Influence of temperature and photoperiod on embryonic development in the dragonfly Sympetrum striolatum (Odonata: Libellulidae)

Temperature and photoperiod play major roles in insect ecology. Many insect species have fixed degree‐days for embryogenesis, with minimum and maximum temperature thresholds for egg and larval development and hatching. Often, photoperiodic changes trigger the transfer into the next life‐cycle stadium. However, it is not known whether this distinct pattern also exist in a species with a high level of phenotypic plasticity in life‐history traits. In the present study, eggs of the dragonfly Sympetrum striolatum Charpentier (Odonata: Libellulidae) are reared under different constant and fluctuating temperatures and photoperiodic conditions in several laboratory and field experiments. In general, and as expected, higher temperatures cause faster egg development. However, no general temperature or light‐days for eyespot development and hatching are found. The minimum temperature thresholds are distinguished for survival (2 °C), embryogenesis (6 °C) and larval hatching (above 6 °C). Low winter temperatures synchronize hatching. Above 36 °C, no eyespots are visible and no larvae hatch. In laboratory experiments, light is neither necessary for eyespot development, nor for hatching. By contrast to the laboratory experiments, the field experiment show that naturally changing temperature and photoperiod play a significant role in the seasonal regulation of embryonic development. The post‐eyespot development is more variable and influenced by temperature and photoperiod than the pre‐eyespot development. This developmental plasticity at the end of the embryogenesis might be a general pattern in the Libellulidae, helping them to cope with variation in environmental conditions.     

Thermal factors affecting egg development in the wandering glider dragonfly, <Emphasis Type="Italic">Pantala flavescens</Emphasis> (Odonata: Libellulidae)

The wandering glider dragonfly, Pantala flavescens (Fabricius), arrives in Japan from tropical regions every spring. The offspring colonize areas throughout Japan, with rapid increases in populations in the autumn, but all individuals die in the winter, suggesting low tolerance to low temperatures. However, few quantitative data on egg development and water temperature have been reported for this species. Females at the reproductive stage were collected from fields throughout the flying season and their eggs released using an artificial oviposition technique. Almost all of the eggs were fertilized. Egg size was stable throughout the seasons. Most eggs hatched within a period of 5 days at high water temperatures (35 and 30 °C), which were recorded in the shallow ponds and rice paddy fields from summer to early autumn. However, the egg-stage duration increased with declining water temperature. All eggs in water at 15 °C had failed to hatch by 90 days. The calculated critical temperature of water was determined to be approximately 14.3 °C; the total effective temperature for the egg stage was about 80 degree-days. Thus, low water temperatures in winter may prevent P. flavescens overwintering in Japan.     

Synchronisation of egg hatching of brown hairstreak (Thecla betulae) and budburst of blackthorn (Prunus spinosa) in a warmer future

Synchronisation of the phenology of insect herbivores and their larval food plant is essential for the herbivores’ fitness. The monophagous brown hairstreak (Thecla betulae) lays its eggs during summer, hibernates as an egg, and hatches in April or May in the Netherlands. Its main larval food plant blackthorn (Prunus spinosa) flowers in early spring, just before the leaves appear. As soon as the Blackthorn opens its buds, and this varies with spring temperatures, food becomes available for the brown hairstreak. However, the suitability of the leaves as food for the young caterpillars is expected to decrease rapidly. Therefore, the timing of egg hatch is an important factor for larval growth. This study evaluates food availability for brown hairstreak at different temperatures. Egg hatch and budburst were monitored from 2004 to 2008 at different sites in the Netherlands. Results showed ample food availability at all monitored temperatures and sites but the degree of synchrony varied strongly with spring temperatures. To further study the effect of temperature on synchronisation, an experiment using normal temperatures of a reference year (T) and temperatures of T + 5°C was carried out in climate chambers. At T + 5°C, both budburst and egg hatch took place about 20 days earlier and thus, on average, elevated temperature did not affect synchrony. However, the total period of budburst was 11 days longer, whereas the period of egg hatching was 3 days shorter. The implications for larval growth by the brown hairstreak under a warmer climate are considered.     

Seasonal synchrony of life cycles between the exotic predator,Pseudoscymnus tsugae (Coleoptera: Coccinellidae) and its prey,the hemlock woolly adelgid Adelges tsugae (Homoptera:Adelgidae)

1 The seasonal synchrony between the exotic predator, Pseudoscymnus tsugae and its prey, the hemlock woolly adelgid, Adelges tsugae, was investigated in field cages and in the forest in Connecticut, U.S.A. from 1997–1999. 2 In early spring, egg to adult development took 45 d at 18.7 °C, 39.7 d at 20.2 °C and 31.5 d at 22.7 °C. Earliest emerging F1 adults mated and oviposited in the same year. whereas F1 and F2 females emerging later in the summer mated and reserved most of their egg complement for the following year. 3 A second generation of P. tsugae is possible in Connecticut but may be delayed by cool mid‐spring temperatures. Individuals of three generations of P. tsugae, including overwintering survivors, may coexist in July and August and adults can be found year‐round with A. tsugae in infested hemlock forests. 4 A linear regression model for development from egg to adult under field temperatures gave good agreement with results from constant temperature findings. The model predicted a lower development threshold of 9.5 °C and a sum of effective temperatures of 405 day °C. Development time of P. tsugae is shorter relative to its prey A. tsugae and generation time ratios of predator to prey was 0.16–0.5, with an advantage conferred on the coccinellid. 5 Overwintering ability and behaviour were determined in 1998–1999 and adults remained on infested hemlock branches throughout a mild winter, becoming reproductively active in mid‐April. Peak oviposition period extended from April to July, in synchrony with peak oviposition and developing stages of two generations of A. tsugae.     

Variable egg development of Dinocras spp. (Plecoptera, Perlidae) and the stonefly seed bank theory

1. Temperature dependence of egg development of Dinocras cephalotes (Curtis) (three German and one Norwegian population) and Slovenian D. megacephala (Klapálek) was studied under a constant 14 : 10 light : dark photoperiod and constant temperature ranges of 4–24 °C and 4–18 °C, respectively. D. cephalotes was also incubated under seasonal field conditions; natural daylength and fluctuating temperatures had no modifying effect. 2. Both species have very similar lower threshold temperatures (4 and 3.5 °C, respectively), thermal demand for development (c. 600 degree days) and high dependence of mean incubation period on temperature (exponents of regressions near 1.5). Present data on D. cephalotes agree with the literature on British and Norwegian material of the same species. 3. Development occurs only at cue temperatures above the lower threshold. Cue temperatures range from 6 °C (some D. megacephala) to 14 °C (some D. cephalotes) and vary strongly within and between egg masses of D. cephalotes. Variation is not random, but seems to be genetically determined. 4. The variable temperature response renders study of effects of particular experimental regimes, and comparisons between local populations, difficult. 5. A latitudinal gradient in cue temperatures for development from 6 °C at c. 46 °N to 12 or even 14 °C at c. 61 °N seems to reflect reduced diversity at high latitudes. 6. Average success of spontaneous hatching exceeded 90% between 12 and 20 °C, but declined towards higher and lower temperatures. 7. Unhatched eggs were not dead but in parapause; development at other, higher or lower, temperatures was induced. Spontaneous plus induced hatching success approached 90%. Developing eggs rarely died; most dead eggs were apparently unfertilized. 8. Dormant plecopteran eggs are proposed to form a seed bank in stream bed sediments. Highly successful development after up to 220 days of dormancy was ascertained in Dinocras, and survival for up to 3 years is reported for other Perloidea. 9. Only systellognathan egg morphology provides options for long dormancy; the other plecopteran superfamilies, notably Nemouroidea, follow different strategies.     

Modeling egg development of the pest Clavipalpus ursinus (Coleoptera: Melolonthidae) using a temperature‐dependent approach

Abstract Predicting the population dynamics of insects in natural conditions is essential for their management or preservation, and temperature‐dependent development models contribute to achieving this. In this research the effects of temperature and soil moisture content on egg development and hatching of Clavipalpus ursinus (Blanchard) were evaluated. The eggs were exposed to seven temperature treatments with averages of 7.2, 13.0, 15.5, 19.7, 20.6, 22.0 and 25.3°C, in combination with three soil moisture contents of 40%, 60% and 80%. A linear and two non‐linear (Lactin and Briere) models were evaluated in order to determine the thermal requirements of this developmental stage. Temperature affected significantly the time of development and egg hatching, while no significant effect was observed for moisture content. Thermal requirements were set as: 7.2°C for lower developmental threshold, 20.6°C for optimum developmental threshold, 25.3°C for maximum temperature and 344.83 degree‐days for the thermal constant. The linear model described satisfactorily egg development at intermediate temperatures; nevertheless, a slightly better fit of the observed data was obtained with the Lactin model. Egg development took place inside a narrow range of temperatures. Consequently, an increment of soil temperature could generate a negative impact on the population size of this species or changes in its biological parameters.     

Life history parameters of the cattle long‐nosed sucking louse,Linognathus vituli

Cattle sucking lice, Linognathus vituli (L.) (Phthiraptera: Linognathidae), were obtained from naturally infected cattle and maintained within ‘arenas’ affixed to the backs of cattle confined in controlled environment chambers maintained at a constant temperature of 15 °C. Temperatures measured within the arenas at an ambient temperature of 15 °C were constant at about 34 °C and only slightly above the temperature on nearby skin. The effect of temperature on egg development was determined using a gradient of temperatures between 25 °C and 41 °C. Eggs did not develop at temperatures of < 26 °C or > 39 °C. Survival of eggs was highest at temperatures of 30 °C and 35 °C. The earliest hatch was observed at 5 days post‐oviposition (at 33–35 °C). Development was extended to as long as 13 days at the lower temperatures. Kaplan–Meier survival probabilities were compared for lice kept at two densities in the arenas and showed there to be no effect of density on louse survival. Similarly, the mean number of eggs/louse/day over an 8‐day period was not influenced by louse density.     

Thermal requirements of Fidiobia dominica (Hymenoptera: Platygastridae) and Haeckeliania sperata (Hymenoptera: Trichogrammatidae), two exotic egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Diaprepes abbreviatus is an exotic root weevil occurring in southern US. It is a highly polyphagous species which can complete its entire life cycle on citrus and several woody ornamental plants. The lack of native egg parasitoids for this weevil in citrus orchards has triggered efforts to evaluate candidate egg parasitoids from the Caribbean Region into Florida. The egg parasitoids Fidiobia dominica and Haeckeliania sperata are two exotic natural enemies of D. abbreviatus recently introduced in the US in a classical biological control program. The thermal requirements of both parasitoids were studied in the laboratory. The upper development threshold (UDT) of F. dominica was 30.0°C, its maximal development rate (MDR) occurred at 27.6°C, its lower development threshold (LDT) was 9.6°C and its thermal constant (K) for development from egg to adult was 293.1 DD. For H. sperata, UDT was 35.0°C, MDR occurred at 31.0°C, LDT was around 15°C and K was 188.1 DD. Based on these results, both species would be able to complete 17 to 18 generations annually in southern Florida. However, host availability during critical periods could severely impair the ability of these egg parasitoids to establish and successfully control D. abbreviatus in areas where winter temperatures fluctuate around 12°C, the LDT for this pest.     

Influence of temperature on hatching of winter eggs of fruit-tree red spider mite, Panonychus ulmi (Koch)

The effects of the duration and degree of chilling, and the temperature of incubation, on hatching of winter eggs of Panonychus ulmi (Koch) were investigated. For chilling, 0°C and 5°C were more effective than — 5° and 9°, and the limits for the reaction were close to — 10° and 15°. As the chilling period was increased from 60 to 200 days, the percentage hatch on incubation at 21° increased, and the mean incubation time and its variance decreased. Before the maximum effect of chilling was achieved, percentage hatch on incubation at 9° and 15° was higher than at 21°; 27° was lethal to most winter eggs though not to summer eggs. After chilling, the later stages of diapause development could occur at temperatures from 0° to 21°₎ i.e. above and below the threshold temperature for morphogenesis, 6–7° in both winter and summer eggs. Diapause development cannot, therefore, be a unitary process. The significance of the results is discussed in relation to forecasting the time of hatch in the field, and to the phenological aspects of hatching in the spring.     

Impact of increasing temperatures and exposure duration on egg hatch in the hemlock looper,Lambdina fiscellaria

As the growing season is expected to begin earlier under climate change, insects should initiate reproduction several days or weeks earlier than they used to. In eastern Canada, hemlock looper (HL) Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) females generally oviposit in September, with eggs entering an obligatory diapause quickly after their deposition. We therefore simulated an early start of the HL reproduction cycle of 2, 4, 6, or 8 weeks to examine the extent to which freshly laid eggs from two populations (island and mainland) can withstand exposure to four temperature conditions (15, 20, 25 °C, or fluctuating temperature in an outdoor insectary), with all treatments ending on 1 September 2007. On this date, half the eggs from each population were immediately incubated at 15 °C, while the rest were stored in an outdoor insectary until their incubation at 15 °C the following spring. In a separate experiment, the effect of temperature on pre‐diapause duration was determined from the number of days required for eggs to change colour after oviposition. The pre‐diapause phase was completed faster as temperature increased. Regardless of incubation date and population, percent hatch decreased significantly after 6‐8 weeks of exposure to 25 °C or in the outdoor insectary. Under most treatments, the odds of dying as pharate larvae increased with exposure duration. When eggs were incubated at 15 °C immediately after treatment, time to hatch and diapause duration remained constant over treatments, except at 25 °C when they both decreased. After 8 weeks of exposure to 15 or 20 °C, eggs transferred outdoors were more likely to hatch precociously than those exposed to 25 °C or insectary conditions. Globally, mortality seemed greater among eggs stored outdoors than among those kept indoors. Most eggs that survived the winter hatched synchronously after incubation in spring. Overall, larger eggs from the island population survived better than smaller eggs from the mainland population.     

Life history strategy and egg diapause in the intertidal collembolan Anurida maritima

ABSTRACT.

• 1 In a field survey of 1 year the intertidal collembolan Anurida maritima (Guérin) was found to be a univoltine species. Every year in early May a new generation emerges from eggs that overwinter. The first animals become adult in July. Almost all eggs laid in summer do not hatch, but undergo a period of diapause. Diapause is terminated in autumn by temperatures below 5°C. However, due to the low temperatures in winter further egg development is suppressed until spring.
• 2 The adult animals die, mainly in autumn. One of the causes of mortality may be starvation. In late autumn body size decreases and glycogen and lipid content are lower.
• 3 It is argued that in autumn due to low temperatures A.maritima, which forages during low tide on the open shore and seeks refuge underground before the incoming tide, is too sluggish to find food in the limited period of low water. This probably explains why this cosmopolitan species has developed a strategy to survive the winter in the temperate zone in the egg stage.

     

Age-specific fecundity and life table of Trissolcus semistriatus, an egg parasitoid of the sunn pest Eurygaster integriceps

The effects of temperature on age‐specific fecundity and life table parameters of the egg parasitoid Trissolcus semistriatus (Nees, 1834) (Hymenoptera: Scelionidae) were examined under four constant temperature conditions (17, 20, 26 and 32°C), using eggs of the sunn pest Eurygaster integriceps Puton, 1881 (Hemiptera: Scutelleridae), an important pest of wheat, as hosts. The intrinsic rate of increase increased linearly, while the mean generation time and the doubling time decreased with increases in temperature. The net reproductive rate, however, varied without clear correlation with temperature. Fecundity tended to be higher at higher temperatures. The total number of eggs per female was estimated as 52.0 and 116.4 eggs, respectively, at 17°C and 32°C, with the highest fecundity rate during the first day of oviposition. The oviposition rate fluctuated from 4.4 to 14.3 eggs per day. Oviposition and postoviposition periods and longevity decreased when temperature increased. Maximum longevity for females was 21.6 days at 20°C, and female parasitoids lived longer than males at all temperatures. The development period ranged from 7.1 days (32°C) to 35.6 days (17°C) for males and from 8.4 days (32°C) to 37.2 days (17°C) for females. The development of female T. semistriatus required 166.7 degree‐days (DD) above a theoretical threshold of 11.8°C and the development of males required 142.9 DD above 13.1°C. The numbers of generations per year for female and male T. semistriatus, given the temperature in Tekirdag, Turkey, were estimated to be 9.0 and 8.8, respectively. The potential of the egg parasitoid for the control of E. integriceps is discussed.     

Delayed Egg Hatching and Semivoltinism in the Nearctic Stonefly Megarcys signata (Plecoptera: Perlodidae)

Delayed egg hatching can influence the survival of aquatic insects by reducing exposure to competitors, predators, parasites, or unfavorable environmental conditions. We examined egg development in a Colorado population of the stonefly, Megarcys signata (Plecoptera: Perlodidae), whose larvae inhabit high altitude streams in the Rocky Mountains of western North America. Five-thousand fertilized eggs were collected from 40 different females and incubated in the East River, Gunnison County, Colorado, until late fall, at which time unhatched eggs were transported to incubation chambers in Ithaca, New York. We used three different combinations of photoperiod and temperature (10L:14D, 4°C; 10L:14D, 8°C; 8L:16D, 8°C) in an attempt to induce hatching. Eggs in the treatments with temperatures elevated above normal winter temperatures in the East River (8°C) began developing after 6 months, whereas eggs in the treatment most closely simulating natural stream conditions (4°C) did not hatch after 10 months of incubation. Our data indicate that this population of Megarcys signata has an extended egg stage that persists for almost a year, and that it is semivoltine at these elevations of 2885 and 2895 meters.     

The effect of temperature on the egg incubation period and nymphal growth of two Nemoura species (Plecoptera) from subarctic fennoscandia

Field studies of Nemoura arctica and N. viki showed that the two species preferred different biotopes and indicated differences in their life‐cycles. N. arctica seemed to have a semivoltine life‐cycle, at least in some years, this was not the case for N. viki.

Laboratory studies showed that the temperature tolerance of the eggs of N. arctica was wider than for those of N. viki. The length of the egg incubation period of both species was influenced by the ambient temperature, but no significant interspecific difference existed between the regression lines of the relationship between the temperature (T°C) and egg incubation period (Y days), as given by the regression equation Y = aT^?b for the log values. Reared at constant food supply, nymphal growth occurred in two periods. Firstly a rapid growth to about 4 mm, followed by a period of slow growth until emergence. During the first period growth (G)at (D) days was linear, according to the simple linear regression equation G = a+bD . The temperature tolerance of the nymphs of N. arctica was wider than for those of N. viki and significant interspecific differences between the species in growth were recorded at relatively high rearing temperatures, such as 12° and 16°C, but not at low temperatures. At constant food supply, nymphal growth was greatly influenced by the rearing temperature. At a mean temperature of 16°C N. arctica nymphs grew rapidly and emerged after 120 days; whereas at a mean temperature of 4°C growt h was slow and the nymphs did not even manage to reach the emergence stage after 700 days.     

Effects of temperature and soil moisture on survival of eggs of the mosquito Psorophora columbiae (Diptera: Culicidae)

The results of laboratory tests indicated the average survival rates for Psorophora columbiae eggs remained quite high for all of the egg populations exposed to a temperature of 27°C (range 83.0–100.0% survival) after 96 days of exposure, except for the non‐diapausing eggs on dry soil (66.3%). In regard to the exposure of egg populations to moderately cold temperatures (i.e. 8°C, 4°C and ?2°C) for periods of up to 16 days, survival rates for egg populations exposed to 8°C continued to remain relatively high (average >85%) for the remainder of the experimental exposure period (i.e. 96 days). Diapausing Ps. columbiae eggs were more tolerant (82.0% survival) to low temperatures (?2°C) than non‐diapausing eggs (2.4% survival) for 64 days, particularly at temperatures of and below 4°C. Diapausing and non‐diapausing eggs were similar in their ability to survive under high temperatures (34°C and 38°C). High soil moisture (30–40%) or substrate moisture (95% relative humidity) content appeared to enhance the ability of the mosquito eggs to survive both low and high temperature extremes.     

Population dynamics, growth and production of Sigara selecta (Fieber, 1848) (Hemiptera, Corixidae) in a Mediterranean hypersaline stream

1. This is the first study on the life cycle, growth and production of Sigara selecta, a Palearctic corixid species typical of brackish and saline waters, at the warmest limit of its European distributional range. The study combines field and laboratory approaches. 2. The S. selecta population studied was multivoltine, producing four asynchronous cohorts from early spring to December and overwintering in the adult state. Development time from egg to first adult ranged from 2 to 3 months. A minimum temperature threshold of 10 °C and diel amplitude of ≥10 °C were observed for reproduction and oviposition. 3. Maximum density and biomass were reached in mid spring and early autumn. The sex ratio was unbalanced, females dominating during most of the year, except in spring, when the sex ratio was balanced or dominated by males during the first adult emergence. 4. Laboratory rearing experiments at constant temperatures (18, 22 and 26 °C) pointed to a significant effect of temperature on egg development and nymphal growth. In the range of temperatures tested, both egg and nymphal instar duration decreased with increasing temperature. Mean nymphal development time varied from 43 days at 26 °C to 71 days at 18 °C, with a mean of 57 days. Survivorship was independent of temperature. 5. A reduction in nymphal and adult length was observed with increasing temperature. 6. Growth rates decreased with increasing body mass and increased as temperature increased. The first nymphal instar had the highest length increments and growth rates in all temperature treatments. 7. Satisfactory agreement was found between the field and laboratory degree‐days required for complete development from egg to first adult. At constant and variable thermal regimes, degree‐days decreased with increasing temperature. 8. Rate of growth in the field could be predicted with reasonable accuracy from a simple model obtained as a function of body mass. The model explained 67% of the variability in growth rates. 9. Annual production and production/biomass ratio (P/B) of S. selecta estimated by the Instantaneous Growth method were 1.28 g m^?2 year^?1 and 13.71, respectively. Spring and autumn cohorts contributed 32% and 54%, respectively, of total annual production. Maximum production corresponded to intermediate temperature periods, although summer production may have been underestimated because of the longer sampling interval relative to cohort interval production. The Size Frequency method underestimated production by at least 18% with respect to the Instantaneous Growth method.     

Life history and host-plant relationships of the rare endemic Arctic aphid Acyrthosiphon calvulus in a changing environment

This article examines the abundance, life history, host‐plant relationships, and overwintering biology of Acyrthosiphon calvulus Ossiannilsson (Homoptera: Aphididae) as a precursor to understanding its rarity and potential response to a changing climate. Acyrthosiphon calvulus is restricted to a few scattered localities on the west coast of Spitsbergen, Svalbard, Norway, where it reproduces on Salix polaris WG (Salicaceae) and its taxonomically unrelated root parasite Pedicularis hirsuta L. (Scrophulariaceae). Acyrthosiphon calvulus overwinters as eggs. Hatching fundatrices give rise directly to males and oviparae, which mate and lay overwintering eggs. The life cycle is closely synchronized with the phenology of S. polaris and appears genetically programmed, lacking summer generations of viviparae. Alate forms are similarly unknown. The progeny sequence of fundatrices resulted in a sex ratio for the sexuales that is strongly female biased (3:1). Eggs hatch coincided with budburst in early June and fundatrices developed on the expanding leaves. Egg production by oviparae corresponded with leaf senescence in July and August. Overwintering egg survival was high, with supercooling points ranging from ?29 to ?40 °C, lower than the extreme winter minimum temperature recorded (?28 °C). Egg development and hatching occurred at or below 5 °C and sub‐zero temperatures were not required to break diapause. The scarcity and fragmented distribution of A. calvulus is discussed in the context of the ubiquity of its host plants on Spitsbergen.     

Temperature effects on egg and larval development and phenological forecasting of the smaller fruit tortrix,Grapholita lobarzewskii

The effects of temperature on egg and larval development of Grapholita lobarzewskii Nowicki (Lepidoptera: Tortricidae) were studied under controlled conditions to complement the basis for phenological forecasting and thus to optimize the timing of monitoring and control measures with respect to sustainable pest management. Egg development lasted on average 28.1 days at 12.7 °C and 5.5 days at 26.1 °C. Egg mortality was generally low, varying between 12 and 14% within a temperature range of 12.7–22.0 °C, but slightly increased to 20% at 26.1 °C. For egg development, a lower thermal threshold of 9.7 °C and a thermal constant of 90.6 degree days were established. Larval development took on average 76.0 days at 12.7 °C and 21.5 days at 26.1 °C. Larval mortality was 51% at 12.7 °C but only 6–12% at temperatures above 17 °C. The lower thermal threshold and the thermal constant for larval development were 7.6 °C and 389.2 degree days, respectively. Final larval weight increased with temperature from 18.6 mg at 12.7 °C to a maximum of 23.9 mg at 22.0 °C. Based on mortality rates, the optimal temperature range was between 12.7 and 22.0 °C for egg development and between 17.1 and 22.0 °C for larval development, which was confirmed based on the weight of fully grown larvae. These biological parameters of egg and larval development enabled us to parameterise a phenology model for G. lobarzewskii, which was incorporated into an existing decision support system for fruit pests. Precise forecasts of pest phenology facilitate the optimal timing of monitoring and control measures, improve their efficiency, and thereby contribute to sustainable crop protection.     

The apple sawfly, Hoplocampa testudinea: egg development and forecasting of egg hatch

The effect of temperature on egg development of the apple sawfly Hoplocampa testudinea Klug was studied under controlled conditions. Based on a linear model describing the relationship between temperature and developmental rates a thermal threshold of 6.9 °C and a thermal constant of 85 day-degrees were established. The experimental results were used to expand and parameterise an existing phenology model to include egg development and hatching of first instar larvae. The model thus became a valuable forecasting tool not only for adult emergence and the optimal monitoring period but also for egg hatch and the best timing of control measures against first instar larvae. The model was validated by comparing predictions with independent observations on egg-laying and subsequent hatching of first instar larvae under semi-field conditions.