Postharvest disinfestation of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae) on persimmons: hot water immersion and coolstorage

The mortality response of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae Koch) on persimmons to hot water immersion treatments between 44 and 54 °C was examined, for potential as a quarantine treatment. The mean immersion time for mean 99% mortality (LT₉₉) of diapausing mites at 44 °C was 211 min, and this time decreased with increasing temperature to 3.6 min at 54 °C. Non-diapausing mites were found to be less tolerant to temperatures below 48 °C, with an estimated LT₉₉ of 102 min at 44 °C, but had similar thermotolerance above 48 °C. In 47 °C water the immersion time required to kill 99% of diapausing mites was estimated at 67 min. This time was not reduced by subsequent coolstorage at 0 °C for up to eight weeks. Rather, coolstorage had the effect of keeping mites alive, relative to LT₉₉ estimates calculated for mites stored at 20 °C. Similarly the thermotolerance of mites did not change with increased time in diapause, even though mites in diapause for 12 weeks had high control mortality. Hot water immersion appears to be a potentially useful disinfestation method for persimmons.     

Cold storage ofPhytoseiulus persimilis (Phytoseiidae)

Phytoseiulus persimilis is commerelally mass-reared for use as a biological control agent for spider mites, primarilyTetranychus urticae, and cold storage is a potentially valuable aspect of mass-production. Cold storage ofP. persimilis in empty containers was found to be unsatisfactory, but provision of moisture during cold storage greatly increased survival. Provision of food further increased survival even though the mites were stored at temperatures below their threshold for development of 11°C. When food was provided, survival at 7.5°C was 97% after 4 weeks and 80% after 6 weeks. Subsequent longevity and fecundity of mites that survived 8 weeks at 7.5°C was comparable to mites taken directly from mass-rearing cultures. Survival of mites packaged in bran or vermiculite and held at 6°C for 10 days ranged from 75% to 85% and was not decreased by agitating the containers to simulate shipping. However, survival of mites held in bran or vermiculite at 5°C or 8°C for 4 weeks was poor, ranging from 0–19%, due to growth of mould in the media.Phytoseiulus persimilis can be successfully stored for 4 to 6 weeks in containers provisioned only with food and moisture; granular media used for distribution of the mites should be added just prior to shipping.     

Cold-hardiness in the predatory miteAmblyseius potentillae (Acari: Phytoseiidae)

Cold-hardiness was studied in the predatory miteAmblyseius potentillae (Garman) by determining the mortality after exposure to –5°C. Predators reared under diapause-inducing conditions were more cold-resistant than mites that had been kept under long-day conditions. An acclimatization period at 4°C prior to exposure to sub-zero temperatures had a positive effect on the cold-hardiness of the predator, and was remarkable in diapausing mites.Lower temperatures during diapause induction had a positive effect on cold resistance in this predator; mites in which diapause was induced at 15°C were more cold-resistant than mites that had been subjected to short-day conditions at 18 and 20°C.A day/night temperature rhythm did not increase the cold-hardiness of the mite when grown under long-day conditions. Such a rhythm did increase the cold-hardiness of the diapausing predator when given a short acclimatization period, but this effect disappeared after longer acclimatization periods.     

The impact of temperature on activity and consumption rate of moth eggs by Blattisocius tarsalis (Acari: Ascidae)

The activity of adult female Blattisocius tarsalis was investigated at temperatures of 7–13°C. At 7°C only 33% of the mites walked and these individuals all walked less than 1.5 cm min–1. All mites walked at 9°C and at 12°C all were highly active, walking more than 1.5 cm min–1. Daily food consumption rates of adult female B. tarsalis offered young eggs of Ephestia kuehniella as food were investigated at temperatures of 9–27°C. Food consumption below 13°C was very low. At temperatures of 13–19°C the mean number of fully ingested eggs had a level of between 0.5 and 1.0 egg in 24 h. At temperatures of 21–27°C the mean number of fully ingested eggs was above 1.0 egg in 24 h. The mean number of destroyed eggs per female at temperatures above 13°C ranged from three to five eggs per day. © Rapid Science Ltd. 1998     

High Temperatures Eliminate Wolbachia, a Cytoplasmic Incompatibility Inducing Endosymbiont, From the Two-spotted Spider Mite

Wolbachia can induce cytoplasmic incompatibility (CI) in the arrhenotokous two-spotted spider mite between uninfected females and infected males. Cytoplasmic incompatibility is expressed through a male-biased sex ratio and a low hatchability, and can be suppressed by removing Wolbachia from spider mites reared on a diet with antibiotics. Here we investigated whether heat-treatment can elimate Wolbachia from infected mites. Using a PCR assay with a Wolbachia-specific primer pair (ftsZ), and by standard crosses, we were able to show that 71 per cent of the mites had lost the Wolbachia infection after rearing the infected population at 32 ± 0.5 °C for four generations. The infection could be completely removed when mites were reared at 32 ± 0.5 °C for six generations. Curing through high temperatures could be one of the reasons why mixed infected/uninfected populations occur in the field. An additional consequence of rearing mites at 32 ± 0.5 °C was the shortened development time. The effect of environmental temperature on the abundance of Wolbachia and possible behavioural consequences for the spider mite are discussed.     

Plant regeneration from a cryopreserved embryogenic cell suspension of a commercial sugarcane hybrid (Saccharum sp.)

Efficient plant regeneration was obtained from a cryopreserved embryogenic cell suspension of sugarcane established from leaf derived callus. Pregrowing the cells for three days in MS basal medium supplemented with 0.33 M sorbitol was essential to the process. The cells were cooled at a rate of 0.5°C/min to –40°C and then stored in liquid nitrogen. Thawing was carried out rapidly in water at +40°C, and the cells were then plated without washing onto filter paper discs placed on a semi-solid regeneration medium (MS basal + 3% sucrose + 0.13 mg/1 2,4-D +0.25 mg/1 BAP + 0.25 mg/1 kinetin + 0.25 mg/1 zeatin). The filter paper discs, along with the cells, were transferred to the same, fresh medium after five hours. After 24 hours the cells were scraped off, placed on fresh semi-solid medium and incubated at 28°C in the dark for two weeks before transfer to light. A regeneration efficiency of 92% was obtained (regenerated plants, expressed as a percent of unfrozen control). Plants regenerated from cryopreserved cells, and grown to maturity in the greenhouse, were morphologically identical to regenerated control plants.Abbreviations DMSO dimethyl sulfoxide - PEG polyethylene glycol - 2,4-D 2,4-dichlorophenoxyacetic acid - BAP benzyl aminopurine - TTC 2,3,5-triphenyl tetrazolium chloride     

Effect of temperature,humidity and photoperiod on mortality of Mononychellus tanajoa (Acari: Tetranychidae) infected by Neozygites cf. floridana (Zygomycetes: Entomophthorales)

The effect of temperature, humidity and photoperiod on the development of Neozygites cf. floridana (Weiser and Muma) in the cassava green mite, Mononychellus tanajoa (Bondar) was studied in the laboratory. Dead infected mites began to appear 2.5 days after inoculation. At 33 and 28°C peak mortalities were higher and occurred earlier (after 2.5 days), than at 23 and 18°C. Mean LT₅₀ (time for half the infected mites to die) decreased with increasing temperature as follows: 3.9, 3.0, 2.9 and 2.5 days at 18, 23, 28 and 33°C, respectively. When placed under conditions of high relative humidity for a period of 24 h, the percentage of dead infected mites from which the fungus sporulated was highest at 28°C (51.4%) and lowest at 33°C (6.5%). The development of the fungus inside the mite was not significantly affected by ambient humidity or photoperiod. No significant interactions between tested factors were found.     

A method to obtain rapid zoosporogenesis of Pythium insidiosum

Nine strains of Pythium insidiosum the etiologic agent of pythiosis, were inoculated on 2% water agar plus grass blades and then incubated one day at 25°C, 35°C and 37°C. Sporangium and secondary biflagellate-type zoosporas from the parasitized grass blades were noticed in induction medium after one hour of incubation at 35 °C and 37 °C. The number of sporangia and zoospores were lower at 25 °C, than 35 °C and 37 °C. Increasing the days of incubation of the parasitized grass blades resulted in the increase in the time of incubation in the induction medium. Corn meal agar, Schmitthenner medium and Sabouraud dextrose agar were also tested but the sporangium and zoosporas were always observed after five hours of incubation in induction medium.     

Cryopreservation of in vitro-grown apical meristems of lily by vitrification

Apical meristems from adventitious buds induced by culturing of bulb-scale segments of Japanese Pink Lily (Lilium japonicum Thunb.) were successfully cryopreserved by a vitrification. The excised apical meristems were precultured on a solidified Murashige & Skoog medium, containing 0.3 M sucrose, for 1 day at 25°C and then loaded in a mixture of 2 M glycerol plus 0.4 M sucrose for 20 min at 25°C. Cryoprotected meristems were then sufficiently dehydrated with a highly concentrated vitrification solution (designated PVS2) at 25°C for 20 min or at 0°C for 110 min prior to a plunge into liquid nitrogen. After rapid warming in a water bath at 40°C, the meristems were placed in 1.8 ml of 1.2 M sucrose for 20 min and then, placed on filter papers over gellan gum-solidified MS medium. The revived meristems resumed growth within 5 days and directly produced shoots. The rate of shoot formation was approximately 80% after 4 weeks. When bulb-scale segments with adventitious buds were cold-hardened at 0°C for more than 7 days before the procedure, the rates of shoot formation were significantly increased. This vitrification method was successfully applied to five other lily cultivars. Thus, this vitrification procedure for cryopreservation appears promising as a routine method for cryopreserving meristems of lily.Abbreviations DMSO dimethylsulfoxide - EG ethylene glycol - LN liquid nitrogen - MS medium Murashige & Skoog (1962) medium - PVS2 vitrification solution     

Maturation and germination of walnut somatic embryos

Walnut somatic embryos were multiplied by repetitive embryogenesis on a solid basal DKW medium at 25°C in the dark. When the embryos were isolated at early cotyledonary stage (1–2 mm long) from the primary embryos and cultured on the medium for 3 weeks, they developed into mature embryos showing white, enlarged cotyledons and shoot and root apex. After transfer to light on solid germination medium, however, few mature embryos (0–5%) germinated. Germination percentage increased to about 10% when the mature embryos were pretreated by a storage at 4°C in the dark for 2 months, or by desiccation at 25°C in the dark for 3 or 5 days under an air-humidity conditioned by saturated salt solutions (Mg(NO₃)₂.6H₂O, or ZnSO₄.7H₂O). Similar results were obtained by the addition of gibberellic acid (GA₃) to the germination medium. When mature embryos were desiccated and then placed on medical cotton compresses in liquid germination medium, 45% of the embryos germinated into complete plantlets. These plantlets continued their growth after transplanting to a mixture of peat and vermiculite in pots.Abbreviations GA₃ gibberellic acid - DKW medium Driver & Kuniyuki Walnut medium     

Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Effects of temperature on the establishment potential of the predatory mite Amblyseius californicus McGregor (Acari: Phytoseiidae) in the UK

Amblyseius californicus was introduced into the UK in the early 1990s as a biocontrol agent against glasshouse red spider mite Tetranychus urticae. This study investigated the effects of temperature on the establishment potential of A. californicus in the UK in the light of recent reports of their successful overwintering outside of glasshouse environments. The developmental thresholds were 9.9 and 8.6 °C respectively using simple and weighted linear regression. Using the day-degree requirement per generation calculated by weighted regression (143 day-degrees) in combination with climate data, it was estimated that up to seven generations would be possible annually outdoors in the UK. Non-diapausing adult females froze at −22 °C, with 100% mortality after reaching their freezing temperature. Up to 90% of mites died before freezing after short exposures to low temperatures. Significant acclimation responses occurred; 90% of acclimated individuals survived 26 days exposure at 0 °C and 11 days at −5 °C (acclimated mites were reared at 19 °C, 6L:18D followed by 1 week at 10 °C, 12L:12D). Non-diapausing adult females survived over 3 months outdoors in winter under sheltered conditions and oviposition was observed. The experimental protocol used in this study is discussed as a pre-release screen for the establishment potential of other Amblyseius species, and similar non-native biocontrol agents.     

An improved method for rearing Halotydeus destructor (Acari: Penthaleidae) in the laboratory

We developed an improved method for rearing Halotydeus destructor in the laboratory. Mite numbers increased rapidly over the summer of 1992–1993 when fed on vetch, Vicia sativa cv Blanchefleur; in contrast mite numbers were low and fell over the second half of the summer of 1990–91 when fed on subterranean clover, Trifolium subterraneum cv Junee. On V. sativa at a fluctuating temperature from 11 to 18°C 200 mites produced a mean of 1308 and 1455 progeny per transfer in 2 years, a 6–7-fold rate of increase per transfer. The mean transfer time was 35 days and using the interval between transfers as a measure of generation time, the mites completed six to seven generations with no evidence for development of diapause eggs from August until April. There was considerable variability in the numbers of mites produced per pot, associated in part with the presence of Verticillium sp. fungus in 35% of the pots during transfers. Improvement in H. destructor rearing resulted from the use of V. sativa cv Blanchefleur as a food source, maintenance of high humidity and adequate ventilation within cages, and the transfer of mites to fresh food sources at early nymphal stages, which reduced the spread of fungal infections.     

Regulation of histidine biosynthetic enzymes in a mutant of Escherichia coli with an altered histidyl-tRNA synthetase

Summary A mutant of Escherichia coli was isolated that grew at a normal rate in minimal medium at 26°C, grew at a normal rate in minimal medium at 37°C only if exogenous histidine was supplied, and grew more slowly than normal at 42°C even in the presence of histidine. In very rich media the growth rate of the mutant was normal at 26°C and 30°C, but not at 37°C or 42°C. It may be described as a temperature-conditional histidine bradytroph with a decreased ceiling to its growth rate.The histidyl-tRNA synthetase of the mutant was found to be abnormal; in crude extracts the enzyme activity was less stable and had approximately a tenfold higher apparent K _Mfor histidine than normal.Under many growth conditions the histidine biosynthetic enzymes in the mutant were derepressed several hundred fold compared to the wild strain, even in the presence of exogenous genous histidine. In general, the degree of derepression in the mutant was proportional to the difference in growth rate between the mutant and normal strains; this relationship, however, did not hold below 30°C or above 37°C.The properties of the mutant could be related to the properties of its histidyl-tRNA synthetase by assuming that the enzyme participates both in protein synthesis and in histidine biosynthetic enzyme regulation and that at low temperature it functions relatively more effectively in protein synthesis than in repression, while at high temperature it functions relatively more effectively in repression.Abbreviations used tRNA transfer RNA - AICAR aminoimidazole carboxamide ribose-5-phosphate     

Effect of temperature on carbohydrate content,ADP glucose pyrophosphorylase,and ATP- and PPi-dependent phosphofructokinase activity of potato tuber callus tissue

Callus derived from Lemhi Russet and Russet Burbank tuber tissue was incubated at 20°C and 30°C on a high sucrose medium for starch-formation and subjected to simulated storage and reconditioning treatments at 5°C and 25°C after transfer of the callus to a medium without a carbon source. Percent dry weight of callus from both cultivars averaged about 21% after starch formation and 5% after storage and reconditioning treatments. Total sugars were higher in callus incubated on the starch forming treatment. Lemhi Russet callus contained predominantly reducing sugars, while Russet Burbank callus contained mostly non-reducing sugars. Total sugar content was generally lower for both cultivars after the storage and reconditioning treatment in callus after starch formation at 20°C. Starch content was generally higher in Lemhi Russet tissue. After starch formation at 20°C Lemhi Russet had higher starch after the storage and reconditioning treatment than tissue from 30°C, while the opposite trend was found in Russet Burbank tissue. Total protein declined in Russet Burbank tissue during the storage and reconditioning treatment regardless of prior incubation conditions, while this decline only occurred in Lemhi Russet tissue initially incubated at 30°C during the starch formation treatment. In tissue of both cultivars, ATP- and PPi-dependent phosphofructokinase activities were inversely proportional to total sugar concentrations, while in RB callus ADP glucose pyrophosphorylase activities were proportional to starch content.Research Paper 91B1 of the Idaho Agricultural Experiment Station.     

The effect of temperature on viability of carbon- and nitrogen-starved Escherichia coli

Escherichia coli was grown in a defined medium at optimum temperature and then transferred to each of five different starvation regimes at 5°C, 20°C, or 37°C, for 1000 hours. Cells were maintained with growth-limiting amounts of carbon or nitrogen, or without either or both nutrients. Bacterial cell viability was assessed by dilution plating, the reduction of 2(p-indophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT), direct viable counts (DVC), and microcolony development. The recoverability of cells on solid medium declined most rapidly, and to the greatest extent in most cases, in cultures maintained at 37°C. Only nitrogen-starved cells maintained at 5°C became completely nonculturable. The reduction of INT consistently indicated higher numbers of viable cells compared to the other methods in all cultures. The viabilities of carbon- and nitrogen-limited cells, assessed by all methods, were similar to one another at each of the temperatures. Viability was lowest at 37°C. Nutrient-downshifted cells also followed a temperature-dependent pattern of survival with viability lowest at 37°C. Morphological differences were noted at different temperatures but were most obvious for nitrogen-starved cells at 37°C, which increased in length. Correspondence to: R.W. Attwell     

Effects of acclimation and diapause on the thermal tolerance of the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is a worldwide pest species that overwinters as diapausing females. Cold hardening is presumed to start during diapause development to ensure the successful overwintering of this species. To address this hypothesis, we compared cold tolerance between non-diapausing and diapausing females. We measured supercooling point (SCP) and survival to acute cold stress by exposing the mites at a range of sub-zero temperatures (from −4 to −28 °C for 2 h). The mean SCPs of non-diapausing and diapausing females were −19.6±0.5 and −24.7±0.3 °C respectively, and freezing killed the mites. Diapausing females were significantly more cold tolerant than non-diapausing ones, with LT₅₀ of −19.7 and −13.3 °C, respectively. Further, we also examined the effects of cold acclimation (10 d at 0 or 5 °C) in non-diapausing and diapausing females. Our findings indicated that diapause decreased SCP significantly, while cold acclimation had no effect on the SCP except for non-diapausing females that were acclimated at 5 °C. Acclimation at 5 °C enhanced survival to acute cold stress in diapausing and non-diapausing females, with LT₅₀ of −22.0 and −17.1 °C, respectively. Altogether, our results indicate that T. urticae is a chill tolerant species, and that diapause and cold acclimation elevate cold hardiness in this species.     

Expression and characterization of the chitinases from Serratia marcescens GEI strain for the control of Varroa destructor, a honey bee parasite

Serratia marcescens GEI strain was isolated from the gut of the workers of Chinese honey bee Apis cerana and evaluated in the laboratory for the control of Varroa destructor, a parasite of western honey bee A. mellifera. The supernatant and the collected proteins by ammonium sulfate from the bacterial cultures showed a strong miticidal effect on the female mites, with 100% mite mortality in 5 days. Heat (100 °C for 10 min) and proteinase K treatment of the collected proteins destroyed the miticidal activity. The improved miticial activity of this bacterial strain on chitin medium indicated the involvement of chitinases. The expressed chitinases ChiA, ChiB and ChiC1 from S. marcescens GEI by recombinant Escherichia coli showed pathogenicity against the mites in the laboratory. These chitinases were active in a broad pH range (5-9) and the optimum temperatures were between 60 and 75 °C. Synergistic effects of ChiA and ChiB on the miticidal activity against V. destructor were observed. The workers of both honey bee species were not sensitive to the spraying and feeding chitinases. These results provided alternative control strategies for Varroa mites, by formulating chitinase agents and by constructing transgenetic honey bees.     

Effect of temperature on sporulation of Neozygites floridana isolates from different climates and their virulence against the tomato red spider mite, Tetranychus evansi

The fungal pathogen Neozygites floridana Weiser and Muma has been evaluated as a classical biological candidate for introduction into Africa against the invasive tomato red spider mite Tetranychus evansi Baker and Pritchard. In this study, the effect of temperature on sporulation, germination and virulence of three isolates of N. floridana collected from T. evansi in three climatically distinct regions of Brazil and Argentina was determined. Six constant temperatures of 13 °C, 17 °C, 21 °C, 25 °C, 29 °C and 33 °C were tested for their effect on the ability of the three fungal isolates to sporulate, germinate and kill the mites. Six alternating-temperature regimes of 17-13 °C, 21-13 °C, 29-13 °C, 33-13 °C, 33-23 °C, 33-28 °C under a 12 h photophase were also tested to estimate virulence of the three isolates against T. evansi. The Vipos isolate discharged more conidia than isolates from Recife or Piracicaba at all temperatures and sporulation was strongly temperature dependent. Optimal sporulation rates were observed at 25 °C while optimal germination rates were observed at 25 °C and 29 °C. At 29 °C, the shortest mean survival time of T. evansi (3.16 days, 95% CI of 3.05-3.27) was observed for the isolate from Vipos, while the longest LT₅₀ (3.47 days, 95% CI 3.34-3.59) was observed for the isolate from Piracicaba. Mortality of mites increased as the differences between alternating day and night temperatures increased from 8 °C (21-13 °C), to 10 °C (33-23 °C), to 16 °C (29-13 °C), with smallest and highest temperature differences of 4 °C (17-13 °C) and 20 °C (33-13 °C), both producing low mortalities. The overall results suggest that the Vipos isolate is better adapted to a wider range of temperatures than the other isolates tested.