The Time–Dose–Mortality Modeling and Virulence Indices for Two Entomophthoralean Species, Pandora Delphacis and P

Biological Control 17, 29–34 (2000) Article ID bcon.1999.0767, available online at http://www.idealibrary.com on

The Time–Dose–Mortality Modeling and Virulence Indices for Two Entomophthoralean Species, Pandora delphacis and P. neoaphidis, against the Green Peach Aphid, Myzus persicae

Jun-Huan Xu and Ming-Guang Feng1 Department of Biological Sciences, Huajiachi Campus, Zhejiang University, Hangzhou 310029, People’s Republic of China

Received August 11, 1998; accepted June 30, 1999

mophthorales (Feng et al., 1995), but none has been Bioassays of two entomophthoralean fungi, Pandora well investigated. More effort is needed on microbial delphacis and P. neoaphidis, were conducted on the agents for aphid control (Milner, 1997) because of aphid green peach aphid, Myzus persicae. For inoculation, resistance to chemical insecticides (Devonshire, 1989) batches of I3-day-old nymphs on detached cabbage and increasing limitations of their use on vegetables leaves were exposed to conidial showers of varying grown in the outskirts of central cities in China (Feng time lengths from sporulating fungal mats produced in and Li, 1995). liquid culture. Eight dosages of each pathogen were The entomophthoralean fungus Pandora neoaphidis used to inoculate 88–345 nymphs each. The nymphs (Remaudiere & Hennebert) Humber is a well-known inoculated were maintained at 18–20°C and L:D (12:12) pathogen frequently causing aphid epizootics (De- at high humidity and were examined daily for mortal- dryver, 1983; Pickering et al., 1989; Feng et al., 1991, ity. The resulting data were analyzed using a time–dose– 1992), whereas P. delphacis (Hori) Humber usually mortality modeling technique, yielding the parameters for time and dose effects of the two fungal infects planthoppers (Melissa and James, 1987) but species. P. delphacis killed the aphid more rapidly rarely aphids, though it has been found infecting the than P. neoaphidis, though both had similar slopes for cotton aphid, Aphis gossypii Glover, in controlled bioassay (Shimazu, 1977). The two Pandora species have dose effect. The values of LD50 estimated on days 3–7 after exposure decreased from 18.1 to 0.9 conidia/mm2 similar morphological characteristics and are distin- for P. delphacis and from 17.0 to 0.04 conidia/mm2 for P. guished primarily on the basis of their hosts, i.e., neoaphidis. The estimates of LT50 for the two patho- aphids or planthoppers and leafhoppers (Humber, 1989). gens were similar at dosages of more than 5 conidia/ In recent years, we obtained isolates of the two fungal mm2 but differed at lower dosages. Based on the time– species from cadavers of the English grain aphid, dose–mortality relationships ﬁtted and the virulence Sitobion avenae (F.), and the brown planthopper, indices estimated, P. delphacis is a promising micro- Nilaparvata lugens Stål, in the late-season rice crop in bial agent for aphid control and is competitive with P. Hangzhou, Zhejiang Province. Despite similarities in neoaphidis. ௠ 2000 Academic Press morphology, the isolates from the planthopper species Key Words: Pandora delphacis; Pandora neoaphidis; grow much more rapidly on plates or in liquid medium Myzus persicae; virulence. than those from the aphid species (Xu and Feng, 1998). In the present study we attempt to determine the time–dose–mortality relationships between the two INTRODUCTION pathogens and M. persicae, estimate their virulence indices, and evaluate their potential for use in aphid The green peach aphid, Myzus persicae (Sulzer), control. infests up to 40 families of plants, including various important crops in the ﬁeld as well as in the greenhouse (Blackman and Eastop, 1984). It commonly devastates MATERIALS AND METHODS cruciferous vegetables in China (Liu, 1991). Microbial agents naturally occurring on aphids in China include Preparation of Inocula a few species of entomopathogenic fungi, mostly Ento- The two isolates, P. delphacis F95129 and P. neoaphidis F97006, were obtained from two cadavers of N. 1 To whom correspondence should be addressed. Fax: 86-571-697- lugens and S. avenae collected on rice plants in Hang- 1278. E-mail: [email protected]. zhou, Zhejiang in October 1995 and 1997, respectively.

29 1049-9644/00 $35.00 Copyright ௠ 2000 by Academic Press All rights of reproduction in any form reserved. 30 XU AND FENG

Both were maintained on SEMA (80% Sabouraud dex- min with P. neoaphidis because P. delphacis sporulated trose agar, 11.5% fresh milk, 8.5% egg yolk) plates at more abundantly than P. neoaphidis. Colonies consist- 15°C and a photoperiod of L:D (12:12) by subculture ing of 186 and 250 nymphs on detached leaves without every month. Preparation of P. delphacis inocula started exposure to the conidial shower were included as from the growth of the isolate on SEMA at 25°C for 7 controls for bioassays 1 and 2, respectively. days. The mycelia of the resulting fungal colony were After exposure, the aphid colonies on detached leaves moved into a 100-ml flask containing 30 ml Sabouraud in the petri dishes were maintained in a growth cham- dextrose broth [SDB: 1% peptone, 1% yeast extract, and ber at 18–20°C and L:D (12:12). Live and dead aphids 4% glucose plus 20 µg PSN antibiotic mixture (penicil- were recorded daily for 7 days. Dead aphids were lin 25%, streptomycin 25%, and neomycin 50%; Gibco- removed from the colonies and examined individually BRL, Grand Island, NY) per milliliter]. Shaken in the for verification of infection after overnight incubation dark at 28 Ϯ 1°C for 24 h (150 rpm), the liquid culture in a moist chamber. There was no need for leaf change was transferred into 80 ml liquid medium in a 200-ml during the observation period because the nutrient flask for further growth for another 24 h under the solution around the petioles kept the leaves fresh for same regime. Finally, 10 ml liquid culture was poured approximately 2 weeks. onto a 90-mm petri dish containing 1.5% agar only. Excessive water was removed using filter paper. Incu- Data Analysis bated at 25°C and L:D (12:12) for 24 h, the fungal mats on the plates sporulated uniformly and were ready for A time–dose–mortality modeling technique (Robert- use. The procedures for preparation of P. neoaphidis son and Preisler, 1992; Nowierski et al., 1996; Feng et inocula were the same as above but took much longer: al., 1996, 1998) was used to analyze the resulting 15 days on SEMA at 20°C, 2 days in 30 ml SDB, and 5 time–dose–mortality data of P.delphacis and P.neoaphi- days in 80 ml SDB. dis for M. persicae. Considering a bioassay that in- cludes I dosages and J times of observation, the cumulative mortality probability, pij, caused by the dose di Aphid Colonies for Bioassay (i ϭ 1,2,···,I) at the time tj ( j ϭ 1,2,···,J) can be A laboratory M. persicae population initiated from expressed as individuals collected in the field was maintained on ϭ Ϫ Ϫ ␶ ϩ␤ cabbage, Brassica oleracea L. (cv. Jingfeng 1), at 20– pij 1 exp [ exp ( j log10(di ))], (1) 24°C and L:D (12:12). For bioassay, vigorous apterae were selected from the population to produce offspring where ␤ is the slope to describe the dose effect and ␶j is on detached cabbage leaves (15 aphids/leaf) in 150-mm the parameter(s) for the time effect of di during the petri dishes. For longer maintenance, each petiole was period from start to the jth observation (t1, t2,···,tjϪ1, wrapped with cotton saturated with Hoagland–Snyder tj, tjϩ1,···,tJ). To guarantee that the observed mortal- nutrient solution (Adams and van Emden, 1972). Three ity probability is independent of time, the true mortal- days later, the apterae were removed and the nymphal ity induced with di at the interval [tjϪ1, tj] must be colonies left on the leaves were ready for use in the considered. This true mortality, qij, is called the condi- bioassay. tional mortality probability (Robertson and Preisler, 1992) and is given as follows Exposure of Aphids ϭ Ϫ Ϫ ␥ ϩ␤ qij 1 exp [ exp ( j log10(di ))], (2) Bioassays of the two fungal pathogens against the aphid species were conducted in March 1998 (bioassay where ␤ is equal to that in Equation 1 and ␥j describes 1) and repeated in May 1999 (bioassay 2). Following the conditional time effect of di at the interval [tjϪ1, tj]. Feng and Johnson (1991) and Feng et al. (1998), The independence between time intervals of observa- detached leaves with nymphs were gently moved to tion allowed the fitting of data to Eq. [2] by approaching 150-mm petri dishes lined with moistened filter paper. the binomial response variable to the maximum likeli- A sporulating fungal mat in a dish was inverted onto hood equation (Feng et al., 1996, 1998; Nowierski et al., each dish containing one or two leaves with aphids. The 1996), yielding ␥j and ␤. Then, the values of ␶j were sporulating fungal mat was rotated 90° each quarter of calculated using the formula (Robertson and Preisler, the exposure time. One 20-mm glass coverslip was 1992) below: placed at the center of each dish to receive conidia discharged from the plate. After exposure the conidial j dosage was determined based on the counts of the ␶ ϭ ␥k j ln ͚ e . (3) conidia from five random fields of the coverslip (0.785 1kϭ1 2 mm2/field) under microscope. Eight dosages were included in each bioassay, resulting from the exposures of The procedures, including modeling, estimation of 1–120 min, 0.3–30 min with P. delphacis, and 1–180 time- and dose-effect parameters for both conditional Pandora SPP. AGAINST GREEN PEACH APHID 31 and cumulative models, test for goodness of fit, and killed by P. delphacis were nearly triple the density and estimation of virulence indices (LD50 and LT50) using twice the length of cystidia from aphids killed by P. the parameters, were conducted using DPS data pro- neoaphidis in the moist chamber. cessing system software (Tang and Feng, 1997). The numbers of surviving aphids during the 7 days after exposure to varying conidial dosages are listed in RESULTS AND DISCUSSION Table 1. The deaths attributed to infection by P. delphacis and P. neoaphidis were observed mostly on days 2–5 Both Pandora species infected M. persicae. The aphids and days 3–6 after exposure, respectively. All aphids infected by P. delphacis died more rapidly than those killed by the two fungal species sporulated well and infected by P. neoaphidis. Fresh cadavers killed by P. displayed typical signs of Pandora infection under delphacis were more yellowish brown than those killed microscopic examination after overnight incubation in by P.neoaphidis. Notably, cystidia produced from aphids the moist chamber. The cumulative mortality at the

TABLE 1 The Time–Dose–Mortality Records from the Bioassays of Pandora delphacis and P. neoaphidis against Myzus persicae Nymphs

Number of surviving aphids after exposure Dosagea No. aphids Moratlity spores/mm2 treated Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 (%)

P. delphacis in bioassay 1 0.13 (1) 118 116 105 96 87 85 82 80 32.2 0.23 (2) 113 111 98 83 82 80 78 75 33.6 0.51(5)11611294757168656147.4 0.89 (10) 103 100 82 64 57 55 53 51 50.5 2.93 (20) 153 148 121 95 78 71 66 62 59.5 5.09 (30) 107 103 83 65 54 47 42 37 65.4 7.70 (60) 104 100 81 53 32 29 25 22 78.8 42.04 (120) 216 204 159 97 57 46 43 39 81.9 P. neoaphidis in bioassay 1 0.06(1)888886756056514647.7 0.19 (2) 168 168 167 141 117 92 67 60 64.3 0.45 (5) 106 106 98 82 69 56 39 35 67.0 0.64 (20) 167 165 154 121 88 57 49 38 77.2 0.83 (30) 99 97 88 66 45 25 17 12 87.9 1.85 (60) 102 99 89 64 42 21 14 12 88.2 11.59 (120) 97 92 81 57 36 16 13 10 89.7 18.60 (180) 96 87 67 45 28 12 9 6 93.8 Control 1 186 186 184 182 176 174 172 172 7.5 P. delphacis in bioassay 2 0.18 (0.3) 145 139 128 113 106 101 99 99 31.7 0.73 (1) 279 268 249 210 198 189 188 187 33.0 1.51 (2) 172 160 147 111 99 89 86 85 50.6 3.56 (5) 225 211 186 134 100 90 87 86 61.8 7.64 (6) 179 167 138 88 70 60 59 58 67.6 27.7 (10) 241 226 186 123 93 81 77 76 68.5 44.6 (20) 205 175 139 98 67 55 52 49 76.1 55.6 (30) 190 164 121 76 56 49 46 41 78.4 P. neoaphidis in bioassay 2 0.06 (1) 316 313 305 268 230 215 204 200 36.7 0.11 (2) 239 236 229 204 147 132 116 110 54.0 0.22 (5) 345 336 308 252 182 144 125 116 66.4 0.63 (20) 262 256 232 190 124 95 79 73 72.1 1.22 (30) 240 230 202 143 97 77 69 61 74.6 2.98 (60) 237 230 212 152 83 57 48 45 81.0 4.56 (120) 204 195 177 114 67 49 44 39 80.9 10.49 (180) 210 198 172 115 53 33 25 22 89.5 Control 2 250 250 247 245 244 244 243 242 5.3

a Table entries in parentheses are the time length (min) of spore shower leading to the corresponding dosages. 32 XU AND FENG end of observation was 32.2–81.9% and 31.7–78.4% for TABLE 2 P. delphacis and 47.7–93.8% and 36.7–89.5 for P. neo- The Dose- and Time-Effect Parameters Estimated from the aphidis in bioassays 1 and 2, respectively, increasing Modeling of the Time–Dose–Mortality Data of Pandora del- with conidial dosages. The cumulative background phacis and P. neoaphidis against Myzus percisae mortality of the aphids in controls 1 and 2 were 7.5 and 5.3% on day 7 (Table 1). Conditional mortality model Cumulative mortality model The time–dose–mortality data in Table 1 were ad- (Eq. [2]) (Eq. [1]) justed using the background mortality records and Param- Param- a b a then fitted to the conditional mortality probability eter Value S.E. t eter Value Var(␶i) Cov(␤, ␶i) model (Eq. [2]), yielding parameters for conditional P. delphacis in bioassay 1 dose and time effects (␤, ␥j) of the two fungal species assayed (Table 2). The parameters for cumulative time ␤ 0.548 0.033 16.71 ␤ 0.548 0.001 0.001 ␥1 Ϫ3.641 0.367 9.92 ␶1 Ϫ3.641 0.135 Ϫ0.001 effects, ␶j, were thus calculated using the values of ␥j. ␥2 Ϫ1.958 0.057 34.33 ␶2 Ϫ1.788 0.006 Ϫ0.001 The t statistics for all parameters estimated were ␥ Ϫ1.559 0.074 20.97 ␶ Ϫ0.974 0.003 Ϫ0.001 Ͻ 3 3 significant (P 0.0001). The Hosmer–Lemeshow test ␥4 Ϫ1.831 0.048 38.30 ␶4 Ϫ0.620 0.002 Ϫ0.001 for heterogeneity of the goodness of fit (Nowierski et al., ␥5 Ϫ2.731 0.168 16.26 ␶5 Ϫ0.506 0.002 Ϫ0.001 ␥ Ϫ ␶ Ϫ Ϫ 1996) was insignificant for both P. delphacis (H-L, 6 2.961 0.210 14.11 6 0.423 0.002 0.001 ␥ Ϫ ␶ Ϫ Ϫ C ϭ 6.40, P ϭ 0.60 in bioassay 1; H-L, C ϭ 13.47, 7 2.891 0.260 11.12 7 0.342 0.002 0.001 P ϭ 0.10 in bioassay 2) and P.neoaphidis (H-L, C ϭ 9.81, P. neoaphidis in bioassay 1 P ϭ 0.28 in bioassay 1; H-L, C ϭ 10.71, P ϭ 0.22 in ␤ 0.568 0.044 12.96 ␤ 0.568 0.002 0.002 ␥ Ϫ ␶ Ϫ Ϫ bioassay 2). Thus, the data of P. delphacis and P. 1 3.826 0.158 24.20 1 3.826 0.025 0.001 ␥ Ϫ ␶ Ϫ Ϫ neoaphidis against M. persicae nymphs fit well to the 2 2.520 0.084 29.89 2 2.280 0.006 0.001 ␥3 Ϫ1.417 0.093 15.32 ␶3 Ϫ1.065 0.005 Ϫ0.001 time–dose–mortality model. ␥ Ϫ1.187 0.074 16.01 ␶ Ϫ0.431 0.003 Ϫ0.001 ␤ 4 4 The estimates of the parameter for dose effect ( ) ␥5 Ϫ0.892 0.063 14.06 ␶5 0.058 0.001 0.000 were not significantly different between P. delphacis ␥6 Ϫ1.203 0.067 17.74 ␶6 0.307 0.001 0.000 ␥ Ϫ ␶ and P. neoaphidis in bioassays 1 (t ϭ 0.36, P ϭ 0.78) 7 1.613 0.194 8.33 7 0.444 0.001 0.000 and2(t ϭ 0.30, P ϭ 0.81) or between the two bioassays P. delphacis in bioassay 2 ϭ ϭ for P. delphacis (t 0.22, P 0.86) and P. neoaphidis ␤ 0.559 0.039 14.39 ␤ 0.559 0.002 0.002 ϭ ϭ (t 0.11, P 0.93). The parameters for the conditional ␥1 Ϫ3.019 0.082 37.01 ␶1 Ϫ3.019 0.007 Ϫ0.002 ␥ Ϫ ␶ Ϫ Ϫ time effects were in order of ␥ Ͻ␥ Ͻ␥ Ͼ␥ Ͼ␥ Ͼ␥ 2 2.341 0.083 28.21 2 1.931 0.005 0.002 1 2 3 4 5 6 ␥ Ϫ ␶ Ϫ Ϫ ␥ Ͻ␥ Ͻ␥ Ͻ 3 1.620 0.054 29.78 3 1.070 0.003 0.002 for P. delphacis in the two bioassays and 1 2 3 ␥ Ϫ ␶ Ϫ Ϫ ␥ Ͻ␥ Ͼ␥ Ͼ␥ 4 2.058 0.044 46.35 4 0.754 0.002 0.001 4 5 6 7 for P. neoaphidis in bioassay 1 and ␥ Ϫ2.661 0.134 19.85 ␶ Ϫ0.615 0.002 Ϫ0.001 ␥ Ͻ␥ Ͻ␥ Ͻ␥ Ͼ␥ Ͼ␥ Ͼ␥ 5 5 1 2 3 4 5 6 7 in bioassay 2. This ␥6 Ϫ3.905 0.265 14.71 ␶6 Ϫ0.579 0.002 Ϫ0.001 indicates that the true mortality of the aphids tested ␥7 Ϫ4.303 0.200 21.53 ␶7 Ϫ0.555 0.002 Ϫ0.001 peaked on days 3 and 4 or 5 after exposures to P. P. neoaphidis in bioassay 2 delphacis and P. neoaphidis, respectively. The time for ␤ 0.574 0.032 17.99 ␤ 0.574 0.001 0.001 the largest estimate of ␥ corresponds to the estimate of j ␥1 Ϫ3.507 0.187 18.74 ␶1 Ϫ3.507 0.035 0.000 latent period for a microbial agent tested (Feng et al., ␥2 Ϫ2.464 0.050 49.69 ␶2 Ϫ2.162 0.004 0.000 ␥ Ϫ ␶ Ϫ 1998) and in this study was 3 days for P. delphacis and 3 1.341 0.041 32.40 3 0.976 0.001 0.000 ␥ Ϫ ␶ Ϫ 4 or 5 days for P. neoaphidis against M. persicae, 4 0.842 0.040 20.87 4 0.214 0.001 0.000 ␥ Ϫ ␶ respectively. The conditional time–dose–mortality rela- 5 1.409 0.054 26.29 5 0.051 0.001 0.000 ␥6 Ϫ1.891 0.076 25.02 ␶6 0.185 0.001 0.000 tionships between the two Pandora species and the ␥7 Ϫ2.521 0.153 16.52 ␶7 0.249 0.001 0.000 aphid pest in bioassays 1 and 2 are displayed in Fig. 1 based on the fitting of Eq. [2]. a The subscripts represent the number of the days or the ith day The parameters estimated for the cumulative time– after the exposure. b The t statistics were highly significant for all parameters esti- dose–mortality models were used to compute virulence mated (P Ͻ 0.0001). indices using formulae given by Feng et al. (1996, 1998) and Nowierski et al. (1996). The values of log10(LD50) with standard errors were a function of the time after hand, the estimates of LT50 for both fungal pathogens in exposure to the conidial showers (Fig. 2). The values of the two bioassays were close to each other at the 2 LD50 estimated for days 3–7 after exposure to P. delpha- dosages of 5–18 conidia/mm , ranging from 3 to 4 days, cis were 12.8, 2.9, 1.8, 1.3, and 0.9 conidia/mm2 in and were much more similar (approaching 3 days) at bioassay 1 and 18.1, 4.9, 2.8, 2.4, and 2.2 conidia/mm2 dosages of more than 18 conidia/mm2 (Fig. 3). However, in bioassay 2, respectively. The same estimates for P. at dosages of less than 5 conidia/mm2, P. neoaphidis neoaphidis were 17.0, 1.3, 0.2, 0.07, and 0.04 conidia/ tended to have smaller estimates of LT50 than did P. mm2 in bioassay 1 and 11.5, 0.5, 0.2, 0.1, and 0.08 delphacis. conidia/mm2 in bioassay 2, respectively. On the other The equivalent slopes for dose effects and the viru- Pandora SPP. AGAINST GREEN PEACH APHID 33

FIG. 1. The conditional time–dose–mortality relationships ﬁtted for Pandora delphacis (A and B) and P. neoaphidis (C and D) on Myzus persicae.

FIG. 2. The logarithms of the values of LD50 (associated with standard errors in bars) estimated for Pandora delphacis and P. FIG. 3. The values of LT50 estimated for Pandora delphacis and neoaphidis against Myzus persicae. PD1, P. delphacis in bioassay 1; P. neoaphidis on Myzus persicae. PD1, P. delphacis in bioassay 1; PD2, P. delphacis in bioassay 2; PN1, P. neoaphidis in bioassay 1; PD2, P. delphacis in bioassay 2; PN1, P. neoaphidis in bioassay 1; PN2, P. neoaphidis in bioassay 2. PN2, P. neoaphidis in bioassay 2. 34 XU AND FENG lence indices shown above indicate that P. delphacis Feng, M. G., Hu, G. C., and Huang, S. W. 1995. Epizootics and can be considered as promising a microbial agent for associated fungal pathogens in Myzus persicae in southern China. aphids as is P. neoaphidis, the well-known aphid patho- In ‘‘Proceedings of the 1995 National Symposium on Biological Control,’’ 15–20 October 1995, Beijing. [in Chinese]. gen. The conditional time effects show that P. delphacis Feng, M. G., and Johnson, J. B. 1991. Bioassay of four entomophtho- killed more aphids than P. neoaphidis during the first 3 ralean fungi (Entomophthorales) against Diuraphis noxia and days after inoculation (Fig. 1). Moreover, the produc- Metopolophium dirhodum (Homoptera: Aphididae). Environ. Ento- tion of P. delphacis mycelia in liquid culture is much mol. 20, 338–345. easier and faster than that of P. neoaphidis, as shown in Feng, M. G., Johnson, J. B., and Halbert, S. E. 1991. Natural control this study and elsewhere (Xu and Feng, 1998). Addition- of cereal aphids (Homoptera: Aphididae) by entomopathogenic ally, P. delphacis can be easily cultured in vitro at a fungi (Zygomycetes: Entomophthorales) and parasitoids (Hymenop- tera: Braconidae and Encyrtidae) on irrigated spring wheat in wider range of temperatures (10–30°C) than P. neoaphi- southwestern Idaho. Environ. Entomol. 20, 1699–1710. dis, which usually grows poorly above 25°C (unpub- Feng, M. G., and Li, Z. 1995. The entomophthoralean fungi as lished data). The tolerance of P. delphacis to a wider microbial control agents. In ‘‘Microbial Control of Pest Organisms: range of temperatures may allow it to better adapt to Principles and Technology’’ (T. Chen, Ed.), pp. 273–291. Hubei field environments. Though P. delphacis became less Science and Technology Publishing House, Wuhan. [in Chinese]. virulent than P. neoaphidis from 4 days after inocula- Feng, M. G., Nowierski, R. M., Johnson, J. B., and Poprawski, T. J. 1992. Epizootics caused by entomophthoralean fungi (Zygomyce- tion (Fig. 2), its LD50 on day 7 was very small (0.9 and 2.2 conidia/mm2 in bioassays 1 and 2) compared with tes, Entomophthorales) in populations of cereal aphids (Hom., 2 Aphididae) in irrigated small grains of southwestern Idaho, USA. those previously reported, e.g., 34 conidia/mm for J. Appl. Entomol. 113, 376–390. Zoophthora anhuiensis against M. persicae (Feng et al., Feng, M. G., Tang, Q. Y., Hu, G. C., and Huang, S. W. 1996. 2 1998), 1.4–8.1 and 25–47 conidia/mm for P. neoaphidis Susceptibility of seven species of aphids to a Beauveria bassiana and Z. radicans isolates against cereal aphids, respec- isolate: Analysis of time–dose–mortality model. J. Basic Sci. Eng. tively (Feng and Johnson, 1991), and 11.3–27.3 conidia/ 4, 22–33. [in Chinese]. mm2 for Z. radicans isolates against Therioaphis trifo- Feng, M. G., Liu, C. L., Xu, J. H., and Xu, Q. 1998. Modeling and lii f. maculata (Milner and Soper, 1981). Differences in biological implication of the time–dose–mortality data for the entomophthoralean fungus, Zoophthora anhuiensis on the green sporulation, conidial discharge, and secondary infec- peach aphid, Myzus persicae. J. Invertebr. Pathol. 72, 246–251. tion of aphid cadavers killed by both fungal species Humber, R. A. 1989. Synopsis of a revised classification for the were unknown in this study because all fresh cadavers Entomophthorales (Zygomycotina). Mycotaxon 34, 441–460. were removed for verification of Pandora infection. Liu, S. S. 1991. The influence of temperature on the population Thus, further study is needed to investigate epizooti- increase of Myzus persicae and Lipaphis erysimi. Acta Entomol. ological features of both Pandora species in aphid Sin. 34, 189–197. [in Chinese]. colonies as well as their virulence. Melissa, K. M., and James, D. H. 1987. Occurrence of Erynia With virulence, easiness of culture, and adaptation to delphacis in the three cornered alfalfa hopper, Spissistilus festinus temperatures in mind, P. delphacis is a promising (Homoptera: Membracidae). J. Invertebr. Pathol. 50, 81–83. microbial agent for aphid control and is competitive Milner, R. J. 1997. Prospects for biopesticides for aphid control. Entomophaga 42, 227–239. with P. neoaphidis. Milner, R. J., and Soper, R. S. 1981. Bioassay of Entomophthora against the spotted alfalfa aphid Therioaphis trifolii f. maculata. J. ACKNOWLEDGMENTS Invertebr. Pathol. 37, 168–173. Nowierski, R. M., Zeng, Z., Jaronski, S., Delgado, F., and Swearingen, We thank Qian Xu for long-term maintenance of the fungal isolates W. 1996. Analysis and modeling of time–dose–mortality of Melano- used in this study and other technical assistance and two anonymous plus sanguinipes, Locusta migratoria migratorioides, and Schisto- reviewers for their critical and editorial comments on the early draft cerca gregaria (Orthoptera: Acrididae) from Beauveria, Metarhiz- of the manuscript. This work was supported by the Foundation of ium, and Paecilomyces isolates from Madagascar. J. Invertebr. China for the Outstanding Young Scientists and the Natural Science Pathol. 67, 236–252. Foundations of China and Zhejiang Province. Pickering, J., Dutcher, D., and Ekbom, B. S. 1989. 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