Effects of temperature and food level on growth and development of a planktonic water mite

We analysed the relative effects of food availability and temperature on rates of growth and development of a predatory planktonic water mite, Piona exigua. Growth in length of mites fed Daphnia, Ceriodaphnia and Chydorus was analysed by Gompertz or von Bertalanffy curves; these curves were compared by parallel curve analysis. Growth rates of nymphs and adult female mites increased with temperature; the duration of the imagochrysalis stage decreased. Females grown at 10 °C were smaller at final size than females grown at 15 °C, 18 °C or 22 °C. Females reared at food levels of 15 or 30 prey l⁻¹ grew more slowly and were smaller than those provided with 60 or 120 prey l⁻¹. Nymphs grew more slowly when Daphnia were the only prey, than when smaller prey were available. Food level did not affect nymph growth at 10 °C or 15 °C, but growth at 18 °C or 22 °C may have been slowed at the lowest food levels. Synergistic effects of temperature and food level on nymph growth were apparent only from analysis of growth curves and not from stage duration data.     

The combined effects of temperature and food consumption on body weight,egg production and developmental time in Chaoborus crystallinus De Geer (Diptera: Chaoboridae)

Summary Chaoborus crystallinus fourth-instar larvae were reared individually at 14°, 17° and 20° C under different food conditions. Daphnia magna of 1.25 mm average length served as prey. The following were measured: amount of prey ingested, larval weight gain, duration of fourth instar, body weight of the adults, and egg number per female. At a given temperature, the body weight, egg-number and developmental rate increased with food consumption. At a given food consumption, higher temperatures caused a decrease in body weight and egg number, and an increase in developmental rate. Gross production efficiencies for fourth-instar larvae were highest at temperatures around 17° C. The results clearly indicate that from an energetic point of view higher temperatures are disadvantageous. In C. crystallinus vertical migration is evidently a way of lowering the temperature to which the animals are exposed and hence optimizing food conversion into biomass and offspring production, especially if prey densities are below the saturation level.     

Adaptability and efficacy of transgenic and wild-type Metaseiulus occidentalis (Acari: Phytoseiidae) compared as part of a risk assessment

Comparisons between transgenic (T) and wild-type Metaseiulus occidentalis colonies (COS) were made under laboratory conditions as part of a risk assessment effort prior to proposed field releases. There were no differences between the transgenic T18 colony and the COS strain in the daily egg production, hatchability at three temperatures and four relative humidity (RH) conditions, diapause incidence, or proportion of female progeny produced. Metaseiulus occidentalis eggs do not hatch at 38°C under any RH tested, nor at 33.5°C under 100% RH, indicating that high temperature and extreme RH affect egg hatch negatively. At 28.5 and 33.5°C, fewer eggs hatched at 32.5% than at 75.5 and 93% RH. Metaseiulus occidentalis cannot survive on any plant tested without prey nor on a diet of pollen alone; adult female mites cannot prey or survive on a diet of eggs and larvae of two lepidopteran species, indicating that the suitability of food sources has not been altered in the transgenic strain. Two subcolonies, derived from two transgenic strains using single females, differed in the rate of egg hatch at 28.5°C under 32.5 and 100% RH, indicating that reduced genetic variation and/or random genetic drift in the two lines may have led to differences in some biological characters. Since we did not find any significant differences between the T18 and COS colonies in the traits tested, the T18 colony is not expected to exhibit any new biological attributes in a proposed short-term field release.     

Prey selectivity of Piona exigua,a planktonic water mite

Summary Females, males and nymphs of Piona exigua were observed during prey capture and ingestion. The encounter radius of the mite was very small, allowing the escape of some crustaceans, such as the calanoid copepod Boeckella. Cladocerans, such as Bosmina or Chydorus, with little or no pre-contact escape response were the most vulnerable to mite predation. Preference values in size-selection experiments varied widely between individual mites. Adult mites presented with two sizes of Daphnia carinata generally preferred the smaller prey. When four sizes were presented simultaneously, however, the preferences of female mites for each size were not significantly different. Patterns of prey selection varied with predator age and sex; for example, female mites preferred Daphnia to Simocephalus, Ceriodaphnia and Chydorus, while nymphs showed a strong preference for Chydorus over Ceriodaphnia. When two prey types were present in equal proportions, differences in total prey density (range 5 or 10/1 – 30 or 50/1) did not alter preferences between the prey species. The preference of female mites for a particular prey type generally increased with increasing relative abundance of the prey type in each of three experiments (Daphnia: Ceriodaphnia, Ceriodaphnia: Chydorus, and Daphnia: Simocephalus). These results imply switching behaviour in these mites. Our results indicate the value of direct observation of predatory behaviour as an adjunct to prey selection experiments. It is also apparent that predatory behaviour in the presence of more than one prey type may not be predictable from that observed in single-prey situations. Predation rates on particular prey species were sometimes reduced in the presence of another species. The relative proportions of prey eaten when two species were present could not be predicted from the number of each species eaten when they were presented separately.     

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     

Growth,reproduction and longevity in nematodes from sewage treatment plants

The growth, reproduction and longevity of Diplogasteritus nudicapitatus, Paroigolaimella bernensis and Rhabditis curvicaudata were investigated under conditions of excess food within the temperature range 5°C–20°C. In all three species growth rate increased with temperature, and in D. nudicapitatus and R. curvicaudata the adult size attained varied significantly with temperature. P. bernensis did not reproduce at 5°C, but showed a progressive increase in reproductive output at higher temperatures. D. nudicaitatus showed increased egg production as temperature increased while R. curvicaudata had maximum egg output at 10°C. Longevity is temperature dependent, decreasing with higher temperatures. Virgin females survived for longer than reproducing females. The data indicate that while D. nudicapitatus and P. bernensis are thermophilic species, R. curvicaudata is adapted to lower temperatures.     

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.     

Thermal dependence of reproductive allocation in a tropical lizard

In ectotherms, environmental temperature is the most prominent abiotic factor that modulates life-history traits. We explored the influence of environmental temperature on reproduction in the Madagascar ground gecko (Paroedura picta) by measuring reproductive traits of females at constant temperatures (24, 27, 30 °C). Females of this species lay clutches of one or two eggs within short intervals. For each female, we measured egg mass for the first five clutches. For one clutch, we also measured the energetic content of eggs via bomb calorimetry. Temperature positively influenced the rate of egg production, but females at 30 °C laid smaller eggs than did females at either 24 or 27 °C. Dry mass of eggs scaled allometrically with wet mass, but this relationship was similar among thermal treatments. Females at all temperatures produced eggs with similar energy densities. Females at 24 °C allocated less energy per time unit (≈8 mW) to reproduction than did females from higher temperatures (≈12 mW). However, females at either 24 or 27 °C allocated significantly more energy per egg than did females at 30 °C. Our results demonstrate that a complex thermal sensitivity of reproductive rate can emerge from distinct thermal sensitivities of egg size, egg composition and clutch frequency.     

The effect of temperature on development and fecundityof Scymnus levaillanti

Development and fecundity of Scymnus levaillanti(Mulsant) were recorded at fiveconstant temperatures ranging from 15 to 35 ± 1 °C in 5 °C increments, 60 ± 5% RHand 16 h of artificial light (5000 Lux). Developmentaltime (egg to adult) of S. levaillantisignificantly decreased with increasing temperatures,ranging from 63.9 days at 15 °C to 11.1 days at35 °C. Development from egg to adult required305.2 DD above a developmental threshold estimated as11.7 °C. Oviposition periods lasted 86.5, 76.1,47.2, and 31.5 days at 20, 25, 30 and 35 °C,respectively. No eggs were deposited at 15 °C.Higher temperatures resulted in shorter generationtimes (T_O) and in decreased net reproductiverates (R_O) of the coccinellid. S.levaillanti kept at 30 °C produced 0.151females/female/day, the highest per capita rate ofpopulation growth (r_m). The `functional response'of larvae and adults of S. levaillanti matcheswell that described by Holling (1959) as Type 2.Daily number of eggs deposited by females increased toa plateau with increasing prey density. Resultsobtained here provide information about the biology ofS. levaillanti, and its feeding capacityindicates that it may act as an important control agent.     

Temperature influence on cohort parameters and demographic characteristics of the two cowpea coreids Clavigralla tomentosicollis and C. shadabi

Age-specific life tables of two important pests of cowpea, Vigna unguiculata (L.) Walp., the pod sucking bugs Clavigralla tomentosicollis Stål and C. shadabi Dolling (Heteroptera: Coreidae), were obtained from observations carried out at different temperatures. A biophysical model was found satisfactory to describe the temperature-response of developmental and mortality rates of egg and nymphal stages, with a peak developmental rate around 34°C in both species. The variability in development times was small and the experimental data did not permit any conclusion with regard to the Erlang probability density function. Survival of eggs and nymphs remained high between 20° and 30°C for both species. At temperatures above 34°C, C. tomentosicollis survivorship and fecundity was higher than that of C. shadabi, which in turn laid more eggs at temperatures between 20° and 30°C. Maximum fecundity is estimated to be at 29°C for C. tomentosicollis (99 eggs/female) and 26°C for C. shadabi (261 eggs/female). At 30°C, the intrinsic rate of increase reached a maximum in both species, 0.152 per day for C. tomentosicollis and 0.145 per day for C. shadabi, and remained high for C. tomentosicollis until 36°C. C. tomentosicollis performed significantly better on pigeonpea, Cajanus cajan Millsp., than on cowpea at higher temperatures.