Dispersal of single‐ and double‐brood populations of the European earwig,Forficula auricularia: a mark‐recapture experiment

Quantitative information on dispersal of insects should be taken into consideration for making efficient pest management decisions. Such information was not available for the European earwig, Forficula auricularia L. (Dermaptera: Forficulidae), an important biocontrol agent in fruit orchards. A mark‐recapture experiment was carried out in Belgian orchards, where marked earwigs were released at a single point and recaptured after 1 month. Dispersal from this release point was analysed using an analytical formula of a simple diffusion model with disappearance (e.g., as a result of death) derived by Turchin & Thoeny (1993; Quantifying dispersal of southern pine beetles with mark‐recapture experiments and a diffusion model. Ecological Applications 3: 187) . The cumulative number of recaptured earwigs as a function of the distance of release was used to fit the model and estimate parameters. A derived expression, in terms of these parameters, was used to estimate the frequency distribution of the population, as the radius of a circle enclosing various proportions of the earwigs’ dispersal distances. In Belgium, populations of the European earwig can have two life‐history strategies, single‐ (SBP) and double‐brood populations (DBP). Therefore, mark‐recapture experiments were carried out on both population types. We fitted data from SBP (n = 10) and DBP (n = 16) successfully in both the diffusion model and in an exponential curve. Because of the biological relevance, estimates of the diffusion model were used for calculating the frequency distributions. Males and females dispersed the same distances. No differences were found between orchards with different spatial structures (apple and pear). According to literature data, mobility of earwigs is very low compared with other arthropods, which has consequences for the efficiency of biocontrol interventions, like mass releases of earwigs or the use of hedgerows for the establishment of healthy (source) populations. Quantitative results revealed that earwigs of SBP dispersed four times further than earwigs of double‐brood populations. For instance, 95% of the population remained within a radius of 28.6 m in SBP and 7.54 m in DBP.     

Abundance,interannual variation and potential pest predator role of two co‐occurring earwig species in citrus canopies

Earwigs are usually considered pest predators in orchards. Because of its worldwide distribution, most research on earwigs focuses on the European earwig Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae). However, very little is known of this species in Mediterranean citrus orchards. Earwigs and aphids were collected monthly during 5 years (2006–2010) from citrus canopies. Two species of earwigs were found: F. auricularia and Forficula pubescens Gené (=Guanchia pubescens), with the latter seldom cited in the literature. The goals of this study were (i) to document the abundance of these two earwig species in Mediterranean citrus canopies; (ii) to determine whether they are positively or negatively associated with each other, or randomly distributed; (iii) to measure the interannual variation of the abundance of both species during a 5‐year period and (iv) to evaluate the potential role of earwigs as pest predators in citrus canopies. As compared to colder regions, F. auricularia active period in citrus canopies in our study site lasted longer. Both species co‐occurred randomly in canopies. In 2006, both species showed approximately the same abundance, but in 2010, F. pubescens abundance in canopies was 28 times greater than that of F. auricularia. The potential role of earwigs as pest predators is higher in the Mediterranean than in other colder regions, because of the longer active period. F. auricularia is a sedentary generalist predator, already present in citrus canopies at the onset of most pest outbreaks, while F. pubescens arrived later to the canopies, but most likely was abundant enough to contribute in the control of citrus pests.     

Partial characterization and isolation of earwig `allatostatins'': biological activities in earwigs and cockroaches

Allatostatins are a family of neuropeptides first isolated from the cockroach, Diploptera punctata, that inhibit juvenile hormone production in that species (but do not do so in earwigs), and inhibit hindgut muscle contractions in some insects, including the earwig, Euborellia annulipes. We examined whether material from earwig brains is similar to cockroach allatostatins biochemically, immunologically and physiologically. Brain extracts from adult female earwigs were separated by high performance liquid chromatography (HPLC), followed by radioimmunoassay using antibodies to cockroach allatostatin (Dip-AST). Fractions that co-eluted with cockroach allatostatins were immunoreactive, and at least two peaks of immunoreactivity were detected. Material from each peak at 10 nM Dip-AST equivalents inhibited juvenile hormone biosynthesis in vitro by corpora allata of 2-day virgin D. punctata cockroaches; 1 nM was less effective, and non-immunoreactive fractions failed to inhibit juvenile hormone biosynthesis. Both crude and Sep-Pak (Waters) purified extracts of brains of earwigs containing 1 nM Dip-AST equivalents failed to suppress hindgut contractions in vitro of 2-day earwigs and of brooding female earwigs. In contrast, 1 nM cockroach allostatin 1 (Dip-AST 7) reversibly inhibited hindgut contractions in vitro. These results suggested the presence of another brain factor, such as proctolin, that counteracts the inhibitory effects of Dip-AST. In support of this hypothesis, proctolin stimulated hindgut contractions in vitro at 1 nM; the effects of equal concentrations of allatostatin and proctolin varied with the stage of the female. Furthermore, HPLC-separated fractions that co-eluted with cockroach allatostatin and were immunoreactive with antibodies to Dip-AST suppressed hindgut contractions in vitro of 2-day female earwigs. Finally, crude brain extracts of earwigs suppressed earwig juvenile hormone biosynthesis in vitro in glands of low, but not in glands of high, activity. Thus, earwig brain extract after HPLC separation has Dip-AST-like material that inhibits cockroach corpora allata and suppresses earwig hindgut contractions. Sep-Pak-extracted earwig brain material, however, does not inhibit earwig gut contraction. Although synthetic Dip-AST 7 does not inhibit juvenile hormone synthesis by earwig corpora allata, there is heat-stable material in earwig brain extract that does have this action.     

Compatibility between Forficula auricularia and entomopathogenic nematodes to be used in pome fruit pest management

Use of predators, parasitoids and entomopathogens as biocontrol agents in pome fruit production can lead to more efficient and sustainable pest management programmes. The European earwig (Forficula auricularia Linnaeus [Dermaptera: Forficulidae]) is a major predator of key pests in pome fruit orchards, and entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae are obligate parasites of a large number of insect species. Therefore, the interaction between earwigs and EPNs can play an important role in pest management programmes. Susceptibility of the European earwig to Steinernema carpocapsae, Steinernema feltiae (Steinernematidae) and Heterorhabditis bacteriophora (Heterorhabditidae) was evaluated. S. carpocapsae was the only tested EPN capable of killing the European earwig. However, the European earwig can detect the presence of S. carpocapsae and therefore avoid nematode‐treated shelters. An earwig deterrent activity in EPN‐killed codling moth larvae that reduces the foraging of European earwig on insect cadavers containing nematodes and allows nematodes to complete their life cycle was also assessed with the three species of nematodes. These findings suggest a positive compatibility between the European earwig and EPNs.     

Predation potential of the earwig Euborellia annulipes on fruit fly larvae and trophic interactions with the parasitoid Diachasmimorpha longicaudata

The earwig Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae), a generalist predator, has been observed in fruits infested with fruit fly larvae, which are frequently parasitized by parasitoid wasps. Neither the capacity of earwigs to predate on fruit flies nor intraguild interactions between earwigs and fruit fly parasitoids have been investigated. Here, we studied in laboratory conditions the predation on the fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) by the earwig E. annulipes, and whether parasitism of fruit fly larvae by the parasitoid wasp Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) influences predation by the earwig. We evaluated the predation capacity, functional response and prey preference of E. annulipes for parasitized and non-parasitized fruit fly larvae in choice and no-choice tests. We found that earwigs prey on second- and third-instar larvae and pupae of C. capitata and consumed larger numbers of second-instar larvae, followed by third-instar larvae and pupae. Females prey on larger numbers of fruit flies than did males, regardless of the prey developmental stage, but both sexes exhibited a type II functional response. Interestingly, males killed but did not consume fruit fly larvae more than did females. In no-choice tests, earwig females consumed equal numbers of parasitized and non-parasitized fruit fly larvae. However, in choice tests, the females avoided feeding on parasitized larvae. Subsequent tests with hexane-washed parasitized and non-parasitized larvae showed that putative chemical markings left on fruit flies by parasitoids did not drive the earwig preference towards non-parasitized larvae. These findings suggest that E. annulipes is a potential biological control agent for C. capitata, and that, because the earwig avoids consuming larvae parasitized by D. longicaudata, a combination of the two natural enemies could have an additive effect on pest mortality.     

Temporal activity of spiders and earwigs during winter in apple trees under a Mediterranean climate

It is well known that spiders are present in high numbers in orchards and may contribute to biocontrol. Some recent studies in central Europe further showed that some spiders are active year-round and consume pests even in winter. Using cardboard traps laid every two weeks, we carried out a survey to determine which spider and earwig species are active from September to May in an experimental, pesticide-free, apple orchard under a Mediterranean climate. We observed that spider activity was never completely absent. The structure of the spider communities showed a marked seasonality in three periods (so-called ‘autumn’, ‘winter’ and ‘spring’). Only two spider genera, Philodromus and Trachelas, were highly active in winter (percentage of catches during this season above 40%) and six others (Lathys, Clubiona, Gnaphosa, Theridion, Phrurolithus) had moderate activity (between 20 and 40%). The two earwig species had different patterns of winter activity with Forficula auricularia almost absent whereas F. pubescens was moderately active on trees. Spider community abundance, diversity and evenness significantly decreased between autumn and winter and remained low in the following spring probably because the attractiveness of the traps is much lower at this time of year due to mild temperatures and the presence of leaves on the trees. Winter-active spiders could contribute to pest biocontrol during the cold season and we advocate that the use of broad-spectrum pesticides at the end of winter, as classically applied in orchards, may be counter-productive for pest control.     

Parasitism and predation as agents of mortality of winter moth populations in neglected apple orchards in Nova Scotia

Abstract.

• 1 This study compared the roles of pupal mortality and parasitism in winter moth (Operophtera brumata) population dynamics in Nova Scotian apple orchards and assessed the importance of beetles as pupal predators.
• 2 The component of pupal mortality termed predation accounted for greater stage-specific mortality of winter moth than parasitism by Cyzenis albicans in four neglected orchards.
• 3 Parasitism by Cyzenis albicans was not spatially density-dependent in any orchard, whereas the predation component of pupal mortality was spatially density-dependent in the two orchards most densely populated by winter moth.
• 4 Field experiments indicated that over 60% of pupal predation may be attributed to beetles, and that about 46% of pupal predation occurred within 4 weeks after pupal drop.
• 5 Mortality of introduced populations of winter moth in Nova Scotia resembles that of native populations in England where density-dependent predation regulates the winter moth population and reduces the parasitoid population to minimal levels. The situation in Nova Scotia appears to have changed appreciably since the establishment of parasitoids into the system in the 1950s.

     

OBSERVATIONS ON BROWN ROT (SCLEROTINIA FRUCTIGENA) OF APPLES IN RELATION TO INJURY CAUSED BY EARWIGS (FORFICULA AURICULARIA)

Observations in West Midlands orchards in 1947–50 on the apple varieties Cox's Orange Pippin and Laxton's Superb showed that brown rot was often associated with shallow holes in the fruit. Laboratory experiments with undamaged apples proved that earwigs ( Forficula auricularia ) could cause this type of injury.
Bands of sacking soaked in BHC placed around trunks of Laxton's Superb trees in 1949 and 1950 trapped many earwigs; less brown rot occurred in the banded than on control trees. A survey of picked fruit in 1950 showed close correlation between degree of earwig damage and amount of brown rot.
Earwig damage was appreciable in fruit from ten out of thirteen grass orchards, but was negligible in fruit from nine arable plantations.     

European earwig (Forficula auricularia) as a novel host for the entomopathogenic nematode Steinernema carpocapsae

The natural history of many entomopathogenic nematode species remains unknown, despite their wide commercial availability as biological control agents. The ambushing entomopathogenic nematode, Steinernema carpocapsae, and the introduced European earwig, Forficula auricularia, forage on the soil surface. Since they likely encounter one another in nature, we hypothesized that earwigs are susceptible to nematode infection. In the laboratory, the LC₅₀ for F. auricularia was 226 S. carpocapsae/earwig and the reproductive potential was 123.5 infective juvenile nematodes/mg tissue. This susceptibility depended on host body size with significantly higher mortality rates seen in larger earwigs. In a study of host recognition behavior, S. carpocapsae infective juveniles responded to earwig cuticle as strongly as they did to Galleria mellonella cuticle. We also found that earwigs exposed to S. carpocapsae cleaned and scratched their front, middle and back legs significantly more than controls. Coupled with previous field data, these findings lead us to suggest that F. auricularia may be a potential host for S. carpocapsae.     

Parasitism of the common earwigForficula auricularia [Dermaptera: Forficulidae] by tachinid flies in an apple orchard

Earwigs (Forficula auricularia L.) were collected from an untreated apple orchard every 2 weeks from June to October 1979. Percentage parasitism at the times of collection was calculated from the numbers of parasitoids that emerged. Two tachinidsRhacodineura pallipes Fallen andDigonochaeta spinipennis Meigen parasitised earwigs, starting between 21 June and 5 July and continuing through July. Parasitism byR. pallipes reached a peak of 16 % in late July; fewer earwigs were parasitised byD. spinipennis. Both tachinids had one generation per year;D. spinipennis overwintered as puparia, andR. pallipes as larvae in earwig hosts or as adults. In the orchard, puparia of both tachinid species were hyperparasitised byDibrachys cavus (Walker) (Pteromalidae) andPhygadeuon vexator (Thunberg) (Ichneumonidae).     

Biology and host range testing of Triarthria setipennis and Ocytata pallipes (Diptera: Tachinidae) for the control of the European earwig (Forficula auricularia)

The European earwig (Forficula auricularia) is an invasive species in the Falkland Islands, causing considerable problems for local horticulture, as well threatening indigenous ecosystems. To assess the potential of a classical biological control introduction two parasitoid fly species, Triarthria setipennis and Ocytata pallipes (Diptera: Tachinidae), were collected from sites in southern and northern England and then tested for their suitability as earwig biological controls at Egham, UK. Both species had previously been introduced into North America for earwig control however little is known of their long-term efficacy and host specificity. Host range tests including both target and non-target species were done. As there are no native Dermaptera on the Falkland Islands, tests were restricted to the field cricket Gryllus assimilis and the Dubia cockroach Blaptica dubia, as representatives of insect orders phylogenetically closely related to earwigs. A second cricket species (Gryllus bimaculatus) was included in an egg-depositing experiment for O. pallipes. Both tachinid species successfully parasitised and emerged from earwigs under laboratory conditions but no signs of parasitisation and development were observed in either the cricket or cockroach.     

Optimizing biocontrol using phenological day degree models: the European earwig in pipfruit orchards

• 1 Phenological day degree models are often used as warning systems for the emergence of arthropod pests in agricultural crops or the occurrence of natural enemies of the pest species. In the present study, we report on a case study of the European earwig Forficula auricularia L., which is an important natural enemy in pipfruit orchards, and describe how such a day degree model can be used to avoid negative effects of crucial orchard management, such as spray applications and soil tillage. A precise timing of these interventions in relation to the phenology of natural enemies will enhance biocontrol.
• 2 Earwig population dynamics are characterized by single‐ and double‐brood populations, each with specific biological characteristics.
• 3 A day degree model capable of predicting the phenology of local earwig populations of both population types was developed. The model was checked for accuracy by comparing the first field observation dates of various life stages with predicted values using temperature data from the nearest weather station. In addition, variation in development time was assessed using field data.
• 4 The model was able to make predictions on a global scale. Although single‐ and double‐brood populations differ in phenology, the predictions of first appearance dates were similar. Variation in development time showed that single‐brood populations were more synchronized.
• 5 Our phenological model provides an accurate tool for predicting and simulating earwig population dynamics, as well as for enhancing the biocontrol of pests in pipfruit orchards.

     

Earwig (Forficula auricularia) predation on the woolly apple aphid, Eriosoma lanigerum

Woolly apply aphid predation by the common earwig, Forficula auricularia L., and other predators was compared in high, intermediate and low earwig density plots of mature apple trees at an experimental orchard in the Netherlands. Aphid colonies were discovered and exterminated primarily by earwigs much more rapidly in the high and intermediate earwig density plots than in the low density plots. Where earwigs were excluded from trees by Tanglefoot bands around the trunks, woolly apple aphids infested 30–35% of new growth shoots whereas less than 10% of the shoots were infested where earwigs were relatively abundant.Several factors including the availability of alternate prey (e.g. Aphis pomi De Geer), earwig developmental phenology and weather probably influenced the outcome of the predation experiments. Nevertheless earwigs play an important role in suppressing woolly apple aphid populations and are potentially important, naturally occurring biological control agents for this pest.

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Résumé L'action prédatrice exercée sur le puceron lanigère par le perceoreille commun, Forficula auricularia, et par d'autres prédateurs, a été comparée dans des parcelles d'un verger expérimental de pommiers adultes aux Pays-Bas. Ces parcelles étaient caractérisées par des densités fortes, intermédiaires, et basses en perce-oreilles. Les colonies de pucerons ont été découvertes et exterminées principalement par les perce-oreilles beaucoup plus rapidement dans les parcelles à forte et moyenne densité de perce-oreilles que dans celles à faible densité. Les pucerons lanigères ont colonisé 30 à 35% des nouvelles pousses lorsque les perce-oreilles étaient exclus par une barrière mécanique (Tanglefoot), alors que moins de 10% des pousses ont été infestées lorsque les perce-oreilles étaient relativement abondants.Plusieurs facterus ont probablement influencé le résultat des expériences de prédation, notamment la présence de proies alternatives (par exemple Aphis pomi), la phénologie du développement des perce-oreilles et le climat. Néanmoins, les perce-oreilles ont joué un rôle important en limitant les populations du puceron lanigère, et constituent potentiellement d'importants agents de contrôle naturel de ce ravageur.

     

Overwintering survival and spring emergence inMeligethes aeneus: Effects of body weight, crowding, and soil treatment withBeauveria bassiana

High overwintering mortality was recorded forMeligethes aeneus in the field in Finland, ranging from 85 to 98% depending on the source of the overwintering population. The main factor explaining, variation in survival was the body weight of the beetles in the autumn: only the heaviest beetles survived. Body weight, on the other hand, was influenced by treatment of the rape field soil withBeauveria bassiana, resulting in a 50% decrease in winter survival compared with the reference. The soil treatment did not appear to have direct mortality effects (pathogenesis) on the beetle neither in the summer nor in the winter, and there was no apparent effect on survival of crowding of the insects at the overwintering site. Density dependence in overwintering survival ofM. aeneus may function through the availability of pollen food in the autumn, and intraspecific competition for it. Treatment of the rape field soil withB. bassiana may be a feasible way to increase, the winter mortality and to lower the pollen beetle populations, but requires further research.     

轮耕对关中一年两熟区土壤物理性状和冬小麦根系生长的影响

针对关中地区土壤连续单一耕作存在的主要问题,进行了土壤轮耕效应研究。2009年至2012年在关中一年两熟区采用连续4a旋耕(RT)、翻耕-免耕-翻耕-免耕(PNT)和深松-免耕-深松-免耕(SNT)3种耕作处理,对土壤容重、紧实度及小麦根系生长进行了研究。结果表明,与试验前相比,夏玉米收获后(2013年10月)两种轮耕处理显著(P0.05)降低了0—10、10—20 cm土壤容重,旋耕处理在0—10 cm处差异不显著,而10—20 cm土壤容重显著增大;与旋耕处理相比,两种轮耕处理0—10、10—20 cm土壤容重在第4季冬小麦整个生育期内变异系数较小,土壤紧实度较低,且改善效果在冬小麦生育中后期10—20 cm土层体现更为显著;旋耕处理0—10、10—20 cm土壤紧实度与含水量均呈显著负相关,相关系数分别为-0.89、-0.85,两种轮耕处理相关性不显著;0—40 cm土层根重密度和根系活力表现为:两种轮耕处理连年旋耕。可见,长期旋耕后进行轮耕(免耕与翻耕、深松)有利于改善土壤物理状况,促进作物根系生长。     

Do night and around-the-clock firefighters’ shift schedules induce deviation in tau from 24 hours of systolic and diastolic blood pressure circadian rhythms?

Systolic (S) and diastolic (D) blood pressures (BP) [SBP and DBP] are circadian rhythmic with period (τ) in healthy persons assumed to be maintained at 24.0h. We tested this assumption in a sample of 30 healthy career (mean >12 yrs) 30-to-46 yr-old male Caucasian French firefighters (FFs) categorized into three groups according to work schedule and duties: Group A – 12 FFs working 12h day, 12h night, and occasionally 24h shifts and whose primary duties are firefighting plus paramedical and road rescue services; Group B – 9 FFs working mostly 12h day and 12h night shifts and whose duties are answering incoming emergency calls and coordinating service vehicle dispatch from fire stations with Group A personnel; Group C – 9 day shift (09:00–17:00h) FFs charged with administrative tasks. SBP and DBP, both in winter and in summer studies of the same FFs, were sampled by ambulatory BP monitoring every 1h between 06:00–23:00h and every 2h between 23:01–05:59h, respectively, their approximate off-duty wake and sleep spans, for 7 consecutive days. Activity (wrist actigraphy) was also sampled at 1-min intervals. Prominent τ of each variable was derived by a power spectrum program written for unequal-interval time series data, and between-group differences in incidence of τ≠24h of FFs were assessed by chi square test. Circadian rhythm disruption (τ≠24h) of either the SBP or DBP rhythm occurred almost exclusively in night and 24h shift FFs of Group A and B, but almost never in day shift FFs of Group C, and it was not associated with altered τ from 24.0h of the circadian activity rhythm. In summer, occurrence of τ≠24 for FFs of Group A and B differed from that for FFs of Group C in SBP (p=0.042) and DBP (p=0.015); no such differences were found in winter (p>0.10). Overall, manifestation of prominent τ≠24h of SBP or DBP time series was greater in summer than winter, 27.6% versus 16.7%, when workload of Group B FFs, i.e. number of incoming emergency telephone calls, and of Group A FFs, i.e. number of dispatches for provision of emergency services, was, respectively, two and fourfold greater and number of 12h night shifts worked by Group B FFs and number of 24h shifts worked by Group A FFs was, respectively, 92% and 25% greater. FFs of the three groups exhibited no winter-summer difference in τ≠24h of SBP or SDP; however, τ≠24h of DBP in Group B FFs was more frequent in summer than winter (p=0.046). Sleep/wake cycle disruption, sleep deprivation, emotional and physical stress, artificial light-at-night, and altered nutrient timings are hypothesized causes of τ≠24h for BP rhythms of affected Groups A and B FFs, but with unknown future health effects.     

Filariomyces forficulae: occurrence and effects on the predatory earwig, Labidura riparia

Filariomyces forficulae occurs commonly on the earwig, Labidura riparia, in Florida. The hypopial stage of a mite, Histiostoma sp., often associated with L. riparia is also sometimes infected by the same fungus. Some other earwig species that occur with L. riparia were not found to be hosts. Sites of fungal infection on the earwig were highly variable and influenced by several factors. F. forficulae was transmitted by several types of insect contact including mating with varying efficiencies and by a mechanical inoculation technique. Developmental time required by the fungus from ascospore to mature perithecia was 10–12 days at 24°C. In laboratory studies there were small but consistent differences between longevities of infected and noninfected groups of earwigs and infected populations of earwigs died sooner than noninfected ones. Infection resulted in differences in pattern of egg production; however, no numerically significant differences in total egg production or egg-hatching ability between the two groups were found.     

Time course study of Bactrocera oleae (Diptera: Tephritidae) pupae predation in soil: the effect of landscape structure and soil condition

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机械化保护性耕作条件下土壤质量的数值化评价

通过9年的长期田间定位试验研究了陕西关中平原中部冬小麦 夏玉米轮作条件下深松耕（ST）、旋耕（RT）、秸秆还（SR）、免耕（NTS）等保护性耕作措施及传统耕作（TT）对土壤理化性状和作物产量的影响,并采用主成分分析方法进行土壤质量的综合评价.结果表明：与传统耕作相比,保护性耕作模式提高了土壤肥力质量,改善了土壤物理环境条件;显著提高了土壤脲酶和碱性磷酸酶的活性;除秸秆覆盖免耕处理的玉米和小麦产量低于传统耕作外,其他保护性耕作措施均不同程度地提高了作物产量,其中小麦增产13%～28%,玉米增产3%～12%.与传统耕作相比,保护性耕作土壤质量指数提高了19.8%～44.0%.综合考虑经济效应和生态效益,隔年深松、秸秆粉碎联合旋耕作业以及秸秆覆盖联合深松作业不仅能增加作物产量还可改善土壤质量,可在研究区进行推广应用.     

Effects of tillage systems on wheat and weed water relationships over time when growing together,in semiarid conditions

Water availability directly influences interactions and competition between weeds and crops. This article is based on the idea that relative water content (RWC) indicates the water uptake within plants and that it is possible to explain the water relationships between plants that are growing together. A field experiment carried out for 3 years (2013–2014, 2014–2015 and 2015–2016) compared the short-term effects of years and tillage systems on wheat grain yield, weed density, wheat-RWC, weed-RWC and soil water content (SWC), at tillering and flowering stages in a winter wheat monoculture system. The three tillage treatments were conventional tillage (CT), minimum tillage (MT) and no-tillage (NT). Wheat grain yield was low all years of study, because of low interannual rainfall, and we did not observe differences between tillage systems. Weed density was also affected by year and not by tillage systems. Lowest winter rainfall (73.4 mm from Nov to Feb) in the last year of the study (2015–2016), decreased the weed density in all tillage systems. Despite the rainfall variability over the 3 years of study, the NT system presented higher weed density (73 plants/m²) than MT and CT systems (39.83 and 46.33 plants/m²). We also observed a higher number of weed species for the NT system, facilitated by a high soil water storage in this system. The wheat-RWC, at tillering stage, varied with years and tillage systems; we found that high winter rainfall (2013–2014) led to higher values in CT (64.5%) compared with MT (52.9%) and NT plots (52.9%). Weed-RWC values did not vary and SWC was greater in NT than in CT and MT. At flowering stage, the year (2015–2016) with highest spring rainfall favoured higher wheat-RWC in NT (56.9%) compared with CT (48.3%). However, the lowest spring rainfall coincided with the lowest weed-RWC, (18% in NT plots) and SWC was always higher in NT soils. The results showed that climatic conditions affected the water competence dynamics between weeds and wheat in different ways. Seemingly, weeds can tolerate a lack of water availability until crop tillering stage independently of tillage system; however, the competition for water was not a problem as crops overcame the high weed density by flowering stage.