Comparative laboratory studies on three fungal pathogens of the elm bark beetle Scolytus scolytus: Effect of temperature and humidity on infection by Beauveria bassiana,Metarhizium anisopliae, and Paecilomyces farinosus

Larvae of the elm bark beetle, Scolytus scolytus, were inoculated with conidia of the entomogenous fungi Beauveria bassiana (two strains), Metarhizium anisopliae (two strains), and Paecilomyces farinosus (two strains) and incubated over a range of temperatures (2°, 6°, 10°, 15°, and 20°C). One strain each of B. bassiana and P. farinosus caused infection even at 2°C, whereas the two strains of M. anisopliae caused no infection below 10°C. Infection of adult beetles by B. bassiana (one strain) and M. anisopliae (one strain) was tested at 15°, 20°, and 25°C (B. bassiana) and at 15° and 20°C (M. anisopliae). Fungal infection occurred at all three temperatures, but at 25°C beetles tended to succumb to bacterial infection. The effect of relative humidity on infection of larvae by B. bassiana (one strain), M. anisopliae (one strain), and P. farinosus (one strain) was tested at 51, 74, 86, 90, 95, 97.5, and 100% relative humidity. B. bassiana and M. anisopliae caused some infection at all humidities: with P. farinosus there was no infection at the two lowest humidities. Mortality due to infection by these fungi was most rapid at the highest humidities.     

The influence of food availability on population dynamics of a supralittoral isopod, Ligia dilatata brandt

Size frequency analysis of monthly samples of the isopod Ligia dilatata Brandt in the rocky supralittoral region on the west coast of the Cape Peninsula, South Africa, over a 20-month period shows that L. dilatata lives for 2 yr and that annual recruitment occurs from spring until autumn. Females start reproducing at 12 months but, unlike males, probably do not survive to breed twice. The brood period is 5–6 wk. Fecundity is described by the regression equation N = 1.9L – 3.7 (N =no. of eggs in brood pouch, L = length of females in mm). Growth is slow during summer but faster in winter when food is more plentiful. Two distinct phases of mortality are evident; a constant slow mortality for the first 9 months after recruitment, and a faster second phase culminating in the elimination of the cohort after a further 11 months. The in situ temperature range is only 6.2°C (mean: 14.6°C) due to the insulating effect of kelp debris and appears to be less important than food availability in influencing the regular annual cycles observed.     

Effects of temperature and host age upon the encapsulation of Metaphycus stanleyi and Metaphycus helvolus eggs by brown soft scale Coccus hesperidum

Encapsulation of eggs inserted by Metaphycus stanleyi (Hymenoptera: Encyrtidae) into the brown soft scale Coccus hesperidum (Homoptera: Coccidae) became more frequent as the host matured. This occurred with both laboratory reared and field-collected parasites. After parasitism for 24 hr at 27°C, encapsulation frequency did not differ in hosts reared at 20° or at 27°C, but significantly increased in hosts reared at 33°C. When parasitism and rearing were carried out at the same temperature, the percentage of eggs encapsulated increased from 48.7% at 27°C to 94.1% at 33°C. With M. helvolus, the percentage of eggs encapsulated was considerably higher than with M. stanleyi; e.g., 99.3 vs 48.7%, respectively, at 27°C. At 20° and 27°C, some M. helvolus development occurred in the larvae of brown soft scale but none at 33°C; the adult stages of the host encapsulated all the parasite eggs at these temperatures.     

Cellular immune competence of a Drosophila mutant with neoplastic hematopoietic organs

In the Tum^l mutant of Drosophila melanogaster, the larval hematopoietic organs undergo neoplastic changes and release into circulation large numbers of blood cells. The lamellocytes, and to a lesser extent the plasmatocytes from which they are derived, are the cells that encapsulate various endogenous tissues and form melanotic tumors. The mutation is temperature sensitive, with maximum gene expression manifested at 29°C. The ability of Tum^l larvae to encapsulate eggs of the wasp parasite Leptopilina heterotoma is dependent not only on temperature, with host larvae much more immune reactive at 29°C than at lower temperatures (15° or 21°C), but also on the interval of time following infection when temperature shift experiments are performed. When the shift of parasitized larvae from 21° to 29°C is delayed by 18 hr the hosts are not as immune reactive as those shifted immediately after infection. Since Tum^l larvae are potentially highly immune reactive at the time of infection (with sufficient numbers of lamellocytes in circulation to encapsulate parasites), the low degree of immune competence in hosts shifted to 29°C after 18 hr or maintained at lower temperatures suggests that the increased capacity of blood cells to react against foreign surfaces is dependent on the cells acquiring new or altered recognition and adherence properties at 29°C. The 18-hr delay may provide the parasite with an opportunity to interfere with the acquisition of these specific cellular alterations. Differential hemocyte counts from parasitized larvae show abnormally low lamellocyte counts in susceptible hosts, indicating that successfully developing parasites interfere with the differentiation of hemocytes.     

The influence of maternal thermal environments on reproductive traits and hatchling traits in a Lacertid lizard,Takydromus septentrionalis

The thermal environment can induce substantial variation in important life-history traits. Experimental manipulation of the thermal environment can help researchers determine the contribution of this factor to phenotypic variation in life-history traits. During the reproductive season, we kept female northern grass lizards, Takydromus septentrionalis (Lacertidae), in three temperature-controlled rooms (25, 28 and 32 °C) to measure the effect of the maternal thermal environment on reproductive traits. Maternal thermal environment remarkably affected reproductive frequency and thereby seasonal reproductive output, but had little effect on reproductive traits per clutch or hatchling traits. Females kept at 32 °C produced more clutches and thus had shorter clutch intervals than females from 28 to 25 °C. Clutch size, clutch mass, relative clutch mass, egg size and hatchling traits did not vary among the three treatments. The eggs produced by the females were incubated at 27 °C and the traits of hatchlings were measured. The result that egg (offspring) size was independent of maternal thermal environments is consistent with the prediction of the optimal egg size (offspring) theory. The eggs produced by low temperature females (28 and 25 °C) took longer time to complete their post-oviposition development than did eggs produced by high temperature females (32 °C). This suggests that the eggs from low temperatures might have been laid when the embryos were at relatively early stages. Therefore, maternal thermal environment prior to oviposition could affect post-oviposition development in T. septentrionalis.     

Effects of temperature on carbon fixation and carbon budget partitioning in the zooxanthellal symbiosis of Aiptasia pallida (Verrill)

Effects of temperature on carbon fixation rates and partitioning between Aiptasia pallida (Verrill) and its symbiotic alga Symbiodinium microadriaticum Freudenthal were examined by ¹⁴C incubation studies. Total fixation varied strongly with temperature, with an optimum of 32 °C. More photosynthate was translocated to the host at 12 °C (82%) than at 27 °C (63%). Partitioning among three fractions (alcohol soluble, ether soluble, and alcohol/ether insoluble) varied with temperature in Aiptasia pallida, but not in the alga. Relative partitioning between host and alga increased with time in favor of A. pallida when maintained at 12 °C, but absolute levels of translocation to the host did not change; however, photosynthate retention by the alga did decline substantially. Total fixation declined by ≈ 80% after 10 days at 12 °C. Turnover rates of fixed carbon also varied with temperature, as determined by pulse-chase studies, and the effect varied for the different fractions.These results suggest that zooxanthellae are less thermally adaptable than their hosts, and may be especially susceptible to low temperatures. Thermal effects on biochemical partitioning may have great importance in relation to growth and reproduction of animal hosts of zooxanthellae and the viability of the symbiotic relationship. These effects, combined with the pronounced effect of temperature on total photosynthate production, probably play a major role in limitation of zooxanthellal symbioses to warm waters.     

The survival of Entomophthora spp. in mummified aphids at different temperatures and humidities

Entomophthora aphidis survived for at least 32 weeks at 0°C and 20 or 50% RH and E. thaxteriana for at least 16 weeks at 10°C and 20 or 50% RH in mummified infected pea aphids, Acyrthosiphon pisum. The fungi produced infective conidia when the aphids were moistened. This probably explains the survival of Entomophthora species infecting aphids during short periods when the weather is unsuitable for conidial discharge and host infection.     

Cloning and expression of the leucine gene from Thermus thermophilus in Escherichia coli

A pBR322-T.leu hybrid plasmid was constructed which contains a 3.75 Md HindIII-fragment derived from Thermus thermophilus HB27 chromosomal DNA. In the Escherichia coli host, this plasmid coded for the β-IPM dehy drogenase (product of leuB) activity, the optimal temperature of which was 80°C, suggesting that information on the thermostability of the enzyme lies in its structural gene. 10-day propagation of E. coli [pBR322-T.leu] at 37°C decreased the temperature optimum from 80°C to 75°C. This change, which was found to depend on the plasmid but not on the host cells, might be due to selection of some mutation at the non-restrictive temperature of 37°C. Our results suggest that the 3.75 Md HindIII-fragment of pBR322-T.leu carries a promoter of the thermophile, which could function in E. coli.     

Some effects of time,temperature and feeding on infection rates with Babesia bovis and Babesia bigemina in Boophilus microplus larvae

Dalgliesh R. J. and Stewart N. P. 1982. Some effects of time, temperature and feeding on infection rates with Babesia bovis and Babesia bigemina in Boophilus microplus larvae. International Journal for Parasitology12: 323–326. Percentages of larval ticks in which Babesia bovis and B. bigemina parasites could be detected (infection rates) were determined after the larvae had been exposed to temperatures between 9°C and 27°C for periods of 1–35 days and then either fed on calves or heated at 37°C to stimulate babesial development. Infection rates with both species increased during 2–4 weeks after the larvae hatched, regardless of the temperature of exposure. Infection rates with B. bovis were higher after exposure of larvae to 14°C than to 27°C. This effect was less pronounced with B. bigemina. Infection rates were higher in fed larvae than in unfed, ‘heat stimulated’ larvae. The findings indicate that infected larval ticks become more efficient vectors of Babesia during the first 2–4 weeks after hatching and that repeated sampling of a tick population is necessary to determine valid infection rates.     

Temperature effects on induction of parasitization by females of Trichogramma principium (Hymenoptera, Trichogrammatidae)

The effects of temperature on induction and stability of parasitization of less preferred factitious host (the Angoumois grain moth, Sitotroga cerealella) eggs by Trichogramma principium females were studied under laboratory conditions. The percentage of parasitizing females at 15°C was significantly lower than that at 20, 25, and 30°C. At constant temperatures of 15, 20, 25, and 30°C, mean durations of pre-oviposition periods were 6.5, 2.1, 0.9, and 0.6 days, respectively (differences were significant between all regimens). In most of females, parasitization induced by high temperature (25°C) continued after the temperature decrease to 15°C. These results suggest that although emerged females are ready to lay eggs, rather prolonged pre-oviposition period may precede parasitization of less preferred hosts, and the duration of this period may depend on temperature.     

Effects of temperature on growth and efficiency of food utilization in fifth-instar caterpillars of the tobacco hornworm, Manduca sexta

Fifth-instar larvae of Manduca sexta were reared from hatching on artificial diet at 15, 20, 25, 30 and 35°C. Total development time decreased with increasing temperature. Very few larvae (12%) survived at 15°C, so this temperature was not considered further. There was some mortality at 30°C (11%), and at 35°C (50%).The absolute rate of growth in the fifth instar was faster at 25 than at 20°C, but was similar at 25, 30 and 35°C. This was true both for caterpillars that were chronically exposed to experimental temperatures (i.e. since hatching) and for those acutely exposed (i.e. reared up to fifth instar at 25°C).There was a progressive decrease with higher rearing temperatures in both the initial and final sizes of chronically exposed fifth-instar larvae. Acutely exposed caterpillars matched for initial size showed smaller temperature related differences in final size. Because of these size differences there were differences in relative growth rate which did not reflect true differences in absolute growth rate.Total food consumed by chronically exposed caterpillars was greatest at the lowest temperature (20°C), and decreased progressively with increasing temperature. The absolute rate of food consumption increased from 20 to 25°C, but did not vary significantly between 25 and 35°C. Differences in the sizes of the insects at the different temperatures meant that there were differences among relative measures of consumption that did not reflect absolute food consumption.For chronically exposed caterpillars, none of the three usual indices of food conversion efficiency (AD, ECI and ECD) varied significantly with temperature between 20 and 35°C. This implies that the effects of temperature on metabolic costs are closely matched to food consumption.Oxygen consumption increased with temperature between 20 and 25°C but was temperature compensated between 25 and 35°C.These findings are discussed in terms of their implications for the optimal temperature for growth in Manduca.     

Effect of temperature on reproduction and parasitism of the egg parasitoid,Anastatus orientalis (Hymenoptera: Eupelmidae)

Anastatus orientalis is a solitary endoparasitoid of Lycorma delicatula (Hemiptera: Fulgoridae) eggs. We investigated the development, longevity, fecundity, and sex ratio of A. orientalis on different temperatures to establish the optimal temperature condition for laboratory mass rearing. There were significant differences in its development and longevity between 15 °C and the rest of temperature conditions (20, 25, and 30 °C), among which were no significant differences. The average number of eggs laid by A. orientalis was higher at 20 and 25 °C, but there was no statistically significant difference in its fecundity between the two temperatures. More females emerged at 15 and 20 °C than higher temperatures.Parasitisms of A. orientalis varied with host egg ages and densities. Even in 14 day old eggs of L. delicatula, parasitoids successfully emerged from 92.3% of the parasitized eggs. On the other hand, parasitism was lowest (13.8%) on just before hatching eggs. Parasitism was negatively dependent on host density.Oviposition behavior for A. orientalis primarily occurred at 1400–1600 h, not at 2400–0800 h. The majority of this parasitoid's emergence occurred at 0800–1000 h, largely before noon. These results may be useful for controlling the adequate time for supplying host eggs and release density of this parasitoid as well as for potentially predicting the accurate time for securing parasitoid adults in laboratory mass rearing of A. orientalis.     

The in vitro culture of the blood stages of Plasmodium berghei

Plasmodium berghei was cultured in medium 199 with 10% serum at various temperatures. At 31° and 37°C the parasite numbers decreased. Experiments at 15°C achieved consistent multiplication rates greater than one, with a maximum of three-fold.     

Effects of varying temperature on the reproduction and damage potential of Heterodera schachtii to Chinese cabbage (Brassica rapa pekinensis)

Heterodera schachtii is a well-known, destructive pathogen of Chinese cabbage (Brassica rapa pekinensis) in Korea, and several studies have attempted to find a potential control measure against it. This study is the first to investigate the effects of varying temperature on the reproduction and damage potential of H. schachtii to Chinese cabbage. Chinese cabbage plants were inoculated with H. schachtii at different densities (1, 2, or 4 juveniles per gram of soil) and grown under three temperature regimes: constant (15, 20, or 25 °C), increasing (10, 14, and 18 °C), and fluctuating (positive, 16.7–22.0 °C; negative, 21.5–11.5 °C). At a constant temperature after 30 days of inoculation, both Chinese cabbage and H. schachtii performed best at 20 °C. However, after 60 days of inoculation, H. schachtii had a significantly higher population at 20 °C, whereas cabbage growth was best at 25 °C. With increasing temperature, the numbers of cysts and females did not change significantly, and reached maxima at an initial temperature of 14 °C. However, the number of leaves and weights of the Chinese cabbage plants significantly differed at 14 °C. Under fluctuating temperatures, temperature decreases reduced the H. schachtii population.     

The replication of a cytoplasmic polyhedrosis virus from Chrysodeixis eriosoma (Lepidoptera: Noctuidae) in Spodoptera frugiperda cells

A cytoplasmic polyhedrosis virus (CPV) from Chrysodeixis eriosoma (Lepidoptera: Noctuidae) replicated in Spodoptera frugiperda cells. Low rates of infection were achieved, even at high multiplicities of infection and TCID₅₀ assays showed that there was negligible release of virus particles from infected cells. In an infected focus assay, based on formation of PIB, the dose-response data demonstrated that a single particle could initiate infection. No loss of infectivity occurred in virus preparations stored at 4°, ?20°, or ?90°C, but infectivity of virus stored at 20°C declined sharply. A small isometric virus contaminant was present in some CPV preparations and its interaction with the CPV is discussed. Limited CPV infection was achieved in Trichoplusia ni cells, but attempts to infect Aedes aegypti cells were unsuccessful.     

Nosema pyrausta infection in Macrocentrus grandii, a braconid parasite of the European corn borer, Ostrinia nubilalis

Macrocentrus grandii which develop within Nosema pyrausta-infected larvae of the European corn borer, Ostrinia nubilalis, develop direct systemic infections from the ingestion of spores at the time of larval emergence from the host. Infections adversely affect pupal development and adult longevity. Infected females are unable to transmit the microsporidian to additional corn borer hosts. Pathogen development in the parasite host appears identical to its development in the corn borer host and mature spores show no morphological differences in size or shape when observed at the ultrastructural level. The prevalence of infection in natural parasite populations is 53.8% and closely parallels the 56.7% prevalence of infection in corn borer populations. Results suggest N. pyrausta may play a significant role in limiting M. grandii populations when levels of N. pyrausta in corn borers are high.     

Environmental modification of nest-building in the white-footed mouse, Peromyscus leucopus

Exposure of Peromyscus leucopus to low ambient temperature (5°C versus 26°C) during a 5-day test resulted in the building of larger nests. The weight of cotton used by the animal was employed as an index of nest size. Animals which had been acclimated to 5°C for 6 weeks prior to testing built larger nests at 5°C and smaller nests at 26°C than did warm-acclimated mice. In addition, warmacclimated P. leucopus maintained for 6 weeks under short photoperiod (LD9:15; L=light, D=dark) built larger nests at both 5°C and 26°C than did animals maintained under long photoperiod (LD 16:8). This pattern of response to environmental conditions approximating winter (low ambient temperature, short photoperiod) indicates that nesting is a component of the physiological-behavioural complex of cold adaptation.     

Impact of short-term temperature challenges on the larvicidal activities of the entomopathogenic watermold Leptolegnia chapmanii against Aedes aegypti, and development on infected dead larvae

The oomycete Leptolegnia chapmanii is among the most promising entomopathogens for biological control of Aedes aegypti. This mosquito vector breeds in small water collections, where this aquatic watermold pathogen can face short-term scenarios of challenging high or low temperatures during changing ambient conditions, but it is yet not well understood how extreme temperatures might affect the virulence and recycling capacities of this pathogen. We tested the effect of short-term exposure of encysted L. chapmanii zoospores (cysts) on A. aegypti larvae killed after infection by this pathogen to stressful low or high temperatures on virulence and production of cysts and oogonia, respectively. Cysts were exposed to temperature regimes between ?12 °C and 40 °C for 4, 6 or 8 h, and then their infectivity was tested against third instar larvae (L3) at 25 °C; in addition, production of cysts and oogonia on L3 killed by infection exposed to the same temperature regimes as well as their larvicidal activity were monitored. Virulence of cysts to larvae and the degree of zoosporogenesis on dead larvae under laboratory conditions were highest at 25 °C but were hampered or even blocked after 4 up to 8 h exposure of cysts or dead larvae at both the highest (35 °C and 40 °C) and the lowest (?12 °C) temperatures followed by subsequent incubation at 25 °C. The virulence of cysts was less affected by accelerated than by slow thawing from the frozen state. The production of oogonia on dead larvae was stimulated by short-term exposure to freezing temperatures (?12 °C and 0 °C) or cool temperatures (5 °C and 10 °C) but was not detected at higher temperatures (25 °C–40 °C). These findings emphasize the susceptibility of L. chapmanii to short-term temperature stresses and underscore its interest as an agent for biocontrol of mosquitoes in the tropics and subtropics, especially A. aegypti, that breed preferentially in small volumes of water that are generally protected from direct sunlight.     

Observations on the morphology and infectivity for cattle of Babesia bovis parasites in unfed Boophilus microplus larvae after incubation at various temperatures

Dalgliesh R. J. and Stewart N. P. 1979. Observations on the morphology and infectivity for cattle of Babesia bovis parasites in unfed Boophilus microplus larvae after incubation at various temperatures. International Journal for Parasitology9: 115–120. The temperature of incubation of unfed Boophilus microplus larvae infected with Babesia bovis influenced the morphology and infectivity of the Babesia within the tick. Incubation at 37°C for 1–3 days stimulated the development of parasites morphologically similar to those usually observed in fed larvae harvested from cattle; similar forms appeared more slowly in larvae incubated at 31°C or 25°C. Extracts prepared from larvae after incubation at 37°C for 3–5 days or 30°C for 8 days were consistently infective for cattle. Prior storage of larvae at 14°C for up to 28 days enhanced the development of infectivity at 37°C; infectivity could still be produced after 65 days storage at 14°C but not after 76 days. Larvae released on a host transmitted B. bovis sooner if they had been incubated at 37°C for 4 days. It was concluded that the development of B. bovis to an infective stage in B. microplus is temperature dependent and does not require the stimulus of feeding by the host.     

Performance of the Striped Mealybug Ferrisia virgata Cockerell (Hemiptera: Pseudococcidae) under Variable Conditions of Temperature and Mating

Mealybugs have strong associations with their host plants due to their limitations for dispersal. Thus, environmental conditions and host quality may impact the biological traits of mealybugs. To the best of our knowledge, we are the first to report on the biology of a Brazilian population of the striped mealybug Ferrisia virgata Cockerell (Hemiptera: Pseudococcidae), which has recently been reported to infest cotton in Brazil. We evaluated the development and reproductive performance of F. virgata reared under different temperatures (25, 27, and 28°C) and mating status. The type of reproduction was also studied with insects reared on a factitious host and on cotton plants. Shorter development was obtained at 28°C as follows: nymphs generating males and females exhibited three and four instars with a mean duration of 19.1 and 20.5 days, respectively. The nymphal viability ranged from 77 to 96%, and was highest at 25°C. Females reared at 28°C initiated reproduction earlier (16.4 days), but the reproductive period was similar in all temperatures (～16.2 days). Females produced more nymphs at 27 and 28°C (440 and 292 neonates) than at 25°C (277 neonates), although they lived longer at 25°C (63 days). Ferrisia virgata females exhibited only sexual reproduction. Thus, only mated females produced offspring, whereas unmated females died without reproducing. Therefore, the studied population of F. virgata exhibited only sexual reproduction with high survival and offspring production when fed cotton. Furthermore, pumpkin is a feasible host for mass rearing this mealybug species in the laboratory, an opening avenue for future studies.