Effects of elicitors of host plant defenses on pear psylla,Cacopsylla pyricola

Pear psylla, Cacopsylla pyricola (Foerster) (Hemiptera: Psyllidae), is a key pest of cultivated pear [Pyrus communis L. (Rosaceae)] in North America and Europe. We examined the effects of foliar applications of three commercially available chemical elicitors of host‐plant defenses — Actigard (acibenzolar‐S‐methyl), Employ (harpin protein), and ODC (chitosan) — on survival, development, feeding, and egg laying of C. pyricola. All three defense elicitors reduced the number of nymphs present on pear (cvs. Bartlett or D'Anjou) 30 days after releasing 10 adults on the trees. Choice assays showed that females settled and oviposited on untreated trees more often than on trees treated with any of the three defense elicitors. Results of no‐choice assays confirmed that the effects of Actigard, Employ, and ODC on C. pyricola were due to activation of systemic plant responses that led to reduced oviposition preference and nymph survival. However, results did not provide evidence that plant responses to elicitors led to reduced nymphal feeding rates or development. Results of our laboratory studies suggest that commercial defense elicitors may be useful in the integrated management of pear psylla once the effects of elicitors at an ecological scale are better understood.     

Tethered flight activity of pear psylla, Cacopsylla pyricola: Seasonal, host, and morphotypic effects

Pear psylla, Cacopsylla pyricola Förster (Homoptera: Psyllidae), was flown in the laboratory to test hypotheses suggested by field observations. Flight durations of the same insects flown on two different days were highly correlated, suggesting that there were biolgical differences among insects in flight tendencies. Flight durations were similar between summerform and winterform morphotypes. Flight frequencies and durations increased between September and November collections of winterforms, results that are consistent with field observations. Long-duration (60+ min) flights were three to four times as frequent in winterforms restricted to senescing pear foliage compared to insects provided access to pear seedlings. Winterforms collected during the fall flight period from a pear orchard and an adjacent apple orchard (an overwintering habitat) showed similar flight durations. There was no correlation between flight durations and any of five body and wing measurements; body size of winterforms increased between September and November. It has been proposed elsewhere that much of the fall movement into adjacent non-pear habitats by winterforms is due to short duration non-migratory flights rather than to a true migratory flight. The lack of differences between apple- and pear-collected winterforms may be consistent with this hypothesis.     

越冬代梨木虱、梨二叉蚜产卵选择对子代种间竞争的影响

梨树萌芽期,越冬代梨木虱Cacopsylla chinensis和梨二叉蚜Schizaphis piricola子代共用同一食物资源,为了解其母代如何避免子代发生种间竞争,通过研究其产卵特点表明,梨二叉蚜和梨木虱在梨树枝条上的产卵位点不同。梨木虱主要在花芽枝上进行产卵,偏好于花芽芽鳞和枝条基部刻痕处产卵,以枝条基部产卵量最多,其次为顶花芽,产卵量随芽位次序依次下降,梨木虱还可在叶芽部位产卵,但数量较少;梨二叉蚜主要于叶芽枝上进行产卵,偏好在叶芽枝的第2、3芽位产卵,顶芽和枝条基部无产卵,未见梨二叉蚜在花芽部位产卵;在花芽枝上,梨木虱卵的空间生态位大于梨二叉蚜、叶芽枝上却相反,两者在梨树枝条上的产卵空间生态位呈分离状态;梨木虱和梨二叉蚜孵化的若虫数量及空间分布特点与卵一致;对梨木虱和梨二叉蚜产卵位点分析表明,其产卵位点的物理性状明显不同。本研究明确了梨木虱和梨二叉蚜母代通过不同产卵位点的选择,降低了子代种间的同位竞争。     

Reduction of Pear Psylla Damage by the Predatory Bug Anthocoris nemoralis (Heteroptera: Anthocoridae): The Importance of Orchard Colonization Time and Neighboring Vegetation

This 5-year field study was aimed at assessing the importance of predatory arthropods in suppressing pear psylla, Cacopsylla bidens (Sulc), and reducing damage caused by psylla in pear orchards in northern Israel. Correlative data suggest that Anthocoris nemoralis (Fabricius) is the only naturally occurring predator in the system that may reduce pear psylla damage; densities of other predacious taxa in the system (Araneidae, Orius spp., Chrysopidae and Coccinellidae) were not correlated significantly with psylla numbers in the orchards. However, A. nemoralis entered pear orchards at least a month after the beginning of pear psylla activity, apparently too late to prevent fruit damage. Data suggest that A. nemoralis reproduction is lower on both wild and cultivated pears than on Rhamnus, Laurus and Pistacia trees in nearby woods. Furthermore, A. nemoralis populations build up on the wild trees in March, but appear in orchards only in late May. We propose that planting R. alaternus trees near pear orchards could enhance the level of biological control of pear psylla by A. nemoralis. Preliminary results indeed show that pear psylla densities were lower on pear trees grown near Rhamnus alaternus trees than on distant trees.     

Polygenic inheritance of resistance to <Emphasis Type="Italic">Cacopsylla pyri</Emphasis> in a <Emphasis Type="Italic">Pyrus communis</Emphasis> × <Emphasis Type="Italic">P. ussuriensis</Emphasis> progeny is explained by three QTLs involving an epistatic interaction

Pear psylla (Cacopsylla pyri) causes severe damage on European pear cultivars, resulting in high yield losses. Its control has become difficult since it developed resistance to a wide range of pesticides, while the number of authorized molecules for pest control has decreased. Identifying pear psylla resistance factors should help breeding new resistant pear cultivars. We analyzed the quantitative resistance to psylla inherited from the genotype NY 10355 derived from Pyrus ussuriensis. Quantitative trait locus (QTL) analysis was carried out after counting the number of nymphs and estimating the nymphal development rate using a free-choice test performed on a large segregating progeny. We mapped two new loci for pear psylla resistance on linkage groups LG01 and LG04 of NY 10355 and confirmed the QTL previously detected on LG17. A strong epistatic interaction between the two QTLs detected on LG01 and LG17 appeared to be a major factor controlling the psylla infestation in the genotype NY 10355.     

Foliar spraying of elicitors in pear trees induced resistance to Cacopsylla bidens

The pear psylla, Cacopsylla bidens (?ulc, 1907) (Psylloidea, Psyllidae, Psyllinae) is a serious pest of pear worldwide. In this research, the effects of salicylic acid (SA), chitosan, γ-aminobutyric acid (GABA), and Serenade Aso (Bacillus subtilis QST713) were studied on the induced resistance of pear trees to C. bidens. The treatments showed a significant difference in terms of population growth of C. bidens after 7 and 14 days during two years. In 2019, the mean population growth of total life stages of C. bidens in the studied treatments was significantly lower than control after 7 and 14 days of spraying. In 2020 (7 and 14 days after spraying), the percent decline in the mean population of pear psylla (total life stages) was highest on chitosan treatment (75 and 85 %, respectively) and the lowest on control (30 and 48 %, respectively). GC–MS analysis revealed the range of chemicals in the pear leaves under different treatments. Based on the results, 23 compounds were identified, including 9 alkaloids, 6 flavonoids, 4 polyphenols, 3 terpenoids, and one glycoside. In all treatments except Serenade, the amounts of alkaloids increased compared to the control. Furthermore, the activity of catalase and glutathione S- transferase enzymes in C. bidens under chitosan treatment was significantly higher than others; but the activity of peroxidase significantly decreased on chitosan compared to SA and GABA. The lower levels of peroxidase in C. bidens reared on trees treated with chitosan indicate this insect has not been able to detoxify plant secondary metabolites effectually. In addition, our findings suggested that chitosan on pear trees could act effectively in reducing the C. bidens population and can be considered in integrated management programs of this pest.     

Diapause status of females affects attraction of male pear psylla, Cacopsylla pyricola, to volatiles from female-infested pear shoots

A companion study showed that male pear psylla, Cacopsylla pyricola (Förster) (Homoptera: Psyllidae) were attracted to volatiles from pear shoots infested with post-diapause females. The present study compared the behavioral response of males to diapause and post-diapause females. Assays were done using a Y-tube olfactometer. We collected male and female winterform psylla from pear orchards at regular intervals between late October (early diapause) and late February (post-diapause). Female-infested shoots were not attractive to males until the February samples, coinciding with ovarian maturation and onset of mating in the field. A second set of assays was done in which we manipulated diapause status in the laboratory either by exposing psylla to a long-day photoperiod or by treating insects with an insect growth regulator, fenoxycarb. In the photoperiod experiments, both short-day and long-day males preferentially selected long-day (post-diapause) females over short-day (diapause) females. Fenoxycarb-treated males preferred fenoxycarb-treated (post-diapause) females over untreated (diapause) females; untreated males showed no preferences. Results support observations made elsewhere that male winterform pear psylla perceive and are attracted to volatile odors associated with pear shoots infested with post-diapause females.     

Insecticidal effect of plant extracts on common pistachio psylla,Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Aphalaridae)

The common pistachio psylla, Agonoscena pistaciae (Hemiptera: Aphalaridae) is one of the most detrimental pests to pistachio trees. Nowadays various pesticides are used to control the common pistachio psylla, but extensive pesticide spraying against this pest over a period of several years has overpowered its natural enemies. The plant’s byproducts come as an alternative ecologically more compatible in substitution to the synthetic insecticides. This work aims to evaluate the insecticidal potential of herbal extracts of fruit peels of Citrus sinensis and Citrus reticulata, seeds of C. sinensis and Rubia tinctorum, and leaves of Lawsonia inermis against common pistachio psylla. Five concentration 40, 47, 56, 67 and 80 µl/ml, of these plant extracts were sprayed on the fifth instar nymphs of common pistachio psylla by Potter Spray Tower under laboratory conditions (26?±?2?°C, 60–70% RH and a photoperiod of 16L: 8D h). Results showed significant differences among the treatments of the plant extracts and between the concentrations. The LC₅₀ values of C. sinensis peels, C. reticulata peels, C. sinensis seeds, R. tinctorum seeds and L. inermis leaves were 62.04, 38.84, 43.60, 59.01 and 33.99 µl/ml, respectively. Also, all extracts showed the greatest mortality effect in 80 µl/ml concentration. According to these results, these plant extracts may use as herbal pesticides chemical control programme of common pistachio psylla.     

外源性氮磷添加及林分密度对大叶相思林土壤酶活性的影响

研究了林分密度和外源性氮(N)磷(P)添加及二者的交互作用对土壤酶活性的影响,可以为当前不同密度的亚热带林在氮沉降和施磷肥条件下,影响我国亚热带人工林土壤养分转化的酶学机制提供理论依据。以大叶相思(Acacia auriculiformis)人工林为试验材料,选择氯化铵(NH_4Cl)和二水合磷酸二氢钠(NaH_2PO_4·2H_2O)作为N肥和P肥,氮磷添加设置4个处理,即对照、施N、施P和施N+P;种植密度设置低密度(1667株/hm~2)、中密度(2500株/hm~2)、较高密度(4444株/hm~2)和高密度(10000株/hm~2)4个水平。在4种密度的大叶相思人工林下各设置一个样地(即4个样地),每个样地内5个样方,每个样方内设置4种处理,合计共16个处理,5个重复,80个小区,测定土壤脲酶、磷酸酶和过氧化氢酶活性,分析林分密度和NP添加对大叶相思林地土壤酶活性的影响。研究结果表明:N添加对各林分密度下的土壤脲酶和过氧化氢酶活性均有抑制作用,P添加显著提高了过氧化氢酶活性和高密度林分大叶相思林地的土壤脲酶活性,却降低了低密度林分的土壤脲酶活性;土壤磷酸酶活性在P和N+P添加两种处理下显著小于对照和施N处理;土壤脲酶、磷酸酶以及对照和P添加处理下的过氧化氢酶活性均随着林分密度的升高呈现上升趋势,而土壤过氧化氢酶活性在N和N+P添加后随着林分密度的减小而升高。林分密度和外源性NP添加的交互作用对三种土壤酶的活性均有显著影响。     

Pear transformed with a lytic peptide gene for disease control affects nontarget organism,pear psylla (Homoptera: Psyllidae)

The biology and behavior of pear psylla, Cacopsylla pyricola Foerster, on a transgenic clone of 'Bartlett' pear, Pyrus communis L., containing a synthetic antimicrobial gene, D5C1, was compared with that of a nontransgenic parental clone to determine whether there were any nontarget effects. The gene construct also contained the marker gene nptII (aminoglycoside 3'-phosphotransferase II) that encodes for antibiotic resistance to identify transformed plants. The purpose of the original transformation was to enhance pear resistance to the bacterial disease fireblight caused by Erwinia amylovora (Burr.) Winslow et al. The biology and behavior of pear psylla on a transgenic clone were compared with a nontransgenic parental pear clone in short- (< or = 7-d) and long-term (32-d) studies. Short-term studies indicated pear psylla adults preferred to settle and oviposit, and nymphs fed more and developed slightly faster, on transgenic pear compared with nontransgenic pear. In contrast, a long-term study on psylla colony development showed considerably fewer eggs, nymphs, and adults were produced on transgenic pear. Although adults reared on transgenic pear did not have weight affected, females produced fewer eggs and nymphal hatch was significantly reduced on the transgenic pear clone. Our results suggest that pear psylla biology and behavior are initially enhanced on this transgenic pear clone. However, chronic exposure of psylla populations to transformed pear plants that express the nptII marker and lytic peptide genes had detrimental effects on pear psylla reproductive biology. Field studies would be required to determine the specific effects of each gene on pear psylla biology and behavior and whether these effects would be expressed under natural conditions. The four-fold reduction in psylla population levels that resulted on this disease resistant transgenic pear line would be an added benefit to a pear integrated pest management (IPM) program. Overall, this study demonstrates that genetically altering plants to control one particular organism can have unintentional yet beneficial effects against other nontarget pest organisms in agricultural crops.     

Attraction of male pear psylla, Cacopsylla pyricola, to female-infested pear shoots

Post-diapause winterform pear psylla, Cacopsylla pyricola (Förster) (Homoptera: Psyllidae), exhibit a highly clumped distribution in late winter in pear orchards. The behaviors leading to clumped distributions in this species are unknown, but could include aggregation for mating activities. Choice tests and assays with an olfactometer were done to test whether male psylla of the overwintering morphotype are attracted to pear shoots infested by post-diapause females and to shoots previously occupied by females. Paired choice tests in small arenas showed that males accumulated on pear shoots currently occupied or previously occupied by females if those shoots were paired with uninfested shoots or shoots previously occupied only by males. Assays with an olfactometer showed that males were attracted to volatile odors from female-infested or previously infested shoots. The exact source of the attractants (i.e., the female psylla, the pear shoot, or a combination of these sources) remains to be determined.     

The Role of Chemical Cues in Host and Mate Location in the Pear Psylla Cacopsylla bidens (Homoptera: Psyllidae)

Chemical communication was shown to play a role in the pear psylla, Cacopsylla bidens. Electrophysiological (EAG) and behavioral responses were investigated in males and females pear psylla . Males were found to be attracted to females, and especially to those on host plants, but not to males, uninfested host plants, or plants infested with conspecific larvae. On the other hand, females were not attracted to males or females but displayed some attraction to host plants. Furthermore, females showed a preference for uninfested pear versus plants infested with conspecific larvae. The antennae of males gave highest electroantenographic response to volatiles from pears infested with females but not males, while females, responded also toward the volatiles of pear alone. These results indicate that females of C. bidens emit sex pheromones that are attractive to the males and suggest that, host volatiles may play a role in host selection by pear psylla females.     

江西武夷山珍稀濒危植物南方铁杉种群动态与空间分布

明晰江西武夷山国家级自然保护区内180年生的珍稀濒危植物南方铁杉(Tsuga chinensis var.tchekiangensis)的种群特征,并提出针对性的保护策略,对南方铁杉种群的就地保护具有现实意义。通过分析保护区内6.4 hm~2动态监测固定样地的南方铁杉种群数据,编制了静态生命表,绘制了存活曲线、死亡率和消失率曲线、生存函数曲线,采用了时间序列模型对种群数量特征进行未来预测;同时,运用点格局分析Ripley′s K函数中的成对相关函数g(r)判断不同生长阶段的南方铁杉种群在不同尺度下的空间分布格局。结果表明：(1)南方铁杉种群的年龄结构呈“金字塔”型,属于衰退型种群;各龄级间的数量变化动态关系显示该种群在当前阶段呈增长型,但是种群的天然更新能力较差;(2)南方铁杉种群的存活曲线表现为Deevey-I型,种群个体在进入生理死亡阶段后产生一定的波动;(3)南方铁杉种群的生存率随龄级增加而逐渐下降,累积死亡率逐渐递增;死亡密度整体偏低,在第1—2龄级较高,总体波动幅度较小;危险率曲线总体呈现上升的趋势;(4)在经过不同龄级的时间后,南方铁杉幼龄树数量降低,中龄树和老龄树数量持平...     

Interplant movement by pear psylla (Homoptera: Psyllidae): Effects of sex ratio and reproductive status

Sticky trap catch of pear psylla,Cacopsylla pyricola Foerster, is male biased during the reproductive generations, but not the diapausing generation. In cage studies, we monitored movement by male and female pear psylla between host plants, and tested whether reproductive and diapausing psylla exhibit similar rates of movement. We also experimentally varied sex ratio to determine whether sex ratio affected movement. Male-biased sex ratios prompted increased movement off of the original host by male psylla of the reproductive generations; no such effect was noted for diapausing insects. We interpret these results to indicate that male movements increased under male-biased conditions due to mate-searching activities. There was also evidence in two experiments that severely male-biased sex ratios prompted movement off of the original host plant by reproductive females; this effect may have been due to harassment of ovipositing females by males.     

不同密度樟树(Cinnamomum camphora)幼苗生长和叶片性状对氮磷添加的响应

人类活动改变了氮素从大气向陆地生态系统输入的方式和速率,进而导致森林生态系统养分变化和失衡。研究氮磷添加对不同密度樟树(Cinnamomum camphora)幼苗生长和叶片性状的影响,可以为全球氮磷沉降背景下亚热带地区樟树人工林的经营管理提供依据。本试验以1年生樟树幼苗为试验材料,选择氯化铵(NH_4Cl)作为氮肥模拟大气氮沉降,以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加。氮磷处理设置CK、施N、施P和施N+P 4个水平,种植密度设置10、20、40和80株·m~(-2 )4个水平。实验数据表明:N、P和N+P处理对樟树幼苗的苗高和地径均有促进作用,且N+P处理对幼苗生长的促进效果最好。N、P和N+P处理在整体上均能增加幼苗叶片的SPAD值,N和N+P处理均增加了幼苗叶片的比叶面积(SLA),而P处理减少了幼苗的SLA。随着种植密度的增大,N、P和N+P处理下樟树平均单株幼苗的苗高、地径、SPAD值呈现下降的趋势,各施肥处理下叶片的SLA变化规律不明显。密度和氮磷添加对叶片的SPAD值产生显著的交互作用。     

樟树(Cinnamomum camphora)幼苗细根形态对氮磷添加和幼苗密度的响应

全球氮沉降对森林生态系统结构和功能的影响已成为现代生态学研究热点之一,我国华南地区氮沉降的增长引起了土壤酸化和磷限制加剧等一系列生态问题。密度制约着植物个体对环境资源的吸收利用,是自然界中十分重要的选择压力之一。因此研究樟树(Cinnamomum camphora)幼苗的细根形态对氮磷添加和密度的响应,有利于了解亚热带树木根系对氮沉降和磷添加与林分密度的响应过程和机制,并为全球变化背景下樟树林生态系统的管理提供依据。本研究以1年生樟树幼苗为试验材料,选择氯化铵(NH_4Cl)作为氮肥以模拟大气氮沉降,并且以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加,氮磷处理设置4个水平,即对照、施N、施P和施N+P;种植密度设置10、20、40和80株/m~2 4个水平。测定各处理樟树幼苗细根的根长、表面积、体积和根尖数,分析氮磷添加、密度和两者交互作用对樟树幼苗细根的影响。研究结果表明,与对照处理相比,N、P和N+P处理促进了幼苗细根长度、表面积、体积以及根尖数的增加。低密度条件下的N添加对幼苗根系形态的促进效果强于P添加。N+P处理对10、20、40株/m~2幼苗根系形态的促进效果最佳,而各处理对80株/m~2幼苗根系形态的促进效果均无显著性差异。随着种植密度的增大,幼苗细根长度、表面积、体积和根尖数均减少。樟树幼苗的细根长度、表面积、体积和根尖数在各密度间和不同氮磷添加处理间均有显著性差异,密度和氮磷处理间的交互作用对根系形态各指标均无显著影响。     

Influence of host plant on the mango mealybug,Rastrococcus invadens

Life history traits of the mango mealybug,Rastrococcus invadens Williams, were compared between two neighboring mango trees (Mangifera indica L.), one of which was heavily infested and the other slightly infested. On the infested tree, mealybug survival was high because of good feeding conditions and low escape. The pre-reproductive period of mealybugs on the heavily infested tree was shorter and total offspring production higher than that of mealybugs on the uninfested tree. This significantly affected the intrinsic rate of natural increase and explained the observed differences in population densities among the trees. The results obtained from an additional experiment using juvenile clones from the same two mango varieties, in which environmental factors were uniform, demonstrated the importance of plant genotype on mealybug size and survival.     

Effects of resource availability and propagule supply on native species recruitment in sagebrush ecosystems invaded by Bromus tectorum

Resource availability and propagule supply are major factors influencing establishment and persistence of both native and invasive species. Increased soil nitrogen (N) availability and high propagule inputs contribute to the ability of annual invasive grasses to dominate disturbed ecosystems. Nitrogen reduction through carbon (C) additions can potentially immobilize soil N and reduce the competitiveness of annual invasive grasses. Native perennial species are more tolerant of resource limiting conditions and may benefit if N reduction decreases the competitive advantage of annual invaders and if sufficient propagules are available for their establishment. Bromus tectorum, an exotic annual grass in the sagebrush steppe of western North America, is rapidly displacing native plant species and causing widespread changes in ecosystem processes. We tested whether nitrogen reduction would negatively affect B. tectorum while creating an opportunity for establishment of native perennial species. A C source, sucrose, was added to the soil, and then plots were seeded with different densities of both B. tectorum (0, 150, 300, 600, and 1,200 viable seeds m⁻²) and native species (0, 150, 300, and 600 viable seeds m⁻²). Adding sucrose had short-term (1 year) negative effects on available nitrogen and B. tectorum density, biomass and seed numbers, but did not increase establishment of native species. Increasing propagule availability increased both B. tectorum and native species establishment. Effects of B. tectorum on native species were density dependent and native establishment increased as B. tectorum propagule availability decreased. Survival of native seedlings was low indicating that recruitment is governed by the seedling stage.     

氮素添加和功能群去除对糙隐子草和大针茅根系特征的影响

由于草地不合理利用,中国北方草原严重退化,导致生态系统结构性破坏甚至功能性紊乱。随着草原退化,中能值功能群植物糙隐子草会取代高能值功能群植物大针茅成为群落中优势度最大的植物。为了解大针茅和糙隐子草在氮素添加以及去除功能群的情况下根系特征的变化趋势,选取锡林郭勒盟典型草原中的退化草原群落,分别开展两项实验,实验1:氮素添加梯度实验(0、10.5、17.5、28 gN/m~2),实验2:同时进行功能群的去除和氮素的添加,功能群去除实验(将植物分为高能值植物功能群、中能值植物功能群、低能值植物功能群3个功能群;每个处理分别剪除另外两个功能群,留取单一功能群),并同时进行氮素添加实验(0、17.5 gN/m~2)。在进行两年的实验处理后,通过Delta-T SCAN根系分析仪测量大针茅和糙隐子草根系的长度、直径、面积、体积指标。分析植物根系对氮素添加的响应,以及功能群去除是否改变这两种植物对氮素添加的响应格局。实验1研究结果表明:在受到其他功能群的竞争压力下,大针茅根系长度、面积、体积均在高氮素添加(28 gN/m~2)情况下显著增加,糙隐子草根系直径和体积在中氮素添加(17.5 gN/m~2)的情况下显著高于其他3个处理,退化样地中土壤氮素的增加,促使大针茅根系主要通过增加根系长度扩大在土壤中的空间分布,而促使糙隐子草主要通过增粗生长来扩大土壤分布空间。实验2研究结果表明:功能群的去除,中氮素添加对根系的影响,只有糙隐子草的根系直径显著增加。综合来看,功能群去除实验对大针茅的根系长度和面积有影响,对糙隐子草的根系长度、直径和面积有影响。功能群去除处理与氮素添加的交互作用对大针茅根系没有影响,对糙隐子草的根系直径和体积有影响。     

Eucalypt responses to fertilization and reduced herbivory

Summary We manipulated soil fertility and insect attack for two species of Eucalyptus in natural stands of subalpine woodland on shallow, infertile granitic soils. E. pauciflora and E. stellulata responded in similar ways to simultaneous insecticide and fertilizer treatments. Eliminating herbivorous insects produced the largest changes — improved plant growth, increased leaf N and P, and reduced leaf specific density. Fertilizer regime modified some leaf properties, but had little effect on tree growth. E. stellulata trees were initially shorter than E. pauciflora, but grew faster without herbivores; by the end of the experiment both species were the same size when herbivores were removed. Foliage N and P levels increased most in trees with the most balanced fertilizer addition (NPK), and increased in all trees protected from insects, regardless of fertilizer regime. In this system, herbivorous insects exacerbated the effects of nutrientpoor soils, and may affect dominance of Eucalyptus species in mature forests.