Emergence of the overwintering generation of peach fruit moth (Carposina sasakii) depends on diapause and spring soil temperatures

Vegetation-cover control of between-site soil temperature evolution in a sandy desertland

Vegetation has an important influence on soil temperature (ST). However, the possible effects of surface vegetation on ST and their feedback on microclimate remain uncertain due to the lack of in-situ and long-term environmental records, especially for arid and semiarid regions of the world. A continuous, two-year study was implemented over a bare sand dune (BF) and two scrub-vegetation sites of variable cover in the Mu Us Desert of northwest China. Surface vegetation at the two non-bare sites varied from about 40% (moderate cover, MF) and 80 % (high cover, HF) of their respective surface area. Depiction of the vertical ST-profile was based on an array of field-based measurements taken within the uppermost 180 cm of the soil complex at each site. Compared with the BF site, mean ST at MF and HF decreased by 1.2 and 1.6 °C during the uniform thaw period and increased by 0.1 and 1 °C during uniform freezing. Amplitude of seasonal variation in ST for both vegetated sites, i.e., MF and HF, was reduced by 2.4 and 4.9 °C, respectively. As soil cooling during the uniform thaw period was greater than soil warming during uniform freezing, annual mean ST decreased at both vegetated sites by 1.6 and 1.2 °C (for MF and HF, respectively) compared to ST at BF. Differences in ST among the three sites during the uniform freeze and thaw periods were exponentially correlated with the extent of site vegetation cover, leaf area index, aboveground biomass, and on-the-ground litter thickness. Vegetation cover was shown to reduce the depth of the frost layer by 30 cm and prolonged the uniform thaw period by 1-35 days at the HF site. Mean daily STs at the center of each soil layer at the three sites were simulated with a two-equation model developed for this study, yielding a coefficient of determination (R2) of 0.91 when modeled STs were compared against their corresponding field observations. Increases in winter ST has potential to safeguard ground-dwelling grubs and other agriculturally harmful insects from freezing and dying. Likewise, decreases in annual ST could help promote decreases in litter decomposition, potentially lessening the effects of wind erosion.

Acclimation Effects of Natural Daily Temperature Variation on Longevity, Fecundity, and Thermal Tolerance of the Diamondback Moth (Plutella xylostella)

Simple Summary

Diurnal, monthly, or seasonal temperatures can fluctuate substantially. Daily temperature amplitudes (DTAs) can significantly impact the traits of insects but there is limited evidence from the natural environment. Therefore, we studied the acclimation effects of DTA on the longevity, total fecundity, early fecundity, and thermal tolerance of adult diamondback moths (Plutella xylostella) under environmental conditions. The longevity, total fecundity, early fecundity, and heat thermal tolerance of adults significantly changed under different DTAs. These findings highlight the effects of DTA on the acclimation response in the P.xylostella phenotype, and DTA should be incorporated into prediction models for assessing insect populations and the effects of climate change.

Abstract

Daily temperature amplitudes (DTAs) significantly affect the ecological and physiological traits of insects. Most studies in this field are based on laboratory experiments, while there is limited research on the effects of changes in DTA on insect phenotypic plasticity under natural conditions. Therefore, we studied the acclimation effects of DTA on the longevity, total fecundity, early fecundity, and the thermal tolerance of adult diamondback moths (Plutella xylostella L.) under naturally occurring environmental conditions. As DTAs increased, male longevity and total fecundity decreased, and early fecundity increased. An increase in DTA was significantly associated with the increased heat coma temperature (CT_max) of both males and females, but had no significant effect on their cold coma temperature (CT_min). Our findings highlight the effects of DTA on the acclimation response of P. xylostella and emphasize the importance of considering DTA in predicting models for assessing insect populations and the effects of climate change.

Local climate adaptation and gene flow in the native range of two co-occurring fruit moths with contrasting invasiveness

Invasive species pose increasing threats to global biodiversity and ecosystems. While previous studies have characterized successful invaders based on ecological traits, characteristics related to evolutionary processes have rarely been investigated. Here we compared gene flow and local adaptation using demographic analyses and outlier tests in two co-occurring moth pests across their common native range of China, one of which (the peach fruit moth, Carposina sasakii) has maintained its native distribution, while the other (the oriental fruit moth, Grapholita molesta) has expanded its range globally during the past century. We found that both species showed a pattern of genetic differentiation and an evolutionary history consistent with a common southwestern origin and northward expansion in their native range. However, for the noninvasive species, genetic differentiation was closely aligned with the environment, and there was a relatively low level of gene flow, whereas in the invasive species, genetic differentiation was associated with geography. Genome scans indicated stronger patterns of climate-associated loci in the noninvasive species. While strong local adaptation and reduced gene flow across its native range may have decreased the invasiveness of C. sasakii, this requires further validation with additional comparisons of invasive and noninvasive species across their native range.

Chromosome-level genome of the peach fruit moth Carposina sasakii (Lepidoptera: Carposinidae) provides a resource for evolutionary studies on moths

The peach fruit moth (PFM), Carposina sasakii Matsumura, is a major phytophagous orchard pest widely distributed across Northeast Asia. Here, we report the chromosome-level genome for the PFM, representing the first genome for the family Carposinidae, from the lepidopteran superfamily Copromorphoidea. The genome was assembled into 404.83 Mb sequences using PacBio long-read and Illumina short-read sequences, including 275 contigs, with a contig N50 length of 2.62 Mb. All contigs were assembled into 31 linkage groups assisted by the Hi-C technique, including 30 autosomes and a Z chromosome. BUSCO analysis showed that 98.3% of genes were complete and 0.4% of genes were fragmented, while 1.3% of genes were missing in the assembled genome. In total, 21,697 protein-coding genes were predicted, of which 84.80% were functionally annotated. Because of the importance of diapause triggered by photoperiod in PFM, five circadian genes in the PFM as well as in the other related species were annotated, and potential genes related to diapause and photoperiodic reaction were also identified from transcriptome sequencing. In addition, manual annotation of detoxification gene families was undertaken and showed a higher number of glutathione S-transferase (GST) gene in PFM than in most other lepidopterans, in contrast to a lower number of uridine diphosphate (UDP)-glycosyltransferase (UGT) gene, carboxyl/cholinesterases (CCE) gene and cytochrome P450 monooxygenase (P450) gene, suggesting different detoxication pathways in this moth. The high-quality genome provides a resource for comparative evolutionary studies of this moth and its relatives within the context of radiations across Lepidoptera.

Effects of photoperiod and relative humidity on diapause termination and post-winter development of Rhagoletis cerasi pupae

The European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), is a univoltine species that undergoes obligatory summer-winter diapause at pupal stage in the soil (2-5 cm) beneath host trees. To study the effects of photoperiod and relative humidity on diapause termination and post-winter developmental duration of R. cerasi, pupae collected from Dossenheim (Germany) were exposed to different photoperiod or relative humidity regimes during a chilling period ranging from 2 to 8.5 months. Specifically, pupae were exposed to four photoperiod regimes: (a) light conditions (24L:00D), (b) dark conditions (00L:24D), (c) short photoperiod (08L:16D) and (d) long photoperiod (16L:08D), as well as to three relative humidity regimes: (a) low (40% RH), (b) medium (60% RH) and (c) high (70-80% RH). Data revealed that relative humidity is not a significant predictor of diapause termination, but it affects the post-winter developmental period. Higher relative humidity promotes post-winter pupae development. On the other hand, photoperiod significantly affected both diapause termination and post-winter development of R. cerasi pupae. Light conditions (24L:00D) accelerate adult emergence, particularly for females. Regardless of the photoperiod (24L:00D, 00L:24D, 08L:16D), rates of adult emergence were high (>75%) for chilling intervals longer than 6.5 months. Nonetheless, exposure to a long day photoperiod (16L:08D), during chilling, dramatically reduced the proportion of adult emergence following 6 months exposure to chilling. Our findings broaden the understanding of factors regulating diapause responses in European cherry fruit fly, local adaptation and synchronization of adult emergence with the ripening period of major hosts.

Pest categorisation of Carposina sasakii

The EFSA Panel on Plant Health performed a pest categorisation of the peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae) for the EU. C. sasakii is not currently regulated in the EU although C. niponensis, a valid species of no economic significance that was previously mistakenly synonymised with C. sasakii, is regulated in Annex IIAI of 2000/29 EC. C. sasakii is a well-defined species that is recognised as a major pest of apples, peaches and pears in eastern China, Japan, Korea and Far East Russia. C. sasakii is not known to occur in the EU. Adult C. sasakii emerge in the spring or early summer. Eggs are laid on host fruits. Larvae burrow into the fruit to develop. Infested fruits often drop early. Larvae exit fruit and overwinter in the soil. In the more southern areas of distribution, there can be two or more generations per year. Import of host fruit provides a potential pathway into the EU. C. sasakii occurs in a range of climates in Asia, some of which occur in the EU. Wild and commercially grown hosts are available within the EU. C. sasakii has the potential to establish within the EU where there could be one or two generations per year. Impacts could be expected in apples, pears and other rosaceous fruit crops. The level of impacts would be uncertain. Phytosanitary measures are available to reduce the likelihood of introduction of C. sasakii. C. sasakii meets all the criteria assessed by EFSA PLHP to satisfy the definition of a Union quarantine pest. C. sasakii does not meet the criteria of occurring within the EU, nor plants for planting being the principal means of spread, so does not satisfy all the criteria for it to be regarded as a Union regulated non-quarantine pest (RNQP).

Patterns of genetic variation among geographic and host-plant associated populations of the peach fruit moth Carposina sasakii (Lepidoptera: Carposinidae)

Background

Populations of herbivorous insects may become genetically differentiated because of local adaptation to different hosts and climates as well as historical processes, and further genetic divergence may occur following the development of reproductive isolation among populations. Here we investigate the population genetic structure of the orchard pest peach fruit moth (PFM) Carposina sasakii (Lepidoptera: Carposinidae) in China, which shows distinct biological differences when characterized from different host plants. Genetic diversity and genetic structure were assessed among populations from seven plant hosts and nine regions using 19 microsatellite loci and a mitochondrial sequence.

Results

Strong genetic differentiation was found among geographical populations representing distinct geographical regions, but not in host-associated populations collected from the same area. Mantel tests based on microsatellite loci indicated an association between genetic differentiation and geographical distance, and to a lesser extent environmental differentiation. Approximate Bayesian Computation analyses supported the scenario that PFM likely originated from a southern area and dispersed northwards before the last glacial maximum during the Quaternary.

Conclusions

Our analyses suggested a strong impact of geographical barriers and historical events rather than host plants on the genetic structure of the PFM; however, uncharacterized environmental factors and host plants may also play a role. Studies on adaptive shifts in this moth should take into account geographical and historical factors.

Electronic supplementary material

The online version of this article (10.1186/s12862-017-1116-7) contains supplementary material, which is available to authorized users.

Effects of temperature, soil moisture and photoperiod on diapause termination and post-diapause development of the wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae)

Sitodiplosis mosellana, one of the most important wheat pests, goes through larval diapause in a cocooned form. It is univoltine, but some individuals exhibit prolonged diapause. In this study, we documented diapause termination rate of cocooned larvae at different diapausing periods and time required for adult emergence when they were brought to 25°C from the field in northern China. We found that field larvae all entered diapause by June, but none terminated diapause until late September when the daily average temperature dropped to below 20°C. Furthermore, termination rate increased significantly as diapausing larvae underwent increasing chilling duration, reaching >95% from early December to early March. Our results suggest that chilling was necessary for diapause to terminate and that field diapause termination ended in early December. To explore low temperature and duration required, we cold-treated field diapausing larvae of different periods at different low temperatures for various lengths of time prior to the 25°C incubation. Chilling at 4-8°C for 60-90days resulted in a higher termination rate (>90%) and shorter adult emergence time in general. Additionally, we investigated the combined effect of temperature (18-30°C) and soil moisture (20-60%, on dry weight basis) as well as the effect of photoperiod (24:0-0:24L:D) on post-diapause development. While photoperiod did not affect adult emergence, soil moisture ranging from 30 to 50% and temperature from 22 to 26°C resulted in the highest adult emergence rates (>46%) within relatively short time (<18days). Mortality and/or prolonged diapause rate drastically increased when incubation conditions were outside the optimal range, especially at 30°C. These findings provide new insight into the diapause process of S. mosellana, and information will be useful for development of field forecasting and laboratory rearing techniques of this pest insect.

Are adult life history traits in oriental fruit moth affected by a mild pupal heat stress?

Thermal stress at one life stage can affect fitness at a later stage in ectotherms with complex life cycles. Most relevant studies have focused on extreme stress levels, but here we also show substantial fitness effects in a moth when pupae are exposed to a relatively mild and sublethal heat stress. We consider the impact of a 35°C heat stress of 2h in three geographically separate populations of the oriental fruit moth (OFM, Grapholita molesta) from northern, middle and southern China. Heat stress negatively affected fecundity but increased adult heat resistance and adult longevity. Fitness effects were mostly consistent across populations but there were also some population differences. In the Shenyang population from northern China, there was a hormetic effect of heat on female longevity not evident in the other populations. Adults from all populations had higher LT₅₀s due to heat stress after pupal exposure to the sublethal stress. These results highlight that the pupal stage is a particularly sensitive window for development and they have implications for seasonal adaptation in uncertain environments as well as changes in pest dynamics under climate warming.

Warming Accelerates Carbohydrate Consumption in the Diapausing Overwintering Peach Fruit Moth Carposina sasakii (Lepidoptera: Carposinidae)

Climate warming provides a challenge for small insects persisting in cold seasons through diapause because they fail to accumulate and maintain adequate reserves to complete this stage successfully. One way of understanding this challenge is to follow physiological changes in these insects under higher temperatures, including the consumption and allocation of energy reserves during and after diapause. We simulated autumn and spring warming conditions to study carbohydrate consumption dynamics during diapause-post-diapause periods by monitoring shifts in carbohydrate levels in a facultative diapause species, the peach fruit moth Carposina sasakii Matsumura (Lepidoptera: Carposinidae). We found carbohydrates were rapidly consumed in the post-diapause phase, which might lead to a trade-off in the allocation of energy reserves between diapause maintenance and post-diapause development. This suggests that temperature increases in autumn and spring may alter diapause maintenance and post-diapause development through changing carbohydrate levels.