DEVELOPMENT AND SURVIVAL OF PODZSUS MACULZVENTRZS (SAY) AND PODZSUS SAGZTTA (FAB.) (HETEROPTERA: ) AT VARIOUS CONSTANT TEMPERATURES P. DE CLERCQand D. DEGHEELE Laboratory of Agrozoology, Faculty of Agricultural Sciences, University of Gent, Coupure Links 653, B-9000 Gent, Belgium

Abstract Can. Ent. 124: 125-133 (1992) Development and survival of the predatory pentatomids rnaculiventris (Say) and (Fab.) were studied at six constant temperatures ranging from 19 to 35OC. Time required for development from egg to adult ranged from 48.9 days (19°C) to 18.9 days (30°C)for P. rnaculiventris and from 5 1.9 days (1 9°C)to 16.9 days (33°C) for P. sagitta. At 33"C, eggs of P. rnaculiventris did not hatch and development of nymphs that had emerged at 23°C was retarded; none of the first-instar nymphs incu- bated at 35OC survived the next moult. A constant temperature of 35°C was fatal to P. sagitta eggs and extended the developmental period of nymphs from 23°C. Egg hatch ranged from 47% (19°C)to 57% (27°C)for P. rnaculiventris and from 54% (33°C) to 71% (27°C)for P. sagitta. Nymphal survival was high at moderate temperatures, with 63-78% and 65-82% of the first-instar nymphs of the respective species reaching adulthood. Mortality during the nymphal stage was significantly increased at high tem- peratures, but was considerably lower for P. sagitta than for P. rnaculiventris. Lower threshold temperatures for egg and nymphal development were estimated to be 10.7 and 1 1.7"Cfor P. rnaculiventris, and 13.3 and 12.2"Cfor P. sagitta. Thermal require- ments for these stages were 78.2 and 275.5 degree-days, and 60.9 and 265.5 degree- days, respectively. These observations suggest that P. sagitta is somewhat better adapted to high temperatures than is P. rnaculiventris.

De Clercq, P., and D. Degheele. 1992. Influence de differentes temptratures constantes sur le dtveloppement et la survie de Podisus maculiventris (Say) et Podisus sagifta (Fab.) (Hete- roptera: Pentatomidae). Can. Enr. 124: 125-133. Resume Le dtveloppement et la survie des pentatomides prtdateurs Podisus rnaculiventris (Say) et Podisus sagitta (Fab.) ont ttt Ctudits six temptratures constantes de 19 a 35°C. La dur6e du dtveloppement de I'oeuf a I'adulte a van6 de 48,9jours (19°C)a 18,9 jours (30°C)pour P. rnaculiventris, et de 51,9 jours (19°C)a 16,9jours (33°C)pour P. sagitta. A 33"C,les oeufs de P. maculiventris ne sont pas tclos, et le dtveloppement des nymphes Ccloses a 23°C a CtC retardC; toutes les nymphes du premier stade incubCes a 35°C sont mortes pendant la premiere mue. Une temptrature constante de 35°C s'est montrte fatale pour les oeufs de P. sagitta et a retard6 le dtveloppement des nymphes tcloses a 23°C.Le pourcentage d'oeufs Cclos a varit de 47% (19°C)a 57% (27°C)pour P. rnaculiventris et de 54% (33°C)a 7 1 % (27°C)pour P. sagitta. La survie nymphale ttait bonne aux temptratures modtrCes, avec 63-78% et 65-82% des nymphes du premier instar des especes respectives arrivant au stade adulte. La mortalit6 au stade nymphal a CtC significativement augmentCe aux temptratures Clevtes, mais elle Ctait considtrablement moins tlevte pour P. sagitta que pour P. maculiventris. Les seuils thtoriques de temptrature pour le dtveloppement des oeufs et des nymphes ont CtC ttablis a 10,7 et 11,7OC pour P. rnaculiventris et a 13,3 et 12,2'C pour P. sagitta. Les besoins thermiques de ces stades ttaient de 78,2 et 275,s degrCs-jours, et 60,9et 265,5 degres-jours pour les especes respectives. Ces observations suggkrent que P. sagitta est plut8t mieux adapt6 2 des temptratures tlevtes que P. maculiventris.

Introduction Stink bugs of the genus Podisus are polyphagous predators with a wide geographic distribution throughout the American continents. Podisus spp. are associated with a wide 126 THE CANADIAN ENTOMOLOGIST JanuaryIFebruary 1992 range of habitats, such as agricultural crops, forests, and orchards, and have been rec- ognized as important predators of several lepidopterous and coleopterous pests (Clausen 1940; LeRoux 1960; Waddill and Shepard 1975; Lopez et al. 1976; McPherson 1982; Gusev et al. 1983). Podisus maculiventris (Say) occurs throughout North America (Torre-Bueno 1939); its biology and predation strategies have been well documented (Couturier 1938; Moms 1963; Mukerji and LeRoux 1965, 1969; Warren and Wallis 197 1; Waddill and Shepard 1975; Evans 1982a, 1982b; Drummond et al. 1984; O'Neil1988; Wiedenmann and O'Neil 1990). Only a few studies, however, have reported on Podisus sagitta (Fab.). According to Kirkaldy (1909), it is distributed from the southern United States into South America. Its laboratory rearing and life history were described by De Clercq et al. (1988) and De Clercq and Degheele (1990a, 1990b). The development of forecasting systems for the use of predators in integrated pest management programmes largely depends on the understanding of the relationship between temperature and development of the species of interest. Several studies have addressed the effects of temperature on the development of P. maculiventris (Couturier 1938; Mukerji and LeRoux 1965; Warren and Wallis 1971; Richman and Whitcomb 1978; Vlasova et al. 1980; Drummond et al. 1984). To our knowledge, however, no attempt has been made to determine developmental thresholds and degree-day accumulations for this species. Detailed developmental studies do not exist for P. sagitta. Therefore, our study was under- taken to compare the effects of temperature on developmental rates and survival of the immature stages of P. maculiventris and P. sagitta. Materials and Methods A laboratory colony of P. maculiventris was started with eggs obtained in 1989 from S.J. Yu (University of Florida, Gainesville, FL). A colony of P. sagitta was started in 1982, using from Surinam. Colonies of both species were maintained at 23 + 1°C, 75 + 5% RH, and a 16L:8D photoperiod and were cultured following the methods of De Clercq et al. (1988). Development and survival of P. maculiventris and P. sagitta were studied in growth chambers at six constant temperatures: 19, 23, 27, 30, 33, and 35 + 1°C. The photoperiod for all experiments was 16L:8D and relative humidity was maintained at 75 + 5%. Eggs were collected from colonies reared at the temperature at which subsequent development was studied, except for the 33 and 35°C experiments. At these latter two temperatures, oviposition of both species was strongly reduced (Couturier 1938; De Clercq and Degheele 1990b). For the experiments conducted at 33 and 35"C, eggs were collected from cultures reared at 23°C. Individual egg batches, less than 12 !I old, were incubated in disk-vented Petri dishes (9 by 1.5 cm). Development of the eggs was monitored twice daily; hatch was recorded at each temperature. Upon emergence, nymphs were provided with a moistened paper plug fitted into a small dish to serve as a source of free water. From the second instar on, nymphs were placed in individual Petri dishes (9 by 1.5 cm) lined with absorbent paper. Nymphs were fed with an excess of larvae of the greater wax moth, Galleria mel- lonella (L.), and were supplied with a moisture source. Development and survival of the nymphal stages were observed twice daily. The sex of the adults was determined. When eggs failed to hatch at the studied temperature, development and survival of nymphs that had emerged at 23°C were monitored. Duration of development at each temperature was compared between P. maculiventris and P. sagitta, using Student's t-test to detect signif- icant differences (P = 0.05). Reciprocals of the observed developmental durations, in days, provided developmental rates for each stage at each temperature. Rate data from those temperatures that appeared linearly related to developmental rate were regressed against temperature by linear regression analysis. Lower developmental threshold tem- peratures were estimated by the X-intercept method of Arnold (1959). Upper developmental Volume 124 THE CANADIAN ENTOMOLOGIST 127 thresholds, i.e. the temperature above which the developmental rate decreases, were esti- mated directly from the data. The mean number of degree-days (DD) required for devel- opment of each life stage was calculated using the equation DD = D(T- t) where D is the developmental duration (days), T is the temperature ("C) during development, and t is the lower developmental threshold ("C) (Price 1984). Thermal requirements of P. maculiventris and P. sagitta were compared using t-tests (P = 0.05). Results and Discussion Development. Both P. maculiventris and P. sagitta completed development at tempera- tures between 19 and 30°C (Table 1). Developmental times of all P. maculiventris stages decreased with increasing tem- perature up to 30°C. Eggs failed to hatch at 33 and 35"C, although eye-spots could be observed after 2-3 days, indicating some development had occurred. At 33"C, nymphs that had emerged at 23°C took significantly longer to complete development than at 30°C and mortality was 95% (see below and Table 4). None of the first-instar nymphs that were incubated at 35°C survived the next moult. These findings are consistent with those reported by Couturier (1938) and Vlasova et al. (1980). Developmental rate of P. sagitta increased with temperature to 33°C. A constant temperature of 35°C was fatal to eggs and slowed development of nymphs that had emerged at 23°C. Time required for development from egg to adult stage of P. maculiventris and P. sagitta ranged from 48.9 days (1 9°C) to 18.9 days (30"C), and from 5 1.9 days (1 9°C) to 16.9 days (33"C), respectively (Table 1). At 19 and 23"C, the immature stages of P. maculiventris developed somewhat faster than those of P. sagitta: significant differ- ences (P<0.05) in developmental times were observed for egg stage, total nymphal stage, and development from egg to adult. At 27"C, however, these developmental times were significantly (P<0.05) shorter for P. sagitta than for P. maculiventris. At 30°C, no con- sistent trends in developmental times between the species could be observed. NO significant differences in developmental times between the sexes of either species were detected (P>0.05 in all cases). Data on immature development of P. maculiventris vary considerably among workers (Table 2). In cases where differences with previously reported data were noted, devel- opmental times observed in our study on Florida specimens of P. maculiventris were mark- edly shorter. Differences can be explained in part by diet: consistently longer develop- mental periods were obtained when nymphs of P. maculiventris were fed on larvae of the Colorado potato beetle, Leptinotarsa decemlineata (L.) (Couturier 1938; Drummond et al. 1984). However, our data on nymphal development differ markedly from those reported by Mukerji and LeRoux (1965), who also mainly used G. mellonella as food. Differences in developmental rates may reflect the adaptation of the studied strains to the climatic conditions of their particular geographic origin. Developmental times of P. maculiventris irnrnatures were generally shorter for Florida specimens (Richman and Whitcomb 1978; present study) than for those originating from New York (Couturier 1938) and Quebec (Mukerji and LeRoux 1965). Also, immature development may have been influenced by the time cultures had been maintained in the laboratory before tests were carried out. To our knowledge, bionomics of P. sagitta have not been studied in detail. El-Refai and Degheele (1988) studied the effect of a limited range of temperatures on development of P. sagitta; their results generally agree with those of our study. Linear regression equations of developmental rate versus temperature were calculated for all stages of both species within the range from 19 to 30°C (Table 3; Figs. 1, 2). Coefficients of determination (R2)for each regression were greater than 0.96, indicating a good linear model fit in all cases. Lower developmental threshold temperatures (t) obtained by the X-intercept method (Arnold 1959) are presented in Table 3. Estimated 128 THE CANADIAN ENTOMOUXIST JanuaryIFebruary 1992 Table I. Duration (days) of the immature stages of P. maculiventris and P,,sagitta at six constant temperatures P. sanitta Temp. P. maculiventris ("C) Stage X 2 SD* (n) 7i 2 SD* 19 Egg 10.7 20.5b Nymphal N1 6.720.4a N2 7.42 1.0b N3 7.0k 1.2b N4 7.821.0b N5 12.32 1.2a N1-N5 41.2?2.3b Total 51.922.5b 23 Egg 6.420.3b Nymphal N 1 3.920.3b N2 4.620.8b N3 4.220.7b N4 4.62 0.7b N5 6.9 20.9a N1-N5 24.22 1.9b Total 30.622.0b 27 Egg 4.320.41, Nymphal N 1 2.920.3b N2 3.2k0.4a N3 3.020.4a N4 3.320.7a N5 4.920.5b N1-N5 17.3 2 1.5b Total 21.621.7b 30 Egg 3.720.3b Nymphal N 1 2.620.4a N2 2.620.5a N3 2.720.6b N4 2.8 20.6a N5 4.62 0.7a N1-N5 15.4?1.lb Total 19.121.la 33 Egg 3.420.2 Nymphal N1 2.5k0.3b N2 2.3 +0.5a N3 2.3 k0.5b N4 2.6?0.5b N5 3.920.4b N1-N5 13.52 1.0b Total 16.92 1.0

35 Egg L Nymphal N1 2.3 20.3 N2 2.4k0.5 N3 2.3k0.4 N4 2.8k0.5 N5 4.620.9 N1-N5 14.3 k 1.3 Total -

*Means within a row followed by the same letter are not significantly different (P>0.05,j-test). volume 124 THE CANADIAN ENTOMOLOGIST 129 Table 2. Development of the immature stages of P. maculiventris strains from different geographic origins Developmental duration (days) Reference Ongin Temp. ("C) Egg stage Nymphal stage Couturier (1938) New York 23 6.5 27-30 27.5 5 20-24 Mukerji and LeRoux (1965) Quebec 27 4-7 25-3 1 Warren and Wallis (1971) Arkansas 2 1 68 28.7 Richman and Whitcomb (1978) Florida 27 5 21.7 Present study Florida 23 5.8 23.2 27 5 18.5

Table 3. Linear regression of developmental rate (y) on temperature (x), lower developmental thresholds (t),and mean number of degree-days (DD) required for development of the immature stages of P. maculiventris and P. sagitta

P. maculiventris Stage Regression equation Regression equation

Egg y = 0.0129~- 0.1383 y = 0.0165~- 0.2192 Nymphal N 1 N2 N3 N4 N5 N1-N5 Total

P. macu~ivantrjs - P. sagitta

- A-

TEMPERATURE ( O C) FIG. 1. Relationship between temperature and rate of development for the egg stage of P. maculiventris and P. sagitta. Solid and broken lines represent linear regressions of all data from 19 to 30°C for P. maculiventris and P. sagitta, respectively. I 30 THE CANADIAN ENTOMOLOGIST January/February 1992

P. maoulivaotris - P. sagitta 0

- rn -

-.L

TEMPERATURE (O C) FIG. 2. Relationship between temperature and rate of development for the nymphal stages of P. maculiventris and P. sagitta. Solid and broken lines represent linear regressions of all data from 19 to 30°C for P. maculiventris and P. sagitta, respectively. lower thresholds for immature development of P. sagitta were consistently higher than those of P. maculiventris. It is difficult to make conclusions from these t-values because t, calculated by extrapolation, is assumed to be a poor estimate statistically (Campbell et al. 1974). Actual rate functions may cease to be linear as developmental rate approaches zero. Nonlinear functions may thus provide more accurate estimations of the relationship between developmental rate and temperature (e.g . Stinner et al. 1974; Taylor 1981 ; Wag- ner et al. 1984). From a practical viewpoint, however, estimation of lower developmental thresholds by linear extrapolation has proven useful for predictive purposes in several insects (Jones and Sterling 1979; Lysyk and Nealis 1988). In experiments on short-term storage of eggs at low temperatures, no development was observed for eggs of P. sagitta at a constant temperature of 10 + 1°C; at this temperature, only 5% of the incubated eggs of P. maculiventris showed some embryonic development (unpublished data). These find- ings are consistent with the t-estimates presented in this study. Our results support Cou- turier (1938) who stated that the lower developmental threshold for eggs of P. maculiventris was 11-12°C. Upper thresholds for development of both egg and nymphal stages (Figs. 1, 2) were estimated to be between 30 and 33°C for P. maculiventris and between 33 and 35°C for P. sagitta, again suggesting a somewhat better adaptation of the latter species to high temperature regimes. Thermal constants for development, expressed in DD, were calculated for each devel- opmental stage using the corresponding lower threshold temperatures as bases (Table 3). Mean DD estimates for nymphal development were not found to be significantly different (P>0.05) between the species, as reflected by the similarity of the slopes of the corre- sponding regression lines in Figure 2. However, Student's t-test analysis revealed that the mean number of DD required by P. maculiventris to complete egg and total immature development were significantly greater (P<0.05) than those for P. sagitta. volume 124 THE CANADIAN ENTOMOLOGIST 131

Table 4. Egg hatch, nymphal survival, and sex ratio of adults of P. maculiventris (Pm) and P. sagitta (Ps) at six constant temperatures

Nymphal survival Egg hatch (%) Sex ratio (8 : Q) Temp. ("C) Pm Ps Pm Ps Pm Ps

*Percentage survival for nymphs that hatched at 23°C and were subsequently incubated at the given temperature.

Survival. At temperatures between 19 and 30°C, hatching of P. maculiventris eggs ranged from 47% (19°C) to 57% (27°C) (Table 4). Temperatures 233°C caused 100% mortality in the egg stage. Survival of P. sagitta was highest at 27°C (71%) and decreased to 58 and 54% at 19 and 33"C, respectively. At a constant 35"C, none of the eggs hatched successfully. Hence, egg hatch was generally higher for the studied laboratory strain of P. sagitta compared with that of P. maculiventris. However, percentages of egg hatch reported in the literature for the latter species were higher than those observed in our study, ranging from 78% (Warren and Wallis 1971) to 94% (Mukerji and LeRoux 1965). Nymphal survival of both P. maculiventris and P. sagitta was high at temperatures <30°C, with from 63 to 78% and from 65 to 82% of the first-instar nymphs reaching the adult stage, respectively. Mortality during the nymphal stage was significantly increased at high temperatures with greatest mortality occurring at the time of moulting. At 33"C, only about 5% of the P. maculiventris first-instar nymphs reached the adult stage. Nymphal survival of P. sagitta was nearly 40% at 33"C, and decreased to about 20% at 35°C. Adults of both species that emerged at such high temperatures were considerably smaller and often deformed; they did not mate or lay eggs and usually died within 1 week (De Clercq and Degheele 1990b). In accord with the results presented here, Couturier (1938) and Vlasova et al. (1980) stated that nymphs of P. maculiventris died at temperatures 235°C. Sex Ratio. Sex ratios of P. sagitta adults ranged from 16 :1 P to 1 6 :1.3 9 at moderate temperatures (Table 4); at high temperatures, the proportion of male progeny was found to be higher, with sex ratios from 16 :0.79 to 16 :0.9 9 . A similar trend was noted for P. maculiventris, except for the 19°C experiment in which more males were observed to emerge (sex ratio: 1 6:0.7?). Sexes in P. maculiventris are reported to be produced in equal numbers under normal laboratory conditions (Mukerji and LeRoux 1965; Warren and Wallis 1971); in laboratory cultures of P. sagitta, sex ratios were normally about 18:1.29 (De Clercq and Degheele 1990~).Unfavourable environmental conditions (e.g. extreme temperatures, food shortage) may alter the sex ratio of insects (Lauge 1985). The observed shift in sex ratio toward males at temperatures 233°C may thus reflect the bugs' response to unfavourable rearing conditions. Mukerji and LeRoux (1965) noted a predom- inance of males in cultures of P. maculiventris during periods of food shortage. Conclusion. At moderate temperatures (i.e. s30°C), time required for immature devel- opment was similar for P. maculiventris and P. sagitta. However, extrapolated lower threshold temperatures for immature development of P. sagitta were consistently higher than those for P. maculiventris. Also, temperatures 333°C were more detrimental to eggs and nymphs of P. maculiventris than to those of P. sagitta. These observations suggest that P. sagitta is adapted to a slightly warmer range of temperatures compared with P. maculiventris. Differences in adaptation to temperature between the two species may 132 THE CANADIAN ENTOMOLOGIST JanuarylFebmary 1992 have practical implications for their use as control agents. Further, developmental rates characteristic of local populations of P. maculiventris suggest the adaptive potential of this pentatomid to varying temperature regimes. Data reported in this study should be helpful in predicting the development of P. maculiventris and P. sagitta populations in the field and should therefore provide valuable information on the use of these predators in inte- grated pest management programmes.

Acknowledgments The authors thank C. Pelerents and Z.C. Hester for their helpful comments on the manuscript and S.J. Yu for kindly supplying eggs of P. maculiventris. This research was supported by grant No. 870028 from the IWONL (Instituut tot aanmoediging van Weten- schappelijk Onderzoek in Nijverheid en Landbouw).

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