Synthetic attractants for the bark beetle parasitoid Coeloides bostrichorum Giraud (Hymenoptera: Braconidae)

Coeloides bostrichorum Giraud parasitoids (Hymenoptera: Braconidae) attack late larval stages of various bark beetle species breeding in spruce. Volatile compounds collected from Norway spruce (Picea abies) infested by Ips typographus L. (Coleoptera: Scolytidae) were analysed by coupled gas chromatography-mass spectrometry (GC-MS) and GC-electroantennographic detection (GC-EAD). Monoterpene hydrocarbons are the predominant volatile compounds of fresh Norway spruce, while the presence of oxygenated monoterpenes indicates damaged trees. Between one and eight EAD-active oxygenated monoterpenes were used, in amounts reflecting their natural abundance in spruce trees containing bark beetle larvae, to prepare five synthetic baits which were tested in wind tunnel bioassays. Odour samples collected from spruce logs containing the preferred host stage were attractive, while similar samples from uninfested logs failed to elicit any flight activity. However, when a four- or an eight-component synthetic bait was added to volatiles collected from uninfested spruce logs, this combination was as attractive as volatiles collected from infested spruce logs.     

Chemically mediated group formation in soil-dwelling larvae and pupae of the beetle Trypoxylus dichotomus

Many insects form groups through interactions among individuals, and these are often mediated by chemical, acoustic, or visual cues and signals. In spite of the diversity of soil-dwelling insects, their aggregation behaviour has not been examined as extensively as that of aboveground species. We investigated the aggregation mechanisms of larvae of the Japanese rhinoceros beetle Trypoxylus dichotomus, which live in groups in humus soil. In two-choice laboratory tests, 2nd- and 3rd-instar larvae gathered at conspecific larvae irrespective of the kinship. The ablation of maxillae, which bear chemosensilla, abolished aggregation behaviour. Intact larvae also exhibited aggregation behaviour towards a larval homogenate. These results suggest that larval aggregation is mediated by chemical cues. We also demonstrated that the mature larvae of T. dichotomus built their pupal cells close to a mesh bag containing a conspecific pupal cell, which indicated that larvae utilize chemical cues emanating from these cells to select the pupation site. Thus, the larvae of T. dichotomus may use chemical cues from the conspecifics in two different contexts, i.e. larval aggregation and pupation site selection. Using conspecific cues, larvae may be able to choose suitable locations for foraging or building pupal cells. The results of the present study highlight the importance of chemical information in belowground ecology.     

Mortality of pollen beetle (Meligethes spp.) larvae due to predators and parasitoids in rape fields and the effect of conservation strips

In 1996–1999, different mortality factors of pollen beetle larvae were investigated in twenty six rape fields in the northern part of Switzerland which had either a wild flower strip or an extensively managed meadow adjacent to the long side of the field. At 3 and 30 m into the crop from the conservation strip, total mortality, mortality from predators, parasitoids and unspecified factors were measured. Total pollen beetle larval mortality was 66–96%. Mortality caused by predators was 16–27% and there was no significant difference between mortality at 3 m and that 30 m from the extensively managed meadows. However, in fields with wild flower strips adjacent to them, the percentage mortality from predators was significantly greater at 30 m than at 3 m. The range of parasitism of pollen beetle larvae was 0–54% and was on average greater at 3 m than at 30 m. In fields with wild flower strips, the percentage parasitism with Tersilochus heterocerus was significantly higher than in fields with extensively managed meadows. However, mortality from all parasitoids was only 1–2% and there was no significant difference between 3 and 30 m. The effect of parasitoids on pollen beetle mortality was masked by the high unspecified mortality and the mortality from predators. The unspecified mortality was 46–72% and was significantly greater in 1998 and 1999 than in 1996 and 1997. These differences are probably because of meteorological factors (wet in 1999 and dry in 1998). The possible influences of the two types of conservation strips on pollen beetle larval density were investigated. The results show that in fields with adjacent wild flower strips, the pollen beetle larvae were more evenly distributed (but not significantly so) than in fields with extensively managed meadows where larval density decreases faster from the edge into the rape field.     

Integument and defence in larva and prepupa of a sawfly living on a semi-aquatic plant

The larvae of the sawfly Rhadinoceraea micans live and feed on a semi-aquatic plant, Iris pseudacorus, and their integument is strongly hydrophobic. The hydrophobicity is part of a chemical defence strategy, easy bleeding, also known from congeners. The prepupae burrow into the soil where they form a cocoon in which they pupate, thus implying different micro-environmental conditions. The cuticle structure and wetting defensive effectiveness of R. micans were compared between larvae and prepupae. The two stages were similarly well defended against attacking ants by the bleeding of a deterrent hemolymph, whereas they were dissimilar in the cuticle surface that presented sculptures and wax crystals at the larval stage only. The integument of prepupae was less structured, and hydrophilic. Larvae of R. micans exhibit, among sawflies, an exceptional cuticle structuring and we assume that they occupy this particular niche of a semi-aquatic environment to avoid encounters with ground-dwelling predators whereas prepupae may benefit from the chemical defence acquired at larval stage.     

Pest outbreak distribution and forest management impacts in a changing climate in British Columbia

This paper examines the risks associated with forest insect outbreaks in a changing climate from biological and forest management perspectives. Two important Canadian insects were considered: western spruce budworm (WSBW; Choristoneura occidentalis Freeman, Lepidoptera: Tortricidae), and spruce bark beetle (SBB; Dendroctonus rufipennis Kirby, Coleoptera: Curculionidae). This paper integrates projections of tree species suitability, pest outbreak risk, and bio-economic modelling.Several methods of estimating pest outbreak risk were investigated. A simple climate envelope method based on empirically derived climate thresholds indicates substantial changes in the distribution of outbreaks in British Columbia for two climate scenarios and both pests. A “proof of concept” bio-economic model, to inform forest management decisions in a changing climate, considers major stand-level harvest decision factors, such as preservation of old-growth forest, and even harvest flow rates in the presence of changing tree species suitability and outbreak risk. The model was applied to data for the Okanagan Timber Supply Area and also the entire Province of British Columbia.At the provincial level, the model determined little net timber production impact, depending on which of two climate scenarios was considered. Several potentially important factors not considered in this first version of the model are discussed, which indicates that impact may be underestimated by this preliminary study. Despite these factors, negative impacts were projected at the Okanagan Timber Supply Area level for both scenarios.Policy implications are described as well as guidance for future work to determine impacts of climate change on future distribution and abundance of forest resources.     

Short- and long-range cues used by ground-dwelling parasitoids to find their host

Parasitoids of phytophagous insects face a detectability–reliability dilemma when foraging for hosts. Plant-related cues are easily detectable, but do not guarantee the presence of the host. Host-related cues are very reliable, but much harder to detect from a distance. Little is known in particular about the way coleopteran parasitoid females use these cues when foraging for a suitable place to lay their eggs. The question is of interest because, unlike hymenopteran larvae, coleopteran parasitoid larvae are highly mobile and able to forage for hosts on their own. We assessed whether females of the parasitoid rove beetle Aleochara bipustulata (L.) (Coleoptera: Staphylinidae) are attracted to plant (Swede roots, Brassica napus) and host-related cues [pupae of the cabbage root fly Delia radicum (L.) (Diptera: Anthomyiidae)]. In the field, A. bipustulata adult females were captured in selective pitfall traps containing pieces of roots damaged by D. radicum larvae, but not in traps containing pieces of healthy roots or D. radicum pupae. However, in the laboratory, the odour of D. radicum pupae attracted A. bipustulata females to mini-pitfalls. Video monitoring in the laboratory showed that foraging A. bipustulata females preferred a zone containing D. radicum pupae and larval tracks rather than one containing an extract of D. radicum-infested roots. Our results suggest a behavioural sequence where A. bipustulata females use plant-related cues at a distance, but then switch their preference to host-related cues at a close range. This would be the first observation of this behaviour in coleopteran parasitoids.     

Elementary budget of stag beetle larvae associated with selective utilization of nitrogen in decaying wood

Wood degradation by insects plays important roles for the forest matter cycling. Since wood is deficient in nitrogen compared to the insect body, wood-feeding insects need to assimilate the nitrogen selectively and discard an excess carbon. Such a stoichiometric imbalance between food and body will cause high metabolic cost; therefore, wood-feeding insects may somehow alleviate the stoichiometric imbalance. Here, we investigated the carbon and nitrogen budgets of the larvae of stag beetle, Dorcus rectus, which feed on decaying wood. Assimilation efficiency of ingested wood was 22%, and those values based on the carbon and nitrogen were 27 and 45%, respectively, suggesting the selective digestion of nitrogen in wood. Element-based gross growth efficiency was much higher for nitrogen (45%) than for carbon (3%). As a result, the larvae released 24% of the ingested carbon as volatile, whereas almost no gaseous exchange was observed for nitrogen. Moreover, solubility-based elementary analysis revealed that the larvae mainly utilized alkaline-soluble-water-insoluble fraction of wood, which is rich in nitrogen. Actually, the midgut of the larvae was highly alkaline (pH 10.3). Stag beetle larvae are known to exhibit coprophagy, and here we also confirmed that alkaline-soluble-water-insoluble nitrogen increased again from fresh feces to old feces in the field. Stable isotope analysis suggested the utilization of aerial nitrogen by larvae; however, its actual contribution is still disputable. Those results suggest that D. rectus larvae selectively utilize alkaline-soluble nitrogenous substrates by using their highly alkaline midgut, and perhaps associate with microbes that enhance the nitrogen recycling in feces.     

Avoidance of nonhost plants by a bark beetle, Pityogenes bidentatus, in a forest of odors

The bark beetle, Pityogenes bidentatus (Coleoptera: Scolytidae), searches in mixed conifer and deciduous forests of northern Europe for suitable branches of its host, Scots pine (Pinus sylvestris). We tested whether odors from several diverse nonhost trees and plants common in the habitat (e.g., mountain ash, Sorbus aucuparia; oak, Quercus robur; alder buckthorn, Frangula alnus; blueberry, Vaccinium myrtillus; raspberry, Rubus idaeus; and grass, Deschampsia flexuosa) would reduce the attraction of the bark beetle to traps releasing its aggregation pheromone components in the field. Volatiles from the leaves or bark of each of these plants significantly reduced the attraction of the beetles to their pheromone. Odors collected from these nonhosts and analyzed by GC/MS contained monoterpenes, sesquiterpenes, and green-leaf alcohols, several of which (e.g., 1-octene-3-ol and -caryophyllene) reduced the attraction to pheromone in the field and elicited electroantennographic responses. In the laboratory, reproduction by the beetle was marginal in nonhost Norway spruce, Picea abies, and was absent in the other nonhost trees. Olfactory avoidance of unsuitable nonhosts may have evolved due to advantages in avoiding mistakes during host selection.     

Vulnerability and behavioral response to ultraviolet radiation in the components of a foliar mite prey–predator system

Ambient ultraviolet-B (UVB) radiation impacts plant-dwelling arthropods including herbivorous and predatory mites. However, the effects of UVB on prey?Cpredator systems, such as that between the herbivorous spider mite and predatory phytoseiid mite, are poorly understood. A comparative study was conducted to determine the vulnerability and behavioral responses of these mites to ultraviolet (UV) radiation. First, we analyzed dose?Cresponse (cumulative irradiance-mortality) curves for the eggs of phytoseiid mites (Neoseiulus californicus, Neoseiulus womersleyi, and Phytoseiulus persimilis) and the spider mite (Tetranychus urticae) to UVB radiation from a UV lamp. This indicated that the phytoseiid mites were more vulnerable than the spider mite, although P. persimilis was slightly more tolerant than the other two phytoseiid mites. Second, we compared the avoidance behavior of adult female N. californicus and two spider mite species (T. urticae, a lower leaf surface user; Panonychus citri, an upper leaf surface user) in response to solar UV and visible light. N. californicus actively avoided both types of radiation, whereas P. citri showed only minimal avoidance behavior. T. urticae actively avoided UV as well as N. californicus but exhibited a slow response to visible light as well as P. citri. Such variation in vulnerability and avoidance behavior accounts for differences in the species adaptations to solar UVB radiation. This may be the primary factor determining habitat use among these mites on host plant leaves, subsequently affecting accessibility by predators and also intraguild competition.     

Arthropods associated with fungal galls: do large galls support more abundant and diverse inhabitants?

Fungus-induced galls can attract spore-feeding arthropods as well as gall-feeding ones, resulting in diverse communities. Do large fungal galls support more abundant and diverse arthropod communities than small fungal galls? To address this question, we investigated the structure of the arthropod community associated with bud galls induced by the fungus Melanopsichium onumae on the tree species Cinnamomum yabunikkei (Lauraceae) in central Japan. Thirteen species of arthropods were associated with M. onumae galls. Dominant arthropod species were represented by the larvae of a salpingid beetle (a spore feeder), a nitidulid beetle (a spore feeder), a cosmopterigid moth (a spore feeder), an unidentified moth (a gall tissue feeder), and a drosophilid species (a gall tissue feeder). Arthropod abundance and species richness were positively correlated with gall diameter. The majority of the most abundant species were more frequently found in large galls than in small ones, indicating that large fungal galls, which have more food and/or space for arthropods, could support a more abundant and diverse arthropod community.     

Strategies of a bark beetle, Pityogenes bidentatus, in an olfactory landscape

 Volatiles from leaves or bark of nonhost birch (Betula pendula) and Norway spruce (Picea abies) dramatically reduced the attraction of the bark beetle, Pityogenes bidentatus (Coleoptera: Scolytidae), to their aggregation pheromone components (cis-verbenol and grandisol) in the field. In addition, odors from both the needles and bark of the host Scots pine (Pinus sylvestris) similarly inhibited attraction. Monoterpenes of pine and spruce (α-pinene, β-pinene, terpinolene, and 3-carene) as well as ethanol, chalcogran and some nonhost green leaf alcohols [(Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, and 1-hexanol], also reduced catches. Collections of volatiles from the field-tested plant tissues indicated they released monoterpenes in amounts similar to the synthetics that inhibited responses. The various plant and insect sources of these inhibitory compounds indicate that P. bidentatus bark beetles have evolved several strategies to increase their fitness by avoiding nonhost and unsuitable host trees in a complex olfactory landscape. Received: 6 June 2000 / Accepted in revised form: 25 September 2000     

Spatial distribution of different stages of mango stone weevil, Sternochetus mangiferae (fabricius) (coleoptera: Curculionidae)

Studies were conducted on the spatial distribution of different stages of the mango stone weevil, Sternochetus mangiferae (Fabr.) at Hessaraghatta farm of the Indian Institute of Horticultural Research, Bangalore, during 1983. The values of various parameters of distribution showed that the eggs are distributed as a negative binomial (contagious) distribution, whereas larvae and adults follow a positive binomial (random) distribution. It is suggested that the change in distribution may be due to the lower population densities in larval and adult stages.     

Antibacterial potency of housefly larvae extract from sewage sludge through bioconversion

Use of the fly to convert sewage sludge into nutrient-rich soil conditioner and amendment is an attractive approach for sludge bioconversion. During this process, fecal coliforms, an indicating pathogen, in sludge were reduced to 5.3 × 102 most probable number /g dry solid from initial 3.32 × 106 MPN/g dry solid. It was also found that the extract of larvae grown in sludge during bioconversion have an observable inhibitory effect against bacteria compared to larvae grown in wheat bran as measured by minimum bacterial concentration tests. In vitro antimicrobial assay tests over time also showed that the extract had strong inhibitory efficiencies of ca. 99% against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Serratia marcescens, while the efficiency was 69% and 57% against Bacillus subtilis and Klebsiella pneumoniae, respectively. The observed pathogenic bacterial cell membrane damage was found to be responsible for the phenomenon mentioned above, with nuclear acids leaching out quickly and alkaline phosphatase increasing in the outer membrane, followed by an increase of β-galactosidase in the inner membrane. Clearly, housefly larvae extract from sewage sludge through bioconversion possesses antibacterial potency against pathogenic bacteria.     

Coordinated gene expression for pheromone biosynthesis in the pine engraver beetle, <Emphasis Type="Italic">Ips pini</Emphasis> (Coleoptera: Scolytidae)

In several pine bark beetle species, phloem feeding induces aggregation pheromone production to coordinate a mass attack on the host tree. Male pine engraver beetles, Ips pini (Say) (Coleoptera: Scolytidae), produce the monoterpenoid pheromone component ipsdienol de novo via the mevalonate pathway in the anterior midgut upon feeding. To understand how pheromone production is regulated in this tissue, we used quantitative real-time PCR to examine feeding-induced changes in gene expression of seven mevalonate pathway genes: acetoacetyl-coenzyme A thiolase, 3-hydroxy-3-methylglutaryl coenzyme A synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, mevalonate 5-diphosphate decarboxylase, isopentenyl-diphosphate isomerase, geranyl-diphosphate synthase (GPPS), and farnesyl-diphosphate synthase (FPPS). In males, expression of all these genes significantly increased upon feeding. In females, the expression of the early mevalonate pathway genes (up to and including the isomerase) increased significantly, but the expression of the later genes (GPPS and FPPS) was unaffected or decreased upon feeding. Thus, feeding coordinately regulates expression of the mevalonate pathway genes necessary for pheromone biosynthesis in male, but not female, midguts. Furthermore, basal mRNA levels were 5- to 41-fold more abundant in male midguts compared to female midguts. This is the first report of coordinated regulation of mevalonate pathway genes in an invertebrate model consistent with their sex-specific role in de novo pheromone biosynthesis.Electronic Supplementary Material  Supplementary material is available in the online version of this article at .     

Impact of wildflower strips on biological control of cabbage lepidopterans

In a 2-year experiment we investigated whether wildflower strips can be used to enhance the control of cabbage moth, Mamestra brassicae L., and cabbage white butterfly, Pieris rapae L. At two sites, including six organically cultivated fields, M. brassicae egg parasitism and predation rates were determined along with an assessment of larval parasitism rates in M. brassicae and P. rapae using a DNA-based approach. Within each field, plots with and without wildflower strips were sampled and a grid design of 3 m × 3 m was used to analyze the spatial pattern of parasitism. The provision of wildflower strips provided an idiosyncratic effect on the control of lepidopterans: parasitism rates in M. brassicae eggs and larvae were not affected, whereas parasitism rates of larval P. rapae were significantly enhanced by the wildflower strips at one of the two sites. Moreover, at one site predation rates on M. brassicae eggs were significantly enhanced in the wildflower strip plots. Geostatistical analysis showed no distinct spatial patterns in parasitism rates. These results demonstrate that the provision of wildflower strips does not necessarily enhance biological control of lepidopteran cabbage pests and suggest that site-specific environmental factors strongly affect the impact of wildflower strips.     

Pre-pupation behaviour of the aphid parasitoid <Emphasis Type="Italic">Aphidius ervi</Emphasis> (Haliday) and its consequences for pre-imaginal learning

Olfactory learning may occur at different stages of insect ontogeny. In parasitoid wasps, it has been mostly shown at adult emergence, whilst it remains controversial at pre-imaginal stages. We followed larval growth of the parasitoid wasp, Aphidius ervi Haliday, inside the host aphid, Acyrthosiphom pisum Harris, and characterised in detail the behaviour of third instar larvae. We found that just before cocoon spinning begins, the third instar larva bites a hole through the ventral side of the mummified aphid exoskeleton. We then evaluated whether this period of exposure to the external environment represented a sensitive stage for olfactory learning. In our first experiment, the third instar larvae were allowed to spin their cocoon on the host plant (Vicia faba L.) surface or on a plastic plate covering the portion of the host plant exposed to the ventral opening. Recently emerged adults of the first group showed a preference for plant volatiles in a glass Y-olfactometer, whereas no preference was found in adults of the second group. In a second experiment, during the period in which the aphid carcass remains open or is being sealed by cocoon spinning, third instar larvae were exposed for 24 h to either vanilla odours or water vapours as control. In this experiment, half of the parasitoid larvae were later excised from the mummy to avoid further exposure to vanilla. Adult parasitoids exposed to vanilla during the larval ventral opening of the mummy showed a significant preference for vanilla odours in the olfactometer, regardless of excision from the mummy. The larval behaviour described and the results of the manipulations performed are discussed as evidences for the acquisition of olfactory memory during the larval stage and its persistence through metamorphosis.     

Energy budget of Pieris brassicae L. larvae (Lepidoptera: Pieridae) fed on four host plant species

Energy budgets were evaluated for the larval development of Pieris brassicae fed on leaves of Brassica oleracea var. capitata, B. oleracea var. botrytis, B. oleracea var. sarson and Nasturtium montanum. Food consumption, assimilation and tissue growth values were maximum for the larvae fed on B. oleracea var. capitata and minimum for the larvae fed on N. montanum. Mean values of approximate digestibility (AD), efficiency of conversion of digested food into body tissue (ECD) and efficiency of conversion of ingested food into body tissue (ECI) fall within the values reported for other leaf-eating lepidopterans. An equivalent weight of the following materials had calorific values in the order given: faeces < food plant < larval stages < pupal stage.     

Effect of SO2 on performance of the turnip moth,Agrotis segetum Schiff

Effect of SO₂-enriched air on the turnip moth, Agrotis segetum Schiff.was investigated by rearing the larvae on rape leaves that had been exposed to 40 or 80 ppb of the air pollutant in field fumigation chambers. An examination on the 11th day showed that the larvae in both treatments survived more, developed markedly faster, their fresh v/eig'ht and mean relative growth rate were significantly greater than those of control insect. Improvement of their growth and development resulted in decrease of total larval duration by 0.5 - 1.0 day. Pupal and adult performances were little affected by SO₂ level to which larval food plant was exposed. Possible reason responsible for enhanced growth and development of the insect species was discussed.     

A review of postfeeding larval dispersal in blowflies: implications for forensic entomology

Immature and adult stages of blowflies are one of the primary invertebrate consumers of decomposing animal organic matter. When the food supply is consumed or when the larvae complete their development and migrate prior to the total removal of the larval substrate, they disperse to find adequate places for pupation, a process known as postfeeding larval dispersal. Several important ecological and physiological aspects of this process were studied since the work by Green (Ann Appl Biol 38:475, 1951) 50 years ago. An understanding of postfeeding larval dispersal can be useful for determining the postmortem interval (PMI) of human cadavers in legal medicine, particularly because this interval may be underestimated if older dispersing larvae or those that disperse longer, faster, and deeper are not taken into account. In this article, we review the process of postfeeding larval dispersal and its implications for legal medicine, in particular showing that aspects such as burial behavior and competition among species of blowflies can influence this process and consequently, the estimation of PMI.