Chemical defence in ladybird beetles (Coccinellidae). I. Distribution of coccinelline and individual variation in defence in 7-spot ladybirds (Coccinella septempunctata)

Summary 7-spot ladybirds secrete alkaloid (coccinelline)-rich fluid (reflex blood) from leg joints as a defence mechanism against predators. A technique is described that enables the collection and accurate quantification of reflex blood produced, and the amount of coccinelline therein. Coccinelline was found distributed throughout the body, although concentrated in the reflex blood. Reflex blood was collected from a large set of beetles at several time points. Significant variation was found among beetles in the amount of reflex blood produced (for males and for females corrected for body weight) and the coccinelline concentration of the reflex blood. The results are discussed in relation to automimicry and the maintenance of variation through energy trade-offs. The relationships between tendency to aggregate, ability to reflex bleed and the possession of aposematic coloration are also considered.     

Is the alkaloid in 2spot ladybirds (Adalia bipunctata) a defence against ant predation?

Garden black ants,Lasius niger L., in a laboratory colony, attacked three species of live ladybirds found near their nest, killing the smaller two species. A second colony was offered artificial diets containing crushed ladybirds of two species, and the ants' choice of feeding site noted. Both the diets were aversive compared to control, but that containing 7spot,Coccinella septempunctata L., was more aversive than the diet containing 2spot,Adalia bipunctata L. The implications of this lesser protection for 2spots in terms of the chemical defence of the species are discussed.     

Toxicity assays of ladybirds using natural predators

Nestling blue titsParus caeruleus L. were given diets containing homogenized ladybirds, to assess the effects of their chemical defences. The 2spot, 10spot and water ladybirds produced no apparent toxic effects when small numbers were given at regular intervals.The pine and kidney-spot ladybirds slightly inhibit growth and may be toxic to very young nestlings. The Water ladybird is extremely distasteful to this predator, despite its lack of toxicity. The results are discussed with reference to the proposed Müllerian and Batesian mimetic relationships between the ladybird species.     

Ladybird defence alkaloids: Structural,chemotaxonomic and biosynthetic aspects (Col.: Coccinellidae)

Summary The defensive mechanisms which protect ladybird beetles (Coccinellidae) against predators are reviewed. Besides behavioural mechanisms, such as thanatosis and reflex bleeding, chemical defence mechanisms are playing a prevalent role. Indeed, ladybirds are protected not only by their smell, but also by repulsive alkaloids, most of which are considered to be of autogenous origin. In a few cases, dietarily-acquired substances are also involved. Particular emphasis is laid on the repellent alkaloids which are contained in the haemolymph of many species. The structures of 34 nitrogen-containing compounds isolated so far are presented, and their distribution within the family is discussed in the light of the most widely accepted classification of these beetles. To conclude, the mode of release of the alkaloids, their variation through the life cycle and their repellent and toxic properties are discussed, as well as the few biosynthetic data yet available.     

Induced alkaloid defence inAtropa acuminata in response to mechanical and herbivore leaf damage

Summary Measurement of tropane alkaloid content in leaves ofAtropa acuminata after mechanical damage showed a maximum increase to 153% of the control 8 days later. There were no changes in the root or stem after similar damage. The plant responded to repeated mechanical damage by doubling its alkaloid content at 11 days after the initial wounding. But on further treatments, there was a slight decrease in alkaloid content with time. Mollusc feeding produced an increase of 164% in alkaloid content after 4 days. These results indicate that induced defence systems in angiosperms can vary considerably from plant species to plant species and that the effects of mechanical damage may differ in different parts of the same plant.     

Intraguild predation by <Emphasis Type="Italic">Harmonia axyridis</Emphasis> on coccinellids revealed by exogenous alkaloid sequestration

Summary.  Under laboratory conditions, the multicolored Asian lady beetle, Harmonia axyridis is well known as an intraguild predator of other ladybirds. However the real impact of this exotic species on native species was poorly investigated in the field. Because many ladybird species produce alkaloids as defensive compounds, we propose here a new method of intraguild predation monitoring in coccinellids based on alkaloid quantification by GC-MS. In laboratory experiments, adaline was unambiguously detected in fourth instar larvae of H. axyridis having ingested one egg or one first instar larva of Adalia bipunctata. Although prey alkaloids in the predator decreased with time, traces were still detected in pupae, exuviae and imagines of H. axyridis having ingested one prey when they were fourth instar larvae. Analysis of H. axyridis larvae collected in two potato fields shows for the first time in Europe the presence of exogenous alkaloids in 9 out of 28 individuals tested. This new method of intraguild predation detection could be used more widely to follow the interactions between predators and potential chemically defended insect preys.     

Modified Cave Entrances: Thermal Effect on Body Mass and Resulting Decline of Endangered Indiana Bats (Myotis sodalis)

Entrances to many caves occupied by the endangered Indiana bat ( Myotis sodalis ) have been modified to control human access. We show that modifying cave entrances can degrade the bats' winter habitat, we demonstrate one mechanism by which this damage occurs, and we document a restoration experiment. We compared a large bar population in an unmodified cave with a small, reduced bat population in a cave with warm winter temperatures resulting from an entrance wall that impeded air exchange. In the modified cave, mean winter temperature at the hibernation site was 5.0° C higher than in the unmodified cave, bats entered hibernation at a 5% higher body mass, bats lost 42% more mass and the frequency distribution of late-winter mass was truncated, with no bats weighing less than 5.4 g. The results describe unacceptable extremes for hibernation: subfreezing temperatures and warm temperatures causing mass-loss rates of more than 0.009 g/day. Over a decade following removal of the entrance-constricting wall, the population increased from 2,000 to 13,000 bats. Previous recommendations, based on common-sense observation, to open blocked cave entrances are confirmed by this study. The similar case of Coach Cave, Kentucky, offers the potential for recovery of 100,000 Indiana bats.     

Ladybird mothers mitigate offspring starvation risk by laying trophic eggs

A large proportion of ladybird beetle (Coleoptera: Coccinellidae) eggs are apparently infertile—they do not develop an embryo and are consumed by larvae hatching within the egg batch. The predicted benefits of egg consumption for larvae are empirically well supported. An important question, however, remains: are these eggs a maternal strategy to feed offspring (i.e., trophic eggs) or did egg eating evolve to exploit unavoidably infertile eggs? We investigated the adaptive value of infertile eggs in laboratory experiments with multicoloured Asian ladybirds (Harmonia axyridis). Female H. axyridis were assigned to low and high resource environments for brief intervals; we predicted that tactics to facilitate egg cannibalism, such as infertile egg production and hatching asynchrony, would be adopted in low food environments in which starvation risk for offspring is greater. We conducted two experiments in this manner that provided females with information about resource levels through prey feeding or scent. We also observed female oviposition patterns and tested for infertile egg distributions that departed from random. Females produced 56% more infertile eggs in the low vs. the high food treatment; however, hatching synchrony did not change. We consider a potential confound between information and nutrition state unlikely because ladybirds are well able to tolerate low food for 24 h, the duration of trials, and because females were in good condition when trials began. Results suggest that ladybirds use information from prey encounter to manipulate the proportion of trophic eggs in a manner consistent with the adaptive hypothesis, the first evidence of trophic egg plasticity in a non-eusocial insect.     

Inorganic mercury and methylmercury in surface sediments and mussel tissues from a microtidal lagoon (Bizerte, Tunisia)

The aim of this study was to investigate the distribution of mercury compounds in marine sediments and mussel tissues collected in the lagoon of Bizerte, Tunisia, during two seasons (summer and winter). Inorganic mercury (Hg²⁺) concentrations in sediments were found to be highly variable, ranging from 0.04 nmol.g¹ to 3.22 nmol.g⁻¹ (dry weight) with a mean value of 0.52 nmol.g⁻¹. Anthropogenic sources of Hg²⁺, most probably metallurgy or tire production industries, have been evidenced. The mean concentration of monomethylmercury (MeHg⁺) in the surface sediments is 2.32 pmol g⁻¹ ranging from below the detection limit (0.45 pmol.g⁻¹) to 14.6 pmol.g⁻¹. No significant variation was observed between winter and summer seasons for both mercury species concentration in the sediments. The Hg²⁺ concentrations in mussel tissues are also variable, ranging from 0.007 to 1.347 nmol.g⁻¹ (dry weight). The mean concentration is 0.70 nmol.g⁻¹. In these tisssues, Hg²⁺ is generally the major compound, making up ca. 88% of total mercury concentrations. However, methylmercury concentrations are significant and homogeneous, ranging from 62 to 121 pmol.g⁻¹ (mean 96 pmol.g⁻¹). The results suggest that a fraction of the inorganic mercury load in the sediments of the lagoon undergoes methylation pathways. MeHg⁺ produced is assimilated in the mussels more readily than Hg²⁺.     

Rodent predation on hibernating peacock and small tortoiseshell butterflies

Insects that hibernate as adults have a life span of almost a whole year. Hence, they must have extraordinary adaptations for adult survival. In this paper, we study winter survival in two butterflies that hibernate as adults and have multimodal anti-predator defences—the peacock, Inachis io, which has intimidating eyespots that are effective against bird predation, and the small tortoiseshell, Aglais urticae, which does not have an effective secondary defence against birds. We assessed predation on wild butterflies hibernating in the attic of an unheated house, as well as survival of individually marked butterflies placed by hand on different sites in the attic. Our objectives were to assess (1) the number of butterflies that were killed during hibernation, (2) whether survival differed between butterfly species, and (3) how predation was related to hibernation site and the identity of the predator. There was a strong pulse of predation during the first 2 weeks of hibernation: 58% of A. urticae and 53% of I. io were killed during this period. Thereafter, predation decreased and butterfly survival equalled 98% during the final 16 weeks of hibernation. There was no difference in survival between the two butterfly species, but predation was site-specific and more pronounced under light conditions in locations accessible to a climbing rodent, such as the common yellow-necked mouse, Apodemus flavicollis. We contend that small rodents are likely important predators on overwintering butterflies, both because rodents are active throughout winter when butterflies are torpid and because they occur at similar sites.     

Resistance of the generalist moth Trichoplusia ni (Noctuidae) to a novel chemical defense in the invasive plant Conium maculatum

Summary. Conium maculatum is an apiaceous species native to Eurasia that is highly toxic to vertebrates due to the presence of piperidine alkaloids, including coniine and γ-coniceine. More than 200 years after invading the United States this species remains mostly free from generalist insect herbivores. The presence of novel chemical defenses in the introduced range could provide invasive species with a competitive advantage relative to native plants. The cabbage looper (Trichoplusia ni) is a generalist lepidopteran found throughout the US that occasionally feeds on C. maculatum. We evaluated the toxicity of piperidine alkaloids to T. ni and determined putative resistance mechanisms, both behavioral and physiological, that allows this insect to develop successfully on C. maculatum foliage. T. ni larvae raised on diets enriched with coniine and γ-coniceine showed a decrease in consumption and longer development time, but no effects on growth were found at any alkaloid concentration. In a diet choice experiment T. ni larvae showed no avoidance of alkaloid-enriched diets, suggesting that the deterrence produced by alkaloids was related to a post-ingestive metabolic response. The ability of T. ni to consume diets high in alkaloid content could be due to at least three different mechanisms: 1) a decreased consumption rate, 2) efficient excretion of at least 1/3 of ingested alkaloids unmetabolized in frass, and 3) partial detoxification of alkaloids by cytochrome P450 s, as shown by the decreased larval growth in the presence of piperonyl butoxide, a P450 inhibitor. Even though T. ni tolerates C. maculatum alkaloids, the use of this species as a host plant could be ecologically disadvantageous due to prolonged larval growth and thus increased exposure to predators. Novel plant secondary compounds do not guarantee increased resistance to generalist herbivores.     

Seasonal anorexia in the male red-sided garter snake,<Emphasis Type="Italic"> Thamnophis sirtalis parietalis</Emphasis>

Many animals show seasonal shifts in behaviors that coincide with breeding, migration, or hibernation. These behavioral shifts provide ideal opportunities to study the regulation of behavior. The red-sided garter snake (Thamnophis sirtalis parietalis) spends 8 months of the year inactive in underground hibernacula, 1 month breeding, and 3 months feeding to build up enough energy stores to survive the following winter. Although they emerge from 8 months of hibernation with severely depleted energy reserves, they do not feed until weeks later, after the breeding season. We tested the hypothesis that this lack of feeding during the breeding season is due to a shift in behavior rather than the distribution of food and potential mates. Male garter snakes were given a series of choices between pursuing a breeding or feeding opportunity. The proportion of tests in which males selected feeding over breeding gradually increased throughout the study period, reaching almost 100% in the final tests. Males also were given opportunities to feed and court at the beginning and end of the study. Males initially refused food and courted females, but when retested at the end of the study they fed and did not court females. Thus aphagia during the breeding season is due at least in part to an endogenous shift in behavior.Communicated by P. Weatherhead     

Some polyphagous Homoptera gain protection from their natural enemies by feeding on the toxic plantsSpartium junceum andErythrina corallodendrum (Leguminosae)

Summary Interactions were studied among alkaloid-containing legumes (Erythrina corallodendrum andSpartium junceum) and non-toxic plants (Citrus sinensis, Cucurbita moschata andEuphorbia tirucalli), several polyphagous homopterans,Aphis craccivora (Aphididae),Icerya purchasi, I. aegyptiaca (Margarodidae),Lepidosaphes ulmi (Diaspididae) andPlanococcus citri (Pseudococcidae), and some major natural enemies of these homopterans. Significant reductions in survival due to negative effects of alkaloid containing as compared with non-alkaloidal plants were recorded for the predatorsRodolia cardinalis andChilocorus bipustulatus, but not forCryptolaemus montrouzieri (Coleoptera: Coccinellidae),Chrysoperla carnea (Neuroptera: Chrysopidae) andSympherobius sanctus (Neuroptera: Sympherobiidae). The development time of the larvae or pupae ofR. cardinalis, C. carnea andS. sanctus was longer on the toxic plants than on the non-toxic ones. The percentage of parasitism ofA. craccivora collected from the non-alkaloidal plantsVicia palaestina andMelilotus albus was much higher than that onS. junceum. The parasitoid complexes ofA. craccivora differed between both plant groups. The nutritive value of honeydew ofI. purchasi andA. craccivora, as expressed by the life span ofEncyrtus infelix (Hymenoptera: Encyrtidae) adults, was also investigated. Life spans were significantly longer when the wasps fed on honeydew produced on non-alkaloidal plants (C. sinensis andPittosporum tobira) than on alkaloid containing plants whenI. purchasi — but notA. craccivora — was the producer. It is suggested that the chemical defense ofE. corallodendrum andS. junceum is exploited by polyphagous phytophages to reduce predation. In nature, population growth and density of four of the investigated homopterans are conspicuously high when they developed on the alkaloid containing plant species, and very low on non-alkaloid plants. The efficiency of their natural enemies may be reduced by sequestration of alkaloids (or other toxic plant compounds) or their transfer into excreted honeydew. Therefore it is assumed that a generalist phytophagous homopteran may be protected from its natural enemies, although at different rates of efficiency, if it can safely sequester the host allelochemical when it develops on toxic species within its host range.     

Chemical defense of the ladybird beetle Epilachna paenulata

Summary. The defensive chemistry of the ladybird beetle Epilachna paenulata (Coleoptera: Coccinellidae) was characterized as a mixture of piperidine, homotropane and pyrrolidine alkaloids. Whole body extracts of adult beetles contain four major alkaloids: 1-(6-Methyl-2,3,4,5-tetrahydro-pyridin-2-yl)-propan-2-one; 1-(6-methyl-2-piperidyl)-propan-2-one; 9-aza-1-methyl-bicyclo[3.3.1]nonan-3-one and 1- (2′′- hydroxyethyl)-2-(12′-aminotridecyl)-pyrrolidine. Comparative studies of the defensive chemistry of eggs, larvae, pupae and adults showed both qualitative and quantitative differences in alkaloid composition among the four life stages, and also within adult age. Laboratory predation bioassays with wolf spiders showed that the adults are better protected than the larvae and pupae. Field tests showed the adult alkaloid extract to be deterrent to ants.     

Role of surface chemical signals in egg cannibalism and intraguild predation in ladybirds (Coleoptera: Coccinellidae)

Summary. The eggs of some ladybirds are known to be toxic to intraguild ladybird predators. However, this defence is of little value if the eggs are killed before their toxicity becomes apparent. The results presented in this paper indicate that chemicals on the surface of the eggs of two species of ladybirds signal the relative risk of cannibalism and intraguild predation. In Adalia bipunctata and Coccinella septempunctata, 87% of the chemicals are alkanes. Each species of ladybird is less reluctant to eat their own eggs than those of the other species. This asymmetry is to be expected because there is a greater risk to ladybirds from intraguild predation than cannibalism. Similar alkanes to those on the surface of the eggs of A. bipunctata are present in tracks left by larvae and on the elytra of the adults of this species. Those in the larval tracks deter females from ovipositing in patches of prey already being attacked by their larvae and those on the elytra are used in mate recognition. That different context dependent messages could be signalled by similar chemicals is an example of semiochemical parsimony. Received 25 February 2000; accepted 22 May 2000     

Allelochemical effects of ergoline alkaloids fromIpomoea parasitica onHeliothis virescens

Lysergol, elymoclavine and three other van Urk-positive alkaloids were identified by 2D chromatography in the seed extract ofIpomoea parasitica. The presence of the same ergoline alkaloids was also demonstrated in vegetative tissue ofI. parasitica. Heliothis virescens larvae reared on a diet containing an alkaloid extract ofI. parasitica showed an increase in the consumption index and a reduction in the effiency of conversion of food. No difference was observed in the approximated digestibility. The percentages of pupation and emergence were reduced and the malefemale ratio was altered in insects fed on a diet containing the alkaloid extract ofI. parasitica or lysergol. The increases in the concentration of ergoline alkaloids inI. parasitica at the seedling stage and at flowering support the theory that these compounds play a defensive role against herbivory in the plant.     

Hibernation clustering and its consequences for associative nest foundation in<Emphasis Type="Italic"> Polistes dominulus</Emphasis> (Hymenoptera Vespidae)

Various studies indicate that cuticular hydrocarbons (CHCs) act as cues for nestmate recognition in paper wasps and other social insects. A recent study showed that associative nest foundation in Polistes dominulus is mainly performed by foundresses coming from the same locality. In the present study, we induced future foundresses of P. dominulus collected in two different localities to hibernate in the laboratory in aggregates of individuals from the same or different localities. After 2 months of hibernation, foundresses from different localities but from the same experimental cluster did not show any preference to associate, at the time of nest foundation, with individuals coming from the same original locality. The cuticular chemical profiles of individuals from the mixed hibernation clusters were quite similar and significantly different from those of individuals which hibernated with other foundresses from the same locality. These findings suggest that, in this species, mechanisms other than nestmate chemical recognition play a major role in the spring association of gynes during the foundation of a new nest.Communicated by R.F.A. Moritz     

Distribution, seasonal abundance and bycatch of basking sharks (Cetorhinus maximus) in New Zealand, with observations on their winter habitat

Basking sharks occur throughout New Zealand, but are most common in cool temperate latitudes of 39-51°S. Inshore records from miscellaneous sources peaked in spring-summer, with few winter records. Two records were of sharks observed in a large brackish water lake. About 203 basking sharks were observed caught by commercial trawlers between 1986 and 1999. Multiple captures were common, including 14 in one tow. Most trawl-caught sharks were taken near or outside the 250 m depth contour, and 91% came from three small regions - East Coast (EC) and West Coast (WC) of South Island and Snares-Auckland Islands (SA). The highest catch (93 sharks) and catch rate (58 sharks per 1,000 tows) were from EC, where sharks were caught only in spring-summer. In SA, sharks were caught mainly in summer, and in WC all were caught in winter. The modal seabed depths for shark tows were 300-400 m at EC, 700-800 m at WC and 150-250 m at SA. Sharks were therefore caught in the deepest water in winter at WC. It was impossible to determine the actual depths of capture, but circumstantial evidence indicates that most sharks were caught on or near the bottom. The capture of some sharks in midwater in winter argues against hibernation, because hibernating sharks are unlikely to hover in midwater. Males dominated catches in all regions, particularly in WC and SA. In WC and SA, most sharks (94%) were 7-8 m long, whereas in EC most sharks (73%) were <7 m. Based on their lengths, many of the WC and SA males could have been mature, but most EC males were probably immature. Few of the females would have been mature. This study provides support for the hypothesis that basking sharks over-winter in deep water on the continental slope.     

Ri质粒诱导喜树毛状根培养基中喜树碱的研究

喜树(Camptotheca acuminate)可产生具有抗癌作用的喜树碱,有许多用细胞培养方法制备喜树碱的尝试,但都因极低的产率而无从深入。植物毛状根培养的应用将成为一种生物碱生产的替代方法。以发根农杆菌(Agrobacterium rhizogenes)A41.2556感染喜树诱导产生毛状根,建立喜树碱毛状根产生体系。甘露碱检测及PCR结果证实发根农杆菌Ri质粒的rolB基因已在喜树毛状根基因组中整合并得到表达。确定了用RP-HPLC测定发根培养基中喜树碱的的方法,比较了不同的吸附树脂对培养基中喜树碱的富集能力,从培养30d的喜树培养基中获得喜树碱干质量分数为0.14mg·g-1。     

The evolution of marmot sociality: II. Costs and benefits of joint hibernation

Summary Social groups of alpine marmots (Marmota marmota) were studied for 7 years. The groups consisted of a territorial pair and up to 18 lower ranking animals of various ages, mostly the pair's offspring (Tables 1, 2). Group members lived in a common home range and always hibernated together in one hibernaculum. Groups with older, subordinate animals experienced slightly higher summer mortality but significantly reduced winter mortality (Fig. 1). Infant winter mortality was further decreased if most older subordinates were potentially their full sibs (Fig. 2). Subordinate group members lost less mass during winter with increasing size of the hibernating group, but this trend was reversed when infants were present. Furthermore, augmented mass loss due to low hibernaculum quality became evident (Fig. 3). Apart from these effects, the presence of infants caused additional mass loss in potential full sibs. The opposite was found in subordinates certainly descending from other parents than those of the infants (Table 3).Winter mortality and mass loss data revealed (i) a general benefit of joint hibernation, (ii) an unavoidable cost of infants' presence to other group members, (iii) that only potential full sibs helped in warming infants, (iv) that helping was energetically expensive and increased infant survival. The evolution of postponed dispersal in ground-dwelling squirrels has been attributed to the direct fitness gained by enhanced reproductive chances of offspring when not expelled from the natal territory (Armitage 1981, 1987, 1988). This study shows that group living in alpine marmots has benefits during winter and indicates the additional importance of kin selection in marmot social evolution.