Egg parasitism of the yellow rice borer,Scirpophaga incertulas [Lep.: Pyralidae] in Bangladesh deepwater rice

Studies on deepwater rice in Bangladesh from 1977 to 1980 showed that 61–89% of the egg masses of the yellow rice borer,Scirpophaga incertulas (Walker), were attacked by hymenopterous parasites. Egg parasitism increased from 43–48% in broods 2–4 (May–August) to 64–88% in broods 5–6 (September–November). Parasitism was reduced in broods 4 and 5 in 1979 (because of lower host densities) and in 1980 (possibly due to extreme late flooding). Telenomus rowani (Gahan), active throughout the year, parasitized 64% of the eggs in the masses it attacked, 32 larvae/mass surviving.Tetrastichus schoenobii Ferrière first appearing at medium host densities, increased rapidly to attack half of the brood 5 and 6 masses. More than 98% of the eggs in the attacked masses were parasitized, leaving only 1.6 surviving larvae/mass. In 1979 its appearance was delayed by 10 weeks and fewer masses were parasitized due to lower host densities.Trichogramma japonicum Ashmead andTelenomus sp. (a new record) were less important. Multiple parasitism of masses rose from 7% in brood 2 to 28% in brood 5. Egg parasites clearly reduce the numbers ofS. incertulas, a major pest, and thus probably improve the yields of deepwater rice.     

The effect of precipitation on the break of diapause in the white rice borer Rupela albinella (Cr.) in surinam (South America)

Diapause was studied in the white rice borer to find a sound basis for an effective rice stubble destruction programme. Diapausing larvae of this borer remain in the stubble after harvesting and carry the species over a period during which the hostplant may be scarce or absent. The influence of rainfall on the duration of diapause was experimentally analysed. As a rule the higher the amount of precipitation, the sooner the moths make their appearance. This break of diapause is accelerated the longer the diapausing larvae stayed in the dry stubble. It is suggested that under the prevailing weather conditions stubble destruction within one month after harvest will prevent the appearance of the moths.

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Résumé L'auteur a étudié la diapause chez le borer du riz Rupela albinella afin de trouver une base solide pour un programme de destruction des chaumes du riz. Les chenilles en diapause restent abritées dans le chaume après la récolte. L'influence des précipitations sur la durée de la diapause a été analysée expérimentalement. L' auteur observa une corrélation directe entre la quantité des précipitations et l'apparition des papillons. Ce réveil des chenilles en diapause est acceléré en fonction de la durée de leur séjour dans le chaume sec.L'auteur suggère que la destruction des chaumes dans le mois suivant la récolte peut empêcher l'apparition des papillons.

     

Seasonal parasitism by egg parasites of the yellow rice borer,Scirpophaga incertulas [Lepidoptera: Pyralidae]

Scirpophaga incertulas (Walker) [Lep.: Pyralidae] is a common pest of rice in West Bengal, India. A three year study (1978–1981) revealed that egg parasites were important in reducing the borer population in an uninterrupted rice cultivation practice. The parasite activity showed periodical fluctuation coinciding with the moth emergence. It was evident thatTelenomus spp. were most common and most dominating in the early summer crop and became highly adaptive under diverse crop growing situations. Among three species ofTelenomus, T. rowani Gahan was the most abundant durint the summer and winter seasons.Tetrastichus schoenobii Ferriere was second in importance in regulating the borer population and its attack was heaviest on the later broods in rice crops cultivated during winter.Trichogramma japonicum Ashmead was very sporadic and had a particular preference for the dry period. It usually occurred in association with other two parasites in the later part of the year. Parasitism of egg masses by two or more species of the parasites was also common during the peak period of parasite activity.      

再生稻与三化螟越冬幼虫的关系的研究

在华南,秋季水稻收获后,留在田间的一些稻桩,既含有再生稻株,亦藏蛰伏的三化螟幼虫,当再生稻桩率为14％～19％时,其中藏有的三化螟幼虫占该虫总数的47％～65％。由于三化螟得到再生稻株的保护,在整个越冬期间藏于再生株内的蝗虫死亡率偏低,至多为非再生株同时的50％,再生株百株活虫数为26～42头,而非再生株内仅为1～7头。     

Cyanobacteria in the Australian northern savannah detect the difference between intermittent dry season and wet season rain

This research was conducted in the northern Australian savannah at Boodjamulla National Park where cyanobacterial crusts dominate the soil and rock surfaces in between tussock grasses. It is widely accepted that terrestrial cyanobacteria are drought tolerant and rapidly recommence photosynthesis once moisture is available. Initial tests at the research site indicated that cyanobacteria did not respond to rehydration during the dry season, even after several days. We hypothesised that resurrection had not taken place and new growth from survival cells had to take place during the follow-up wet season. To further understand the desiccation–resurrection processes we tested photosystem II (PSII) responses both during the dry and wet seasons. In the 2009 dry season after 125 days without rain, crust samples were regularly rehydrated. Over the 10 day trial cyanobacteria did not recover PSII activity or CO₂-uptake. Although new colonies of Nostoc grew other cyanobacteria remained inactive, even though liverworts and lichens in the same crusts had responded within 24 h. Dry season cyanobacterial crusts were collected in 2010 then reintroduced into their natural environment and exposed to rainfall during the 2011 wet season. Within 24 h PSII in cyanobacteria from a range of crust types had resurrected and CO₂-uptake was verified, although different crust types responded at significantly different rates. These are the first studies that have demonstrated that PSII does not respond to rainfall during the dry season and cyanobacterial function appears controlled by other environmental conditions. It is likely that mass extracellular polysaccharide (EPS) production during the wet season, once dry, protects cyanobacteria from premature resurrection in the dry season. We propose that EPS regulates moisture penetration, thus the resurrection of PSII at the onset of the wet season, at which time moisture and humidity alters the rheological properties of EPS permitting rehydration.     

Phosphorus supply and the growth of frequently defoliated white clover (Trifolium repens L.) in dry soil

A previous study found that increased phosphorus (P) supply to frequently defoliated white clover plants, growing in a low-P, dry soil, alleviated water stress symptoms and increased plant recovery on rewatering. In this study we determined how these stresses influence white clover growth. Measurements were made of the leaf canopy, stolon infrastructure and root system of the white clover plants growing in a low-P soil. Treatments included the factorial combination of four levels of P supply, two defoliation frequencies and two soil water treatments. White clover growth declined markedly when P-deficient plants were exposed to frequent defoliation and dry soil conditions. Leaf area was more affected than other parameters, in that the combination of stresses reduced leaf area to 2% of maximum observed for infrequently defoliated plants growing in high-P soil, with adequate water. Increased P supply generally increased the growth of all plant parts. Frequently defoliated plants growing in dry soil produced similar or greater leaf mass and leaf area as plants from similar treatments growing in wet soil, when the P supply increased to 50 mg P kg-1 soil. Higher P rates were able to negate the effect of dry soil on these frequently defoliated plants, as a result of larger water and P uptake. Also, the frequently defoliated plants with restricted root growth did not respond to a small increase in P supply (17 mg P kg-1 soil) for the leaf growth, irrespective of whether they were growing in wet or dry soil. Infrequently defoliated plants with greater root growth, compared to frequently defoliated plants, more than doubled their leaf mass with this P treatment.     

Movement of Mexican rice borer (Lepidoptera: Crambidae) through the Texas rice belt

Pheromone-baited traps were used to monitor the movement of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), through the Texas rice belt from 2000 to 2005. Based on location of discovery in each county and year, the average rate of spread from 1980 to 2005 was 23 km/yr. From 2000 to 2005, the leading edge of the infestation has moved 16.5 km/yr toward Louisiana. The 1.8-fold increase (99% confidence interval) of the area occupied from 2000 to 2005 in the Texas rice belt indicates an expansion of the distribution of E. loftini. If movement continues to occur at similar rates, E. loftini will reach Louisiana by 2008.     

Correlation between large-scale atmospheric fields and the olive pollen season in Central Italy

Olives are one of the largest crops in the Mediterranean and in central and southern Italy. This work investigates the correlation of the Olea europaea L. pollen season in Perugia, the capital city of the region of Umbria in central Italy, with atmospheric parameters. The aim of the study is twofold. First, we study the correlation between the pollen season and the surface air temperature of the spring and late spring in Perugia. Second, the correlation between the pollen season and large-scale atmospheric patterns is investigated. The average surface temperature in the spring and late spring has a clear impact on the pollen season in Perugia. Years with higher average temperatures have an earlier onset of the pollen season. In particular, a 1°C higher (lower) average surface temperature corresponds to an earlier (later) start of the pollen season of about 1 week. The correlation between the pollen season and large-scale atmospheric patterns of sea level pressure and 500-hPa geopotential height shows that the cyclonic activity in the Mediterranean is unequivocally tied to the pollen season in Perugia. A larger than average cyclonic activity in the Mediterranean Basin corresponds to a later than average pollen season. Larger than average cyclonic activity in Northern Europe and Siberia corresponds to an earlier than average pollen season. A possible explanation of this correlation, that needs further investigation to be proven, is given. These results can have a practical application by using the seasonal forecast of atmospheric general circulation models.     

Water relations of Caatinga trees in the dry season

The Caatinga is one of the world's richest dry forests. This forest occurs only in Brazil, but is the least studied and protected Brazilian ecosystem. There are few reports about drought tolerance mechanisms in Caatinga trees. This work evaluates water relations of six adult species in the middle of the dry season to further understand water relations in this ecosystem, which will be important for future reforestation and management projects. Based on results, the trees were classified into four groups: (I), Mimosa caesalpiniifolia had low leaf water potential (Ψ_w) at predawn and no significant decrease at midday. Stomatal conductance (g_s) analyses indicates that plants have reached its lowest Ψ_w; (II), Caesalpinia pyramidalis and Auxemma oncocalyx had low Ψ_w at predawn and significant decrease at midday. For these species the recuperation of water status at night may have been sufficient for maintaining stomata open during the day; (III), Caesalpinia ferrea and Calliandra spinosa had relatively high Ψ_w at predawn and a significant decrease at midday. These species might maintain their water status similar to individuals of group II, but they might also have deeper root systems; and (IV), Tabebuia caraiba with the highest Ψ_w at predawn and no significant decrease at midday, possibly indicating a combination of good stomatal control of water loss and a deeper root system. Moreover, except for individuals of group I, both in species with lower and higher Ψ_w at predawn it was not observed strong inhibition of g_s.     

氮肥和密度对双季杂交稻干物质积累和产量的影响

以早稻“陆两优996”,晚稻“Y两优86”为试验品种,设4个氮肥水平、3个栽插密度,研究了双季超级杂交稻在不同氮肥水平和栽插密度条件下的干物质积累、冠层光能截获率和产量及其构成因素的特性.结果表明:早晚稻产量与氮肥水平呈现单峰曲线关系,以中氮处理产量最高,分别为10245.04和11015.37 kg· hm-2,有效穗随施氮量的增加而增加,但每穗实粒数以中氮处理(早N135、晚N180)最高,分别达143.92和142.80粒·穗-1;3个栽插密度之间早晚稻产量差异不显著,且对早稻产量构成因子无显著影响,但对晚稻有效穗、结实率的影响有极显著差异,高密度处理有效穗高、结实率低,低密度处理有效穗低、结实率高;氮肥与密度互作对早晚稻产量均无显著影响,但从高产高效节氮栽培综合考虑,双季早稻“陆两优996”和晚稻“Y两优86”的适宜施氮量分别为135和180 kg· hm-2,栽插密度为45×104和30×l04穴·hm-2.     

Scanning the European corn borer (Ostrinia spp.) genome for adaptive divergence between host-affiliated sibling species

It has recently been shown that the European corn borer, a major pest of maize crops, is actually composed of two genetically differentiated and reproductively isolated taxa, which are found in sympatry over a wide geographical range in Eurasia. Each taxon is adapted to specific host plants: Ostrinia nubilalis feeds mainly on maize, while O. scapulalis feeds mainly on hop or mugwort. Here, we present a genome scan approach as a first step towards an integrated molecular analysis of the adaptive genomic divergence between O. nubilalis and O. scapulalis. We analysed 609 AFLP marker loci in replicate samples of sympatric populations of Ostrinia spp. collected on maize, hop and mugwort, in France. Using two genome scan methods based on the analysis of population differentiation, we found a set of 28 outlier loci that departed from the neutral expectation in one or the other method (of which a subset of 14 loci were common to both methods), which showed a significantly increased differentiation between O. nubilalis and O. scapulalis, when compared to the rest of the genome. A subset of 12 outlier loci were sequenced, of which 7 were successfully re‐amplified as target candidate loci. Three of these showed homology with annotated lepidopteran sequences from public nucleotide databases.     

New in silico insight into the synteny between rice (Oryza sativa L.) and maize (Zea mays L.) highlights reshuffling and identifies new duplications in the rice genome

A unigene set of 1411 contigs was constructed from 2629 redundant maize expressed sequence tags (ESTs) mapped on the maizeDB genetic map. Rice orthologous sequences were identified by blast alignment against the rice genomic sequence. A total of 1046 (74%) maize contigs were associated with their corresponding homologues in the rice genome and 656 (47%) defined as potential orthologous relationships. One hundred and seventeen (8%) maize EST contigs mapped to two distinct loci on the maize genetic map, reflecting the tetraploid nature of the maize genome. Among 492 mono-locus contigs, 344 (484 redundant ESTs) identify collinear blocks between maize chromosomes 2 and 4 and a single rice chromosome, defining six new collinear regions. Fine-scale analysis of collinearity between rice chromosomes 1 and 5 with maize chromosomes 3, 6 and 8 shows the presence of internal rearrangements within collinear regions. Mapping of maize contigs to two distinct loci on the rice sequence identifies five new duplication events in rice. Detailed analysis of a duplication between rice chromosomes 1 and 5 shows that 11% of the annotated genes from the chromosome 1 locus are found duplicated on the chromosome 5 paralogous counterpart, indicating a high degree of re-organisations. The implications of these findings for map-based cloning in collinear regions are discussed.     

Seasonal expression of Bt proteins in transgenic rice lines and the resistance against Asiatic rice borer Chilo suppressalis (Walker)

Laboratory bioassays and field surveys were carried out to compare the resistance of three transgenic rice (Oryza sativa L.) lines including Bt-DL expressing a single gene cry1Ab, Bt-KF6 expressing stacked genes cry1Ac and CpTI genes and Bt-SY63 expressing a fusion gene cry1Ab/cry1Ac, respectively, to an important rice pest Chilo suppressalis (Walker). In addition, enzyme-linked immunosorbent assays (ELISA) were conducted to monitor the Bt protein expressions in rice leaves and stems at different rice growth stages. Results showed that all the transgenic rice lines exhibited significantly high resistance to the pest compared with their corresponding nontransformed isolines. Among the transgenic rice lines, Bt-SY63 and Bt-KF6 had higher resistance to C. suppressalis at early growth stage, but lower resistance at late stages, while the pest resistance of Bt-DL was relatively stable throughout the growing season. The results were consistent with ELISA results showing that Bt protein levels in Bt-SY63 or Bt-KF6 leaves decreased in late growth stages, but were relatively stable in Bt-DL at all growth stages. This demonstrates that the resistance to a pest by Bt plants is positively correlated with Cry protein expression levels in plant tissues. Compared with Bt-SY63 and Bt-KF6, the Bt protein expression levels were significantly lower in Bt-DL, while its resistance to C. suppressalis was the highest. This may suggest that C. suppressalis is more susceptible to Cry1Ab than to Cry1Ac. The data from the current study are valuable for decision-making for commercial use of Bt rice lines and development of appropriate pest control and resistance management strategies for the transgenic rice lines.     

The influence of nitrogen fertiliser on the population development of the cereal aphids Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.) on field grown winter wheat

The effect of nitrogen fertiliser on populations of the cereal aphids Sitobion avenae and Metopolophium dirhodum on winter wheat was investigated in a three year field experiment. Naturally occurring aphid populations were monitored on three nitrogen treatments; none, nitrogen application using Canopy Management guidelines (130–210 kg ha^-1) and conventional practice (190 kg ha^-1). Inoculations of laboratory reared S. avenae were used to enhance field populations on half the plots. Natural populations of M. dirhodum remained below the current UK spray threshold level of two-thirds of shoots infested at the start of flowering, or five aphids per shoot in all years, whilst populations of S. avenae exceeded the threshold in all years. The response of the two species to nitrogen differed. Significantly higher populations of M. dirhodum were recorded in both treatments which received nitrogen in all years, whilst the response of S. avenae varied between years. In 1994 and 1995 when environmental conditions favoured aphid development, higher populations were recorded in the two treatments which received nitrogen. In 1993 when high rainfall created unfavourable conditions, higher populations were recorded in the plots receiving no nitrogen. Differences in peak density and cumulative aphid index of S. avenae resulted from differences in the rate of population increase between ear emergence and peak density on the different treatments. Populations prior to ear emergence were higher in the plots which received nitrogen but the differences were not statistically significant. There was no evidence of a difference in the timing of population decline in the different treatments. In 1993 higher levels of infection by entomopathogenic fungi were observed in all treatments. Significantly higher levels of infection were recorded in the treatments receiving nitrogen, which may have accounted for the lower S. avenae populations recorded. It is possible that the larger canopies recorded in these treatments produced conditions which favoured infection by fungi, thereby limiting aphid population growth. The results indicate that application of nitrogen increases natural populations of M. dirhodum, and under favourable conditions, populations of S. avenae. However, in suboptimal climatic conditions, the application of nitrogen fertiliser can lead to lower populations of 5. avenae. The data also suggest that there is no consistent difference between a conventional and Canopy Managed approach to nitrogen fertiliser use in terms of the risk of infestation by cereal aphids.     

Correlation between biomass and medium conductivity in suspension cultures of rice cells

Summary An intercept in the linear relationship between the biomass increase and decrease in medium conductivity was found in suspension cultures of rice cells. It was due to the. consumption of medium salts by the cells during the lag phase. An equation was established for accurate monitoring of the cell growth which aids understanding of the cell physiology especially during the initial stage of cell growth.