DEVELOPMENT AND SURVIVAL OF PODZSUS MACULZVENTRZS (SAY) AND PODZSUS SAGZTTA (FAB.) (HETEROPTERA: PENTATOMIDAE) 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 Podisus rnaculiventris (Say) and Podisus sagitta (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 insects 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).