Argyro A. Fantinou

Development of Immature Stages of Sesamia nonagrioides (Lepidoptera : Noctuidae) Under Alternating and Constant Temperatures

Abstract Laboratory studies on the temperature-dependent development of Sesamia nonagrioides (Lefebvre) were performed under five constant temperatures ranging from 20 to 30°C as well as under the corresponding alternating temperatures of 25:10, 27.5:12.5, 30:15, 32.5:17.5, and 35:20°C, at a photoperiod of 16:8 (L:D) h. Both linear and nonlinear (Lactin formula) models provided a reliable fit of developmental rates versus temperature for all immature stages either at constant or alternating temperatures. Developmental thresholds that were estimated by a linear model for eggs, larvae, or pupae were approximately the same and estimated to be 10.57, 8.89, and 10.75°C, respectively, at constant temperatures. Lower values were estimated when immature stages were exposed to the corresponding alternating temperatures (7.23, 6.20, and 6.50°C for eggs, larvae, and pupae). Therefore, the evaluation of the development of immature stages under constant temperatures resulted in an overestimation of the lower thresholds. The Lactin-2 model also was applied, and larval and egg developmental thresholds did not differ from those that were estimated by the linear model. Differences, however, occurred at the pupal stage. Nevertheless, the differences in the estimated values of the lower developmental thresholds of the immature stages under constant or alternating temperatures indicate that a model predicting phenology in the field should be based on fluctuating temperature.

Reproductive responses to photoperiod and temperature by diapausing and nondiapausing populations of Sesamia nonagrioides Lef. (Lepidoptera − Noctuidae)

Abstract.  The influence of long‐ and short‐day cycles on ovipostion and egg hatch of the corn stalk borer, Sesamia nonagrioides were investigated at a range of temperatures. Oviposition was suppressed when insects are exposed to long days through their immature stages and then transferred to short days after mating. Moreover, mean oviposition and egg hatch increased from 15 to 27.5 °C, whereas oviposition declined significantly at 30 °C at both photoperiodic regimes. Females derived from a diapausing population exposed to long days after mating showed a significantly higher egg production compared to females derived from a nondiapausing population. However, when females from a diapausing population were left to oviposit under short days, fewer eggs were produced compared to those exposed to long days after mating. Thus, photoperiod appears to affect reproductive traits of this species in a quantitative manner. Larval diapause duration is positively correlated with fecundity of the adults. There is also a positive correlation between pupal weight of individuals derived from a diapausing population and the postdiapause fecundity of adults.

Temperature-Dependent Development and Life Table of Iphiseius degenerans (Acari: Phytoseiidae)

Abstract The effect of temperature on the development of immature stages of the predator Iphiseius degenerans (Berlese) was studied at 15, 20, 25, 27.5, 30, and 32.5°C with 60% RH and photoperiod of 16:8 (L:D) h when feeding on Tetranychus urticae. The data obtained were used for the estimation of the thermal requirements of this predator by a linear and nonlinear model (Lactin 2-model). Developmental thresholds that were estimated by the linear model for immature stages of egg, protonymph, and deutonymph were approximately the same and found to be 11.71, 10.11, and 11.28°C, respectively, whereas that of the larval stage was found to be lower (7°C). The Lactin-2 model was also applied, and lower values were estimated for all immature stages than those by the linear model. Biological characteristics and life table parameters of the predator were also studied at 15, 20, 25, 30, and 32.5°C. Preoviposition period was shortest at high temperatures of 30 and 32.5°C (1.18 and 1.08 d, respectively), whereas fecundity was highest at 30°C. Longevity of adults and mean generation time was longest at 15°C. The intrinsic rate of increase was highest at 25 and 30°C (0.22 and 0.23 d−1, respectively), whereas doubling time was found to be shortest at 30°C. The results show that this predator develops effectively at a broad range of temperatures. Moreover, it can increase at relatively high temperatures and is well adapted to the high temperatures that occur in Mediterranean region.

Photoperiodic and temperature effects on the intensity of larval diapause in Sesamia nonagrioides

Abstract. The intensity of larval diapause in Sesamia nonagrioides Lef (Lepidoptera: Noctuidae) was investigated under laboratory conditions. Newly hatched larvae were exposed to different stationary photoperiods (from LD 7 : 17 h to LD 14 : 10 h), at a constant temperature of 25 °C. Diapause incidence was higher when larvae were exposed to daylengths shorter than the critical value (LD 12 : 12 h), whereas the within‐treatment variation in the larval period appeared to be significantly correlated with the photoperiod applied. The incidences of diapause and the duration of larval development were also measured after exposing larvae to short photoperiods (LD 8 : 16 h, LD 10 : 14 h or LD 12 : 12 h) in combination with various temperatures (20, 22.5 or 25 °C). Although an increase in the incidence of diapause appeared with the lowering of the temperature, no statistical differences were observed in the time needed for pupation within the photoperiodic treatments at the temperatures of 20 and 22.5 °C. Furthermore, when diapausing larvae were transferred to the long photoperiod of LD 16 : 8 h, they immediately proceeded to pupation, regardless of the photoperiod or the temperature to which they had been previously exposed, indicating that there were no differences in the intensity of diapause. Photoperiodic changes from LD 10 : 14 h to LD 12 : 12 h or to LD 14 : 10 h at different larval ages reduced the intensity of diapause with (a) early age of transfer and (b) increase of daylength. By contrast, when larvae were transferred from the long photoperiod of LD 14 : 10 h to shorter, such as LD 10 : 14 h or LD 12 : 12 h, a small increase in the intensity of diapause with the shortening of the daylength was apparent. These results support the hypothesis that insects may compare the duration of the photoperiod and could classify them as either longer or shorter in relation to the critical value.

Consumption rate, functional response and preference of the predaceous mite Iphiseius degenerans to Tetranychus urticae and Eutetranychus orientalis

The functional response of females of the phytoseiid mite, Iphiseius degenerans (Berlese), to increasing densities of females of its prey, Tetranychus urticae Koch and Eutetranychus orientalis Klein, on bean leaves, were studied under laboratory conditions. Our results indicated that the predator consumed significantly more items of E. orientalis than of T. urticae at all densities treatments. Daily consumption of the predator increased with increasing prey density until a plateau was reached—maximum number of prey consumed was ca. 4 for T. urticae and ca. 12 for E. orientalis. A Type II functional response was determined by a logistic regression model. The highest estimated value a (instantaneous rate of attack) and the lowest value of Th (handling time) were found for the predator feeding on E. orientalis. Prey selection was evaluated by simultaneously presenting both prey species to the predator in various ratios and at increasing densities. I. degenerans showed a higher predation rate and higher preference for E. orientalis at all the ratios and prey densities tested. This may be due to the smaller size or the inactivity of E. orientalis and the inability of the predator to cope with the webbing of T. urticae. Our results suggest that I. degenerans can be considered a suitable biological control candidate based on its preference for E. orientalis in the Mediterranean region.

Effect of Several Different Pollens on the Bio-Ecological Parameters of the Predatory Mite Typhlodromus athenas Swirski and Ragusa (Acari: Phytoseiidae)

ABSTRACT The development, survivorship, and reproduction of the predacious mite Typhlodromus athenas Swirski and Ragusa were studied in the laboratory by rearing the predator on nine different plant pollens [almond (Prunus amygdalis Batsch), apple (Malus domestica Borkh.), apricot (Prunus armeniaca L.), cherry (Prunus avium L.), pear (Pyrus communis L.), plum (Prunus domestica L.), walnut (Juglans regia L.), olive (Olea europaea L.), Typha sp.], and pollen collected from bee hives. All experiments were conducted in environmental chambers at 20 ± 1°C, 65% RH, and a photoperiod of 16:8 (L:D) h. Survival during immature development ranged from 81.1 to 96.0%. The shortest mean developmental time from egg to adult with respect to the range of pollen species was recorded for females and males fed on almond pollen (10.76 ± 0.18 and 10.45 ± 0.21 d, respectively), while the longest was on beehive pollen (26.97 ± 0.23 and 24.00 ± 0.25 d for females and males, respectively). Female longevity varied from 51.63 ± 5.52 d (olive pollen) to 102.81 ± 6.60 d (pear pollen), while fecundity ranged from 5.33 ± 2.35 eggs per female (beehive pollen) to 26.43 ± 1.73 eggs per female (almond pollen). The diet consisting of almond pollen resulted in the highest intrinsic rate of natural increase (rm ) (1.00d-1) and pollen collected from bee hives resulted in the lowest (0.013d-1). These results showed that various pollen could favor the development of T. athenas, and also support the view that alternative food resources may play an important role in the field for sustaining and increasing the predators population.

Effect of Thermoperiod on Diapause Induction of Sesamia nonagrioides (Lepidoptera-Noctuidae)

Abstract We have been studying the factors that control larval diapause of Sesamia nonagrioides (Levebvre), a multivolitine pest of corn, Zea mays L., in the Mediterranean. The effect of various combinations of photoperiod and temperature on the induction of larval diapause of S. nonagrioides was examined. Short daylengths (8–12 h) were the main factor inducing diapause in this species, whereas high temperatures could avert the effect of the photoperiodic signal. Daily temperature cycles with different amplitudes (differences between the thermophase [high phase] and cryophase [low phase] temperatures), could induce diapause under a photoperiod of 12:12 (L:D) h when the cryophase coincided with the scotophase (dark period). In contrast, short daylengths had no effect on diapause when the thermophase coincided with the scotophase. Moreover, greater differences between the high and the low temperatures of the thermoperiod led to a higher incidence of diapause. Diapause also occurred under 24-h thermoperiods at constant darkness; the incidence of diapause correlated with the duration of the cryophase. The thermoperiodic response curve of diapause under constant darkness was analogous to that of the photoperiodic response of a type I, or long-day insect. The cryophase of the thermoperiod must be <17.5°C to obtain a high incidence of diapause. Consequently, it appeared that a thermoperiodic threshold during the cryophase was demonstrated. Hence, both the duration and the temperature of the cryophase of the thermoperiod were important factors controlling the diapause response. The ecological implications of this behavior are discussed.

Seasonal population fluctuation and spatial distribution of Orthoptera in two grassland areas of Attica – Greece

The aim of this study was to investigate the seasonal population fluctuation of orthopteran assemblages and determine the spatial distribution of the most abundant species of Orthoptera among two habitats in Greece. A 2-year study was performed in a lowland area and in a mountain grassland area. The family of Acrididae represented almost 75% of the total orthopteran relative abundance in both sampling areas. Dociostaurus maroccanus and Chorthippus bornhalmi were found to be the most abundant species in the lowland and the mountain sampling stations, respectively. Most populated species were spatially aggregated in the lowland station, whereas the abundant species were found to be distributed either aggregately or randomly among sampling units in the mountain area. Shannon–Wiener index estimate was higher for the lowland in 2007 than for the mountain, whereas the opposite was found in 2008. The factors affecting the population dynamics of Orthoptera are discussed.

A qualitative and quantitative study of mites in similar alfalfa fields in Greece

The present study investigated the mite fauna and the relative abundance of mites present in foliage and litter of two adjacent and similar alfalfa fields, differing only in the number of cuttings, in Kopais Valley (Central Greece) through 2008–2010. We also examined the relationship between assemblage patterns of Mesostigmata, Oribatida and Prostigmata by comparing their population fluctuation, population density, species richness and diversity. Spatial distribution of common dominant and influent mite species was also estimated. Our results showed that both fields supported a very rich and similar mite fauna with eight new species records for alfalfa of Greece, although these species have been previously reported from other habitats in Greece. The pattern of population fluctuation in foliage was similar in both fields, unlike the fluctuation in litter. Population density significantly differed between fields, being higher in the less harvested field, except Prostigmata. Species richness in litter was higher in the less harvested field, whereas it was higher in the foliage of the more harvested field, apart from that of prostigmatic mites in litter, which was higher in the more harvested field, and that of oribatid mites in foliage, which was higher in the less harvested field. The diversity of mites was higher in the more harvested field, with the exception of prostigmatic mites. The spatial distribution of mites in foliage and litter was aggregated in both fields. Our results indicate that despite the considerable similarity of the study fields, the different harvesting frequency might have disturbed differently the mite communities hosted in foliage and litter.

Plant Resources as a Factor Altering Emergent Multi-Predator Effects.

Multiple predator effects (MPEs) can modify the strength of pest regulation, causing positive or negative deviations from those that are predicted from independent effects of isolated predators. Despite increasing evidence that omnivory can shape predator-prey interactions, few studies have examined the impact of alternative plant food on interactions between multiple predators. In the present study, we examined the effects and interactions of two omnivorous mirids, Μacrolophus pygmaeus and Nesidiocoris tenuis, on different densities of their aphid prey, Myzus persicae. Prey were offered to the to single or pairs of mirid predator individuals, either conspecific or heterospecific on a leaf, while simultaneously adding or excluding a flower as an alternative food resource. Data were compared with calculated expected values using the multiplicative risk model and the substitutive model. We showed that predation of aphids was reduced in the presence of the alternative flower resource in treatments with single M. pygmaeus individuals, but not with single N. tenuis individuals. When the predators had access only to prey, the effects of multiple predation, either conspecific or heterospecific, were additive. The addition of an alternative plant resource differently affected MPEs depending on the nature of predator pairings. Predation risk was increased in conspecific M. pygmaeus treatments at intermediate prey densities, whereas it was reduced in conspecific N. tenuis treatments at high prey densities. Observations of foraging behaviour concerning the location of conspecific pairings revealed that M. pygmaeus individuals showed a clear tendency to reside mainly in the flower, whereas N. tenuis individuals were found to reside at different posts in the dish. We suggest that the competition between omnivorous predators may be mediated through the diversity of their plant feeding preferences, which directly affects the strength of MPEs. Consequently, the preferences of the interacting predators for different plant resources should be considered in studies evaluating the outcomes of MPEs.