Fecundity,reproductive rate,longevity, and intrinsic rate of increase of an aphidiid parasitoidLysiphlebia mirzai

A life-table was constructed for a little known aphidiid waspLysiphlebia mirzai, a parasitoid of cereal aphid,Rhopalosiphum maidis. The female parasitoid survived 6.4 ± 1.17 (SD) days and oviposited intensively 4.0 ± 0.47 days. The total fecundity rate, R_t, was 169.2 ± 6.94 mummies/female and net reproductive rate, R_o, was 92.70 female offspring/female. The intrinsic total fecundity rate, r_t, and intrinsic rate of natural increase, r_m, the finite rate of total fecundity, λ^t, and finite rate of increase, λ^m, was 0.27048, 0.24155, 1.31059 and 1.27322 respectively. The mean generation time (18.75 days) and doubling time of the population (2.87 days) was slightly higher than other aphidiids studied so far. The proportion of female progenies decreased significantly on the successive oviposition days.      

Biology and fertility life table of the greenbug,Schizaphis graminum (Hemiptera: Aphididae) on the resistant winter wheat cultivar (Pishgam) in Iran

The greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae) has been known as a major pest of small grains, particularly wheat, worldwide. In this study, the effect of new wheat cultivar (Pishgam) for cold regions on biological characteristics of greenbug was investigated in a greenhouse at 25 ± 2 °C, 55 ± 10% relative humidity and a photoperiod of 16:8 h (L:D). The raw data were analysed based on the age-stage, two-sex life table. The intrinsic rate of increase (r), the finite rate of increase (λ), the net reproduction rate (R₀) and the mean generation time (T) of greenbug were 0.313 ± 0.0019, 1.36 ± 0.0027 females/female/day, 83.33 ± 0.331 females/female and 14.11 ± 0.09 days, respectively. The life expectancy of a nymph is 43.57 days. The maximum reproductive value of females is on the 16th day which coincides with the total pre-reproduction period counted from birth. Hence, the present results may provide helpful information for comprehensive IPM programme of greenbug on this variety in cold regions of Iran. Result revealed that nymphal survival rate of the aphid was 100% on studied cultivar like that on sensitive host plant cultivar.     

Reproduction,adult survival and intrinsic rate of growth ofUrolepis rufipes [Hymenoptera: Pteromalidae], a pupal parasitoid of house flies,Musca domestica

Urolepis rufipes Ashmead, a recently discovered parasitoid of house flies at New York dairies, was reared at 15, 20, 25, 30 and 34°C to measure daily fertility, fecundity and adult survivorship. Little reproduction occurred at 15°C, and only a few ♀ successfully emerged at 34°C. The intrinsic rate of growth was fastest at 30°C (0.282 ♀/day), but fecundity was highest at 25°C (165.5 hosts attacked, producing 124.5 progeny). Some reproductive statistics at 25°C were: net reproductive rate (R₀=72.1 ♀/♀, generation time =18.7 days, intrinsic rate of increase (r_m)=0.228, finite rate of increase (λ)=1.26, daily birth rate =0.302, daily death rate =0.021 and Fisher's reproductive value =418. Sex ratio (average =75.9%) did not vary significantly with temperature (between 20–30°C) nor with mother's age.      

Rearing method and life-table data for the cocoa mirid bug Sahlbergella singularis Haglund (Hemiptera: Miridae)

The mirid bug Sahlbergella singularis feeds on cocoa pods and shoots, causing considerable crop losses. As laboratory experimentation requires numerous insects, this study aimed at improving available rearing method of S. singularis for Cameroon. Fifty second to fifth nymphal stages were collected at a cocoa farm and reared to the adult stage on cocoa pods in an insectary (T = 24.7 ± 0.9°C, RH = 84.5 ± 6.8%, photoperiod: 12 : 12 L : D). Newly emerged females were confined for 5–6 days on cocoa twigs for sexual maturation and each female paired with a male for 24 h. The pairs were returned to the field and enclosed in mousseline sleeves on attached cocoa pods, for egg laying. After 16 days (expected egg lifetime), the sleeve cages were checked daily to detect newly hatched nymphs. Then, the pods were collected and brought to the insectary, where nymphs continued to emerge and develop into adults. Our method allowed the production of 14.6 ± 6.7 nymphs per female per generation, for 15 consecutive generations. Nymphal survival was calculated to be 68.2% and the mean duration of the nymphal development was measured at 22.7 ± 3.1 days. The rearing performance was evaluated using life‐table calculations. The net reproductive rate (R₀) was 6.59; the intrinsic rate of increase (r) was 0.037 per female per day with a population doubling time (T_d) of 18.9 days. On average each female contributed 9.70 individuals to the population given a mean generation time (T_c) of 52.1 days. The percentage of reproductive females and the mean number of nymphs per female were significantly different between generations, with 86.8% and 18.1% in generation G7 as compared to 45.8% and 8.4% for generation G5, respectively. As rainfall showed concordant variations during the period of investigation, we discuss the impact of this factor on mirid fecundity.     

Comparative life table statistics for the ladybeetle Scymnus syriacus reared on the green citrus aphid,Aphis spiraecola,fed on two host plants

Demographic statistics for the ladybeetle Scymnus syriacus Marseul (Coleoptera: Coccinellidae) were investigated when reared on the green citrus aphid, Aphis spiraecola Patch (Homoptera: Aphididae), fed on two host plants: spirea (Spirea sp.) and Thompson orange (Citrus sinensis cv. Thompson) under laboratory conditions (25 ± 1°C, 65 ± 5% relative humidity and 16 h light : 8 h dark). Mean developmental times from egg to adult were 20.32 ± 0.18 and 22.07 ± 0.15 days for spirea and Thompson orange, respectively. The survival rate from egg to adult was higher for spirea (85%) than for Thompson orange (72.5%). The oviposition periods were 41.8 ± 2.47 and 39.71 ± 2.6 days and the total number of eggs per female were 657.6 ± 29.5 and 587.9 ± 32.6 on spirea and Thompson orange, respectively. Fertility life tables were also constructed to compare the effects of host plants. The intrinsic rate of increase (r_m) on spirea was higher than that on Thompson orange. Jackknife estimates of r_m varied from 0.149 on spirea to 0.133 on Thompson orange. The mean population generation times on these host plants were 38.16 and 40.65 days, respectively. These results indicate that spirea‐fed A. spiraecola is more suitable for S. syriacus, producing a higher survival rate and shorter developmental time.     

Fecundity and life table parameters of Campoletis sonorensis (Hymenoptera: Ichneumonidae), an endoparasitoid of the Cabbage Looper Trichoplusia ni Hübner (Lepidoptera: Noctuidae), under laboratory conditions

The fecundity and life table parameters of Campoletis sonorensis females were measured using thirty 4-day-old Trichoplusia ni larvae daily at 24°C, 60% RH and a photoperiod of 12 h L:12 h D. The mean longevity was 34.5±2.8 days, the mean oviposition period was 22.7±1.9 days, and the mean constant oviposition period and the mean post-oviposition period were 15.9±1.3 and 11.9±2.2 days, respectively. The mean realised fecundity and the mean fertility differed significantly at 66.9±7.8 and 60.4±7.8 parasitoids per female, respectively. The mean sex ratio for the mean oviposition period (23 days) was 0.13±0.07, indicating a highly female biased ratio. The life table parameters were: intrinsic rate of natural increase (r _m), 0.135 female/day; gross reproductive rate (GRR), 50.30; net reproductive rate (R _o), 49.96; finite capacity for increase (λ), 1.14 female/day; mean generation time (T), 28.97 days; doubling time (DT), 5.13; capacity for increase (r _c), 0.33; and cohort generation time (T _c), 11.69. Campoletis sonorensis may be a suitable candidate for a biocontrol program of T. ni populations mostly because the primary selection criterion, r_m , obtained for this parasitoid can be similar to or larger than the rate obtained for T. ni.     

Toxic effect of deltamethrin on the life table and development of Helicoverpa armigera (Hubner)

Effect of deltamethrin (Decis 2.8% EC) on the fitness of Helicoverpa armigera (Hübner) was determined using demographic studies. Survivorship (I_x) and expectancy (e_x) was high with commencement of age and gradually decreased with progression of age in the exposed and unexposed groups. Highest number of unhatched eggs (~20%) was recorded with LC₅₀ (79.0 mg/L) opposed to 1% in the control. Daily fecundity rate was significantly greater (200 females/day) in the control than 126 in LC₂₀ (5.13 mg/L). Potential fecundity was lowest (179 females/female/generation) with LC₅₀ treatment than 675 in the control. Smallest value of intrinsic rate of increase (r_m) occurred at LC₅₀ (0.0393 females/female/day) while the highest value (0.0539) was at control. Overall larval development was significantly reduced to 18.0 days with LC₅₀ opposed to 24.1 days at control. Pupal period was shortened to 7.6 days with LC₅₀, while it recorded 9.3 days in control.     

Cross-mating experiments with geographically different populations of <Emphasis Type="Italic">Amblyomma cajennense</Emphasis> (Acari: Ixodidae)

The effect of temperature on the development and fecundity of Sancassania polyphyllae fed on tissues of Polyphylla fullo larvae was studied at 15, 20, 25, 30, and 35 ± 1°C and 65 ± 10% RH in a dark incubator. Mean developmental period of immature stages decreased significantly with increasing temperatures from 15 to 30°C. Developmental periods at 30–35°C were not significantly different. The estimated lower developmental thresholds of the various immature stages ranged between 10.1 and 11.5°C. The thermal constant for the egg-to-female adult was 93.5 degree-days. The pre-oviposition, oviposition, and post-oviposition periods and female longevity were significantly longer at 15°C than at higher temperatures. Mean total and daily fecundity were the highest at 25°C, which were significantly different from those obtained at 15, 20 and 30°C. The net reproductive rate (R ₀) was the highest at 25°C (588.3 ♀/♀). The longest mean generation time (T ₀) occurred at 15°C (36 days) and the shortest occurred at 30°C (9.2 days). The highest intrinsic rate of increase (r _m) for S. polyphyllae was observed at 25 (0.61 ♀/♀/day) and 30°C (0.62 ♀/♀/day).     

Effect of temperature on development rate and intrinsic rate of increase ofAphis gossypii reared on greenhouse cucumbers

Thermal requirements for development and life table statistics ofAphis gossypii Glover (Homoptera, Aphididae) were determined over a range of constant temperatures from 10 to 30°C. The lower development threshold and the sum of effective temperatures were 6.9°C and 90.1°C, respectively, for preimaginal development, and 5.8°C and 113.6°C from birth to the onset of reproduction. Mean total fecundity ranged from 36 larvae per female at 10°C to 76 larvae at 30°C. On a time scale of days, net reproductive rate (R _o ) increased with increasing temperature while generation time (T) decreased causing the intrinsic rate of increase (r _m ) to increase linearly from 0.115 to 0.465. On a day-degree scaler _m only varied from 0.019 to 0.028 because the growth ofR _o was compensated by an increase inT with increase in temperature. The nearly constantr _m in terms of day-degrees, over a wide range of temperatures, greatly simplifies the prediction of future population numbers ofA. gossypii.     

Effect of African nightshade species (Solanaceae) on developmental time and life table parameters of <Emphasis Type="Italic">Tetranychus evansi</Emphasis> (Acari: Tetranychidae)

The effect of five African nightshade (Solanum sp.) species on the biological and demographic parameters of the tomato spider mite, Tetranychus evansi Baker and Pritchard, was examined in the laboratory at 25 ± 1°C, 70–80% RH and 12L:12D photoperiod. Duration of each development stage, reproduction rate, longevity, intrinsic rate of natural increase (r _m), and doubling time (DT) of the tomato spider mite on the five nightshade species were calculated. The results indicated that S. villosum, S. scabrum, S. tarderemotum and S. americanum are more suitable for T. evansi due to a shorter developmental period, longer adult longevity, higher reproduction and intrinsic rate of natural increase ranging between 0.180 and 0.196 females/female/day compared with S. sarrachoides which cannot support T. evansi populations as the r _m (−0.063 females/female/day) and DT were negative on this host. Differences in developmental time and life table parameters among the other host plants were not significant.     

Comparison of development and demographic parameters of Diuraphis noxia (Hem., Aphididae) and its parasitoid,Diaeretiella rapae (Hym., Braconidae: Aphidiinae)

Demographic parameters of Diuraphis noxia (Mordvilko) and its parasitoid, Diaeretiella rapae (McIntosh) were investigated under laboratory conditions at temperatures of 20 ± 1°C, 60 ± 5% relative humidity of 60 ± 5% and a photoperiod of 16: 8 (light: dark) hours. The survival rates (l_x ) and the life expectancy (e_x ) at the beginning of adult emergence were 86% and 25.81 days for D. noxia and 100% and 7.36 days for D. rapae, respectively. Based on the Weibull distribution parameters, the survival curves were type I for both D. noxia and D. rapae, which indicates that mortality mostly occurred in older stages. The r _m-values in aphid and parasitoid were obtained as 0.22 ± 0.002 and 0.19 ± 0.003 day^?1, respectively. Mean generation time (T) and doubling time (DT) were 15.93 ± 0.202 and 3.15 ± 0.031 days for the aphid and 15.33 ± 0.071 and 3.67 ± 0.054 days for the parasitoid, respectively. The R₀ -values of D. noxia and D. rapae were evaluated 33.19 ± 0.961 and 18.07 ± 0.761 females/female/generation, respectively. The gross and net fecundity rates were 59.21 ± 1.94 and 32.825 ± 0.972 nymphs/female/day for the aphid and 37.59 ± 1.46, and 33.8 ± 1.51 eggs/female/day for the parasitoid, respectively. The results of this research indicated that D. rapae is an adequate parasitoid for control of Russian wheat aphid.     

Comparative biology and life tables of Trichogramma cacoeciae,T. brassicae and T. evanescens (Hymenoptera: Trichogrammatidae) with Ephestia kuehniella and Cadra cautella (Lepidoptera: Pyralidae) as hosts at three constant temperatures

Egg parasitoids of the genus Trichogramma (Hym. Trichogrammatidae) have been successfully utilized for biocontrol of several Lepidopteran pests worldwide. Because of their low host specificity Trichogramma can be mass reared more easily in large numbers and on different natural and factitious hosts. Life table parameters were assessed for Trichogramma cacoeciae Marchall, T. evanescens Westwood and T. brassicae Bezdenko on Ephestia kuehniella Zeller and Cadra cautella Walker at three temperatures (20, 25 and 30°C) as the potential factitious hosts for mass rearing. Female longevity ranged between 9.77 and 2.56 days in our experiments. Fecundity ranged from 73 to 91 parasitized eggs in C. cautella and 76–109 parasitized eggs in E. kuehniella. T. brassicae exhibit similar values of the intrinsic rate of increase ratio (r _m) 0.5407 and 0.5478; the finite rates of increase (λ) were 1.717 and 1.7295 and the doubling times 1.28 and 1.26 at 25 and 30°C, respectively, in C. cautella. The mean duration of one generation (T) varied between 8.25 and 13.37 days for T. cacoeciae, 8.14 and 13.47 days for T. brassicae and 8.23 and 13.18 days for T. evanescens in C. cautella. Generation times for T. cacoeciae varied between 8.23 and 14.68 days, 8.28 and 14.37 days for T. brassicae, and 7.74 and 14.58 days for T. evanescens in E. kuehniella eggs. Both species (T. cacoeciae, T. brassicae) had the same intrinsic rate of increase (r _m; 0.5700 and 0.5704), finite rate of increase (λ; 1.7682, 1.7691) and doubling time (Dt, 1.21) at 30°C in E. kuehniella, respectively.     

Life History of Kampimodromus aberrans as a predator of Phytoptus avellanae (Acari: Phytoseiidae, Phytoptidae)

The biology of Kampimodromus aberrans (Oudemans), a predator of the big bud mite, Phytoptus avellanae Nalepa, was studied under laboratory conditions. All experiments were conducted on hazelnut leaf discs in an incubator at 25 ± 1 °C, with 16:8 h L:D, at an average daily relative air humidity of 76%. Observations were made twice daily for the immature stages and daily for the adults to determine developmental time, survival and fecundity. The mean developmental time for females was 6.90 days and for males was 7.10 days, and mean adult longevity for females was 11.67 days. The mean total and daily egg production were 12.67 and 1.85 eggs, respectively. The net reproduction rate (R₀) was 7.09 females/female, intrinsic rate of increase (r_m) was 0.153 female/female/day and mean generation time (T₀) was 12.80 days. The mortality rate of immature stages was 0.66% and the sex ratio was 0.51 female.     

Biology ofMicroplitis mediator [Hym.: Braconidae] a gregarious endoparasite ofAgrotis segetum [Lep.: Noctuidae]

Microplitis mediator (Haliday) a gregarious endoparasite was recorded for the first time fromAgrotis segetum (Schiff) in Ankara, Turkey. The female parasites found their hosts by responding to the faeces of the caterpillars. An average, females laid 15.5±1.6 eggs in the bodies of their hosts. The newly laid eggs were elongated, oval in shape and 0.23±0.004 mm long and 0.07 mm wide. They hatched in 5, 4 and 3 days at 20±2°C, 25±2°C and 30±2°C respectively when maintained at 60–70% R.H. and 14∶10 light∶dark regime. At the same temperatures, the larval stage lasted for 24.9±0.6, 18.2±0.4 and 17.1±0.5 days respectively. The prepupal stage was completed in 2 days at 25±2°C, whereas the prepupal and pupal (cocoon) stage lasted 10.9±0.2, 7.0±0.1 and 6.2±0.1 days respectively at the temperatures mentioned above. The adults started mating and feeding shortly after emergence. Female parasites started laying after one day, 7–11 hours and 5–7 hours at the temperatures stated above. At these temperatures females lived for 10.8±0.2, 5.4±0.1, 4.6±0.1 days and laid on average 556, 484 and 363 eggs respectively, whereas the males survived 10.5±0.3, 4.7±0.1 and 4.4±0.1 days respectively.      

Comparative life-history traits of three phytoseiid mites associated with Tetranychus urticae (Acari: Tetranychidae) colonies in clementine orchards in eastern Spain: implications for biological control

The management of Tetranychus urticae, a key pest of clementine trees, is mainly based on the use of acaricides. However, more environmentally safe measures, such as biological control, are being encouraged. Life-history traits of the three most abundant phytoseiid mites associated with T. urticae on this crop (Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus) were studied. The experiments were performed under laboratory conditions (25°C, 80 ± 5% RH and 16:8 h (L:D)) on clementine leaves and T. urticae as prey. Euseius stipulatus could not complete its life cycle, whereas P. persimilis and N. californicus completed it satisfactorily. The estimated intrinsic rate of increase (r _m) was significantly higher for P. persimilis (0.344 day⁻¹) than for N. californicus (0.244 day⁻¹) and both were higher than the r _m value of T. urticae on clementine leaves. Implications of these results for the biological control of T. urticae in this crop are discussed.     

Detection of ‘Candidatus Cardinium’ Bacteria from the Haploid Host Brevipalpus Californicus (Acari: Tenuipalpidae) and Effect on the Host

Brevipalpus californicus (Banks) was infected with ‘Candidatus Cardinium’ bacteria (Cardinium). Tetracycline-treated females produced many male progeny even though untreated females produced only female progeny. B. californicus appears to be feminized by Cardinium. The values for net reproduction rate (R₀), generation time (T) and intrinsic rate of natural increase (r_m) calculated for B. californicus were 7.48/day, 31.45 days and 0.064/day, respectively. The comparison of infected females with uninfected males and other closely related species, indicated that Cardinium does not have a negative effect on the fitness of B. californicus.     

Fertility life table parameters of different strains of Trichogramma spp. collected from eggs of the carob moth Ectomyelois ceratoniae

Fertility life table parameters were assessed for five populations (strains) of two Trichogramma species, T. embryophagum Hartig and T. principium Sugonyaev & Sorokina, collected from eggs of the carob moth Ectomyelois ceratoniae (Zeller) in Iranian pomegranate orchards. Four combinations of two constant temperatures (25°C, 30°C) and two relative humidity levels (50% RH, 70% RH) were used. The overall intrinsic rate of natural increase (r_m) was significantly decreased with decreased relative humidity but was uninfluenced by temperature. The highest and lowest r_m values were observed in T. embryophagum from Qum (0.34 ± 0.004) and T. embryophagum from Varamin (0.13 ± 0.01), respectively. Two‐way interaction analyses revealed that the strains had significantly different responses in their r_m values at different temperatures and relative humidities. In general, r_m values were significantly higher at 25°C and 70% RH than at 30°C and 50% RH. The Qum strain of T. embryophagum was the most promising candidate to be considered as a biocontrol agent against E. ceratoniae due to its high reproductive rate (0.27 ± 0.01) at conditions (30°C and 50% RH) similar to the actual climatic conditions in Iranian pomegranate orchards during the major part of the growing season.     

Life history of <Emphasis Type="Italic">Eretmocerus mundus</Emphasis>, a parasitoid of <Emphasis Type="Italic">Bemisia tabaci</Emphasis>, on tomato and sweet pepper

Eretmocerus mundus is native to the Mediterranean region where it is often observed to enter greenhouses to parasitize B. tabaci on fruiting vegetables and other host crops. Fecundity on tomato and pepper was evaluated by placing newly emerged pairs (n = 15) of E. mundus on leaf discs infested with second instar B. tabaci, the preferred stage, maintained at 25 °C and changed daily until death of the female. All whitefly nymphs were observed for host feeding and inverted to count parasitoid eggs. Adult longevity was estimated at 7.3±0.8 d on tomato and 10.1±1.0 d on sweet pepper. Fecundity (number of hosts parasitized) was estimated 147.8±12.6 per female on tomato and 171.1±21.5 on pepper. Incidence of host feeding (number of hosts killed) was significantly greater on sweet pepper than on tomato, 15.6±1.9 vs. 10.4±1.3 nymphs per female, respectively. No significant differences were detected in the duration of life stages between sweet pepper and tomato. Preimaginal survivorship in clip cages was estimated at 69.5±11.9% on tomato and 76.6±10.5% on sweet pepper, with no statistical differences. Net reproductive rate (R _o) was estimated at 63.8±8.2 and 51.0±4.4 on tomato and sweet pepper respectively. Generation time (T) was significantly greater on sweet pepper (19.3±0.5) than on tomato (17.9±0.4), but the estimate of intrinsic rate of increase (r _m) was not statistically different at 0.216±0.005 and 0.219±0.004 respectively. These values are well above those reported for B. tabaci on any crop, indicating the potential of E. mundus to control this pest on solanaceous crops in the greenhouse.     

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.     

Life-history traits of the six Panonychus species from Japan (Acari: Tetranychidae)

Six species of the genus Panonychus are known from Japan. Life-history parameters of all six species were investigated at 25 °C, and for three species two strains of different geographical origin were included. The intrinsic rate of natural increase (r _m ) ranged from 0.172/day for the P. osmanthi albino strain to 0.209/day for P. citri, while the net reproductive rate (R ₀) varied from 23.98 in the thelytokous species P. thelytokus to 46.61 in P. citri. Both values were higher in the polyphagous species (P. ulmi, P. mori and P. citri), which are considered crop pests, than those in the oligophagous species (P. thelytokus and P. osmanthi), considered non-pests. The only exception was P. bambusicola, an oligophagous non-pest species with R ₀- and r _m -values closely resembling those of the three polyphagous species. This revised version was published online in July 2006 with corrections to the Cover Date.