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1.
The banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), is the most economically important pest of banana (Musa spp.) fields in Hawaii. Recently, there has been a concerted effort in Hawaii to learn more about the biology and ecology of this pest. However, limited work has been directed at determining the distribution of P. nigronervosa in banana fields and developing an integrated pest management plan. Therefore, a survey was conducted in banana fields throughout the Hawaiian Islands to determine the distribution and density of P. nigronervosa within banana mats from plants of different stages. Another aim was to determine whether the presence of ants on banana plants could be used as a reliable indicator of aphid infestations. Results of the survey showed that plants < or = 1.5 m (small sucker) in height contain the highest aphid populations per meter in plant height and that mother plants (> or = 2.5 m) had the lowest aphid counts and rate of infestation compared with small and intermediate suckers (> 1.5 < 2.5 m). More specifically, aphid population was reduced by approximately 12 aphids for every meter increase in plant height and that aphids are rarely found > or = 2.5 m within the plant canopy. Although there was an increase likelihood of finding ants on banana plants with higher aphid densities, results suggest that ants would be present on plants in the absence of aphids. Implications of these and other findings with respect to sampling and managing P. nigronervosa and associated Banana bunchy top virus are discussed.  相似文献   

2.
The impact of natural coccinellid larvalpredation on the balsam twig aphid was evaluated bysystematically removing coccinellid egg masses in a6–8 year-old balsam fir (Abies balsamea)Christmas tree plantation in southwesternQuebec. Among coccinellid species hunting on firfoliage during development of Mindarus abietinusfundatrices in May, the indigenous Anatis mali was by far the most abundant and themain one to oviposit on trees. Comparison of trees onwhich coccinellid larval predation was excluded withcontrol trees showed that A. mali had a markedimpact both during and after the phase of rapid M. abietinus population growth that followedfundatrix maturation. On trees where coccinellidlarvae were allowed, aphid colonies became inactive(i.e. no live aphids in the colony) about two weeksearlier than on controls. A strong dampening effect onaphid density was also observed in those colonies thatremained active until the end of the aphid life cycle.Predation on aphid colonies reduced sexualsproduction, as the density of M. abietinusoverwintering eggs per shoot subsequently was reducedby 32%. Predation by coccinellid larvae occurred toolate to prevent needle damage to current year shoots,which affects the aesthetic value of Christmas trees.However, current year shoots measured in the mid-crownof trees late in the season were 19% longer on treeswhere aphid predation by coccinellid larvae wasallowed, compared with trees where they were excluded.Rearing all larval stages of A. mali on 4thinstar and adult sexuparae of M. abietinusindicated an average consumption of 269 aphids tocomplete larval development and pupate, which wasequivalent to at least seven colonies of M.abietinus at maximum aphid density at theexperimental site. Anatis mali is an importantnatural control factor of balsam twig aphid inChristmas tree plantations, hence its activity shouldbe protected and possibly stimulated by favourablepest management practices.  相似文献   

3.
Eight species of the brown alga Sargassum have been recorded from Tung Ping Chau Marine Park in Hong Kong and the phenology of four of these was monitored from 1996 to 2000. All four species followed a typical growth cycle of Sargassum species reported elsewhere but with some annual variations. For S. hemiphyllum, the maximum mean (±SD) plant length, ranging from 38.5 ± 10.5 to 61.9 ± 19.9 cm, was recorded in January to March. The peak reproductive season was also mainly in February to March with up to 89% of the plants being reproductive. Some plants, however, remained reproductive until May. For. S. henslowianum, the maximum mean plant length, ranging from 45.5 ± 25.5 to 77 ± 24.8 cm, was recorded mainly in November to January. The peak reproductive season was in November to February with up to 100% of the plants being reproductive. For S. siliquastrum, the maximum mean plant length, ranging from 48.2 ± 29.9 to 63.4 ± 22.1 cm, was also recorded mainly in January. The reproductive plants were found mainly between late December and mid February with up to 98% of the plants being reproductive. For. S. patens, the maximum mean plant length ranging from 87.6 ± 62.4 to 118.7 ± 41.3 cm was recorded in January to March. Reproduction of this species was not monitored. Changes in water temperature over seasons were likely to be critical in affecting the phenological patterns of these species.  相似文献   

4.
Banana bunchy top disease caused by Banana bunchy top virus is the most serious viral disease of banana and plantain worldwide. The virus is transmitted by the aphid vector Pentalonia nigronervosa in a persistent manner. This paper deals with the effect of the interaction between plant growth promoting endophytic bacteria, Banana bunchy top virus, and the banana aphid Pentalonia nigronervosa in the expression of Pathogenesis-related proteins (PR-proteins) and defense enzymes in banana. The existence of virus in the aphids was confirmed by ELISA, DIBA and PCR. PCR could amplify 1100-bp replicase gene of BBTV from viruliferous aphids. A significant increase in the enzymatic activity of all measured PR proteins and defense enzymes, as compared to control plants, was seen in the plants inoculated with endophytic bacteria and challenged with viruliferous aphids. Native gel electrophoresis revealed expression of more isoforms of PR proteins viz., peroxidase and chitinase in the banana plants challenged with mixtures of plant growth promoting endophytic bacteria and viruliferous aphids. Enhanced activity of a PR-2 protein viz., β-1,3-glucanase was also noticed in the viruliferous aphids infested plants. Some of the defense-related enzymes viz., Polyphenol oxidase and Phenylalanine ammonia lyase and phenolic compounds were also upregulated, up to 5 days after aphid infestation and thereafter there was a reduction in the enzymatic activity. Thus, there exist a differential accumulation of PR proteins and defense-related enzymes, when there is tri-tropic interaction between endophytic bacteria, virus, and insect and the role of the endophytic bacteria in the defense mechanisms against insect pests needs to be elucidated.  相似文献   

5.
Seasonal incidence of aphid, Amphorophora ampullata on Hypolepis polypodioides was recorded throughout the year from November 2012 to November 2013 at weekly interval. Peak incidence of aphid was recorded during third week of November 2012 (25.94 ± 2.39 aphids/pinna), later the aphid population gradually decreased from December 2012 onwards and reached below threshold level during the last week of January (0.1 ± 0 aphids/pinna). The aphid population starts building up again from first week of February 2013 (1.6 ± 0.13 aphids/pinna) and attained its peak in the last week of August (32.17 ± 1.22 aphids/pinna) then decreased gradually in the first week of September (20.82 ± 4.70 aphids/pinna). Aphid densities again increased gradually from second week of September (21.62 ± 3.02 aphids/pinna) to November 2013 and reached maximum aphid densities during November (56.55 ± 4.34 aphids/pinna). Among weather parameters, aphid population showed significant positive correlation with relative humidity during morning hours.  相似文献   

6.
Aphidophagous coccinellid larvae have a wide range of potential prey in alfalfa and during times of low aphid abundance, larvae may supplement their diet with alternative prey. To understand the effects of the seasonal aphid availability on alternative prey use, an order-specific monoclonal antibody, DrosW-VI-B8, was used to examine the frequency of dipteran predation by these important natural enemies. Over 400 larvae were hand-collected from alfalfa and, in parallel, arthropod abundance was recorded. Harmonia axyridis and Coccinella septempunctata larvae were abundant early in the season when aphid populations were at their peak and Coleomegilla maculata larvae were collected later in the season when potato leafhoppers were abundant in the alfalfa. A relatively low proportion of field-collected H. axyridis, C. septempunctata, and C. maculata tested positive for dipteran proteins throughout the season. Similar to prior studies examining stage differences in coccinellid food breadth, older instars tested positive for dipteran proteins (3rd instar, 6% positive; 4th instar, 7% positive) but no early instars screened positive. This study provides a valuable insight into the trophic linkages that exist between coccinellid larvae and Diptera.  相似文献   

7.
The red-striped soft scale Pulvinaria tenuivalvata (Newstead) (Hemiptera: Coccidae) is a pest attacking sugarcane (Saccharum officinarum L.) recently recorded in Upper Egypt governorates. Sugarcane plantations in Upper Egypt were thoroughly inspected for 2 years from January 2001 until December 2002 to record infestation with P. tenuivalvata and its population density. Also, crops, plants and weeds growing near sugarcane fields were examined to determine the host range of this pest. A pest species of soft scale insect has become increasingly dangerous on sugarcane in Egypt. The insect occurrence was from 3?–?8 months on the infested hosts. The red-striped soft scale was active from May until December. Sugarcane, Cogon grass and Deccan grass were the hosts, which harboured all insect stages. The infestation was restricted on the lower surface of the leaves and lower numbers were found on the upper surface. Damage to sugarcane including withering of the leaves and reduced yield, with reduction in the sucrose content of the juice. The growth rate of pest population infesting the sugarcane plants in season 2001, increased gradually during the period from June to September and decreased from October to December. The same trend was found for the growth rate of population in season 2002. At the high growth rate it is advisable to use chemical control. The effect of weather factors on the population density of the P. tenuivalvata (the correlation between the total number of pests and temperature or RH.) were positive to both seasons. Many predators and parasites were collected, identified and counted.  相似文献   

8.
The growth and maturation period of the autumn-fruiting population ot Sargassum horneri C. Agardh (Phaeophyta) was investigated in Hiroshima Bay, Seto Inland Sea. Surveyed traits were compared to those of the spring-fruiting type and ecological features of this species were discussed. The annual lifetime of the autumn-fruiting population could be divided into four phases according to the daily increase in thalius length:phase I from December to May (increase in length < 0.1 mm/ day), phase II from May to September (= 0.3–1.0 mm/ day), phase Ml (from September to December > 10 mm/day) and phase IV which was the senescence phase from December to March. Receptacle formation‘as observed in November and gamete release from November to February. Conversely, the spring-fruiting type germinated in April and exhibited swifter growth in its early stage of development than the autumn-fruiting type. Rapid increase in thalius iength in autumn was common in both fruiting types, although the spring-fruiting type continued to grow during winter. Receptacle formation of the spring-fruiting type started in February but gamete release was not observed until April and May. The difference in life-history patterns of both types of S. horneri was in the overwintering period. The autumn-fruiting type spent that season as germi-ings or as young plants exhibiting slow-paced growth, while the spring-fruiting type overvwintered as adult thal-li preparing for gamete release in spring.  相似文献   

9.
Using a 30 day time series of aphid Aphis helianthi and coccinellid counts on 107 mapped racemes of Yucca glauca, we demonstrate progressive, predation‐induced self‐organization of aphid colonies on individual racemes into extremely low and extremely high population sizes. This was driven by a two‐attractor structure of density dependence that developed only in the presence of coccinellid predators. Foraging movements of the coccinellids among plants produced a power law relationship (average power = 0.142) between aphid and coccinellid numbers. This resulted in increased predation pressure on mid‐size colonies and decreased predation pressure on small and large populations. A field‐parameterized mathematical model predicts a two‐attractor structure in broad agreement with our observations. The overall system was integrated by the influence of the largest aphid populations, which determined the total number of coccinellids present, and thus the predation pressure throughout the system. Our study provides clear evidence of predator‐driven self‐organization of prey populations in a patchy environment.  相似文献   

10.
Generalist natural enemies may be well adapted to annual crop systems in which pests and natural enemies re-colonize fields each year. In addition, for patchily-distributed pests, a natural enemy must disperse within a crop field to arrive at infested host patches. As they typically have longer generation times than their prey, theory suggests that generalist natural enemies need high immigration rates to and within fields to effectively suppress pest populations. The soybean aphid, Aphis glycines Matsumura, is a pest of an annual crop and is predominantly controlled by coccinellids. To test if rates of coccinellid arrival at aphid-infested patches are crucial for soybean aphid control, we experimentally varied coccinellid immigration to 1 m2 soybean patches using selective barriers and measured effects on A. glycines populations. In a year with low ambient aphid pressure, naturally-occurring levels of coccinellid immigration to host patches were sufficient to suppress aphid populations, while decreasing coccinellid immigration rates resulted in large increases in soybean aphid populations within infested patches. Activity of other predators was low in this year, suggesting that most of the differences in aphid population growth were due to changes in coccinellid immigration. Alternatively, in a year in which alate aphids continually colonized plots, aphid suppression was incomplete and increased activity of other predatory taxa contributed to adult coccinellid predation of A. glycines. Our results suggest that in a system in which natural enemy populations cannot track pest populations through reproduction, immigration of natural enemies to infested patches can compensate and result in pest control.  相似文献   

11.
The pattern of growth of the total population of Musculista arcuatula over a period of thirteen months was built up plotting length-percentage frequency histograms each month. From the shifting of the modes it was noticed that the increase in size from November to December was 2 mm, the growth during December to January 3 mm. In February the growth was nil. In March the size increasing by 6 mm and in April by 1 mm, when mortality of the largest size groups started to get completed in May. In June a conspicuous mode appeared at 9 mm, grew 1 mm in July, 2 mm in August and 3 mm in September. Growth remained stationary in October and November. The rate of increase in length was found to follow exponential law. The growth rate of this bivalve goes on increasing at a steady pace, the rate being 1.086 mm per month. The mean size of the females was found to be significantly larger than that of the males. The proportion of the males in the size group 3 mm to 10 mm was found to be significantly larger than in the entire population. But in the larger size groups there was no difference in the number of males and females and the proportion was almost 1:1. Throughout the year only one age class was recognizable in the natural population. There appears to be an excessive post reproductive mortality of adults rendering the population during most of the year of a single age class recruited through the various months of spawning. The maximum longevity was found to be at the most 18 months.  相似文献   

12.
In the Calicut population of P. hydrodromous, eyestalk principles are either directly or indirectly involved in maintenance of the differential growth rate of the sexes during the latter half of the first year of the life cycle. The prebreeding season (September—November), which is distinct in crabs 4.0 cm and over in carapace width (cw), is either absent or not distinct in young females (cw 2.8–3.2 cm), though the latter enter their first reproductive cycle by December, when 8–9 mth old. December—March is a period of active vitellogenic growth; from March onwards, there is a distinct swing in favor of somatic growth in females, though the proecdysis per se is not initiated until May. A typical brachyuran, Paratelphusa restricts its reproductive activity to intermolt and somatic growth chiefly to premolt; there are, however, definite phases within the intermolt itself when the physiological tilt favors somatic growth or alternatively reproduction. In females above cw 4.0 cm, the tendency for somatic growth is suppressed once they attain this cw after the monsoon (June—July) molt; eyestalk ablation during the prebreeding season precipitates accelerated ovarian growth. Administration of β-ecdysone in premolt titers failed to restrain this ovarian response and to promote somatic growth sufficiently. Conceivably, gonadal growth-promoting principles keep under check the responsiveness of the target tissues involved in somatic growth perhaps by affecting ecdysone receptors. The present investigations do not indicate a vitellogenesis-inhibiting role for β-ecdysone.  相似文献   

13.
1. Following its recent global spread, Harmonia axyridis (Coleoptera: Coccinellidae), an aphid predator of East Palearctic origin, dominated local coccinellid communities. While long‐term trends in this change are well documented, little is known about seasonal changes. 2. Seasonal changes in communities of adult Coccinellidae were investigated in central Europe (Prague), from April to November in 2010–2014. The beetles were collected at 2‐weekly intervals by net‐sweeping particular stands of trees (Tilia spp., Acer spp. and Betula sp.). The numbers of beetles caught were recalculated per unit effort, and average species abundance and community richness, dominance and diversity were calculated for each 2‐week period. 3. Frequencies of 21 established species varied throughout the vegetative season and general trends in this variation were similar in each of the 5 years of this study. In May–June the abundant species was Adalia decempunctata, which was later replaced by Harmonia axyridis as the most abundant species in late summer. Coccinella septempunctata colonized trees occasionally in summer. This sequence of species substitution occurred every year and was reset during winter. Species richness decreased and dominance increased during the course of each vegetative season. The diversity of the coccinellid community (Shannon index H′) significantly decreased during the course of the vegetative season. This was caused by a gradual increase in the dominance of H. axyridis, the abundance of which explained 88% of variation in H′. 4. The existence of a significant seasonal difference indicates that it is important to take this into consideration when comparing coccinellid communities.  相似文献   

14.
Vector transmission of Banana streak virus in the screenhouse in Uganda   总被引:2,自引:0,他引:2  
Although mealybug transmission of Banana streak virus.(BSV) by Planococcus citri and Saccharicoccus sacchar has been demonstrated elsewhere, these mealybugs have not been identified on bananas in Uganda and their role and that of other agents in BSV transmission is not well documented. Insect samples were collected from banana farms in sites with low, moderate and high BSV infections in Uganda. Subsequently, live mealybugs and aphids were again collected and used in acquisition, retention and transmission tests, and BSV diagnosed using TAS‐ELISA. Dysmicoccus brevipes (pineapple mealybug), S. sacchari (sugarcane mealybug) and Pentalonia nigronervosa (banana aphid) were the most abundant insect species from banana fields sampled. Abundance of D. brevipes was positively and significantly correlated with BSV incidence unlike that of. P. nigronervosa. Transmission studies in the screenhouse showed that mealybugs acquired BSV one day after feeding on virus sources and approached optimum acquisition after the third day. Pineapple and sugarcane mealybugs retained BSV up to 5 days from the day of transfer from the virus source. BSV was first detected in the recipient banana plants 4 wk after transmission using pineapple mealybug and 6 wk after inoculation using sugarcane mealybug. Under screenhouse conditions, both mealybugs therefore appear to transmit BSV semipersistently.  相似文献   

15.
Summary I used a factorial experiment repeated in two years to assess the relative effects of natural enemy attack, interspecific competition, and water availability to the host plant, and of interactions among these factors, on the population dynamics of the aphid Aphis varians feeding on fireweed (Epilobium angustifolium). The impact of a suite of coccinellid and syrphid predators emerged as the predominant factor affecting the success of aphid colonies: colonies protected from natural enemies grew in size at a rate of ten percent per day, were only one tenth as likely to go extinct, and produced over ten times more dispersing alates. In contrast, I found only minor effects of removing flea beetles, the most abundant herbivore with which A. varians colonies cohabit fireweed stems, and of supplementing water availability to fireweed host plants, in spite of a significant effect of watering frequency on aphid growth in the green-house. There was no evidence of significant two- or three-way interactions among factors. Hence, despite the potential complexity of the food web in which it is embedded, the dynamics of A. varians appears to be driven predominantly by a single factor, i.e. interactions with natural enemies.  相似文献   

16.
 The nuclear genome of wild-type banana accessions was investigated for repetitive elements. We report here the occurrence, in the banana genome, of a sequence family of species-specific repetitive elements: Brep 1. This sequence family is distributed throughout the Musaceae with various copy numbers. The two species Musa acuminata and M. schizocarpa carry the highest copy numbers in contrast to M. balbisiana and tested representatives of different other sections. PCR primers were defined in the core consensus sequence for specific amplifications, which allow representatives of this sequence family to be easily detected in wild and cultivated banana clones. Sequence data were analysed and hypotheses on the evolution of banana cultivars from the wild-type banana clones are discussed. Received: 17 January 1997 / Accepted : 7 March 1997  相似文献   

17.
The effect of growth rate and maturation on the proximate composition and energy content of Atlantic cod, Gadus morhua L., was investigated over 10 months for each of two consecutive years, 1978–1980 at 5 and 8 °C. Relative energy and lipid content of whole cod increased with specific growth rate for all three sampling periods (November, January, March), each at 5 and 8 °C. Relative water content decreased with specific growth rate and temperature, and was lower in March than in January and November. Relative protein content was positively correlated with specific growth rate, but to a lesser degree than with temperature and age. Relative ash content was negatively correlated with specific growth rate. The effect of season and temperature on the proximate content of gonad, liver, muscle, and carcass was also determined. The major energy and lipid source in cod was the liver. Energy, lipid, and water were highly correlated to each other, and regressions are provided to allow for their prediction, given one of the components. Energy budgets for cod at 5 and 8 °C are calculated and the effect of increased ration size on the budget is estimated. The prediction of short-term specific growth rates of cod from the proximate composition is proposed. The proximate composition of cod is affected by growth rate and thus feeding level, and in turn directly affects behaviour. The relative proximate content of maturing and immature 3-yr-old cod was not found to be significantly different. Keywords: specific growth rate; proximate; bioenergetics; Atlantic cod; energy budget; temperature; season  相似文献   

18.
  1. The giant willow aphid (Tuberolachnus salignus) is an invasive pest that can attain large populations on willows (Salix spp.). This has the potential to have a negative impact on the extensive use of willows for soil conservation, and as a source of pollen and nectar for honey bees in New Zealand.
  2. A willow nursery field trial was established to evaluate the aphid populations, and the survival and growth of young plants of several willow species and hybrids, during two growing seasons from planting.
  3. The willow species and hybrids varied widely in their susceptibility to the aphid, with large aphid populations and plant mortality in the most susceptible willows, and reductions in plant growth in all but aphid-resistant willows. The effects on the plants were not seen in the first season, but occurred during the second season.
  4. The aphid can be expected to have some negative impacts in New Zealand, with reductions in growth of some willows commonly used for soil conservation, and for pollen and nectar for honey bees.
  相似文献   

19.
Predators (mainly coccinellid adults and larvae and syrphid larvae), although few, were important in decreasing numbers of Aphis fabae on a small plot of field beans during the early stages of infestation in a year favourable to the aphid. At the same time, ants (Lasius niger L.), attending aphids on other plants on the same plot, effectively protected the aphids from predators for about 2 weeks, enabling the attended aphids to multiply faster than the unattended. When all aphid populations started to decline, predators became more numerous and accelerated the decline on both sets of plants. Bean plants without aphids yielded fifty-six seeds per plant; those with aphids but free from ants gave seventeen; and those with ant-attended aphids, eight seeds per plant. The damage and loss of yield was caused by the large aphid populations that developed when the pods were maturing, and not by the fewer aphids present when the plants were in flower. It appears that small, temporary infestations during flowering might increase the yield of field beans.  相似文献   

20.
Fusarium wilt disease of banana is one of the most harmful fungal diseases affecting banana production worldwide. We hypothetically proposed that the loss of indigenous endophytes in tissue culture propagation of banana might be related to increased disease severity on banana plants. In the present study, a mixture of uncultivated endophytes, which was originally derived from native healthy banana plant in plantation, was used to artificially inoculate banana tissue culture plantlets. A broad spectrum of bacterial communities was detected in the roots of artificially inoculated plantlets by 16S ribosomal RNA gene analysis, and γ-Proteobacteria was identified as the dominant group. Banana wilt pathogen Fusarium oxysporum f. sp. cubense race 4 was inoculated to the plantlets after potting to investigate disease progress. With early diagnosis of fungal pathogen infection, 54% reduction was detected in artificially inoculated plantlets compared to endophyte-free control plantlets. The re-introduction of naturally-occurring endophytes into tissue culture banana plantlets led to a 67% suppression rate of wilt disease at the fifth month after pathogen infection on plantlets in the greenhouse. In addition to disease suppression, growth of host plantlets was also promoted with the inoculation of endophytes. The artificial inoculation method provided a foundational understanding of ecological enrichment to control banana wilt disease in future.  相似文献   

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