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Phenotypic plasticity is an important attribute that enables plants to survive across a range of environments. We conducted two experiments to investigate the plasticity of architectural traits and biomass ratios for Fagopyrum esculentum Moench in response to population density and sowing date. These included (1) inter-planting distances of 5, 10, 15, or 20 cm; and (2) sowing on 25 July, 1 August, 5 August, or 10 August. Many traits exhibited phenotypic plasticity that was coupled with changes in plant size. However, variations in leaf/mass ratio from either experiment, as well as leaf/root ratios in response to sowing date, were independent of size. When coefficients of variation were computed, some consistency was found in the magnitude of trait plasticity for both density and sowing date. For each experiment, leaf/root ratios, leaf/mass ratios, and stem/mass ratios were most plastic. Although this suggests that biomass ratios could be more responsive to environmental changes, a wide array of traits should be considered if we are to fully understand the mechanism for these phenomena.

he Asian corn borer (ACB), Ostrinia furnacalis, is a serious maize pest in Southeast Asia, responsible for substantial economic losses to the maize crop every year. To establish insect biocontrol programmes, it is crucial to determine the ideal numbers and developmental stage of natural enemies to release. The purpose of the present study was to assess the parasitism ability of Trichogramma dendrolimi and Trichogramma ostriniae, which are the most promising biocontrol agents of the ACB, under two different methods of inundative release in maize fields. A total of 10,000 wasps of both species were released using two different methods, i.e. wasps at the same developmental stage (SDS) and wasps at different developmental stages (DDS). The results showed that T. dendrolimi wasps exhibited significantly higher parasitism of ACB eggs when they were released with the DDS method than when they were released with the SDS method. In the SDS release method, T. dendrolimi parasitized ACB eggs for only 3 days after release, while in the DDS release method, parasitism of ACB eggs occurred for 6 days. However, the two release methods had no significant impact on the performance of T. ostriniae in maize fields. In both release methods, T. ostriniae parasitized a high percentage of ACB eggs. The results of the present study clearly indicate that the poor field performance of T. dendrolimi due to the host-age factor can be improved using the DDS release method.

The oriental armyworm Mythimna separata (Walker) is a major cereal crop pest, causing severe economic losses worldwide every year. Yet, few studies documented the biological control of M. separata using natural enemies such as egg parasitoids of the genus Trichogramma. To evaluate the possibility of biological control of M. separata eggs at various ages (0-, 1-, 2-, and 3-day old), we compared under laboratory conditions the parasitism, emergence, development, and female progeny (sex ratio) of five Trichogramma species indigenous in China: Trichogramma dendrolimi Matsumura, T. chilonis Ishii, T. ostriniae Pang & Chen, T. leucaniae Pang & Chen, and T. japonicum Ashmend. All five Trichogramma species parasitized M. separata at all egg ages but showed a preference for younger eggs. T. dendrolimi parasitized 55.1, 36.6, 19.3, and 14.3 hosts in 24 h on 0-, 1-, 2-, and 3-day-old eggs, respectively, and it exhibited the highest parasitism and suitability on all egg ages. T. japonicum showed the lowest parasitism rate and the poorest host acceptance. T. ostriniae, T. leucaniae, and T. chilonis presented similar rates of adult emergence and sex ratio for all M. separata egg ages. T. ostriniae developed significantly slower on 2- and 3-day-old M. separata eggs. With the exception of T. leucaniae, all species showed no difference in adult emergence at all egg ages. T. dendrolimi was identified as the best for biological control of M. separata. The present study provides valuable information for future development of Trichogramma species in biological control programs targeting M. separata as pest.

The rice stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae), is a key rice pest, causing major yield loss in Asia. Trichogramma japonicum Ashmead (egg parasitoid) and Beauveria bassiana Balsamo Vuillemin (entomopathogenic fungi) are two important organisms used in sequence or integrated for C. suppressalis management. However, few information is available on potential antagonism between the two biocontrol agents. Under laboratory conditions, we assessed whether the presence of B. bassiana had an impact on the oviposition preference of T. japonicum for C. suppressalis eggs. We characterized parasitic behavior of T. japonicum exposed or not to B. bassiana on C. suppressalis eggs (varying in age) by carrying out observation experiments and using a Y-tube olfactometer. We also evaluated the response of T. japonicum to B. bassiana-affected vs. -unaffected C. suppressalis eggs. Olfactometer tests showed that T. japonicum-vectored B. bassiana and/or C. suppressalis eggs immersed in B. bassiana did not have major effects on choices made by the parasitoid. T. japonicum attacked C. suppressalis eggs of 0-d, 2-d and 4-d old and had preference to fresh host eggs (0-d). However, the contaminated T. japonicum were not able to distinguish between eggs of 0-d old and 4-d old in contrast with the uncontaminated parasitoids. A reduction in insect locomotion (no-response number) of T. japonicum contaminated by B. bassiana preferring to 4-d-old host eggs was found, which was compared to the no-response number of uncontaminated T. japonicum preferring to 0-d-old host eggs. The parasitic behavior of host searching time, checking time, drilling and oviposition time and the parasitism rate (in 24 h) did not differ between the fresh eggs immersed with B. bassiana and control (eggs without B. bassiana). On the other hand, searching and checking times were slightly higher when parasitoids were contaminated by B. bassiana (drilling and oviposition times as well as the parasitism rate in 24 h were not impacted). Therefore, T. japonicum may be used together with B. bassiana in integrated program targeting C. suppressalis.

Egg batches of Spodoptera moths are protected by scales deposited by females around and/or over eggs as a physical defense. These scales may affect the parasitism of some parasitoids, rendering biocontrol of Spodoptera eggs ineffective. In this study, we investigated the daily oviposition pattern of moths and the dynamics of egg mass scales of three Spodoptera species and examined the fitnesses of three potential egg parasitoid species to different egg mass scale thicknesses. The observations revealed that the three Spodoptera species share similar scale dynamics. From initial oviposition, S. exigua egg batches maintained a relatively high level of scale thickness (> 134.7 mu m) for 2 days and S. frugiperda and S. litura for 3 days (> 105.9 mu m, > 161.2 mu m, respectively). During this period, the scales effectively hindered parasitism by Trichogramma species (parasitized 0.4%-14.9% eggs). Thereafter, the thickness of the scales decreased daily. The scales of the three Spodoptera species were all relatively thin (< 20.0 mu m) after oviposition for 8 days, and subsequently, Trichogramma parasitized eggs more actively (parasitized up to 33.4%-36.5% eggs). Relatively, Trichogramma dendrolimi on S. frugiperda eggs, and Trichogramma chilonis on S. exigua eggs had higher parasitism. Meanwhile, Telenomus remus maintained a very stable and better performance than Trichogramma on Spodoptera species eggs with different scale thicknesses (parasitized 100% egg masses and 46.2%-60.0% eggs), which demonstrated its excellent potential as a Spodoptera species biocontrol agent. The findings elucidate the effect of egg mass scale thickness on effective parasitism by these egg parasitoid species and provide baseline information for the mixed use of Te. remus and Trichogramma against Spodoptera species.

The Japanese giant silkwormCaligula japonicaMoore is an emerging defoliator pest of forest and fruit trees, causing severe economic losses in East Asia. To identify biological control agents for this pest, we comparatively evaluated six indigenous eupelmid egg parasitoids (Anastatus fulloi,A. gansuensis,A. japonicus,A. meilingensis,Mesocomys albitarsisandM. trabalae) from China, in terms of their performances (number of parasitized eggs, developmental time, offspring emergence and sex ratio) onC. japonicaeggs of four different ages (0, 10, 20 and 30-d old). Results showed that all six parasitoids readily parasitizedC. japonicaeggs of all tested ages, butA. japonicuswas the most efficient species based on the number of parasitized eggs, followed byM. albitarsisandM. trabalae, and the other three parasitoid species. All fourAnastatusspecies parasitized more old than young eggs, whileM. albitarsisdid not show a strong host age preference andM. trabalaeparasitized the oldest less than young eggs. For all host ages, developmental time was longest inA. gansuensisand shortest inM. albitarsis, offspring emergence was high (> 90%), and progeny was strongly female biased (> 70%) among all parasitoids except forA. gansuensiswhich produced all female progeny. Portions ofA. japonicusoffspring (< 13.1%) entered diapause as pre-pupae. Accordingly,A. japonicus,M. albitarsisandM. trabalaewere identified as the most suitable agents againstC. japonica. This information may also help improve rearing and field-release protocols, in terms of host age-related effects on these parasitoids.

Hole-nesting tits Parus spp. have been classified as “unsuitable” hosts for cuckoo parasitism because cuckoos cannot enter a cavity if the entrance is too small. However, Chinese tits could reject alien eggs and egg ejection rate increased with the local diversity of parasitic cuckoo species. Antiparasitic behavior among Chinese tits may have evolved due to greater size variation among sympatric cuckoo species. This raises the question of whether differently sized parasitic cuckoos pose different threats to Chinese tits. A green-backed tit Parus monticolus population that is sympatric with Asian emerald cuckoo Chrysococcyx maculatus (eme-cuckoo, small-sized parasite) and common cuckoo Cuculus canorus (com-cuckoo, large-sized parasite), and a cinereous tit P. cinereus population that is only sympatric with com-cuckoo were chosen as study organisms. We observed behavioral response and recorded alarm calls of the 2 tit species to eme-cuckoo, com-cuckoo, chipmunk Tamias sibiricus (a nest predator) and dove Streptopelia orientalis (a harmless control), and subsequently played back alarm calls to conspecific incubating females. In dummy experiments, both tit species performed intense response behavior to chipmunk, but rarely responded strongly to the 3 avian species. In playback experiments, both tit species responded strongly to conspecific chipmunk alarm calls, but rarely responded to dove alarm calls. The intensity of response of incubating female green-backed tits to eme-cuckoo and com-cuckoo alarm calls were similar to that of chipmunk alarm calls, while the intensity to eme-cuckoo alarm calls was higher than the intensity to dove alarm calls which was similar to that of com-cuckoo alarm calls. In contrast, few female cinereous tits responded to eme-cuckoo and com-cuckoo alarm calls. These findings indicated that the threat level of eme-cuckoo was slightly greater than that of com-cuckoo for sympatric green-backed tits, but not for allopatric cinereous tits.

The age ofTrichogrammaparasitoids could influence biological traits which are of great importance for effectiveness of mass rearing systems. Recent studies demonstrated thatTrichogramma ostriniae(TO) could parasitizeAntheraea pernyieggs through multiparasitism along with other Trichogrammaspecies, although few adults could emerge successfully. It is important to characterize the factors modulating the performance of TO onA. pernyieggs, notably in order to try enhancing its quantitative emergence through multiparasitism for further use in biological control. In this context, irrespective of host age, we tested different ages of TO females (from 0.5-day- to 6-day-old postemergence) in multiparasitism withTrichogramma chilonis(TC) onA. pernyieggs. The results of the present study confirmed that TO parasitism onA. pernyieggs was largely age dependent. Higher percentage of multiparasitism and higher number of emerged TO adults were recorded in the treatment where 3-day-old TO females were used for parasitization with TC onA. pernyihost. In addition, we also tested different female ratios of bothTrichogramma species to find out an optimal ratio for use in mass production. The highest percentage of multiparasitism, emergence and optimum emerged number of TO (perA. pernyiegg) was observed with the ratio 3:2 (TO:TC) per 1 host egg. This study demonstrated that the age of TO females can significantly affect their performance in multiparasitism of largeA. pernyieggs. These results prompt for more research in order to develop an effective multiparasitism-based production of TO at the industrial scale.

Trichogramma parasitoids are important biological control agents for insect pest management. However, efficient means for mass production of Trichogramma parasitoids are needed, particularly for T. ostriniae, which often fail to form emergence holes on host eggs of Chinese oak silkworm, Antheraea pernyi, because of the hard chorion. In the present study, we evaluated the possibilities to enhance adult emergence of T. ostriniae by utilizing emergence holes made by T. dendrolimi during multiparasitism on host eggs of A. pernyi and other biological parameters such as pre-emergence time, parasitism rate, and emergence rate of the two parasitoids, which were also evaluated between the two parasitism regimes of multi- and monoparasitism. Our data showed that multiparasitism on host eggs of A. pernyi significantly facilitated the emergence of adult T. ostriniae. Generally, both Trichogramma species favored parasitizing A. pernyi eggs, with multiple parasitoid adults emerged per host egg. The overall performance of T. dendrolimi was similar between the two parasitism regimes, although a significantly higher number of unemerged adults were found in the multiparasitized eggs than in the monoparasitized. For T. ostriniae, significantly more adults emerged, and a higher emergence rate was recorded on host eggs multiparasitized with T. dendrolimi than that on monoparasitized. Furthermore, significantly fewer unemerged adults were found in multi- than monoparasitized host eggs. The results of this study provided useful information on the feasibility of mass production of T. ostriniae via multiparasitism with T. dendrolimi on large eggs of A. pernyi.

Exploring the effects of straw return and environmental factors on the spatiotemporal variation of soil organic matter (SOM) in black soil regions is essential for soil carbon sequestration research. However, studies seldom quantified the effects of long-term straw return on a long-term SOM variation at a regional scale in typical black soil areas. The case was conducted in one of the three major black soil regions in the Northern Hemisphere, where the straw return policy has been implemented for a long time. The study obtained the SOM spatial distribution in 2007, 2009, 2012, 2015, and 2018 with approximately 9000 samples and analyzed the effects of soil types, texture, elevation, and human management on the spatiotemporal variation. The results indicated that from the 1980s to 2007, before the straw return policy implementation, the mean SOM content decreased from 24.38 g kg−1 to 18.94 g kg−1. In contrast, the mean SOM content gradually increased from 2007 to 2018 after implementing straw return practices. In addition, the area of SOM within 20–30 g kg−1 increased gradually, with 32.2%, 40.5%, 50.2%, 49.4%, and 60.5% in 2007, 2009, 2012, 2015, and 2018, respectively. Surprisingly, the SOM within 30–40 g kg−1 emerged in 2018. The results indicated that returning straw to the field might promote SOM accumulation. However, the SOM contents in Phaezems (19.25–21.82 g kg−1) were lower than that in natural Phaezems (40–60 g kg−1), indicating severe degradation. The clay content positively correlated to SOM and was a major explanatory variable for the response of SOM to straw return. Straw return practices are promising measures in the black soil region and are worth exploring more effective approaches to allow straw return to play a better role.