Population Parameters and Growth of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) under Fluctuating Temperature.

In this study, we determined the influence of fluctuating temperatures on the development and fecundity of the bean bug Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) by collecting life table data for individuals exposed at a constant temperature (24 °C) and three fluctuating temperatures (24 ± 4 °C, 24 ± 6 °C, and 24 ± 8 °C). The raw life history data were analyzed using an age-stage, two-sex life table to take into account the viable development rate among individuals. Based on these analyses, the population projections enabled us to determine the stage structure and variability of population growth under different temperature treatments. Our results revealed shorter periods of immature development and a higher pre-adult survival rate at 24 ± 6 °C than under the other assessed temperature conditions. Furthermore, significant reductions in female longevity were recorded at 24 °C, whereas the fecundity, net reproductive rate, and intrinsic and finite rates of increase were highest at 24 ± 6 °C. These findings reveal that fluctuating temperatures have a positive influence on the life history traits of R. pedestris and indicate that observations made under constant temperatures may not explain sufficiently enough the temperature dependent biological performances of pests in the field.

Thermal Effects on the Population Parameters and Growth of Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae).

The pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) is a cosmopolitan and polyphagous species. An evaluation of A. pisum's demographic parameters and growth was carried out after rearing aphids on faba bean plants (Vicia faba) under five different temperature conditions (10 °C, 15 °C, 20 °C, 25 °C and 30 °C). We analyzed the raw life history data, including developmental time, survival, longevity and reproduction, using an age-stage, two-sex life table to consider variable developmental rates among individuals. The population fluctuation of A. pisum determined the stage-specific population structure and potential population growth under different temperature conditions. A. pisum individuals developed successfully from nymphs to adults at all temperatures in this study. The developmental rate of A. pisum increased as the temperature increased. Our results indicated that A. pisum showed a higher pre-adult mortality, lower total fecundity and a negative intrinsic rate of increase at 30 °C. The highest intrinsic rate of increase (0.30) and finite rate of increase (1.35) were observed at 25 °C. Comparisons of population parameters and their analytical methods between different A. pisum populations from other geographic areas are also discussed.

Thermal effect on the fecundity and longevity of Bactrocera dorsalis adults and their improved oviposition model.

The oriental fruit fly, Bactrocera dorsalis, is a destructive polyphagous pest that causes damage to various fruit crops, and their distribution is currently expanding worldwide. Temperature is an important abiotic factor that influences insect population dynamics and distribution by affecting their survival, development, and reproduction. We examined the fecundity, pre-oviposition and oviposition periods, and longevity of adult B. dorsalis at various constant temperatures ranging from13°C to 35°C. The longevity of female B. dorsalis ranged from 116.8 days (18.8°C) to 22.4 days (34.9°C), and the maximum fecundity per female was 1,684 eggs at 28.1°C. Females were only able to lay eggs at 16.7°C to 34.9°C, and both the pre-oviposition and oviposition periods were different depending on the temperature. We modeled female reproduction in two oviposition models (OMs): 1) the current model developed by Kim and Lee, an OM composed of a fecundity model, age-specific survival model, and age-specific cumulative oviposition rate model, and 2) a two-phase OM modified the logic structure of the current model by separating pre-oviposition, so that oviposition was estimated with the female in oviposition phase who had complete pre-oviposition phase. The results of the two-phase OM provided more realistic outputs at lower and higher temperatures than those of the current model. We discussed the usefulness of the two-phase OM for the reproduction of insects with long pre-oviposition periods.

Development, Reproduction, and Life Table Parameters of the Foxglove Aphid, Aulacorthum solani Kaltenbach (Hemiptera: Aphididae), on Soybean at Constant Temperatures.

We investigated several characteristics of the development and reproduction of the aphid Aulacorthum solani raised on soybean (Glycine max) at 10 constant temperatures between 2.5 and 30 °C, and described the relationship between temperature and several critical biological characteristics using mathematical models. We found that A. solani could survive and reproduce on soybean at temperatures ranging from 5 to 27.5 °C. High fecundity was observed at temperatures from 12.5 to 20 °C. The lower developmental threshold and thermal constant for this species' nymphal stages were estimated to be 5.02 °C and 131.2 degree-days, respectively, using a linear model. The upper developmental threshold was estimated to be 33.9 °C using the Lactin-2 model. The optimum temperature for nymphal development was estimated to be 26.9 °C. The maximum total fecundity was estimated as ca. 76.9 nymphs per adult at 18.1 °C. The daily fecundity sharply increased at earlier adult ages, and slowly decreased thereafter until final parthenogenesis occurred, over a range of temperatures from 12.5 to 25 °C. The maximum daily fecundity was estimated to be ca. 6.1 nymphs per adult per day for a 5.2 day old of adult at 21.3 °C using an age- and temperature-dependent model of adult fecundity. In terms of life table statistics, the intrinsic rates of increase and the finite rate of increase were both highest at 25 °C, while the net reproductive rate was highest at 20 °C.

Application of insulin signaling to predict insect growth rate in Maruca vitrata (Lepidoptera: Crambidae).

Insect growth is influenced by two major environmental factors: temperature and nutrient. These environmental factors are internally mediated by insulin/insulin-like growth factor signal (IIS) to coordinate tissue or organ growth. Maruca vitrata, a subtropical lepidopteran insect, migrates to different climate regions and feeds on various crops. The objective of this study was to determine molecular tools to predict growth rate of M. vitrata using IIS components. Four genes [insulin receptor (InR), Forkhead Box O (FOXO), Target of Rapamycin (TOR), and serine-threonine protein kinase (Akt)] were used to correlate their expression levels with larval growth rates under different environmental conditions. The functional association of IIS and larval growth was confirmed because RNA interference of these genes significantly decreased larval growth rate and pupal weight. Different rearing temperatures altered expression levels of these four IIS genes and changed their growth rate. Different nutrient conditions also significantly changed larval growth and altered expression levels of IIS components. Different local populations of M. vitrata exhibited significantly different larval growth rates under the same nutrient and temperature conditions along with different expression levels of IIS components. Under a constant temperature (25°C), larval growth rates showed significant correlations with IIS gene expression levels. Subsequent regression formulas of expression levels of four IIS components against larval growth rate were applied to predict growth patterns of M. vitrata larvae reared on different natural hosts and natural local populations reared on the same diet. All four formulas well predicted larval growth rates with some deviations. These results indicate that the IIS expression analysis explains the growth variation at the same temperature due to nutrient and genetic background.

HR-Mediated Defense Response is Overcome at High Temperatures in Capsicum Species.

Resistance to Tomato spotted wilt virus isolated from paprika (TSWV-Pap) was overcome at high temperatures (30 ± 2°C) in both accessions of Capsicum annuum S3669 (Hana Seed Company) and C. chinense PI15225 (AVRDC Vegetable Genetic Resources). S3669 and PI15225, which carrying the Tsw gene, were mechanically inoculated with TSWV-Pap, and then maintained in growth chambers at temperatures ranging from 15 ± 2°C to 30 ± 2°C (in 5°C increments). Seven days post inoculation (dpi), a hypersensitivity reaction (HR) was induced in inoculated leaves of PI152225 and S3669 plants maintained at 25°C ± 2°C. Meanwhile, necrotic spots were formed in upper leaves of 33% of PI15225 plants maintained at 30 ± 2°C, while systemic mottle symptoms developed in 50% of S3669 plants inoculated. By 15 dpi, 25% of S3669 plants had recovered from systemic mottling induced at 30 ± 2°C. These results demonstrated that resistance to TSWV-Pap can be overcome at higher temperatures in both C. chinense and C. annuum. This is the first study reporting the determination of temperatures at which TSWV resistance is overcome in a C. annuum genetic resource expressing the Tsw gene. Our results indicated that TSWV resistance shown from pepper plants possess the Tsw gene could be overcome at high temperature. Thus, breeders should conduct evaluation of TSWV resistance in pepper cultivars at higher temperature than 30°C (constant temperature).

Erratum: The Effects of High Temperature on Infection by Potato virus Y, Potato virus A, and Potato leafroll virus.

[This corrects the article on p. 321 in vol. 32, PMID: 27493607.].

The Effects of High Temperature on Infection by Potato virus Y, Potato virus A, and Potato leafroll virus.

We examined the effects of temperature on acquisition of Potato virus Y-O (PVY-O), Potato virus A (PVA), and Potato leafroll virus (PLRV) by Myzus persicae by performing transmission tests with aphids that acquired each virus at different temperatures. Infection by PVY-O/PVA and PLRV increased with increasing plant temperature in Nicotiana benthamiana and Physalis floridana, respectively, after being transmitted by aphids that acquired them within a temperature range of 10-20°C. However, infection rates subsequently decreased. Direct qRT-PCR of RNA extracted from a single aphid showed that PLRV infection increased in the 10-20°C range, but this trend also declined shortly thereafter. We examined the effect of temperature on establishment of virus infection. The greatest number of plants became infected when N. benthamiana was held at 20°C after inoculation with PVY-O or PVA. The largest number of P. floridana plants became infected with PLRV when the plants were maintained at 25°C. PLRV levels were highest in P. floridana kept at 20-25°C. These results indicate that the optimum temperatures for proliferation of PVY-O/PVA and PLRV differed. Western blot analysis showed that accumulations of PVY-O and PVA coat proteins (CPs) were lower at 10°C or 15°C than at 20°C during early infection. However, accumulation increased over time. At 25°C or 30°C, the CPs of both viruses accumulated during early infection but disappeared as time passed. Our results suggest that symptom attenuation and reduction of PVY-O and PVA CP accumulation at higher temperatures appear to be attributable to increased RNA silencing.

Effects of Temperature on Development and Voltinism of Chaetodactylus krombeini (Acari: Chaetodactylidae): Implications for Climate Change Impacts.

Temperature plays an important role in the growth and development of arthropods, and thus the current trend of climate change will alter their biology and species distribution. We used Chaetodactylus krombeini (Acari: Chaetodactylidae), a cleptoparasitic mite associated with Osmia bees (Hymenoptera: Megachilidae), as a model organism to investigate how temperature affects the development and voltinism of C. krombeini in the eastern United States. The effects of temperature on the stage-specific development of C. krombeini were determined at seven constant temperatures (16.1, 20.2, 24.1, 27.5, 30.0, 32.4 and 37.8°C). Parameters for stage-specific development, such as threshold temperatures and thermal constant, were determined by using empirical models. Results of this study showed that C. krombeini eggs developed successfully to adult at all temperatures tested except 37.8°C. The nonlinear and linear empirical models were applied to describe quantitatively the relationship between temperature and development of each C. krombeini stage. The nonlinear Lactin model estimated optimal temperatures as 31.4, 32.9, 32.6 and 32.5°C for egg, larva, nymph, and egg to adult, respectively. In the linear model, the lower threshold temperatures were estimated to be 9.9, 14.7, 13.0 and 12.4°C for egg, larva, nymph, and egg to adult, respectively. The thermal constant for each stage completion were 61.5, 28.1, 64.8 and 171.1 degree days for egg, larva, nymph, and egg to adult, respectively. Under the future climate scenarios, the number of generations (i.e., voltinism) would increase more likely by 1.5 to 2.0 times by the year of 2100 according to simulation. The findings herein firstly provided comprehensive data on thermal development of C. krombeini and implications for the management of C. krombeini populations under global warming were discussed. *Scientific Article No. 3278 of the West Virginia Agricultural and Forestry Experiment Station, Morgantown, West Virginia.

Effects of Temperature on Systemic Infection and Symptom Expression of Turnip mosaic virus in Chinese cabbage (Brassica campestris).

Using the Chinese cabbage (Brassica campestris) cultivar 'Chun-goang' as a host and turnip mosaic virus (TuMV) as a pathogen, we studied the effects of ambient temperature (13°C, 18°C, 23°C, 28°C and 33°C) on disease intensity and the speed of systemic infection. The optimal temperature for symptom expression of TuMV was 18-28°C. However, symptoms of viral infection were initiated at 23-28°C and 6 days post infection (dpi). Plants maintained at 33°C were systemically infected as early as 6 dpi and remained symptomless until 12 or 22 dpi, depending on growth stage at the time of inoculation. It took 45 days for infection of plants grown at 13°C. Quantitative real-time polymerase chain reaction (q-PCR) results showed that the accumulation of virus coat protein was greater in plants grown at 23-28°C. The speed of systemic infection increased linearly with rising ambient temperature, up to 23°C. The zero-infection temperature was 10.1°C. To study the effects of abruptly elevated temperatures on systemic infection, plants inoculated with TuMV were maintained at 10°C for 20 d; transferred to a growth chamber at temperatures of 13°C, 18°C, 23°C, 28°C, or 33°C for 1, 2, or 3 d; and then moved back to 10°C. The numbers of plants infected increased as duration of exposure to higher temperatures and dpi increased.

A Model for Predicting Spring Emergence of Monochamus saltuarius (Coleoptera: Cerambycidae) from Korean white pine, Pinus koraiensis.

Monochamus saltuarius Gebler is a vector that transmits the pine wood nematode, Bursaphelenchus xylophilus, to Korean white pine, Pinus koraiensis, in Korea. To reduce the damage caused by this nematode in pine forests, timely control measures are needed to suppress the cerambycid beetle population. This study sought to construct a forecasting model to predict beetle emergence based on spring temperature. Logs of Korean white pine were infested with M. saltuarius in 2009, and the infested logs were overwintered. In February 2010, infested logs were then moved into incubators held at constant temperature conditions of 16, 20, 23, 25, 27, 30 or 34°C until all adults had emerged. The developmental rate of the beetles was estimated by linear and nonlinear equations and a forecasting model for emergence of the beetle was constructed by pooling data based on normalized developmental rate. The lower threshold temperature for development was 8.3°C. The forecasting model relatively well predicted the emergence pattern of M. saltuarius collected from four areas in northern Republic of Korea. The median emergence dates predicted by the model were 2.2-5.9 d earlier than the observed median dates.

Micromorphology of epicuticular wax structures of the garden strawberry leaves by electron microscopy: syntopism and polymorphism.

Ultrastructural aspects of leaf epicuticular wax structures were investigated in the garden strawberry Fragariaxananassa by scanning and transmission electron microscopy. Both the adaxial and abaxial surfaces of two cultivars (Maehyang and Red Pearl) were collected and subjected to surface observations and ultrathin sections. The most prominent leaf epicuticular wax structures included membraneous platelets and angular rodlets. Most wax platelets were membraneous, and appeared to protrude from the surface at an acute angle. Angular rodlets were usually bent and had rather distinct facets in the abaxial surface of the two cultivars. Membraneous platelets were predominant on the adaxial surface of Maehyang, whereas the adaxial surface of Red Pearl was characterized by angular rodlets. However, both cultivars possessed angular rodlets on the abaxial surface, simultaneously. The combination of air-drying without vacuum and in-lens imaging of secondary electron signals with a field emission gun could impart the superb resolution at low electron dose with minimal specimen shrinkage. In vertical profiles of the leaf epidermis, epicuticular waxes were observed above the cuticle layer, and measured approximately as 50nm in thickness. The natural epicuticular waxes were seemingly mixtures of electron-dense microfibrils, and heterogeneous in shape on ultrathin sections. Distinct crystal-like strata could be hardly discernable in the wax structures. These results suggest that the garden strawberry has the nature of syntopism within one plant and polymorphism within the same species in the formation and occurrence of leaf epicuticular waxes.