Oviposition responses to patch quality in the larch ladybird Aphidecta obliterata (Coleoptera: Coccinellidae): effects of aphid density, and con- and heterospecific tracks

The effects and persistence of oviposition-deterring semiochemical cues from conspecific and heterospecific larval tracks on the oviposition rate of Aphidecta obliterata (Linnaeus) females were investigated. In addition, the effects of varying aphid prey density were considered and also whether any resulting response originated from differential nutritional status of females and/or due to aphid odour stimuli. The existence of oviposition responses to conspecific egg chemicals was also considered. Gravid A. obliterata females were deterred from oviposition by conspecific larval tracks and the effect was density dependent. Females actively avoided searching in these contaminated areas. Tracks induced a significant effect on oviposition for up to three days. Heterospecific tracks of the coccinellid Adalia bipunctata (Fabricius) or the chrysopid Chrysoperla carnea (Stephens) did not induce any oviposition response in A. obliterata females. Increasing aphid density induced increased oviposition rate in A. obliterata females. Nutritional status of females was an important factor in the relationship between aphid density and oviposition rate, but aphid associated cues (odours) were not. There was an inhibitory effect of extracts of conspecific egg-surface chemicals on oviposition by A. obliterata females. In the field, cannibalism, competition and limited food availability represent the major threats to egg and larval survival. Patch quality assessment mechanisms enable females to lay eggs at sites where offspring survival is maximized. Oviposition-deterring semiochemicals tend to promote more even distribution of predators over prey patches.     

Variability of the mitochondrial gene for cytochrome oxidase I within the Adalia bipunctata species and within species of ladybird beetles (Coleoptera: Coccinellidae)

Intergeneric, interspecific, and intraspecific genetic variation of the 310-bp 3'-end region of the mitochondrial gene of cytochrome oxidase I (COI) has been assessed in ladybirds (Coleoptera: Coccinnellidae). The phylogenetic distances between eight species of ladybirds have been determined. Mitochondrial DNA (mtDNA) nucleotide sequences have been compared in Adalia bipunctata L. differing in the elytron and pronotum colors that have been sampled from several geographically remote populations. The taxonomic statuses of two morphs from the genus Adalia, A. bipunctata bipunctata and A. bipunctata fasciatopunctata, have been identified.     

Eat or be eaten: prevalence and impact of egg cannibalism on two-spot ladybirds, Adalia bipunctata

Ladybirds commonly engage in cannibalistic behaviour. Egg cannibalism by first instars is considered advantageous to the cannibal, because it not only results in direct metabolic gain but also a reduction in potential competitors. In this study, we quantified the effect of cannibalism on the development rate and survival of Adalia bipunctata (L.) (Coleoptera: Coccinellidae) larvae through development to the adult stage. We also assessed the synchrony of egg‐hatching in relation to laying order and compared the proportion of eggs cannibalized in egg batches laid as clusters or linearly. Larvae that had consumed a conspecific egg after hatching reached the adult stage 1.65 days earlier than those larvae that had not. Larval and pupal mortality was lower for cannibals compared to non‐cannibals; only 46% of non‐cannibalistic individuals reached the adult stage whereas 81% of cannibals pupated successfully. Egg cannibalism is undoubtedly advantageous to A. bipunctata larvae both in terms of faster development and increased survival. There is a positive correlation between laying and hatching order for eggs laid linearly or in a cluster. There was no significant difference in the proportion of eggs hatching in clusters or in a line (80 and 77%, respectively). The remaining eggs were either cannibalized or did not hatch. The ecological implications of these results are discussed with particular reference to trophic egg plasticity.     

Avoidance responses of an aphidophagous ladybird, Adalia bipunctata, to aphid-tending ants

Abstract.  1. Insect predators often aggregrate to patches of high prey density and use prey chemicals as cues for oviposition. If prey have mutualistic guardians such as ants, however, then these patches may be less suitable for predators.
2. Ants often tend aphids and defend them against predators such as ladybirds. Here, we show that ants can reduce ladybird performance by destroying eggs and physically attacking larvae and adults.
3. Unless ladybirds are able to defend against ant attacks they are likely to have adaptations to avoid ants. We show that Adalia bipunctata ladybirds not only move away from patches with Lasius niger ants, but also avoid laying eggs in these patches. Furthermore, ladybirds not only respond to ant presence, but also detect ant semiochemicals and alter oviposition strategy accordingly.
4. Ant semiochemicals may signal the extent of ant territories allowing aphid predators to effectively navigate a mosaic landscape of sub-optimal patches in search of less well-defended prey. Such avoidance probably benefits both ants and ladybirds, and the semiochemicals could be regarded as a means of cooperative communication between enemies.
5. Overall, ladybirds respond to a wide range of positive and negative oviposition cues that may trade-off with each other and internal motivation to determine the overall oviposition strategy.     

Assessment of patch quality by ladybirds: role of larval tracks

Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches. Received: 14 March 1997 / Accepted: 26 August 1997     

How do the consumption and development rates of the conifer specialist Aphidecta obliterata respond to temperature,and is it better adapted to limited prey than a generalist?

This study aimed to address the effect of temperature on the consumption and development rates of Aphidecta obliterata and to compare the responses of Ap. obliterata (specialist) with that of Adalia bipunctata (generalist) to prey limitation. Temperature had a significant and positive effect on the time to egg hatch of Ap. obliterata . The duration of the larval instars was not affected by prey species at 15°C but was significantly shorter, 12.1 days at 20°C compared with 21.1 days at 15°C. The proportion of time spent in each instar, however, was not affected by temperature or prey species, but the duration of the pupal stage was significantly affected by temperature. The average daily consumption of prey aphids increased with instar and was significantly influenced by temperature. There was a significant difference in the length of the pupal stage between coccinellid species but not that of the larval stage. The duration of the larval period increased under conditions of prey shortage. The pupal period of Ap. obliterata was significantly affected by the food regime but not that of Ad. bipunctata . There was a significant interaction between species and food supply on the length of the pupal stage and the larval stage and the final fresh weight achieved by the newly emerged adults. Male adults weighed significantly less than the females in all regimes. Larvae of Ap. obliterata and Ad. bipunctata did not consume any of the alternative prey (Collembola or Psocoptera) provided. There was no significant difference in the consumption of prey between the two coccinellid species. The results suggest that both of these coccinellids are well adapted to low-density-specific prey. There were no obvious differences between the two, which would tend to favour either species in an environment of limited prey.     

Reproductive development and maternal effects in the pine weevil Hylobius abietis

1. In a laboratory study of maturation feeding of female pine weevil Hylobius abietis on current and 1‐year‐old stem bark of transplants of Scots and Corsican pine, Norway and Sitka spruce, Douglas fir, and hybrid larch, the length of the pre‐oviposition period was influenced by the species on which weevils fed. The shortest pre‐oviposition period was on hybrid larch (11.8 days) and the longest on Douglas fir (15.5 days). 2. The species on which weevils fed also affected fecundity but there was evidence of a species–year interaction. Over a period of 36 days, most eggs were laid by weevils feeding on current stem of Norway spruce and Corsican and Scots pine and fewest on current stem of Sitka spruce. 3. Significant maternal effects on egg size were observed both in relation to female size and conifer species. The largest eggs were laid on Corsican pine and the smallest on Douglas fir, with no evidence of a trade‐off between number of eggs laid and their size. 4. There was a positive relationship between egg and larval size and between larval size and survival on logs of four conifer species. Residual resistance mechanisms in the bark of recently cut stumps and larval competition are discussed briefly in relation to the importance of the observed maternal effects on weevil population dynamics.     

Egg composition and reproductive investment in aphidophagous ladybird beetles (Coccinellidae: Coccinellini): egg development and interspecific variation

Abstract Most studies of insect reproductive allocation concentrate on propagule size and number and very few consider egg composition, which is likely to be equally important. In the present study, data are provided on changes in egg lipid, glycogen, free carbohydrate and protein during embryonic development of the aphidophagous ladybird Adalia bipunctata (L.) and the compositions of A. bipunctata, Adalia decempunctata and Anisosticta novemdecimpunctata eggs are compared. In A. bipunctata, egg mass, lipid and glycogen decline strongly during development and egg protein declines more weakly. Free carbohydrate declines early in egg development and increases at egg hatching. Lipid is energetically the most important developmental fuel, although approximately half of the initial egg lipid remains in the neonate larva. Across the three species, energy per unit egg mass is lowest in the least specialized species, A. bipunctata, which also has the largest eggs, and is highest in the most specialized, An. novemdecimpunctata, which has the smallest eggs. Two possible explanations for the observed pattern are discussed: (i) species laying smaller eggs may incur higher developmental costs per unit mass than species laying larger eggs and (ii) more specialized species, which reproduce at lower aphid densities, may provision neonate larvae better to facilitate location and capture of aphids.     

Reduced realised fecundity in the pine looper Bupalus piniarius caused by host plant defoliation

1. Whether the potential fecundity of herbivorous insects is realised or not may depend on female behaviour, which in turn may be influenced by host plant acceptability. Female Bupalus piniarius were observed to discriminate against needles growing out the year following defoliation (current‐year needles) of its host plant Pinus sylvestris. 2. It was hypothesised that the discriminatory behaviour was due to current‐year needles being less secure as a substrate. Field and laboratory experiments were designed to test this hypothesis and to estimate the discrepancy between potential and realised fecundity when females were offered defoliated branches. 3. In a laboratory oviposition experiment, B. piniarius females were exposed to branches bearing either current‐year needles only or both mature and current‐year needles. Daily oviposition rate, egg batch size, longevity, and mature eggs and fat retained at death were recorded for each female. In field experiments, the rate at which eggs dropped from expanding needles and the capacity of neonate larvae hatching from the dropped eggs to colonise a tree were assessed. 4. Significantly fewer eggs were laid when females were exposed to defoliated branches. 5. Twenty‐six and 16% of the eggs laid on current‐year needles dropped from the needles in 1998 and 1999 respectively, whereas no eggs dropped from mature needles in 1998 and only one egg (< 1%) dropped in 1999. 6. A very small proportion of larvae hatching on the forest floor (simulated egg drop) was able to recolonise host trees. 7. These results emphasise the importance of oviposition behaviour on realised fecundity when analysing insect population dynamics. In the case of B. piniarius, egg placement, although a minor detail during the normal course of events, became of key importance when defoliation deprived females of their preferred egg attachment site.     

Intraspecific and Interspecific Variation of the Mitochondrial Gene of Cytochrome Oxidase I in Ladybirds (Coleoptera: Coccinellidae)

Intergeneric, interspecific, and intraspecific genetic variation of the 310-bp 3-end region of the mitochondrial gene of cytochrome oxidase I (COI) has been assessed in ladybirds (Coleoptera: Coccinnellidae). The phylogenetic distances between eight species of ladybirds have been determined. Mitochondrial DNA (mtDNA) nucleotide sequences have been compared in Adalia bipunctata L. differing in the elytron and pronotum colors that have been sampled from several geographically remote populations. The taxonomic statuses of two morphs from the genus Adalia, A. bipunctata bipunctata and A. bipunctata fasciatopunctata, have been identified.     

Attack strategy of ladybird beetles (Coccinellidae): factors shaping their numerical response

Summary Temporal changes in aphid abundance pose a considerable challenge to ovipositing aphidophagous ladybirds, as in order to maximize their fitness they need to synchronize their reproduction with the early development of aphid populations. Field census data and laboratory experiments were used to determine how ovipositing females of the two-spot ladybird, Adalia bipunctata (L.), assess whether an aphid population is suitable for exploitation. In the field, two-spot ladybirds usually laid eggs well before aphid populations peaked in abundance. In the laboratory they showed a marked reduction in their reproductive numerical response in the presence of larvae of their own species but not of other aphidophagous ladybirds. At the highest aphid density this was not a consequence of competition for food between larvae and ovipositing females. In the presence of conspecific larvae gravid females were very active and as a consequence more likely to leave an area, and when confined with other conspecific females or larvae laid fewer eggs and later than females kept on their own. The extent of the inhibition of egg laying is negatively correlated with the rate of encounter with larvae. Thus it is proposed that gravid females appear mainly to use the presence of conspecific larvae to assess the potential of an aphid colony for supporting the development of their offspring.     

Sexual size dimorphism in the two spot ladybird beetle Adalia bipunctata: developmental mechanism and its consequences for mating

Abstract  1. The literature on ladybirds indicates that males are consistently smaller than females but take the same length of time to complete their development. Rearing Adalia bipunctata at 20 and 25 °C confirmed that protandry cannot account for sexual size dimorphism in this species, nor can a difference in egg size.
2. Female larvae consumed more food and had a higher relative growth rate in the fourth instar than did male larvae.
3. When food is limited, small males appear to be more successful at mating than are large males.
4. To account for these results, it is hypothesised that the gonads of male larvae compete more strongly with the soma for resources and that this reduces the growth potential of the soma of male larvae relative to that of female larvae. The greater mating success of small males when food is limited supports the eat or mate hypothesis, which predicts that when food is limited small males will spend less time feeding and more time mating than will large males.     

Oviposition strategies employed by the western spruce budworm: tests of predictions from the phylogenetic constraints hypothesis

1 Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in an eruptive forest Lepidopteran species, the western spruce budworm. 2 In previous work, we established that western spruce budworm females exhibit oviposition preferences with regard to tree age, tree vigour and host species. However, there was no evidence to support a link between oviposition preference and larval performance, which supports the Phylogenetic Constraints Hypothesis. 3 Our preference data led us to test whether female budworms use oviposition strategies to select the sites where they lay their egg masses. Our experiments were designed to make direct comparisons between latent and eruptive insect herbivores with respect to two oviposition behaviours: egg retention and avoidance of conspecifics. This type of research has not previously been conducted on any eruptive forest Lepidopteran. 4 Female budworms retained eggs instead of laying them on less preferred hosts in two of three experiments, but the percentage of eggs they retained was significantly less compared to latent insect herbivores. 5 In addition, female budworms actively avoided oviposition in areas with the highest density of conspecific egg masses, but they laid egg masses in all the other locations provided. This contrasts with the pattern seen in latent insect herbivores, which consistently avoid laying their eggs near any sites already used by conspecifics. 6 Our research indicates that there are extreme differences between latent and eruptive insect herbivores with respect to egg retention and avoidance of conspecifics, thus supporting the Phylogenetic Constraints Hypothesis.     

The effects of two microsporidian pathogens on the two-spotted lady beetle, Adalia bipunctata L. (Coleoptera: Coccinellidae)

Two-spotted lady beetles, Adalia bipunctata L. are available for biological pest control in North America. Lady beetles are known to host microsporidia and although these pathogens are able to infect more than one host under laboratory conditions, little is known regarding the effects of more than one microsporidian pathogen on host fitness. In this study, egg cannibalism was used to examine the effects of the microsporidium Tubulinosema hippodamiae from Hippodamia convergens and an undescribed microsporidium from A. bipunctata (alone and in combination) on A. bipunctata host fitness (larval development and mortality, sex ratio, adult fecundity and longevity). Development was prolonged significantly for larvae that were infected with the undescribed microsporidium but T. hippodamiae had no effect and as a result, conclusions could not be made regarding the effects of both pathogens on larval development. The two microsporidia had no effect on sex ratios (1♀:1♂) or on adult fecundity and longevity. Spores were detected in the majority of smear preparations of individuals that were fed microsporidia-infected eggs and molecular analysis confirmed the identity of both pathogens in sampled individuals. T. hippodamiae spores were smaller than spores of the undescribed microsporidium (3.76±0.03×2.32±0.02 μm and 5.43±0.06×2.75±0.03 μm, respectively) and although the former stained less intensely than did those of latter, spores of the two pathogens are difficult to differentiate when examined by light microscopy alone. The ability of some microsporidia to infect more than one lady beetle host makes it difficult to conclude with certainty as to the number of species that are present in infected Adalia when specimens are examined solely by light microscopy.     

Age and experience influence patch assessment for oviposition by an insect predator

Abstract.  1. Dynamic models of optimal foraging predict that an animal's decision to accept or reject a patch depends not only on the environment and patch quality, but also on its internal state. Previous experiments have shown that the two-spot ladybird beetle, Adalia bipunctata (L.), is reluctant to lay eggs in a patch of prey contaminated by the oviposition-deterring pheromone produced by conspecific larvae.
2. An experiment was conducted to test whether the internal state of an A. bipunctata female affects its oviposition response to oviposition-deterring pheromone. Firstly, the oviposition response to oviposition-deterring pheromone of young and old females was compared. Secondly, the oviposition response to oviposition-deterring pheromone of females previously exposed continuously to oviposition-deterring pheromone was compared with that of females of the same age but with no previous experience of oviposition-deterring pheromone.
3. Old females and females with previous experience of oviposition-deterring pheromone were less reluctant to lay eggs in the presence of oviposition-deterring pheromone than young and naive females. These results are consistent with the predictions of optimal foraging theory.     

Predation and oviposition by predatory Stethorus japonicus, Oligota kashmirica benefica, and Scolothrips takahashii in egg patches of various spider mite species

Predation and oviposition by three predacious insects [ Scolothrips takahashii Priesner (Thysanoptera: Thripidae), Stethorus japonicus H. Kamiya (Coleoptera: Coccinellidae), and Oligota kashmirica benefica Naomi (Coleoptera: Staphylinidae)] were examined using egg patches of three spider mite species [ Amphitetranychus viennensis (Zacher), Tetranychus urticae Koch, and Panonychus mori Yokoyama (all Acari: Tetranychidae)] that are pest species on Japanese pear [ Pyrus serotina Rehder (Rosaceae)]. Scolothrips takahashii females consumed more prey and laid more eggs in A. viennensis and T. urticae egg patches than in P. mori egg patches. Females also left P. mori egg patches sooner than they left other egg patches even at high prey density. Predation and oviposition of S. takahashii in a prey patch were greatly enhanced by the complicated webs produced by A. viennensis . Stethorus japonicus females consumed significantly more prey and laid more eggs in A. viennensis egg patches than in P. mori egg patches, with intermediate values in T. urticae egg patches, reflecting the quality of each spider mite species as prey. Oligota kashmirica benefica females consumed more prey and laid more eggs in A. viennensis and T. urticae egg patches than in P. mori egg patches, particularly at high prey density. However, predation and oviposition by O. kashmirica benefica increased greatly with increasing prey density, even in P. mori egg patches, indicating that prey density was the most important factor in predation and oviposition by this species. These results are discussed in relation to the potential effect of each predator on the suppression of different spider mite species on Japanese pear.     

Presence of haemocyte-like cells in coccinellid reflex blood

Abstract.  Contrary to current assumptions, the reflex blood of two-spot ladybirds, Adalia bipunctata , and seven-spot ladybirds, Coccinella septempunctata , contains haemocyte-like cells. Furthermore, DNA can be extracted and amplified from coccinellid reflex blood, confirming the presence of haemocyte-like cells and demonstrating a nondestructive method of DNA extraction.     

Differences between the 7-spot and 2-spot ladybird beetles (Coccinellidae) in their toxic effects on a bird predator

Abstract. 1. Experiments with nestling blue tits Parus caeruleus L. examined the effects of feeding them 7-spot ladybird Coccinella septempunctata (L.), 2-spot ladybird Adalia bipunctata (L.) or controls Tenebrio sp.
2. A feeding rate of 51/3 7-spot ladybirds per day 'killed' nestlings within 2 days. Three of six nestlings fed at half this rate survived 4 days. In contrast, all experimental birds survived sixty-four 2-spot ladybirds fed over 4 days (equivalent by weight to the high 7-spot diet).
3. Nestlings fed 7-spot ladybirds also grew more slowly than birds fed 2-spot ladybirds. The latter birds showed no difference in weight gain from the controls although they begged more strongly for food.
4. Cadavers of birds fed 7-spot ladybirds showed evidence of severe liver damage.
5. The results indicate a substantial difference between the ladybird species in their toxicity to nestling blue tits. They support the hypothesis that 2-spot ladybirds are largely-edible, polymorphic Batesian mimics of well-protected, monomorphic species such as the 7-spot ladybird.     

Distribution of cytoplasmically inherited bacteria Spiroplasma causing female bias in the Eurasian populations of Adalia bipunctata

Two-spot ladybirds Adalia bipunctata were collected from the populations of Western and Eastern Europe and Central Asia. The agent killing males at the early embryonic stage in these populations was identified as bacteria of the genus Spiroplasma. Bacteria found in A. bipunctata proved to be phylogenetically related to Spiroplasma ixodetis (typical line Y-32) found in tick Ixodes pacificus but not to Spiroplasma causing the death of male embryos in Drosophila.     

Evaluation of tebufenozide carry-over and residual effects on spruce budworm (Lepidoptera: Tortricidae)

Laboratory and field studies investigated carry-over effects of tebufenozide on spruce budworm, Choristoneura fumiferana (Clemens). In the laboratory, third and fourth instars were fed either sublethal doses of tebufenozide (10 ppm) or water onAbies balsamea (L.) Mill. needles, reared to adulthood and allowed to oviposit on laying surfaces 1 or 14 d after being sprayed with water or tebufenozide concentrations of 17.5, 35.0, and 70.0 g/liter. Percentage adult emergence and sex ratio were not affected by larval ingestion of the tebufenozide. Also, the mean number of eggs laid on untreated wax paper by moths reared from tebufenozide-treated larvae was similar to the controls. Hence, tebufenozide did not inhibit carry-over effects on treated larvae. Oviposition on tebufenozide-treated wax paper by moths reared from untreated larvae was affected by both the substrate concentration and the age of the treatment residue. When offered treated and untreated laying surfaces simultaneously, C. fumiferana did not show a preference. However, significantly fewer eggs were laid on both laying surfaces by fewer females than when tebufenozide was absent. Residual tebufenozide on wax paper did not affect egg hatch but topical applications were toxic to eggs. Field studies appear to corroborate laboratory results and suggest that although the ingestion of tebufenozide by larval spruce budworm might not impair adult reproduction, the insecticide's presence in the environment could inhibit oviposition. This inhibition was considered to be a primary factor in tebufenozide's multi-year effects against spruce budworm populations.