Habrobracon hebetor</Emphasis> Say (Hymenoptera: Braconidae)

Habrobracon hebetor Say is one of the most important ectoparasitoids of the larval stage of many invasive agricultural pests such as noctuid and pyralid moths. Lethal and sublethal effects of carbaryl and abamectin were assessed on the ectoparasitoid H. hebetor in laboratory conditions. Dose–response bioassays were carried out on immature and adult stages by using dipping and contact residue methods, respectively. LC₅₀ (lethal concentration for 50%) values of carbaryl and abamectin were 31.19 and 4.16 mg a.i. l⁻¹ on larval stage and 12.6 and 4.42 mg a.i. l⁻¹ on adults, respectively. In order to assess the sublethal effects, adult wasps were exposed to an LC₃₀ of each insecticide and then the demographic parameters of live wasps were studied. The results showed that the intrinsic rate of increase (r _m ), finite rate of increase (λ), net reproductive rate (R₀) and gross reproductive rate (GRR) were significantly affected by the insecticides. The highest and the lowest r _m values were 0.23 and 0.17 in control and carbaryl-treated insects, respectively. The sex ratio of H. hebetor offspring was not significantly affected by either insecticide. The results showed that carbaryl had more adverse effects on population parameters of the parasitoid compared to abamectin. Field studies are needed to determine the total effects of the pesticides on H. hebetor.     

Effects of traditional insecticides on Habrobracon hebetor (Hymenoptera: Braconidae): bioassay and life-table assays

The lethal and sublethal effects of the insecticides chlorpyriphos and fenpropathrine, which are overused in tomato production, were evaluated on the larval, pupal and adult stages of the parasitoid Habrobracon hebetor in the laboratory. Dose-response bioassays were carried out on immature and adult stages by using dipping and contact residue methods, respectively. The LC₅₀ of chlorpyriphos varied from 40 to 2000 times less than the recommended field rate and 10–100 times less for fenpropathrine treatments on the different life-history stages. To assess the sublethal effects, all life-history stages were exposed to LC₂₅ equivalent concentration of each insecticide and the demographic parameters of surviving parasitoids were studied. In LC₂₅ tests on adult stage, mean longevity and fecundity showed significant differences between chlorpyriphos (15.93?±?1.37 d and 128.20?±?20.20 eggs) and fenpropathrine (12.76?±?0.78 d and 124.00?±?12.27 eggs) as compared with the control (20.41?±?0.72 d and 281.00?±?12.95 eggs). In addition, net reproductive rate and intrinsic rate of increase indicated significant differences between chlorpyriphos (22.89?±?6.43 and 0.19?±?0.02) and fenpropathrine (14.44?±?3.58 and 0.17?±?0.02) as compared with the control (55.55?±?12.54 and 0.24?±?0.02). Briefly, we can conclude that both insecticides had negative effects on H. hebetor. However, the negative effect of fenpropathrine on r_m was higher than that of chlorpyriphos. In conclusion, field studies are recommended to determine the total effects of these insecticides on H. hebetor.     

Sublethal toxicity of two insect growth regulators on Habrobracon hebetor (Hymenoptera: Braconidae) under laboratory conditions

The sublethal effects of lufenuron and lufenuron?+?fenoxycarb were tested on the adult stage of the parasitoid wasp Habrobracon hebetor under laboratory conditions. Bioassay tests were carried out in the incubator at a temperature of 26?±?1?°C, relative humidity of 65?±?10% and photoperiod of 16:8 (L:D). Exposure cages were used for the experiments. Tests were conducted in three replications. Young female wasps were exposed to the residues of the pesticides’ sublethal concentrations (LC₂₅) after 1, 24, 48 and 72 h, and then their mortalities were recorded. Results showed that both insecticide treatments had significant differences compared to the control, but not between themselves (df?=?1, F?=?29.21, α?<?.0001). It was also revealed that the time between insecticides application and H. hebetor release would significantly affect the survival of searching parasitoids (df?=?3, F?=?237.01, α?<?.0001). In this regard, the releasing programme should be postponed for at least 24 h after using these insect growth regulators.     

Parasitism Rate of <Emphasis Type="Italic">Habrobracon hebetor</Emphasis> to <Emphasis Type="Italic">Ephestia kuehniella</Emphasis> Larvae: Residual Effect of Deltamethrin,Fenvalerate and Azadirachtin

Sublethal concentrations of chemical insecticides may cause changes in some behavioral characteristics of natural enemies such as functional responses. The residual effect of three synthetic insecticides including deltamethrin, fenvalerate and azadirachtin were studied on functional response of Habrobracon hebetor Say to Ephestia kuehniella Zeller larvae. Seven host densities (2, 4, 8, 16, 32, 64 and 96) were used during a 24 h period. The resulting data were appropriately fit to Type II functional response models in all treatments: (1) control (0.0916 h^?1; and T _h  = 0.2011 h); (2) deltamethrin (a = 0.0839 h^?1; and T _h  = 0.3560 h); (3) fenvalerate (a = 0.0808 h^?1 and T _h  = 0.3623 h); and (4) azadirachtin (a = 0.0900 h^?1 and T _h  = 0.2042 h). Maximum theoretical parasitism rate (T/T _h ) was 119.34 estimated for control wasps. There was no significant difference between the values of attack rates (a and a + D _a ) in all treatments while the handling time was statistically affected in female wasps treated with fenvalerate. Our findings will be useful in safe application of these insecticides in pest management programmes.     

Lethal and sublethal effects of thiacloprid on survival,growth and reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae)

The cotton bollworm Helicoverpa armigera (Hübner) is the most destructive pest of cotton, tomato and chickpea in Iran. In this study, the lethal and sublethal effects of thiacloprid were evaluated against cotton bollworm under laboratory condition at 26?±?1?°C, 70?±?5% RH and a photoperiod of 16:8 (L:D). Bioassay experiments were conducted on first larval instars by mixing the insecticide dilutions with artificial diet. The LC₅₀ value of thiacloprid was 329?mg a.i./l. Sublethal effects of LC₃₀ concentration of thiacloprid was studied on biological parameters. In the study of sublethal effects, thiacloprid at LC₃₀ concentration significantly increased larval and pupal developmental times and reduced adults longevity compared with control but showed no significant effects on fecundity of cotton bollworm. Sublethal effects of thiacloprid also significantly reduced pupal weight compared with control. In general, sublethal effects studies showed that thiacloprid had adverse effects on biological parameters of the pest. Thus, our data suggest that thiacloprid had moderate potential against cotton bollworm.     

Effect of ellagic acid on the larvae of Spodoptera litura (Lepidoptera:Noctuidae) and its parasitoid Bracon hebetor (Hymenoptera:Braconidae)

The present study was aimed at investigating the effect of plant based compound, ellagic acid on parasitoid Bracon hebetor (Say) through its host, the common cutworm, Spodoptera litura (Fabricius). The effect on S. litura was ascertained by feeding six days old larvae on artificial diet incorporated with different concentrations (5 ppm, 25 ppm, 125 ppm, 625 ppm, 3125 ppm) of ellagic acid and water as control. Its effect on B. hebetor was determined by allowing the adult B. hebetor to parasitize the treated host larvae. The mortality of S. litura larvae was increased whereas adult emergence declined with increasing concentration of ellagic acid. The developmental period was delayed significantly and all the nutritional indices were reduced with treatment. Ellagic acid at LC₃₀ (7.70 ppm) had not much influence on the growth of parasitoid B. hebetor but LC₅₀ (43.45 ppm) adversely influenced the development of the parasitoid, B. hebetor when reared on treated larvae of S. litura. This was evident from reduced parasitization, fecundity, egg laying, egg hatching, emergence, increased larval mortality, reduced pupation and prolonged development of the immature stages at LC₅₀. However, parasitization, egg hatching and larval mortality of the parasitoid were not significantly impacted at LC₃₀ indicating the possibility of its use in integrated pest management programmes.     

Functional Response of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) to Sugarcane Whitefly Aleurolobus barodensis (Maskell) in Laboratory Conditions

A functional response study of Chrysoperla carnea (Stephens) larvae to different densities of sugar cane whitefly Aleurolobus barodensis (Maskell) was conducted in test tubes at 26?±?2 °C, 65?±?5 % RH. Chrysoperla carnea showed two different types of functional response in larval instars. First instar exhibits type II. However, second and third larval instars revealed type III functional response. Based on modified Holling’s disk equation, the highest searching rates (a) of 0.82?±?0.0247 h^?1 was found for first instar larva. For second and third larval instars, the attack coefficient (b) were 0.002?±?0.030 and 0.0025?±?0.0424 respectively. The shortest handling time (T_h) per prey was observed at third instar stage (1.574?±?0.0568 h) followed by second and first instar with 1.72?±?0.0411 h and 1.919?±?0.0568 h respectively.     

Acute toxicity and sub-lethal effects of a pyrethroid (cypermethrin) on survival,development and fitness of Helicoverpa armigera

The chickpea pod borer, Helicoverpa armigera (Hübner) is one of the most destructive pests of India and most of the countries. In this experiment, sub-lethal effects of cypermethrin were evaluated against sixth instar larvae of this pest that had ingested insecticide-treated chickpea pods. The LC₅₀, LC₃₀ and LC₁₀ values of cypermethrin were 80.38, 26.65 and 5.41?mg a.i.?L^?1, respectively, against sixth instar. The sub-lethal effects on fitness, eggs, larvae, pupae, adult longevity and reproduction were observed in H. armigera population that survived exposure to the sub-lethal doses of LC₅₀, LC₃₀ and LC₁₀ of cypermethrin. Survivorship was reduced to 36?days if H. armigera exposed to the sub-lethal dose of LC_50, whereas it was 42?days in unexposed groups. Larvae treated with LC₅₀ dose exhibit lowest intrinsic rate of increase (r_m) (0.0413 females/female/day) and highest (0.0517) with the unexposed group. Time taken by H. armigera to complete one generation (T_c) was 40.09?days, while this time significantly lowered to 32.85?days when exposed to the sub-lethal dose of LC₃₀. Hatching eggs were greatly reduced in the larvae exposed to cypermethrin at all the sub-lethal doses. About 430 eggs/female/generation were recorded after treatment with 80.38?mg/L as compared with untreated females (1390). Larvae that were exposed to sub-lethal concentrations of cypermethrin exhibited lower pupal weight and prolonged pupal developmental times compared control larvae. The overall fitness performance was better in the unexposed population as compared to the population exposed to sub-lethal doses.     

Sublethal effects of pyriproxyfen,a juvenile hormone analogue,on Plutella xylostella (Lepidoptera: Plutellidae): life table study

The sublethal effects of pyriproxyfen (PYR, a juvenile hormone analogue) were investigated for two consecutive generations on life-history parameters, such as developmental time, pupal weight, fecundity, fertility and longevity of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). After topical application bioassay of third instar larvae, the LC₂₅ and LC₅₀ values (as sublethal doses) were determined to be 1.49 and 2.01 μg/μl, respectively. The results showed that the egg incubation period, larval and pupal duration times and oviposition period were increased in treated groups compared with the control (treated with distilled water). Pupal weight, adult longevity, fecundity and fertility were significantly reduced in the treatment groups compared with the control. Using the age-stage, two-sex life table analysis, we found that the intrinsic rate of increase (r), finite rate of increase (λ), gross reproduction rate (GRR) and net reproductive rate (R ₀) significantly decreased while the mean generation time (T) and doubling time (DT) increased in two treatment groups compared with the control. In addition, administration of PYR induced morphogenetic abnormalities including untanned pupae, larval–pupal intermediates and various defective adults. The LC₅₀ value was more effective on all of the above biological characteristics than the LC₂₅ for both generations, although parents were more affected than the offspring. In general, our results revealed that PYR was highly effective against P. xylostella in the laboratory both directly (causing mortality) and indirectly (disruption of normal growth and development). We conclude that PYR is an excellent candidate for suppressing populations of P. xylostella through its sublethal effects.     

八种杀虫剂对韭菜迟眼蕈蚊发育和繁殖的亚致死效应

用胃毒触杀法确定8种常用杀虫剂对韭菜迟眼蕈蚊Bradysiaodoriphaga 3龄幼虫的LC₂₀和LC₅₀剂量后,以其LC₂₀分别处理3龄幼虫,将存活幼虫正常饲养,测定该剂量药剂对韭菜迟眼蕈蚊化蛹率、蛹重、羽化率,成虫存活率、雌雄比、单雌产卵量及卵孵化率等指标的影响。结果表明:毒死蜱等4种药剂的影响较显著,其影响程度由高到低依次为毒死蜱＞辛硫磷＞阿维菌素溴虫腈;而另4种药剂丙硫克百威、灭多威、丁硫克百威和吡虫啉则影响不显著。此外也测定了用后4种药剂LC₅₀剂量处理的存活试虫的上述生物学指标,结果表明：除化蛹率和羽化率较对照降低且差异显著外,其他生物学指标与对照处理无明显变化。     

Effect of fenitrothion on Spodoptera exigua larval development and ultrastructure of follicle cells

The effect of four sublethal concentrations (from 0.01165 to 0.3025 μg per insect, responding to LC₁₀/10, LC₁₀, LC₃₀ and LC₅₀) of the organophosphorus insecticide, fenitrothion, on Spodoptera exigua (Lepidoptera, Noctuidae) larval development and ultrastructure of follicular cells of adult female moths was tested. The most prominent malformations were: breaks in the cuticle, increased mortality during larval/pupal molting, alterations of nuclear envelope, changed heterochromatin pattern and abnormalities in mitochondrial ultrastructure. Some of the alterations are dose-dependent, but the other ones, like organization of rough endoplasmic reticulum (RER), show non-linear response: cells exposed to lower concentrations (LC₁₀/10 and LC₁₀) of the insecticide possessed clusters of accumulated RER, which were absent within the cells exposed to higher ones (LC₃₀ and LC₅₀). Formation of the eggshell was also markedly postponed within the groups exposed to lower doses. These findings prove that even minute amounts of xenobiotics may cause significant changes within exposed populations.     

Lethal and sub‐lethal effects of spinosad on the life‐history traits of army worm,Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), and its fitness cost of resistance

Spodoptera litura is one of the most destructive polyphagous insect pests, with more than 120 host‐plant species. In our present study, a field‐collected population of S. litura when selected with spinosad for 11 consecutive generations resulted in the development of 3921‐fold resistance to spinosad as compared to the susceptible strain. The spinosad‐resistant strain of S. litura had a relatively high fitness cost (0.17) as compared to the susceptible strain. Furthermore, the lethal and sub‐lethal effects of different concentrations of spinosad were checked on the susceptible strain at different levels; i.e., LC₄₀, LC₃₀, LC₂₀ and LC₁₀, which revealed that the impact of spinosad on the life‐history traits of S. litura increased with the increase in concentration of spinosad. A significant impact of spinosad was recorded on the larval duration, pre‐pupal weight, pupal duration, pupal weight, reproductive potential and adult emergence. The outcomes of the current research clearly indicate that fitness cost of spinosad and its sub‐lethal effects have a significant impact on population dynamics of S. litura, for which it can be incorporated in integrated pest management.     

Consumption rate and functional response of the predaceous mite<Emphasis Type="Italic"> Kampimodromus aberrans</Emphasis> to two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in the laboratory

Prey stage preference of female Kampimodromus aberrans (Oudemans) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), functional response types and parameters of the predator females to the varying densities of eggs, larvae, protonymphs and deutonymps of T. urticae were determined in order to establish its potential for the mite biological control. Experiments were conducted at 25 ± 1°C, 65 ± 10% RH and 16:8 (L:D) photoperiod. Our results indicated that the predator consumed significantly more prey larvae than other prey stages. Functional response type of predator was determined by a logistic regression model. The predator exhibited a Type II response on all prey stages. The attack rate (α) and handling time (T _h ) coefficients of a Type II response were estimated by fitting a “random-predator” equation to the data. The lowest estimated value α and the highest value of T _h (including digestion) were obtanined for the predator feeding on deutonmph. The lowest value of T _h were obtained for the predator feeding on prey larvae, but the attack rate value obtained on larva wasn’t different than that obtained on egg and protonymph. According to our results, K. aberrans could be an efficient biological control agent of T. urticae at least at low prey densities. However, further field based studies are needed to draw firm conclusions.     

Sublethal effects of hexaflumuron on development and reproduction of the diamondback moth,Plutella xylostella (Lepidoptera: Yponomeutidae)

Abstract Effects of hexaflumuron at 10% lethal concentration (LC₁₀) and LC₂₅ on development and reproduction parameters of the diamondback moth, Plutella xylostella (Linnaeus, 1753) (Lep.: Yponomeutidae) were investigated. Estimated LC₅₀, LC₁₀ and LC₂₅ values of leaf dip bioassay of hexaflumuron on the third instar larvae of the P. xylostella were 1.48, 0.59 and 0.91 mg/L, respectively. Hexaflumuron decreased pupal weight in the parent generation at sublethal concentrations but in the offspring generation, this effect was not observed. Sublethal concentrations increased egg, first and second larval instar and pupa developmental time and shortened life span of adults, but did not change the third and fourth larval instars and pre‐pupa developmental period. Also fecundity of females reduced significantly but hatchability of treatments and control were similar. Survival rate of pre‐adult stages declined significantly at LC₂₅ concentration. Reproduction parameters such as reproductive rate (R₀) and intrinsic rate of increase in sublethal concentrations were significantly lower compared with control, but gross reproduction rate (GRR) at the LC₁₀ concentration was increased and it could be hormoligosis. Also hexaflumuron significantly increased doubling time (Dt). We conclude that the sublethal effects of hexaflumuron might exhibit significant effects on the population dynamics of P. xylostella.     

Functional response of Trichogramma chilonis to Galleria mellonella and Chilo sacchariphagus eggs

A biological control programme using inundative releases of Trichogramma chilonis Ischii (Hymenoptera: Trichogrammatidae) reared on Galleria mellonella L. (Lepidoptera: Pyralidae) is currently underway to reduce infestations of Chilo sacchariphagus Bojer (Lepidoptera: Crambidae) in sugarcane, Saccharum spp., on Réunion Island. To assess the potential of the parasitoid as an inundative biocontrol agent, the functional response of three T. chilonis strains was tested with G. mellonella and one strain with C. sacchariphagus host eggs in glass tubes in the laboratory. The shape of the functional response (type II or III) was determined using logistic regression, and attack coefficients and handling times (T_h) were determined using non‐linear least‐square regression. The behaviour of all three strains with G. mellonella host eggs corresponded to a type III response. The St Benoît T. chilonis strain had a significantly shorter estimate of T_h than the St Pierre strain (P<0.05) and may, therefore, be more appropriate as a biocontrol agent. The functional response with C. sacchariphagus host eggs was a type II with the St Benoît T. chilonis strain. More T. chilonis wasps developed per host egg from the larger C. sacchariphagus host eggs (2.9) relative to G. mellonella (1.1). Superparasitism at low host egg densities was, therefore, likely to have been less frequent with C. sacchariphagus. Black eggs were chosen as an estimate of number of eggs parasitized, although they represent the number of eggs where parasitism led to complete pupal development. The low rate of detected parasitism at low host densities with G. mellonella eggs may be due to incomplete pupal development due to superparasitism rather than lack of parasitism, thus explaining the type III functional response.     

Susceptibility of Oriental armyworm,Mythimna separata (Lepidoptera: Noctuidae) larvae and pupae to native entomopathogenic nematodes

The Oriental armyworm, Mythimna separata Walker (Lepidoptera: Noctuidae) is a major pest of cereal crops, and its outbreaks result in complete crop loss. In this study, we tested the pathogenicity and reproductive potential of indigenous entomopathogenic nematodes (EPNs), Heterorhabditis indica Poinar, Karunakar, & David NBAIIH38, Steinernema abbasi Elawad NBAIISa01, S. carpocapsae Weiser NBAIISc05 and S. siamkayai Stock, Somsook and Reid NBAIRS92 against larval and pupal stages of M. separata under laboratory conditions. Steinernema carpocapsae caused significantly greater mortality in second- and fourth-instar larval stages than other EPNs species. Steinernema carpocapsae caused greatest mortality 100% in larval stages and 75% in pupal stages. Significant differences were observed in the lethal concentration values (LC₅₀ and LC₉₀) of EPNs species against different stages of M. separata. Differences in penetration and multiplication in the fourth-instar larval stages of M. separata were observed amongst the EPNs species. However, further studies are needed to reveal the field performance of EPN isolates tested to be included in the IPM programme of M. separata.     

Host-stage preference and functional response of aphid parasitoid Diaeretiella rapae (McIntosh) (Hym.: Braconidae) on greenbug,Schizaphis graminum (Rondani) (Hem: Aphididae)

Searching capacity is of great importance in the efficiency of natural enemies. In this research, the host-stage preference and functional response of Diaeretiella rapae (McIntosh) to different densities of greenbug, Schizaphis graminum (Rondani) were determined on Pishtaz wheat leaves at 25 ± 1°C, 60–70% relative humidity, and a photoperiod of 16:8 h (L:D). The host-stage preference was investigated by exposing 60 number of all nymphal instars and adults of greenbug to individual parasitoid females at eight replicates. Results indicated significant preference of D. rapae to second instar nymphs of S. graminum to perform functional response experiment. Densities of 2, 4, 8, 16, 32, 50, 64, 90 and 130 second instar nymphs of greenbugs were exposed to individual mated female wasps at 10 replicates for 24 h. Type of functional response was determined by logistic regression and its parameters, searching efficiency (a) and handling time (T _h), were estimated by non linear regression. The results indicated that the functional response of D. rapae was type III and values of searching efficiency, handling time and maximum rate of parasitism were calculated by two models as 0.1364 ± 0.084, 0.5761 ± 0.0179, 41.6594; 0.06489 ± 0.00652 (h^?1), 0.5628 ± 0.0173 (h) and 42.6439 (aphids/parasitoid/day), respectively.