Matilda Savopoulou-Soultani

Development, Survivorship, and Reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae) Under Constant and Alternating Temperatures

Abstract Laboratory studies were conducted to assess the effect of temperature on the survival, development, fecundity, and longevity of Helicoverpa armigera (Hübner) at 11 constant temperatures ranging from 12.5 to 40°C, as well as at five alternating temperature regimes (25–10, 30–15, 32.5–17.5, 35–20, and 35–27.5°C) and under a photoperiod of 16:8 (L:D) h. H. armigera reared at constant temperatures did not develop from egg to adult (emergence) outside the temperature range of 17.5–32.5°C. The alternating conditions expanded this range from 10 to 35°C. The lowest developmental thresholds of the immature stages were estimated by a linear model and ranged from 10.17 (pupal stage) to 11.95°C (egg stage) at constant temperature regimes and from 1.1 to 5.5°C, respectively at alternating temperatures. The values of developmental thresholds estimated using the nonlinear (Lactin-2) model were lower than those estimated by the linear model for constant and alternating temperature regimes except for larval and pupal stages at constant temperatures. Mean adult longevity fluctuated from 34.4 d at 15°C to 7.6 d at 35°C. Females reared under all alternating temperature regimes laid more eggs than females reared at any, except the 25°C, constant temperature treatment. The intrinsic rate of increase was highest at 27.5°C, at both the constant and the corresponding alternating temperature regimes (0.147 and 0.139, respectively). Extreme temperatures had a negative effect on life table parameters.

Temperature-Driven Models for Insect Development and Vital Thermal Requirements

Since 1730 when Reaumut introduced the concept of heat units, many methods of calculating thermal physiological time heat have been used to simulate the phenology of poikilothermic organisms in biological and agricultural sciences. Most of these models are grounded on the concept of the “law of total effective temperatures”, which abstracts the temperature responses of a particular species, in which a specific amount of thermal units should be accumulated above a temperature threshold, to complete a certain developmental event. However, the above temperature summation rule is valid within the species-specific temperature range of development and therefore several empirical linear and nonlinear regression models, including the derivation of the biophysical models as well, have been proposed to define these critical temperatures for development. Additionally, several statistical measures based on ordinary least squares instead of likelihoods, have been also proposed for parameter estimation and model comparison. Given the importance of predicting distribution of insects, for insect ecology and pest management, this article reviews representative temperature-driven models, heat accumulation systems and statistical model evaluation criteria, in an attempt to describe continuous and progressive improvement of the physiological time concept in current entomological science and to infer the ecological consequences for insect spatiotemporal arrangements.

Temperature-Dependent Bionomics and Modeling of Anarsia lineatella (Lepidoptera: Gelechiidae) in the Laboratory

Abstract Laboratory studies were conducted to assess the effect of constant temperatures (15, 20, 25, 30, and 35°C) on life history traits of peach twig borer, Anarsia lineatella Zeller (Lepidoptera: Gelechiidae). Developmental rate, survival, longevity, and fecundity were studied in environmental chambers from individuals reared on peach, Prunus persica L., twigs until adulthood. Temperature-dependent relationships of various developmental events were characterized, and applied models were evaluated. Total developmental time ranged from 20.4 d (30°C) to 124 d (15°C). Lower developmental thresholds for egg-to-adult development assessed to 11.2 or 11.8°C, according to a linear weighted regression or the reduced major axis method, whereas development required on average 400 degree days (DD) or 424.4, respectively. Survival was substantially reduced at lower (15°C) and higher (35°C) temperatures. First-instar larvae exhibited higher sensitivities during development in all treatments. Mean longevity ranged from 12.1 d (35°C) to 45.8 d (15°C) and from 10.4 d (15°C) to 50.3 d (35°C) for females and males, respectively. A significantly higher number of eggs was laid at the moderate temperatures (126.9 at 25°C), whereas at the extremes, females laid the fewest (40.4 and 26.3 at 15 and 35°C, respectively). A new model, based on a β type distribution function, fitted on the temperature-dependant developmental data to predict population dynamics. Relative accuracy of the above-mentioned formula was validated using root mean square error (RMSE), index of agreement (d) and the mean square error quotient (E1,2) with respect to a proved model.

Overwintering survival and spring emergence of Helicoverpa armigera (Lepidoptera: Noctuidae) in northern Greece.

ABSTRACT Overwintering survival of Helicoverpa armigera (Hübner) was studied under field conditions during the winter of 2004–2005 and 2005–2006 to clarify whether a local population of this insect is established in northern Greece. Additionally, the postdiapause eclosion times of the overwintering generation was compared with adult male dynamics using pheromone traps. Our study supplies strong evidence that part, if not all, of the late-season generation of H. armigera overwinters as diapausing pupa in northern Greece, suggesting that a local population exists in this area. Pupae enter diapause during September and October in response to declining temperatures and photoperiod. A limited number of degree-days in autumn prevented part of the population from developing to the diapausing pupal stage. Larvae of H. armigera that were placed in field conditions late in October were not able to pupate and died. The termination of diapause and the eclosion of adults in the following spring were determined by the local soil temperatures. Diapause terminated between mid-April and early May, and adult emergence occurred within a 4- to 6-wk period from late April to early June. Females emerged slightly earlier than the males. The emergence of 10, 25, 50, 75, and 90% of adults required 153, 199, 252, 303, and 347 DD, respectively. Differences in timing and degree of overlap between adult emergence from the experimental population and pheromone trap catches suggests that the spring population of this species also includes immigrants.

Developing Optimum Sample Size and Multistage Sampling Plans for Lobesia botrana (Lepidoptera: Tortricidae) Larval Infestation and Injury in Northern Greece

The purpose of this research was to quantify the spatial pattern and develop a sampling program for larvae of Lobesia botrana Denis and Schiffermüller (Lepidoptera: Tortricidae), an important vineyard pest in northern Greece. Taylors power law and Iwaos patchiness regression were used to model the relationship between the mean and the variance of larval counts. Analysis of covariance was carried out, separately for infestation and injury, with combined second and third generation data, for vine and half-vine sample units. Common regression coefficients were estimated to permit use of the sampling plan over a wide range of conditions. Optimum sample sizes for infestation and injury, at three levels of precision, were developed. An investigation of a multistage sampling plan with a nested analysis of variance showed that if the goal of sampling is focusing on larval infestation, three grape clusters should be sampled in a half-vine; if the goal of sampling is focusing on injury, then two grape clusters per half-vine are recommended.

Population dynamics of Anarsia lineatella in relation to crop damage and the development of economic injury levels

Developing a relationship between pest abundance and damage to crops is essential for the calculation of economic injury levels (EILs) and to anticipate informed management decisions. Field studies were conducted for three successive years (2005, 2006 and 2007) in peach orchards of northern Greece to examine relationships between densities of Anarsia lineatella Zeller (Lepidoptera: Gelechiidae) populations and peach (Prunus persica) yields. According to a linear regression model, the increase in moth’s densities during the 1st flight resulted in a significant reduction in yield (y = 0.436x + 10.22, R2 = 0.635, d.f. = 2,11, P < 0.05). Correlation of male moths captured during the 2nd flight and observed yield loss was significant (y = 0.5231x + 17.204, R2 = 0.792, d.f. = 2,11, P < 0.05). Moreover, according to a linear model by counting the number of shoot strikes, during the first observation period, a forthcoming yield loss can be estimated (y = 27.389x−6.304, R2 = 0.711, d.f. 2,11, F = 22.09, P < 0.05). A significant relationship was observed between the numbers of the 2nd generation larvae and yield loss (y = 163x, R2 = 0.890). Regression coefficient of the above function represents yield loss per pest and was applied in the calculation of EIL’s and fixed Economic thresholds (ET’s). In addition, parameter of the price commodity was estimated for 2009 by applying stochastic autoregressive moving average model. By integrating above information, EIL and fixed ET estimated as 112 larvae and 84 larvae per sampling unit for a mean value (€4/0.1 ha) of cost management tactics and a 90% efficacy.

Age‐dependent changes in tolerance to cold and accumulation of cryoprotectants in overwintering and non‐overwintering larvae of European corn borer Ostrinia nubilalis

Abstract The age‐dependent cold hardiness profile of Ostrinia nubilalis is compared between nondiapausing and diapausing larvae, as well as with field‐collected larvae. The results suggest that both cold tolerance and accumulation of cryoprotectants depends upon the age of O. nubilalis larva. Late fifth‐instar nondiapausing larvae are more cold tolerant than younger fifth‐instars because they show enhanced ability to withstand sub‐zero temperatures. No appreciable difference is observed between the experimental groups of diapausing larvae as far as their supercooling ability and tolerance at sub‐zero temperatures above the supercooling point. In general, both field‐collected and diapausing larvae are more cold tolerant than nondiapausing larvae, indicating a direct link between diapause and cold hardiness. The age of diapausing larvae affects the ability to accumulate glycerol. Glycerol levels of 45‐day‐old diapausing larvae are significantly higher (2.7‐fold) compared with 90‐day‐old diapausing larvae. Moreover, diapausing larvae display a five‐ to 13‐fold higher glycerol content compared with nondiapausing larvae. There is a trend for an age‐dependent cold hardiness profile in O. nubilalis and further tests that could demonstrate a causal relationship between age and cold tolerance are needed.

Abiotic Factors and Insect Abundance

1 Laboratory of Applied Zoology and Parasitology, Faculty of Agriculture, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece 2 Laboratory of Entomology and Agricultural Zoology, Department of Agriculture Crop Production and Rural Environment, University of Thessaly, Fytokoy Street, N. Ionia, 38446 Magnisia, Greece 3Department of Entomology and Agricultural Zoology, Benaki Phytopathological Institute, S. Delta 8, 14561 Kifissia, Greece 4 Laboratoire Evolution Genomes Speciation, IRD/CNRS, Avenue de la Terrasse, BP 1, Gif-sur-Yvette, 91198 Paris Cedex, France

Seasonal abundance and population dynamics of Adoxophyes orana (Lepidoptera: Tortricidae) in northern Greece

Abstract The phenology and population dynamics of the tortricid moth Adoxophyes orana were studied using pheromone traps and periodic sampling of shoots and fruits sampling in peach orchards in northern Greece (latitude 40.3° North). We combined diapause and development in a day-degree model of A. orana phenology. Each year adult activity occurred in early May or after 418 day-degrees had been accumulated from 1 February, when diapause development is completed. Larval activity began in early spring (March). According to larval instar distribution, by October diapause course is irreversible. Combining data on trap captures and larval activity reveals three distinct generations in the area. Larval densities increased at the end of summer when also fruit damage is possible. Three parasitoids were identified, Colpoclypeus florus being the most abundant. Applying the Weibull function and a logistic distribution to cumulative percentage of trap captures and larval development, respectively, the phenology of A. orana is forecasted with the accumulated day-degrees. The prediction of the models agrees well with the observed flight curves of A. orana males. The practical implications concerning population dynamics and use of the models for control of this pest are discussed.

Cold hardiness attributes of a field population of the potato tuberworm, Phthorimaea operculella

The potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a worldwide pest of solanaceous crops especially devastating to potatoes. In the present study, we investigated the cold hardiness profile of acclimated and non‐acclimated immature and adult stages of a field population of P. operculella. For both acclimated and non‐acclimated individuals mean supercooling point (SCP) did not differ significantly among developmental stages. Unlike supercooling capacity, acclimation at 5 °C for 5 days enhanced the ability to survive at subzero temperatures after a 2‐h exposure. Median lethal temperature (LT50) of all developmental stages (egg, late instar, pupa, and adult) decreased after acclimation, nevertheless only adults displayed a significant difference among acclimated and non‐acclimated individuals concerning their LT50 (−11.1 and −8.3 °C, respectively). Generally, pupae were the most cold‐tolerant developmental stage followed in decreasing order by the eggs and adults, whereas late instars were the least cold tolerant. Non‐freezing injury above the SCP was well‐documented for all developmental stages indicating a pre‐freeze mortality and suggesting that P. operculella is considered to be chill tolerant rather than freeze intolerant. Nevertheless, given its high degree of cold hardiness relative to habitat temperatures, winter mortality of P. operculella due to low temperatures is not likely to occur and pest outbreaks may take place following a mild winter.