INITIAL SETTLEMENT BEHAVIOUR AND SURVIVORSHIP OF LITHOPHAGA BISULCATA (d'ORBIGNY) (MYTILIDAE: LITHOPHAGINAE)

Although infaunal associates of living reef building coralsindude numerous phyla, initial settlement on the coral hosthas never been described. Experiments described here includedraising the larvae of a common Caribbean coral-boring mussel,Lithophaga bisulcata to observe their behaviour in the presenceof a variety of settlement substrates. On Stephanocoenia michelini,the most common host, larvae moved about the coral surface withimpunity, exploring the surface with the foot. On this coralspecies, competent pedi-veligers were ingested by the coralbut not necessarily digested. Penetration of the coral is initiatedby entering the coelenteron, where metamorphosis will presumablytake place. On species which L. bisulcata rarely inhabits, thelarvae appeared to be stung by nematocysts and withdrew thefoot rapidly from contact with the tissue Habitation of a living coral substrate appeared to be beneficialto the bivalve. Although L. bisulcata inhabits both riving anddead coral, there is evidence that survival, longevity and reproductiveoutput are enhanced when the mussel is surrounded by livingcoral tissue (Received 9 June 1987;     

PHOSPHOGLUCOMUTASE ALLOZYME EVIDENCE FOR AN OUTCROSSING MODE OF REPRODUCTION IN THE HERMAPHRODITIC BROODING BIVALVE MYSELLA TUMIDA (GALEOMMATACEA)

Allozyme variation of a Mysella tumida population in PatriciaBay, B.C., Canada was investigated at the phosphoglucomutase(PGM) locus. Seven alleles were detected. The observed frequencyof allelic combinations did not differ significantly from randommating expectations (0.25 < P < 0.50), however, heterozygositylevels were slightly greater than expected (Selander's D = 0.022).These results, together with previous work on the M. tumidareproductive cycle, indicate that natural populations of thisbivalve rarely, if ever, self-fertilize. ^*Present Address: Friday Harbor Laboratories, University ofWashington, Friday Harbor, WA 98250, U.S.A. ^**Present Address: Museum of Zoology, University of Michigan,Ann Arbor, M1 48109, U.S.A. (Received 30 December 1986;     

Suspension feeding and kleptoparasitism within the genus Trichotropis (Gastropoda: Capulidae)

The marine gastropod Trichotropis cancellata is a facultativekleptoparasite, either suspension feeding or parasitically stealingfood from tube-dwelling polychaete worms. To determine whetherconclusions drawn from long-term studies in the San Juan Islands,Washington, about the relative importance of suspension feedingand kleptoparasitism can be applied generally to T. cancellataacross its biogeographic range, I expanded earlier studies toAlaska and British Columbia. Kleptoparasitism is pervasive throughoutthe range of T. cancellata, occurring with equal frequency throughoutthe areas studied. The average density and size of worm hostsare relatively constant across this range. Snail and worm densitiesare not significantly correlated at the larger scale of site(averaged over nearby sampling locations clustered around acity), but are correlated at the smaller local scale (withina sampling location). Larger worms do not support more snails.The abundance of uninfected worm hosts is usually not limiting,except potentially in some sampling locations in southwest Alaskawhere the use of a novel host (a holothurian) may be the resultof low densities of uninfected worms. Additionally, I documentedthe feeding behaviours of other trichotropid species in theseregions. Trichotropis conica is the second confirmed kleptoparasitewithin the genus Trichotropis, with kleptoparasitism as frequentin this species as in T. cancellata. Like T. cancellata, allsizes observed of T. conica are kleptoparasites. On the otherhand, Trichotropis insignis is an obligate suspension feeder.Further studies are needed to determine exactly how many timesthis behaviour has arisen and been lost in Capulidae and relatedfamilies. (Received 31 May 2007; accepted 19 October 2007)     

Seasonal dynamics in the abundance of Micromonas pusilla (Prasinophyceae) and its viruses in the Gulf of Naples (Mediterranean Sea)

To assess the role of viruses in the bloom dynamics of Micromonaspusilla in the Gulf of Naples (Mediterranean Sea), variationsof host and virus abundance were followed over one annual cycleand in late winter–spring of three consecutive years.Micromonas pusilla was recorded from autumn to spring, withpeak values up to 6.6 x 10³ cells ml^–1, but was undetectablein summer. Free M.pusilla viruses were detectable in all seasons,with concentrations from 0.02 viruses ml^–1 to 1.9 x 10³viruses ml^–1, exceeding host abundances only in one case.We found a great intraspecific variability in host susceptibilityto viruses present in natural samples, with viral titres rangingover one or two orders of magnitude for the same samples incubatedon different M.pusilla strains. Over the winter–springperiods, a highly dynamic situation was evident, with wide fluctuationsfor both host and virus abundances from one week to another.In some cases, peak host concentrations were accompanied byan increase in viral numbers, whereas in other cases the respectivefluctuations were uncoupled. Although fluctuations of M.pusillaabundance could be influenced by viral infection, there wasno evidence that viruses were able to terminate host blooms.The summer decline of M.pusilla populations did not appear tobe related to the impact of viral infection.     

寄主对桔小实蝇耐寒性的影响

为了研究寄主营养对桔小实蝇耐寒性的作用,测定了以15种果蔬饲养的桔小实蝇1日龄蛹的过冷却点(supercooling points,SCP); 再选取南瓜、西红柿、柑桔、番石榴和杨桃等5种果蔬,测定了桔小实蝇3龄老熟幼虫、1日龄蛹、3日龄蛹、5日龄蛹、7日龄蛹和雌雄成虫的过冷却点,并观察了1日龄蛹的低温存活力。结果表明：（1）15种果蔬饲养所得的桔小实蝇1日龄蛹SCP均值在-11.03℃～-13.17℃,不同寄主发育的桔小实蝇SCP值存在显著性差异,其中以取食蒲桃的最高,为-11.03℃,取食苦瓜的最低,为-13.17℃。（2）5种果蔬饲养所得的桔小实蝇各虫态的SCP均值存在极显著差异(F_(4,863)＝35.6,P<0.01); 同一寄主上的桔小实蝇不同虫态之间SCP均值也达到极显著性差异(F_(6,863)＝392.9,P<0.01); 且寄主和发育龄期之间存在着极显著的交互作用(F_(24,863)＝9.4,P<0.01)。（3）桔小实蝇各发育阶段,SCP值表现一定变化： 老熟幼虫发育至1日龄蛹,SCP值变化不大; 蛹发育至3、5和7天过冷却能力明显增强,降至-20℃左右,但他们之间没有明显区别; 羽化后3～5天的成虫SCP值又升高至-10℃左右。老熟幼虫、1日龄蛹和2～3日龄成虫与3日龄、5日龄和7日龄蛹的SCP值之间有显著性差异。（4）将5种果蔬饲养所得的桔小实蝇1日龄蛹置于6℃和-3℃下进行较长时间(1～8天)和较短时间(1～8 h)的低温处理,发现番石榴、杨桃和南瓜发育的蛹经低温处理后的校正羽化率较西红柿和柑桔发育的蛹高; 同样在0℃、3℃、6℃和9℃处理(2天)的实验中,得出相似的结果。因此,本实验结果表明桔小实蝇幼虫由于生活寄主的不同使得其下一代蛹的耐寒性产生了差异,引起其差异的原因值得进一步研究。     

PREDATION ON THE BIVALVE CHOROMYTILUS MERIDIONALIS (KR.) BY THE GASTROPOD NATICA (TECTONATICA) TECTA ANTON

The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m^–2 andthe population consisted mainly of reproductively mature individualsbetween 20–33 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m^–2month^–1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 4–6 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980;     

Mineral Nutrition of Sandalwood (Santalum spicatum)

Acacia acuminata is a preferred host of the root hemiparasitictree, Santalum spicatum (sandalwood). Comparison between nutrientcontent of adult trees of sandalwood and results for an earlierstudy of the mistletoe, Amyema preissii, on the same host species,A. acuminata, showed similar high levels of K and Na and lowlevels of Zn in both parasites compared with the host plants.Differences in K, Ca, N and Cu levels between parasitized anduninfected Acacias imply that the host plant contributes tothe nutrition of sandalwood. The high K/Ca ratio in sandalwoodconfirms that K uptake in preference to Ca is a general featureof all categories of angiosperm parasites. Patterns of distribution of nutrients between various partsof sandalwood and A. acuminata depend on the type of nutrient,but levels are usually highest in leaves of both species andthe haustoria. Although K, Ca and Na are much lower in the kernelsthan in vegetative parts of the parasite, only seedlings withoutsupplementary Ca in a nutrient omission experiment failed togrow at all in the absence of hosts. Growth is not dependenton the level of K in the unattached plants but other evidenceindicates it may have a role in water uptake in the attachedplant. Calcium supply has a marked effect on internal Ca levelsand growth of unattached plants. Compared with field plants,levels of Ca, and to a lesser extent Zn, were much higher inplants of the Ca/K treatment that produced greatest growth over34 weeks. Haustorial formation is enhanced by the presence of A. acuminataroots. However, competition for nutrients, especially Ca, fromco-planted A. acuminata seedlings results in suppression ofgrowth of young sandalwood compared with their growth in theabsence of the host species. Key words: Mineral nutrients, Santalum spicatum, Acacia acuminata, hemiparasites, K/Ca nutrition, seeds     

美丽青背姬小蜂生物学特性研究

美丽青背姬小蜂Chrysonotomyiaformosa（Westwood）是美洲斑潜蝇的优势天敌,在美洲 斑潜蝇的自然控制中发挥着非常重要的作用。本文对其生物学进行了研究,结果表明：在实验 温度范围内,随着温度的升高,寄生蜂羽化趋早,羽化时间更集中,羽化高峰也更明显;随着 温度的升高,成蜂的寿命逐渐缩短。在提供清水时,寄主可以显著地延长雌蜂的寿命;在有寄 主时,提供10%蜂蜜水,雌蜂的寿命显著延长。美丽青背姬小蜂对3龄寄主幼虫有偏好,对3龄寄 主幼虫的致死率和寄生率都高于对1～2龄寄主幼虫的,且产下后代的雌雄性比为5.11∶1。在 实验温度范围内,发育历期随温度的升高而缩短。     

Adaptive behaviour of honeybees (Apis mellifera) toward beetle invaders exhibiting various levels of colony integration

Social bees generally host fewer nest invaders than do ants and termites. This is potentially explained by the adaptive defensive strategies of host bees when faced with nest invaders exhibiting various levels of colony integration (based on adaptations to the nest habitat and frequency of nest inhabitation). In the present study, experiments are performed to determine the behaviour at the nest entrance of European honeybee guards Apis mellifera L. (Hymenoptera: Apidae) toward beetle invaders of various levels of behavioural integration into colonies. The species used to test this include Aethina tumida Murray (Coleoptera: Nitidulidae), which is regarded as a highly integrated, unwelcome guest (synechthran) or true guest (symphile); Lobiopa insularis Laporte (Coleoptera: Nitidulidae) and Epuraea luteola Erichson (Coleoptera: Nitidulidae) that are accidentals; and Carpophilus humeralis Fabricius (Coleoptera: Nitidulidae), Carpophilus hemipterus L. (Coleoptera: Nitidulidae) and Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), all of which are species that are not integrated into honeybee colonies. The responses of guard bees to a control bead also are noted. In general, bees ignore T. castaneum and E. luteola to a greater extent than other beetle species. Bees make contact with the black glass bead (a non‐aggressive behaviour) more than they do all beetle species. Bees treat A. tumida more defensively than they treat any other beetle species and the level of bee defensiveness varies by colony. These data suggest an adaptive heightened defensive response by bees toward the most integrated colony intruder but a significantly reduced level of response toward invaders representing all other levels of colony integration.     

Biological and Cultural Characteristics of the Effective Frankia Strain HFPCcl3 (Actinomycetales) from Casuarina cunninghamiana (Casuarinaceae)

From homogenates prepared from surface-sterilized nodules ofseedlings of Casuarina cunninghamiana grown aeroponically, astrain of Frankia designated HFPCc13 was isolated and has beengrown in pure filamentous culture in a defined synthetic nutrientmedium. Vesicle and sporangium formation can be induced by removalof combined nitrogen from the medium.Frankia strain HFPCc13nodulates young seedlings of C. cunninghamiana and C. equisetifoliawithin three weeks of inoculation with an optimum root mediumpH of 6–7 for nodulation and optimum temperature of 30–35^°C. The presence of combined nitrogen in the root mediuminhibits nodulation with NH₄⁺ more inhibitory than NO₃^–.Frankia HFPCc13 does not nodulate Allocasuarina species withinthe same family nor several other possible actinorhizal plantstested. Thus this strain is quite precise in its host specificity.The rate of acetylene reduction was greater in C. cunninghamianathan the closely related species C. equisetifolia. In neitherof these host species were vesicles observed to occur withinthe infected root nodules which had been demonstrated to beactively fixing dinitrogen. Root nodules were shown to be activein acetylene reduction over a range of O₂ concentration in thegaseous environment with an optimum at about 20 per cent O₂,the ambient P_O2 of the air. The mechanism(s) for oxygen protectionof nitrogenase within the filamentous form of Frankia withinthese nodules remains to be explained. Casuarina, Frankia, nodulation, nitrogen fixation     

菜蛾盘绒茧蜂卵携带的免疫抑制因子

抑制寄主昆虫的免疫反应是内寄生蜂存活的关键。菜蛾盘绒茧蜂Cotesia vestalis（Haliday）寄生小菜蛾Plutella xylostella （L.）幼虫后,蜂卵如何逃避和抑制寄主的免疫攻击,尚未得到全面揭示。本文采用电镜技术系统观察了菜蛾盘绒茧蜂卵表面的超微结构。结果显示：蜂卵表面覆盖有纤维层和絮状的类病毒样纤丝（VLFs）,同时携带了含多分DNA病毒粒子（PDV）的萼液。在寄生初期,包裹在蜂卵表面的纤维层和VLFs首先起到保护蜂卵不被小菜蛾血细胞包囊的被动防御作用。随后,PDV发挥主动的免疫抑制作用。通过假寄生手段,证明了菜蛾盘绒茧蜂PDV (CvBV) 具有较持久的克服寄主免疫攻击的能力,是主要的免疫抑制因子。在假寄生后连续8 d的观察时间内,菜蛾盘绒茧蜂的蜂卵均未被包囊。结果提示,在菜蛾盘绒茧蜂-小菜蛾寄生体系中,菜蛾盘绒茧蜂采取被动防御和主动攻击两种方式应对寄主小菜蛾的免疫攻击。     

闭弯尾姬蜂与菜蛾盘绒茧蜂寄生菜蛾幼虫时的种间竞争

在室内25℃下,以菜蛾3龄初幼虫作寄主,研究了菜蛾盘绒茧蜂Cotesia plutellae和半闭弯尾姬蜂Diadegma semiclausum的种间竞争。当寄主供2种蜂同时产卵寄生时,2种蜂各自的寄生率与其单独寄生时无显著差异,合计寄生率比一种蜂单独存在时有所提高,但差异不显著。2种蜂均能产卵寄生已被另一种蜂寄生了的寄主幼虫。当寄主被2种蜂寄生的间隔时间很短（少于10 h）时,所育出的蜂绝大部分（80%以上）为绒茧蜂;当寄主先被绒茧蜂寄生,并饲养2天以上再供弯尾姬蜂寄生时,所育出的全为绒茧蜂;当寄主先被弯尾姬蜂寄生,并饲养2天以上再供绒茧蜂寄生时,寄主幼虫绝大部分不能存活,只有少部分能育出寄生蜂,且多为弯尾姬蜂。当2种蜂的幼虫存在于同一寄主体内时,2种蜂的发育均受到另一种蜂的抑制;绒茧蜂1龄幼虫具有物理攻击能力,能将弯尾姬蜂卵或幼虫致死。这些结果表明,菜蛾盘绒茧蜂与半闭弯尾姬蜂在同一寄主中发育时,前者具有明显的竞争优势。     

Seasonal dynamics of the Acartia tumida Willey, 1920 (Copepoda: Calanoida) population in nearshore waters of Kievka Bay, Sea of Japan

In 2002, the neritic copepod Acartia tumida was present in the plankton of Kievka Bay from February through July at a temperature of ?1.2 to 14°C with an average population density of 6812 ind/m³ and a biomass of 532.75 mg/m³ (0.12–65.33 and 2.2–87.84% of total copepod density and biomass, respectively). The maximum population density of A. tumida (45 600 ind/m³) was recorded in the first ten-day period of April at a temperature of 2.2–3.8°C. Seasonal variations in the age and sex structure of A. tumida population were found. From February to July, A. tumida produced two generations.     

Homeobox Genes, Retinoic Acid and the Development and Evolution of Dual Body Plans in the Ascidian Herdmania curvata

Ascidians, along with other urochordates, are the most evolutionarydistant group from vertebrates to display definitive chordate-specificcharacters, such as a notochord, dorsal hollow nerve cord, pharynxand endostyle. Most solitary ascidians have a biphasic lifehistory that has partitioned the development of these charactersbetween a planktonic microscopic tadpole larva (notochord anddorsal nerve cord) and a larger sessile adult (pharynx and endostyle).Very little is known of the molecular axial patterning processesoperating during ascidian postlarval development. Two axialpatterning homeobox genes Otx and Cdx are expressed in a spatiallyrestricted manner along the ascidian anteroposterior axis duringembryogenesis and postlarval development (i.e., metamorphosis).Comparisons of these patterns with those of homologous cephalochordateand vertebrate genes suggest that the novel ascidian biphasicbody plan was not accompanied by a deployment of these genesinto new pathways but by a heterochronic shift in tissue-specificexpression. Studies examining the role of all-trans retinoicacid (RA) in axial patterning in chordates also contribute toour understanding of the role of homeobox genes in the developmentof larval and adult ascidian body plans. Our studies demonstratethat RA does not regulate axial patterning in the developingascidian larval neuroaxis in a manner homologous to that foundin vertebrates. Although RA may regulate the expression of someascidian homeobox genes, ectopic application of RA does notappear to alter the morphology of the larval CNS. However, treatmentwith similar or lower concentrations of RA, have a profoundeffect on postlarval development and the juvenile body plan.These changes are correlated to a dramatic reduction of Otxexpression. Through these RA-induced effects we infer that whileRA may regulate the expression of some homeobox genes duringembryogenesis it has a far more dramatic impact on postlarvaldevelopment where regulative processes predominate.     

Confinement Behavior of Cape Honey Bees (Apis mellifera capensis Esch.) in Relation to Population Densities of Small Hive Beetles (Aethina tumida Murray)

We quantified the effects of increasing small hive beetle (Aethina tumida Murray) populations on guarding behavior of Cape honey bees (Apis mellifera capensis, an African subspecies). We found more confinement sites (prisons) at the higher (50 beetles per colony) rather than lower (25 beetles per colony) beetle density. The number of beetles per prison did not change with beetle density. There were more guard bees per beetle during evening than morning. Neither guard bee nor beetle behavior varied with beetle density or over time. Forty-six percent of all beetles were found among the combs at the low beetle density and this increased to 58% at the higher one. In neither instance were beetles causing depredation to host colonies. Within the limits of the experiment, guarding behavior of Cape honey bees is relatively unaffected by increasing beetle density (even if significant proportions of beetles reach the combs).     

Charting the isophasic endophyte of dwarf mistletoe Arceuthobium douglasii (Viscaceae) in host apical buds

• Background and Aims Dwarf mistletoes (Arceuthobium; Viscaceae)are highly specialized dioecious angiosperms parasitic on manygymnosperm hosts in the northern hemisphere. Several dwarf mistletoespecies are capable of inducing an unusual form of isophasicinfection in which the internal (endophytic) system proliferateseven into the apical buds of its hosts. Studies of the internalendophytic system have, for the most part, focused on the parasitewithin secondary host tissues. The present anatomical and ultrastructuralstudy characterizes the growth pattern of the isophasic endophyticsystem of Arceuthobium douglasii within the dormant apical budsof Pseudotsuga menziesii. • Methods Semi-thin serial sections from dwarf mistletoe-infectedhost apical buds were mounted, stained and micrographed. Graphicfiles were created from the serial micrographs and these fileswere stacked. These stacked files were utilized to describethe pattern of growth of the endophyte within the host tissue.The interface between cells of the mistletoe and host was alsoexamined at the ultrastructural level by transmission electronmicroscopy. • Key Results By utilizing a novel technique of superimposedgraphics, the current study reveals an organized pattern ofmistletoe distribution that penetrates further into host tissuesthan previously known. A consistent pattern of growth occurringeven into the preformed leaves of the host is documented. • Conclusions The apparently non-intrusive growth of theparasite appears to be developmentally synchronized with thatof the host. No symplastic connections were observed in theultrastructural examination of the parasite/host interface withinthe apical buds of Pseudotsuga menziesii parasitized by A. douglasiior of Pinus contorta parasitized by A. americanum.     

Formal Genetics of Ascidians

SYNOPSIS. Our knowledge of ascidian genetics is reviewed. Thepaper is primarily concerned with the author's past and currentwork on the colonial species Bolryllus schlosseri. Five Mendelianloci account for most of its impressive polychromatism. Breedingexperiments have substantiated the hypothesis of a single multialleliclocus for each of three enzymes (MDH, SOD, PGI) suggested byelectrophoretic patterns. The nuclei of three linkage groupshave been revealed. Self—fertilization entails a severeinbreeding depression. A specific self, nonself recognition,expressed by fusion or repulsion of contacting colonies, occursin this species also. At variance with Botryllus primigenus,fusible colonies of B. schlosseri are completely interfertile.This has allowed a more direct genetic analysis of the phenomenon,confirming the alleged control by a single multiallelic locus.In order to fuse, the confronted colonies must share at leastone allele. Young buds grafted in the tunic after removal ofall the zooids develop a new colony at the host's expense onlyif donor and host are fusible. This means that fusibility andhistocompatibility are strictly correlated. Chimerical colonies,obtained either in this way or following the resorption of oneof two fused colonies, are now being investigated for theirrecognition specificity and electrophoretic pattern. Preliminarydata indicate that both can be durably altered, suggesting thatthe allogeneic cell populations are persistent and renewing.     

Multiple mating by both sexes in an invasive insect species,Aethina tumida (Coleoptera: Nitidulidae)

Multiple mating by both sexes is common among sexually reproducing animals. Small hive beetles (SHB), Aethina tumida, are parasites of bee nests endemic to sub-Saharan Africa and have become a widespread invasive species. Despite the considerable economic damages they can cause, their basic biology remains poorly understood. Here we show that male and female small hive beetles can mate multiple times, suggesting that costs for mating are low in this species. In an invasive A. tumida population in the United States, a combination of laboratory experiments for males and paternity analysis with eight polymorphic DNA microsatellite markers for field-caught females were used to estimate the number of mating by both sexes. The data show that females and males can mate multiple times—females mated with up to eight males, whereas males mated with at least seven females. The results also showed that A. tumida displayed a skewed paternity, although this was not consistent among the tested females. Thus, first or last male advantage seem to be unlikely in A. tumida. Our observations that individuals of both sexes of A. tumida can mate multiple times opens new research avenues for examining drivers of multiple mating and determining the role it may play in promoting biological invasions.     

Social parasitism by honeybee workers (Apis mellifera capensis Escholtz): host finding and resistance of hybrid host colonies

We studied possible host finding and resistance mechanisms ofhost colonies in the context of social parasitism by Cape honeybee(Apis mellifera capensis) workers. Workers often join neighboringcolonies by drifting, but long-range drifting (dispersal) tocolonies far away from the maternal nests also rarely occurs.We tested the impact of queenstate and taxon of mother andhost colonies on drifting and dispersing of workers and on the hosting of these workers in A. m. capensis, A. m. scutellata,and their natural hybrids. Workers were paint-marked accordingto colony and reintroduced into their queenright or queenlessmother colonies. After 10 days, 579 out of 12,034 labeled workerswere recaptured in foreign colonies. We found that driftingand dispersing represent different behaviors, which were differentlyaffected by taxon and queenstate of both mother and host colonies.Hybrid workers drifted more often than A. m. capensis and A.m. scutellata. However, A. m. capensis workers dispersed moreoften than A. m. scutellata and the hybrids combined, and A. m. scutellata workers also dispersed more frequently than thehybrids. Dispersers from queenright A. m. capensis colonieswere more often found in queenless host colonies and vice versa,indicating active host searching and/or a queenstate-discriminatingguarding mechanism. Our data show that A. m. capensis workersdisperse significantly more often than other races of A. mellifera,suggesting that dispersing represents a host finding mechanism.The lack of dispersal in hybrids and different hosting mechanismsof foreign workers by hybrid colonies may also be responsiblefor the stability of the natural hybrid zone between A. m.capensis and A. m. scutellata.     

Pectolytic Activity by the Haustorium of the Parasitic PlantOrobancheL. (Orobanchaceae) in Host Roots

The possible involvement of enzymes in the penetration of intrusivecells of the parasitic angiospermOrobancheinto host root tissueswas studied using cytochemical and immunocytochemical methods.Pectin methyl esterase (PME) was detected, with specific antibodies,in the cytoplasm and cell walls ofOrobancheintrusive cells andin adjacent host apoplast. Depletion and chemical changes ofpectins in host cell walls were shown by histochemical stainingwith PATAg, which detects carbohydrates that are sensitive toperiodic acid, especially pectins, and with the monoclonal antibodiesJIM 5 and JIM 7 that label pectins with low and high rates ofesterification, respectively. Galacturonic sequences with lowrates of esterification were more abundant in host cell wallsadjacent to the parasite, which is consistent with pectin de-methylationby PME release from the parasite. Pectins were absent in middlelamellae and in host cell walls neighbouring mature intrusivecells of the parasite, consistent with further degradation ofpectins by other enzymes. These results provide the first directevidence for the presence and activity of a pectolytic enzymein the infection zone of the haustorium of a parasitic angiosperminsitu.Copyright 1998 Annals of Botany Company Broomrape;Orobanche; parasitic weed; haustorium; pectin methyl esterase; pectin; cell wall.