Thermal response and reversibility of diapause in the eggs of Locusta migratoria

Abstract. Eggs of a local population of Locusta migratoria L. (Orthoptera: Acrididae) collected near Hirosaki (40.5^oN) entered diapause when incubated at temperatures between 20 and 35^oC. For diapause development the optimum temperature was 10^oC. The lower thermal threshold for post-diapause development was 14.7^oC. After chilling at 10^oC for 20 days, the rate of hatching varied with incubation temperature, being 0, 61% and 81% at 20, 25 and 30^oC, respectively. After chilling for 40 days or more, however, almost all eggs hatched at 20–30^oC. Diapause with a reduced intensity seemed to be eliminated easily by a high temperature of 25 or 30^oC.
When eggs chilled at 10^oC for 20 days were kept at 20^oC for 7 days or more before incubation at 25^oC, almost all eggs maintained diapause. Most eggs chilled at 10^oC for three 10 day periods separated by 3 days of warming at 25^oC failed to terminate diapause. Daily alternations of 10^oC (18 h) and 25^oC (6h) decreased the diapause-terminating effect of chilling. These facts suggest that diapause intensity can be restored if eggs chilled insufficiently are exposed to a moderately high temperature. This reversible change in diapause intensity would play an important role in maintaining diapause before winter.     

Effects of photoperiod and low temperature on diapause termination in the yellow-spotted longicorn beetle (Psacothea hilaris)

Abstract. .The effects of photoperiod and low temperature on diapause termination in the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae), were examined using a population from Ino, Japan. Diapausing insects obtained by rearing larvae under short daylength (12 or 13 h) at 25^oC were subjected to various treatments. When the photoperiod was changed at the same temperature, diapausing larvae showed a long-day response with a critical daylength between 13.5 and 14h. The diapause was terminated and consequently pupation occurred if the daylength was longer than 13.5 h. Chilling the diapausing larvae at 10^oC for 30 or more days also terminated diapause in most larvae irrespective of the photoperiods during and after chilling treatment. In contrast, the post-chilling photoperiod had a critical effect on development of diapausing larvae chilled for only 15 days.     

Hourglass and oscillator expressions of photoperiodic diapause response in the cabbage moth Mamestra brassicae

Abstract. Both oscillator and hourglass features are found in the photoperiodic response that controls the pupal winter diapause of Mamestra brassicae. The expression of oscillatory response to extended long-night cycles is temperature dependent, i.e. circadian resonance appears at 23 and 25^oC but not at 20 and 28^oC. At 20^oC, scanning of extended scotophases by a short light pulse does not reveal any clear circadian rhythmicity. However, a circadian feature of the photoperiodic response is indicated even at 20^oC by a bistability phenomenon, i.e. either one of the two dark periods in symmetrical skeleton photoperiods determines the diapause response depending on the phase angle with the preceding (entraining) light-dark cycles. At 20 and 25^oC, the incidence of diapause increases as a function of the number of light–dark cycles regardless of the cycle length (T) , if T is 24 h or 2 X 24h (with a 12 h light period). A non-diel cycle (r=36h) is less effective, suggesting that disturbance of the circadian organization partly impairs the diapause-inducing function. The inductive effect of a long night is largely affected by temperature, and becomes saturated with eight cycles at 20^oC and 14 cycles at 25^oC. Presumably, an hourglass mechanism measures the dark time, and a circadian component involved in some later sequence of the photoperiodic response may or may not be expressed depending on the mode of interaction between them.     

Effects of temperature on development of Otiorrhynchus sulcatus (Coleoptera: Curculionidae)

Development of the black vine weevil, Otiorrhynchus sulcatus , was investigated at constant temperatures from 9 to 27 ^oC. Pre-adult development was completed in 200 and 130 days at 15 and 24 ^oC, respectively. Eggs and larvae developed at 27 ^oC, but no pupation took place at this temperature. The developmental threshold temperatures for eggs, larvae + pre-pupae and pupae were 6, 2–6 and 12 ^oC, respectively. Reproductive maturation of females took place at temperatures from 12 to 27 ^oC, but only a few females became reproductive at 12 ^oC. Most females at 12 ^oC, like those at 9 ^oC, had a short maturation feed, but the ovaries did not develop. The pre-oviposition period was temperature dependent. The females showed a cyclic oviposition pattern with three peaks. The significance of soil temperatures for the phenology and distribution of O. sulcatus in Norway is discussed.     

Induction of winged sexuparae in root-inhabiting colonies of the aphid Pemphigus betae

Abstract. Growth chamber experiments were conducted to determine what environmental factors induce the development of sexuparae in root-feeding colonies of the aphid Pemphigus betae Doane (Aphididae: Pemphiginae). Experimental colonies were derived from clones that had been reproducing for at least 15 months under constant laboratory conditions. At constant 20–23^oC, sexuparae were almost never produced regardless of the level of crowding or photoperiod. In contrast, every culture of several clones produced sexuparae when subjected to temperatures alternating between 20 and 15^oC during the light and dark phases respectively. This fluctuating temperature regime resulted in sexupara production regardless of photoperiod. All cultures also produced some sexuparae when cultures were kept in constant darkness at temperatures that were either alternated between 20 and 15^oC or kept constant at 15^oC. Constant 17^oC resulted in sexupara production in most cultures. At 17^oC, experimental manipulation of densities within cultures showed that crowding promotes sexupara production. Thus, within the range of conditions occurring at the time of sexupara induction in the field, photoperiod has no effect on sexupara production, temperature below a threshold between 17 and 20–23^oC triggers sexupara production, and crowding promotes sexupara production but only if temperature is low enough.     

Effects of temperature on virogenesis of bluetongue virus serotype 11 in Culicoides variipennis sonorensis

Abstract. Culicoides variipennis sonorensis females were fed bluetongue virus serotype 11 mixed in sheep blood and were held at constant temperatures of 32, 27, 21 and 15^oC. Virogenesis, as measured by enzyme-linked immunosorbent assay (ELISA), proceeded significantly faster at higher temperatures. Based on ELISA absorbance ≥0.2, some flies first were categorized as infected after 1 day, 2 days and 4 days at 32, 27 and 21^oC, respectively. Peak levels of virus antigen were seen after 5–7, 7–13 and 18–22 days for flies held at 32, 27 and 21^oC, respectively. There was no significant virus replication in flies held at 15^oC for 22 days, but latent virus replicated and was detected easily (44% infection) 4–10 days after these flies were transferred to 27^oC. The implications for temperature effects on bluetongue epizootiology are discussed.     

The potential for control of the blowfly Lucilia sericata using odour-baited targets

Abstract A deterministic simulation model is used to explore the potential for control of the sheep blowfly, Lucilia sericata , using odour-baited targets. The simulations show that the ambient temperatures of 15^oC or 20^oC, 13% and 24% of the females present in a population would need to be killed per day, respectively, to prevent the population growing from its initial spring density during the summer blowfly season. In contrast, if both sexes could be sterilized, so that sterilized males were also able to disrupt the fertility of unsterilized females, only 6.5–13% of both sexes would need to be attracted and sterilized at 15^oC or 20^oC respectively. To examine whether these numbers of individuals could be attracted by targets baited with liver and sodium sulphide, mark-release-recapture studies in sheep pastures were used to quantify sticky target efficiencies. The percentage of the Lsericata population caught on any one day was shown to be positively related to average ambient temperature. At 15^oC each sticky target caught approximately 13% and at 20^oC, 41% of the females within a 20 m radius. The results indicate that, at ambient temperatures between 15 and 20^oC, if distributed at a density of approximately 5/ha, targets baited with liver and sodium sulphide could effectively suppress a population of L.sericata. Lower densities of targets would be required if they were able to sterilize both sexes rather than kill or if more attractive synthetic semiochemical baits could be developed.     

Assessment of phosphine fumigation as a plant quarantine measure against Spodoptera littoralis

In laboratory tests first instar larvae of Spodoptera littoralis were killed by phosphine fumigations of 24 and 48 h at a concentration x time product (CTP) of 36 mg h/1. Eggs aged 1–2 days were, however, tolerant to phosphine at a CTP of 144 mg h/1 and this CTP caused severe damage to chrysanthemum cuttings (cv. Freedom). When eggs aged < 1 day and 1–2 days old were preconditioned at 20 ^oC for 72 h before phosphine fumigation, complete mortality occurred at CTPs at and above 36 mg h/1. Preconditioning for 48 h at 20 ^oC and for 48 and 72 h at 15 ^oC did not produce 100% mortality at a CTP of 288 mg h/1. It was suggested that eggs of S. littoralis pass through a phase of tolerance to phosphine which at 20 ^oC lasts about 4 days after oviposition.
There was no indication that phosphine was toxic to chrysanthemum cuttings (cv. Pollyanne) at concentrations of 0–75 mg/1 (CTPs of 18 and 36 mg h/1). Storage at 15 ^oC was not damaging to cuttings but at 20 ^oC some damage became apparent.     

The effect of temperature and inoculation access period on the transmission of barley yellow dwarf virus byRhopalosiphum padi (L.) and Sitobion avenae (F.)

Winged individuals of Rhopalosiphum padi and Sitobion avenae transmitted the PAV-like and MAV-like isolates of barley yellow dwarf virus respectively. Success of transmission after inoculation access periods of 2, 6, 12, 24, 48 and 72 h were examined and survival, reproduction and movement of the aphid vectors were recorded at these times. The experiment was done at four different temperatures: 6^oC, 12^oC, 18^oC and 23^oC. For both isolates the inoculation efficacy did not increase after a 24 h inoculation access period and there was no difference in inoculation efficiency at the three highest temperatures, that at 6^oC being significantly lower than at 12^oC to 23^oC. The results suggest that autumn temperature is a critical factor for BYDV epidemiology in Britain with a small increase in autumn temperature leading to greatly increased infection rates.     

Life span and ovarian dynamics of the pine beauty moth, Panolis flammea (D&S): the effect of low temperatures after adult emergence on reproductive success

Abstract Adult female Panolis flammea were kept at 2^oC either immediately after emergence from the pupae or immediately after mating, for periods ranging from 5 to 20 days and then placed at 15^oC together with a male moth, food supply and suitable oviposition site ( Pinus contorta foliage). Weight loss over the storage period was directly proportional to the time spent at 2^oC irrespective of whether the moths were virgin or mated. Pre-oviposition period decreased significantly from the control after more than 5 days at 2^oC, but there was no significant difference between late mated and early mated moths. The post-storage life span of late mated and early mated moths decreased in proportion to the time spent at 2^oC but late mated moths had significantly longer life spans than early mated moths. Moths mated prior to storage were significantly less fecund than moths mated after storage except those moths kept at 2^oC for 20 days where the fecundities of both treatments were identical (c. 45 eggs/female). These results are discussed in relation to the conditions likely to be experienced by P.flammea in the field and their bearing on the population dynamics of this insect.     

Survival of parent and brood adult bark beetles, Ips typographus, in relation to size, lipid content and re-emergence or emergence day

ABSTRACT. This study investigated a possible trade-off between bark beetle reproductive effort and future survival. Parent adult Ips typographus (L.) (Coleoptera: Scolytidae) were collected when they re-emerged from a laboratory culture after completing their first brood and held at constant temperatures of 4 or 25^oC. As a comparison, emerging brood adults were collected and held at 25^oC. The longevity of the beetles was related to when they re-emerged or emerged (measured in days since parent introduction) and to their size (pronotal width), fresh weight and lipid content at collection, by multiple regression analysis. The expression (fresh weight x pronotal width ^-2.6), used as an estimate of lipid content of the living beetles, was significantly correlated (r=0.67, P<0.001) with the actual (extracted) lipid content. At 25^oC, fat content was the variable most strongly correlated with survival time in all beetle groups except parent females. In both parent and brood females, re-emergence or emergence day, respectively, contributed significantly to the explanation of survival time, whereas pronotal width and fresh weight never contributed significantly to the regression equation. At 4^oC, fat content was not estimated but, re-emergence day was negatively correlated with survival time. In conclusion, beetles with high fat content and re-emerging or emerging early have longer expected survival than beetles leaving the log later or containing less fat. This means that females laying a large first brood might suffer a somewhat higher mortality than females laying a smaller brood.     

Temperature-dependent development and survival of the lesser mealworm, Alphitobius diaperinus

Abstract. Development, growth and survival of the lesser mealworm, Alphitobius diaperinus (Panzer), were determined at six constant temperatures. No egg hatch or larval development occurred at 17^oC. At temperatures of 20, 25, 30, 35 and 38^oC the median development times (days), respectively, were for eggs (13.4, 6.0, 4.4, 2.6 and 2.6), larvae (133.0, 46.0, 26.2, 22.4 and 23.9), pupae (17.0, 8.0, 5.5, 4.0 and 4.1), and from oviposition to adult emergence (164.4, 60.2, 37.9, 29.0 and 30.8). The Sharpe & DeMichele (1977) model was used to describe the temperature-dependent development. The mean egg survival (hatching) ranged from 61% to 86%, with lowest hatch at 20^oC. Survival of the larvae and pupae ranged from 32% to 73% and from 85% to 95%, respectively, with lowest survival at 20^oC. Pupae had significantly lower weights at 35^oC and adults at 38^oC than at the other temperatures. Female pupae (20 mg) and female adults (16 mg) were significantly heavier than male pupae (17 mg) and male adults (13 mg). Adults (0.5–9 months old) laid 4–7 eggs per female per day at 25^oC.     

Energetics and foraging behaviour of the European seed harvesting ant Messor capitatus: I. Respiratory metabolism and energy consumption of unloaded and loaded workers during locomotion

Abstract The respiratory metabolism of workers of Messor capitatus (Latreille) was measured using standard micro-Warburg techniques on single individuals. The experiments were carried out at 10, 20, 25, 30 and 40^oC, and the respiratory quotient (RQ), measured for the same individuals at 30^oC, was found to be 0.77. The specific respiratory rate (y , in μl O₂/mg dry weight/h) could be described by the following equation: Iny = -2.24 + 0.098r -0.258 In W; where T is temperature and W is the dry weight in mg. The Q₁₀ for M. capitatus in the temperature interval 20–30^oC was 3.4, a higher value than for other ants.
The energy costs of movement and carrying were determined by using the RQ to convert the continuous measurement of CO₂ produced at 30^oC by Enfiuran anaesthetized workers ('resting metabolism'), by running workers and by workers loaded with a 20 mg weight to units of energy. The resting metabolism was 10.0±1.0 mJ/mg fresh weight/h. The cost of running ( Y in joule per km) could be described by: Y = 3.865 + 0.363 Wf , where Wf is fresh weight in mg. The cost of transport for all experiments could be expressed as 0.64 × the cost of running.     

Influence of thermoperiod and photoperiod on reproductive diapause in Bruchidius atrolineatus (Pic) (Coleoptera, Bruchidae)

Abstract Bruchidius atrolineatus (Pic) is a common pest infesting cowpea seeds ( Vigna unguiculata Walp) in Africa. In the Sahelian zone, the adults are in reproductive diapause during the dry season. Diapause induction depends on the climatic conditions during embryonic and post-embryonic development. A strain of B. atrolineatus originating from the Niamey (13^oN) was reared in different thermoperiodic and photoperiodic conditions. In the thermoperiodic regime 40:25^oC, in continuous darkness, induction of diapause was dependent on the duration of the thermophase. Photoperiod could also influence diapause induction but the response depended on the temperature. When the beetles were reared in conditions of LD 12:12 h, 40:25^oC, for seven generations, the proportion of diapausing adults decreased and their sensitivity to photoperiod increased. In LD 14:10 h, 40:25^CC, the proportion of diapausing adults remained high regardless of the photoperiod. In these conditions, the first emerging adults were sexually active and were used for selection of a strain with a low incidence of diapause. After twelve generations, the proportion of diapausing beetles was lower than 5%. The responses of this selected strain to photo- and thermoperiods were reduced. The sensitivity of B. atrolineatus to photoperiod and thermoperiod could be controlled by genetic systems as observed in other insect species.     

Germination ecology of drupelets of the fig (Ficus carica L.)

Abiotic and biotic factors and their effects on germination of fig drupelets were studied. The drupelets germinated between 10^oC and 30^oC.Constant humidity was necessary for germination and frequent drying out of the substrate was unfavourable. Total darkness for the whole duration of the experiments had a slighly negative effect on germination. The fastest germination occurred at constant humidity and an alternating temperature of 20/30^oC with exposure to light for 8 hours (at the higher temperature) and to darkness for 16 hours (at the lower temperature).Natural or artificial removal of drupelets from the syconium guaranteed a high germination percentage, whereas no germination occurred in drupelets left inside the syconium. Hence birds and mammals act as dispersal agents and mediators of germination. As they eat pieces of fig syconium, they free the drupelets from the flesh, eliminating the effect of inhibitors and/or microenvironments with high osmotic pressure inside the syconium. These findings support the hypothesis that germination occurs in autumn or spring depending on the climatic zone in which the species grows.     

Development rates of some pre-adult stages in blowflies with reference to low temperatures

Abstract. Duration of some pre-adult stages of Calliphora vicina Robineau-Desvoidy, C.alpina Zett., C.vomitoria Linn., Phormia terraenovae R.-D. and Lucilia sericata Meig. were determined at 3.5–26^oC, in the context of use of these insects in forensic estimates of post-mortem intervals. Egg development in C. vicina occurs down to at least 3.5^oC, larval growth to 4^oC and puparial formation, development and perfect adult emergence to 5^oC. Growth curves by successive weighing of individual larvae showed specific differences in rates of development of the above species at constant temperatures. Alternating temperatures for 12 h periods (such as 10^oC and 20^oC) to simulate diurnal changes, usually, but not at all temperature pairs tested, caused acceleration of growth relative to the corresponding constant temperature (15^oC in the above case), in C.vomitoria, P.terraenovae and L.sericata , but usually caused retardation of larval growth in C.vicina. In this species, larvae as single individuals on beef liver in small tubes grew on average at the same rates as those (50–100 larvae) growing communally. All species showed variation in larval growth between individuals, more marked in C.vicina , and slower-growing larvae showed increased unexplained mortality. Because of this and to avoid complication by fast-growing larvae from later laid egg batches on a carcass, growth curves given are those of mean weights of the heaviest 25% (upper quartile) of groups of 40–90 feeding larvae. Variation in growth rates, and acceleration or retardation of growth in different species under alternating temperatures, thus affect suggested procedures in obtaining estimates of post-mortem intervals using these insects.     

Cold shock and heat shock: a comparison of the protection generated by brief pretreatment at less severe temperatures

Abstract Brief exposure to low (0^oC) or high (40^oC) temperature elicits a protective response that prevents injury when the flesh fly, Sarcophaga crassipalpis Macquart, is subjected to more severe cold (-10^oC) or heat (45^oC). Both the low and high temperature responses were found in all developmental stages of the fly, but were most pronounced in the pupal and pharate adult stages. The protective responses generated by brief exposure to 0 or 40^oC appear similar in that both result in a rapid acquisition of cold or heat tolerance and a loss of protection after the flies are returned to 25^oC. The protection generated by chilling is obvious within 10 min of exposure to 0^oC while a 30 min exposure to 40^oC is required to induce the high temperature protection. High temperature protects against cold shock injury within a narrow range (around 36^oC) but we have no evidence that low temperature can protect against heat injury. We previously demonstrated that the rapid increase in cold tolerance correlates with concomitant increases in glycerol concentration, but in this study we found no significant elevation in glycerol in heat-shocked flies. Thus the physiological and biochemical bases for the rapid responses to cold and heat appear to be different.     

Arabian sandflies (Diptera: Psychodidae) prefer the hottest nights?

Abstract. A vehicle-mounted net was used to collect hourly samples of sandflies on 15 nights during June in northern Oman. Every half hour, the temperature, relative humidity, wind velocity and light intensity were measured (there was no cloud or rainfall during this period).
The sandflies caught were mainly Phlebotomus alexandri and Sergentomyia clydei. Their circadian activity increased rapidly after sunset (18.50 hours). The high level of activity was fairly constant during 9 h of darkness until dawn, when it decreased rapidly. A few flies were still active at 07.00 hours, 1.5 h after sunrise.
A multiple regression showed that the main factor affecting sandfly activity was light intensity. When this factor was removed, by considering only the 135 catches collected during the 9 h of darkness, the second most important factor was low relative humidity, followed by low wind velocity. Temperature was not a significant factor in the analysis, because of its strong negative correlation with humidity. However, when the effect of humidity was removed from the regression, high temperature became significant, but less important than wind.
The regressions showed that, for flight activity, the optimum humidity was around 10%; the probable maximum wind velocity was 3.5 ms^-1 and 11^oC was the probable minimum temperature. Thus, when the 4 nights with highest catches (200–260 flies/night) were compared with the 4 nights with lowest catches (50–120 flies/night), the best nights had a low humidity (10–25%) and low wind speed (<0.3ms-¹) in combination with highest temperatures (31–43^oC).     

Incubation temperature in the Australasian Gannet Moms senator

Gannets (Sulidae) and some other pelecaniforms incubate their eggs under the webs of their totipalmate feet. These species have a wide latitudinal distribution from tropics to subarctic, but little is known of the incubation temperatures attained. I measured egg temperatures of the Australasian Gannet Morns serrator at Cape Kidnappers, New Zealand, employing a data logger to obtain records every 15 min for day-long sample periods at undisturbed nests. Egg surface temperatures were relatively stable and little affected by ambient temperature. Mean surface temperature of natural eggs was 34.9^oC for samples taken during the first 4 days of incubation, but this then increased and stabilized at 36.5^oC. Internal temperature of pipped eggs was about 1^oC higher, attributable to embryonic heat production. Upper surface temperature of eggs kept in a fixed position was about 2^oC below deep adult body temperature (40.3^oC), suggesting heat is transferred directly from the body through the feet. Clutch size does not appear to be limited by an inability to warm two eggs. These results are in general agreement with measurements from other web incubators and are well within the range for species with conventional brood patch incubation.     

A mutant strain of Chymomyza costata (Diptera: Drosophilidae) insensitive to diapause-inducing action of photoperiod

ABSTRACT. From a Japanese population of Chymomyza costata which has been known to have a photoperiodic larval diapause, we selected a mutant strain which did not respond to photoperiod. However, about 70% of the individuals of this strain entered diapause at 11^oC irrespective of photoperiod, and about the same percentage of those of the photoperiod-sensitive strain also did so in continuous illumination at 11^oC. This indicates that low temperature induces diapause independently of photoperiod. On the other hand, a temperature drop from 18 or 25^oC to 15^oC and chilling at 4^oC did not induce diapause.