Minimum Developmental Thresholds Research Articles

Thermal requirements and life table parameters of the predatory mite, Neoseiulus californicus (McGregor) fed on Tetranychus urticae Koch (Acari: Phytoseiidae: Tetranychidae)

The predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) is an important biological control agent of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) infesting many crops worldwide. Biology, life table parameters and thermal requirements of N. californicus were evaluated in laboratory at 20, 27, 30±2oC and 70±5% RH. Spider mite, T. urticae is an important pest of soybean crop in Egypt. The duration of the immature stages of N. californicus ranged from 4.22 to 7.35 days for female and from 3.80 to 7.10 days for male when they were kept at 20 and 30°C, respectively. The mean generation time (TG) decreased with increasing temperature from 19.48 days to 12.93 days at 20 to 30°C, respectively. The intrinsic rate of increase (rm) and finite rate of increase (λ) were highest at 27 and 30 oC. The highest total consumption rate of prey was 223.4 individuals when adult female fed on T. urticae motile stages at 30 oC, while the lowest rate was 162.60 individuals at 20 oC during the whole life span. Minimum developmental thresholds (t0) of egg, larva, protonymph, deutonymph and total immature stages of N. californicus female averaged 13.20, 12.75, 3.29, 0.0 and 6.66 oC, respectively. The predatory female of N. californicus required 500 DDUs to reach adulthood. Therefore, a thermal range of 27oC was the most suitable condition to rear the target predatory mite.

The Influence of Temperature Variation on Life History Parameters and Thermal Performance Curves of Tamarixia radiata (Hymenoptera: Eulophidae), a Parasitoid of the Asian Citrus Psyllid (Hemiptera: Liviidae).

This study examined the effects of seven constant and fluctuating temperature profiles with corresponding averages of 12 to 38°C on the life history of the Punjab, Pakistan-sourced Tamarixia radiata (Waterston) released in California for biological control of Diaphorina citri Kuwayama. One linear and seven nonlinear regression functions were fit to egg-to-adult development rate data to characterize thermal performance curves. Temperature fluctuations significantly affected both development and longevity of T. radiata. Estimates of degree-days predicted by the linear model were 30% higher for the fluctuating regime than the constant regime. Nonlinear model estimations of theoretical minimum and maximum developmental thresholds were lower for the fluctuating regime when compared to the constant regime. These predictions align with experimental observations. Parasitoids reared under fluctuating profiles at low average temperatures developed faster (15°C) and survived longer (15-20°C) when compared to those reared under constant regimes with corresponding means. In contrast, high average fluctuating temperatures produced parasitoids with an extended developmental period (35°C) and reduced longevity (30-35°C). A meta-analysis of published T. radiata development datasets, together with the results of this study, indicated convergence in degree-days and theoretical minimum developmental thresholds among geographically distinct parasitoid populations. These findings demonstrate the significant effects of temperature on T. radiata life history and have important implications for optimization of mass-rearing and release efforts, improvement of predictions from climate modeling, and comparison of T. radiata population performance across climatic gradients and geographic regions.

Biology and Seasonality of the Reemergent Pest Rhynchaenus pallicornis (Coleoptera: Curculionidae) and Methods for Monitoring Its Abundance.

Rhynchaenus pallicornis (Say) is a pest of commercially grown apples in the upper Midwest. This historic pest has resurged and caused severe yield loss on farms using certified organic production practices. The life history and potential monitoring methods of R. pallicornis are presented. Seasonal abundance data were collected through beat and visual sampling. A phenological model was developed for R. pallicornis. The minimum developmental threshold of R. pallicornis was determined to be 3.5°C with a required degree-day accumulation of 125°D for first adult emergence. Larval damage was observed on >60% of leaves in unmanaged orchards and affected significantly fewer basal leaf clusters (near the trunk), than medially or apically located clusters. Of 2,900 R. pallicornis larval mines collected over two years at three different sites, 18.0% produced at least one adult parasitoid, but the targeted larval stage is unknown. Measurements of R. pallicornis larval head capsules and the simple frequency method were used to determine three larval instars of R. pallicornis The number of larval instars could also be accurately determined by observing the presence or absence of two sets of thoracic sclerites. Pyramid traps, yellow sticky cards baited with olfactory cues (pear essence, benzaldehyde, and an aggregation of adult R. pallicornis) were evaluated as R. pallicornis monitoring tools. None of the traps or lures tested significantly affected the number of adult R. pallicornis per trap.

Onion thrips, Thrips tabaci (Thysanoptera: Thripidae), overwintering in South Auckland, New Zealand: the importance of the local bionomic data/temperature model and biosecurity implications

Onion thrips flights in winter and early spring 1999 were monitored in South Auckland using sticky traps and trap plants. A pair of yellow sticky traps and 10 ‘thrips-free’ onion pot plants per site were changed every 2 weeks. Thrips were detected on traps and plants in June, September and October. Sticky traps were the most reliable method for detecting thrips flights. Wild plants were inspected four times and revealed that thrips bred all winter. There was no diapause. Seedlings that had sprouted in mid July had second instar larvae by 4 October 1999. The nearest source was self-set plants in an adjacent field. Three published temperature models for onion thrips development were compared. Generation times were similar in summer, but very different in winter. The Texas model with minimum developmental threshold of 11.5 °C had the longest winter generation time and required a thrips flight by early August for second instar larvae to develop in the crop by 4 October, whereas the South Auckland model (threshold 8.7 °C) required flights by early September. Thrips flights were detected by traps in September but not August 1999. For cosmopolitan pests that are very variable genetically, it is important to generate local biological data. The biosecurity implications of this variability are discussed.

Temperature-Dependent Development, Life Table Parameters and Predation Rate of Euseius scutalis (A.- H.) Fed on the Two-Spotted Spider Mite

Biological aspects, thermal requirement, predation rate and life table parameters of the phytoseiid predatory mite Euseius scutalis (A.– H.) fed on nymphs of Tetranychus urticae Koch was determined at four temperature degrees, 15, 20, 25 and 30 °C. The total developmental durations of female was correlated negatively with increasing temperature. Minimum developmental thresholds (To) of egg, larva, protonymph, deutonymph, total immature stages and life cycle of E. scutalis female averaged, 4.26, 10.98, 6.90, 1.20, 2.49 and 2.89; respectively. On the other hand E. scutalis female required 208.33 DD to reach adulthood. The net rate of natural increase (rm) was 0.008, 0.126, 0.166 and 0.193, whereas the finite rate of increase (erm) averaged 1.092, 1.134, 1.181 and 1.213 at 15, 20, 25 and 30 o C; respectively.

Thermal requirements and biological life table parameters of the predatory mite Amblyseiella denmarki (Zaher and El-Borolossy) (Acari: Phytoseiidae)

The biological aspects, thermal requirements and life table parameters of the phytoseiid predatory mite Amblyseiella denmarki fed on Aceria dioscoridis was determined at four temperatures, i.e. 15, 20, 28 and 35°C. The total developmental durations for both females and males were correlated negatively with increasing temperature. The minimum developmental thresholds (T 0) of egg, larva, protonymph, deutonymph stages and life cycle of A. denmarki females averaged 13.15, 4.56, 11.22, 12.72 and 11.80, respectively, while those of males were 12.40, 3.01, 9.82, 10.88 and 10.04. On the other hand, females and males required 89.28 and 93.45 degree days (DD), respectively, to reach adulthood. The male life span averaged 63.32, 49.25, 25.39 and 18.26 days while that of female was 90.51, 64.44, 29.51 and 19.99 days when the predator was reared at 15, 20, 28 and 35°C, respectively. The mean generation time (T) averaged 38.84, 24.87, 9.24 and 8.56 days, and the net reproductive rate (R 0) values were 3.79, 10.042, 26.488 and 7.172 when the predator was kept at 15, 20, 28 and 35°C, respectively. The net rate of natural increase (r m) was 0.032, 0.092, 0.354 and 0.230, whereas the finite rate of increase (e rm) averaged 1.032, 1.097, 1.425 and 1.258 at 15, 20, 28 and 35°C, respectively.

The Weather Research and Forecasting (WRF) model: application in prediction of TSWV‐vectors populations

AbstractIn the southeastern United States, millions of dollars worth of crop damage associated with tobacco thrips (Frankliniella fusca Hinds) and western flower thrips (Frankliniella occidentalis Pergande) are reported annually for economically important crops such as cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.). Tobacco thrips and western flower thrips are also important vectors of Tomato spotted wilt virus (TSWV). The populations and spread of both thrips species relies on favourable weather conditions, especially prolonged temperatures above a minimum developmental threshold. Accurate local weather information is, therefore, crucial for early prediction of thrips’ population dynamics during the spring when thrips’ population information could assist farmers in mitigating damage to crops. The objective of this study was to demonstrate the application of the Weather Research and Forecasting (WRF) model predictions for developing high resolution spatial and temporal forecast maps of favourable conditions for thrips’ development even for locations where weather stations are not available. Tobacco thrips and western flower thrips were evaluated based on degree‐day models. The results showed that southwestern Georgia is more favourable for thrips development during the early part of the growing season, although the rate of development varied according to the thrips species. The maps that were produced using WRF output provided high‐resolution forecasts for favourable conditions and scouting guidance in places where weather information was limited. An accurate prediction of pest development based on forecasts of favourable conditions may assist growers in pest management decisions and in timely application of insecticides.

Temperature influence on biology, thermal requirement and life table of the predatory mites Agistemus exsertus Gonzalez and Phytoseius plumifer (Can. & Fanz.) reared on Tetranychus urticae Koch

The effect of temperature on the biology, thermal requirement and life table of Agistemus exsertus Gonzalez and Phytoseius plumifer (Can. & Fanz.) feeding on immatures of Tetranychus urticae Koch, was determined at four temperature degrees, i.e. 20, 25, 30 and 35°C. The total developmental durations of either predatory mite correlated negatively with increasing temperature. Minimum developmental thresholds (T o) of egg, larva, protonymph, deutonymph stages and life cycle of A. exsertus females averaged 0.95, 9.25, 7.80, 1.03 and 5.29 respectively, while those of P. plumifer females were 6.83, 9.35, 15.39, 15.40 and 13.22. On the other hand, A. exsertus and P. plumifer female required 416.66 and 126.58 DD, respectively, to reach adulthood. A. exsertus and P. plumifer net reproductive rate (R 0) averaged 16.13 and 8.23 then increased to 29.67 and 13.67 then sharply declined reaching 12.10 and 7.93 when the predator was kept at 20, 25 and 35°C, respectively. r m values of A. exsertus reached 0.06, 0.11, 0.12 and 0.13 reared at 20, 25, 30 and 35°C, respectively, while those of P. plumifer averaged 0.04, 0.11, 0.12 and 0.16. The doubling time (DT) of A. exsertus was 10.98, 6.10, 5.82 and 5.25, while that of P. plumifer averaged 15.93, 6.18, 5.70 and 4.35 at 20, 25, 30 and 35°C, respectively. Also, gross reproductive rate (GRR) of A. exsertus was 22.05, 51.70, 29.01 and 22.18, while that of P. plumifer averaged 12.67, 18.20, 18.40 and 11.82 at the same temperatures. The finite rate of increase in e rm values of either predator increased positively with increasing temperature degree.

Blind validation of postmortem interval estimates using developmental rates of blow flies

This study evaluated the use of different degree day (DD) models, developmental thresholds and developmental data sources for estimating postmortem interval (PMI) based on developmental rates of blow flies (Diptera: Calliphoridae). Blow fly evidence was collected from three mock crime scenes and sent for blind analysis of PMI. PMI estimates were calculated using averaging, single sine, double sine, single triangle, and double triangle models of DD calculation with minimum developmental thresholds of 0, 6 and 10 °C and Anderson's, Byrd and Allen's, Greenberg's, Nishida's and Kamal's developmental data sets. These estimates were compared with the actual PMI to determine which combination of DD model, developmental threshold and developmental data provided the most accurate estimate. For all three cases, at least one method gave a PMI estimation that was within 1 day of the actual date of death. There was no variability between PMI estimated using the five models of DD calculation. Overall, as lower developmental threshold increased, the PMI interval estimates increased. Depending on the developmental data set used, increasing the lower developmental threshold caused some overestimations of the date of oviposition, with estimates given that were prior to the actual death. Future PMI estimates should include error ranges, so that overestimation of PMI is avoided.

Temperature-Dependent Development and Degree-Day Model of European Leaf Roller, Archips Rosanus

The effect of temperature on the duration of larval, prepupal, and pupal development of the European leaf roller, Archips rosanus L. (Lepidoptera: Tortricidae) was studied at four constant tempera- tures (18, 22, 26, and 30°C) where Malus communis L. (apple, Stark Crimson) was used as food. Signifi- cant positive linear relationships were observed between development rate and temperature for all life stages. Minimum developmental threshold temperatures were estimated as 5.5-6.7°C for first stages, 5.8-5.7°C for second stages, 5.1-6.3°C for prepupae, and 8.1-6.3°C for pupae, male and female, respec- tively. Lower threshold of complete development of adult was estimated as 6.05°C (male) and 6.0°C (fe- male). Median development values of degree-days (DD) for first stages, second stages, prepupae, pupae and complete preimaginal development were 57.5-55.2, 55.2-66.2, 33.1-33.9, 137-175.4 and 476.2-526 for male and female, respectively. A degree-day model was developed using from the laboratory data for predicting the first emergence of the pest and spray application time. Estimated degree-day model predicted the emergence within 3-7 days of that observed at the field site in both 2001 and 2002. Accord- ingly, the degree-day model will be useful to predict the first emergence dates, optimum spray period and to provide a starting point to catches in pheromone traps in the summer for A. rosanus.

Temperature-Dependent Development of the Specialist Predator <I>Laricobius nigrinus</I> (Coleoptera: Derodontidae)

The effect of temperature on the duration of egg, larval, prepupal, and pupal development of the predator Laricobius nigrinus Fender was studied at six constant temperatures (6, 9, 12, 15, 18, and 21°C) where Adelges tsugae Annand was used as prey. Developmental time was inversely proportional to temperature between 6 and 18°C. Laricobius nigrinus did not complete development at 21°C. Significant positive linear relationships were observed between developmental rate and temperature for all life stages. Minimum developmental threshold temperatures were estimated at 5.4°C for eggs, 3.2°C for larvae, 2.9°C for prepupae, and 3.1°C for pupae. Median development times for eggs, larvae, prepupae, and pupae were 59.5, 208.3, 217.4, and 212.8 degree-days (DD) above minimum developmental temperatures, respectively. Development from oviposition to adult eclosion required a minimum temperature of 3.7°C and 666.7 DD. A degree-day model, developed in the laboratory for predicting egg hatch, predicted a degree-day value that was within 4 d of the median egg hatch observed at two field sites in 2000. This regression model is a useful predictor of egg hatch in Victoria, British Columbia, Canada. In addition, the lower development threshold from egg to adult for L. nigrinus (3.7°C) is similar to that for the A. tsugae progrediens (spring) generation from second instar to adult (3.9°C), indicating that L. nigrinus and A. tsugae are adapted to similar climatic regimes.

Temperature and Host Plant Effects on Development, Survival, and Fecundity ofBemisia argentifolii(Homoptera: Aleyrodidae)

Development time and percent survival of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring (formerly referred to as B strain of sweetpotato whitefly), were determined at five constant temperatures ranging from 20 to 358C on two cultivars of cotton, cantaloupe, and pepper (Capsicum sp.). Fecundity was recorded at 308C during the first 10 d of adulthood. Developmental, survival, and fecundity rates were not significantly different between cultivars within crops of either cotton or cantaloupe, but varied between crops. Development time from egg to adult at 20—328C ranged from 14.6 6 0.8 (mean 6 SE) to 36.0 6 1.0 d on cantaloupe and from 16.3 6 0.7 to 37.9 6 2.1 d on cotton, respectively. Whiteflies did not develop at 358C or on pepper at any temperature. Minimum developmental thresholds and degree-days requirements from egg to adult were 11.18C and 312.5 DD on cotton and 13.28C and 250.0 DD on cantaloupe, respectively. Immature survival was high (76.5 6 11.5—100%) on cantaloupe, intermediate (37.3 6 13.3—64.4 6 10.2%) on cotton, and very low (0—8.3 6 8.3%) on pepper from 20—328C. Fecundity ranged from 153.3 6 10.8—158.3 6 9.3 eggs per female on cantaloupe, from 117.0 6 6.0—117.5 6 22.1 eggs per female on cotton, and from 2.1 6 0.7—40.5 6 5.8 eggs per female on pepper, at 308C.

Response of Treefrog Larvae to Drying Ponds: Comparing Temporary and Permanent Pond Breeders

Most amphibian species with an aquatic larval stage use one of two types of breeding habitats: ephemeral or permanent water bodies. A common assumption is that, once a minimum developmental threshold has passed, tadpoles of species that use temporary ponds can respond adaptively to a drying larval habitat by hastening development to metamorphose before the pond dries. We investigated how different pond drying regimes affected the timing of metamorphosis and body size at metamorphosis of two closely related species of hylid treefrogs, one of which commonly breeds in temporary ponds (Hyla gratiosa) and the other in permanent ponds (Hyla cinerea). We experimentally manipulated the water level in cattle-tank communities, exposing tadpoles of each species to a slow drying treatment, a fast drying treatment, and a constant water level treatment. There was no direct effect of pond drying on the larval period or body size at metamorphosis of either species. The drying treatments indirectly affected these traits by increasing larval densities, which extended the larval period and produced smaller sizes at metamorphosis. The timing of metamorphosis and body size at metamorphosis of H. gratiosa were more plastic than the corresponding traits in H. cinerea, but this greater plasticity cannot be interpreted as adaptive. Our results emphasize the utility of the comparative approach in interpreting the potential adaptive responses of species to environmental variation.

RESPONSE OF TREEFROG LARVAE TO DRYING PONDS: COMPARING TEMPORARY AND PERMANENT POND BREEDERS

Most amphibian species with an aquatic larval stage use one of two types of breeding habitats: ephemeral or permanent water bodies. A common assumption is that, once a minimum developmental threshold has passed, tadpoles of species that use temporary ponds can respond adaptively to a drying larval habitat by hastening development to metamorphose before the pond dries. We investigated how different pond drying regimes affected the timing of metamorphosis and body size at metamorphosis of two closely related species of hylid treefrogs, one of which commonly breeds in temporary ponds (Hyla gratiosa) and the other in permanent ponds (Hyla cinerea). We experimentally manipulated the water level in cattle-tank communities, exposing tadpoles of each species to a slow drying treatment, a fast drying treatment, and a constant water level treatment. There was no direct effect of pond drying on the larval period or body size at metamorphosis of either species. The drying treatments indirectly affected these traits by increasing larval densities, which extended the larval period and produced smaller sizes at metamorphosis. The timing of metamorphosis and body size at metamorphosis of H. gratiosa were more plastic than the corresponding traits in H. cinerea, but this greater plasticity cannot be interpreted as adaptive. Our results emphasize the utility of the comparative approach in interpreting the potential adaptive responses of species to environmental variation.

Temperature Dependent Models To Predict Regional Differences in Corn Rootworm (Coleoptera: Chrysomelidae) Phenology

Western corn rootworms, Diabrotica virgifera virgifera LeConte, only recently have become a serious corn pest in New York and other states in the Northeast. Because soil conditions, topography, and climate differ from the Midwest corn belt, questions arose as to the validity of previously published phenology models. Our study evaluated larval occurrence and adult emergence of western and northern corn rootworm, D. barberi Smith & Lawrence, in 11 fields in central New York during 1991 (2 fields), 1992 (3 fields), and 1993 (6 fields). Logistic regression models predicted cumulative occurrence/emergence from Julian date or degree-day accumulations calculated from either soil (base 11°C) or air temperatures. Air temperature degree-days were calculated for minimum thresholds ranging from 1-16°C. Additional accumulations were determined by varying the maximum developmental threshold from 1°C above the lower threshold to 30°C. Minimum thresholds in the latter series of calculations were set equal to 4, 6, 9, and 11°C. Julian date was a relatively poor predictor of all immature and adult stages. However, accuracy of air temperature models was dependent on choice of thresholds. The best fitting air temperature models either used minimum developmental thresholds near 6°C for immature stages and 1-2°C for adult emergence or calculated degree-days using a minimum threshold of 11°C and a maximum threshold of 18°C. Both soil and air temperature models indicated regional differences in immature development and adult emergence. Although site-specific models gave the best prediction of western corn rootworm adult emergence, adult emergence at New York and Illinois sites could be predicted by adjusting daily air temperature degree-days by the expected accumulations from 1 January to 30 September.

Relating Degree–Day Accmuulations to Calendar Dates: Alfalfa Weevil (Coleoptera: Curculionidae) Egg Hatch in the North Central United States

We present a technique for determining dates of alfalfa weevil, Hypera postica (Gyllenhal), egg eclosion by correlating degree-day accumulations with calendar dates. This technique uses historical climate data from various locations to calculate the median date a degree-day accumulation has been reached. ClimProb 3.1, a computer software program and weather database, was used to assess these correlations. We used 165 locations in 12 midwestern states for the analysis. Sixty years (1931-1990) of continuous daily climate data (maximum temperature, minimum temperature, and liquid precipitation) were used for each location. We began degree-day accumulations on 1 January of each year and used a minimum developmental threshold of 8.9°C (48°F). Degree-day accumulations were determined using a sine-wave method. The relationship between the date when the accumulated degree-days reached a threshold and the location (expressed as degrees north latitude) was quadratic from 36° N to 48° N. The technique gives approximate dates when egg hatch is likely to occur throughout the north central United States, and these dates can be used to augment existing decision criteria for initiating sampling programs for alfalfa weevil. This technique can be used for other pest management programs that depend on estimating pest development.