Stefanos S. Andreadis

Frequency of resistance to Bacillus thuringiensis toxin Cry1Ab in greek and spanish population of Sesamia nonagrioides (Lepidoptera: Noctuidae)

Abstract The high-dose/refuge strategy is considered as the main strategy for delaying resistance in target pests to genetically modified crops that produce insecticidal proteins derived from Bacillus thuringiensis Berliner. This strategy is based on a key assumption that resistance alleles are initially rare (<10−3). To test this assumption, we used an F2 screen on natural populations of Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae) from Greece and Spain. In total, 75 lines from Greece and 85 lines from Spain were screened for survival of F2 larvae on Cry1Ab corn, Zea mays L., leaves. No major resistance alleles were found. The frequency of resistance alleles in the Greek population was <9.7 × 10−3 with 95% probability, which was very similar to that of the Spanish population (<8.6 × 10−3 with 95% probability), and the expected frequencies were 3.2 × 10−3 (0–0.0097) and 2.9 × 10−3 (0–0.0086) in Greece and Spain (pooled 1.5 × 10−3). The experiment-wise detection probability of resistance was 94.0 and 97.5% for the Greek and the Spanish population, respectively. Evidence of alleles conferring partial resistance to Cry1Ab was found only for the Greek population. The frequency of alleles for partial resistance was estimated as 6.5 × 10−3 with a 95% credibility interval between 8 × 10−4 and 17.8 × 10−3 and a detection probability of 94%. Our results suggest that the frequency of alleles conferring resistance to Cry1Ab, regarding the population of S. nonagrioides, may be rare enough so that the high-dose/refuge strategy could be applied with success for resistance management.

Cold hardiness of diapausing and non-diapausing pupae of the European grapevine moth, Lobesia botrana

Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae) is a key pest of grapes in Europe. It overwinters as a pupa in the bark crevices of the plant. Supercooling point (SCP) and low temperature survival was investigated in the laboratory and was determined using a cool bath and a 1 °C min−1 cooling rate. Freezing was fatal both to diapausing and non‐diapausing pupae. SCP was significantly lower in diapausing male (−24.8 °C) and female (−24.5 °C) pupae than in non‐diapausing ones (−22.7 and −22.5 °C, respectively). Sex had no influence on SCP both for diapausing and non‐diapausing pupae. Supercooling was also not affected by acclimation. However, acclimation did improve survival of diapausing pupae at temperatures above the SCP. Survival increased as acclimation period increased and the influence was more profound at the lower temperatures examined. Diapausing pupae could withstand lower temperatures than non‐diapausing ones and lethal temperature was significantly lower than for non‐diapausing pupae. Freezing injury above the SCP has been well documented for both physiological stages of L. botrana pupae. Our findings suggest a diapause‐related cold hardiness for L. botrana and given its cold hardiness ability, winter mortality due to low temperatures is not expected to occur, especially in southern Europe.

Fumigant Toxicity of Essential Oils from Basil and Spearmint Against Two Major Pyralid Pests of Stored Products

ABSTRACT The fumigant activity of essential oil vapors distilled from sweet basil Ocimum basilicum L. and spearmint Mentha spicata L. (Lamiaceae) were tested against two major stored products pests Ephestia kuehniella (Zeller) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). Various oil doses (0.5, 2.5, 5, 50, 250, 500, 1,000, and 1,500 µl/liter air), for an exposure period of 24 h, were tested. The essential oils were subjected to gas chromatography—mass spectrometry analysis and revealed that the major compounds were for spearmint oil carvone (67.1%) and limonene (+1,8 cineole; 14.3%) and for basil oil linalool (45.9%), 1,8 cineole (16.7%) and eugenol (10.3%). Apart from a few exceptions, no significant differences in insecticidal action were observed between basil and spearmint oil. Both oils were highly effective against adult moths, given that notable mortality (>80%) was recorded after exposure to low doses such as 2.5 µl/liter. Noteworthy, egg mortality was also recorded, reaching 73–79% for basil and 56–60% for spearmint. Toxicity data indicated that larvae and pupae were the most tolerant stages in all cases. Larval mortality never exceeded 21 and 18%, for basil and spearmint, respectively, irrespective of moth species. Basil and spearmint oils displayed mortalities as high as 38 and 28% in pupae. Lethal doses (LD50 and LD99) values were estimated via probit analysis. Developmental stage proved to be a significant factor, whereas the effect of oil species on insect mortality was insignificant. With the exception of adult individuals, basil and spearmint oils did not show satisfactory overall insecticidal activity against E. kuehniella and P. interpunctella.

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.

Impact of fluctuating temperatures on development of the koinobiont endoparasitoid Venturia canescens.

The effect of temperature on the biology of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) is well understood under constant temperature conditions, but less so under more natural, fluctuating conditions. Herein we studied the influence of fluctuating temperatures on biological parameters of V. canescens. Parasitized fifth-instar larvae of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) were reared individually in incubators at six fluctuating temperature regimes (15-19.5°C with a mean of 17.6°C, 17.5-22.5°C with a mean of 19.8°C, 20-30°C with a mean of 22.7°C, 22.5-27.5°C with a mean of 25°C, 25.5-32.5°C with a mean of 28.3°C and 28.5-33°C with a mean of 30°C) until emergence and death of V. canescens adults. Developmental time from parasitism to adult eclosion, adult longevity and survival were recorded at each fluctuating temperature regime. In principle, developmental time decreased with an increase of the mean temperature of the fluctuating temperature regime. Upper and lower threshold temperatures for total development were estimated at 34.9 and 6.7°C, respectively. Optimum temperature for development and thermal constant were 28.6°C and 526.3 degree days, respectively. Adult longevity was also affected by fluctuating temperature, as it was significantly reduced at the highest mean temperature (7.0 days at 30°C) compared to the lowest one (29.4 days at 17.6°C). Survival was low at all tested fluctuating temperatures, apart from mean fluctuating temperature of 25°C (37%). Understanding the thermal biology of V. canescens under more natural conditions is of critical importance in applied contexts. Thus, predictions of biological responses to fluctuating temperatures may be used in population forecasting models which potentially influence decision-making in IPM programs.

Factors influencing supercooling capacity of the koinobiont endoparasitoid Venturia canescens (Hymenoptera: Ichneumonidae)

BACKGROUND Venturia canescens is a parthenogenetic koinobiont endoparasitoid of several pyralid moth larvae that are major pests of stored products. Low temperatures have been extensively used to control stored-product insects as an alternative to the application of traditional pesticides. However, most studies have focused on the cold hardiness profile of the major stored-product pests. The objective of this study was to investigate how factors such as age, food, host availability and acclimation affect the cold tolerance of V. canescens by determining its supercooling capacity. RESULTS Young adults displayed significantly lower supercooling points (SCPs) than older adults, irrespective of the availability of a host. Host availability had a moderate effect on supercooling, whereas food consumption resulted in a significant enhancement of SCP. Acclimation to low temperatures increased the supercooling capacity considerably. Furthermore, an increase in the duration of exposure to acclimation temperature resulted in lower SCPs. CONCLUSION Adults of V. canescens displayed an enhanced ability to supercool, however, they appear to be less cold tolerant than their respective hosts. This information would be useful in determining the potential of using V. canescens as a biological agent in Integrated Pest Management (IPM) programs, taking into consideration the adverse effects of low temperatures on its survival.