Molecular evidence of facultative intraguild predation by Monochamus titillator larvae (Coleoptera: Cerambycidae) on members of the southern pine beetle guild

The southern pine bark beetle guild (SPBG) is arguably the most destructive group of forest insects in the southeastern USA. This guild contains five species of bark beetles (Coleoptera: Curculionidae: Scolytinae): Dendroctonus frontalis, Dendroctonus terebrans, Ips avulsus, Ips calligraphus, and Ips grandicollis. A diverse community of illicit receivers is attracted to pheromones emitted by the SPBG, including the woodborers Monochamus carolinensis and Monochamus titillator (Coleoptera: Cerambycidae). These woodborers have been traditionally classified as resource competitors; however, laboratory assays suggest that larval M. carolinensis may be facultative intraguild predators of SPBG larvae. This study used polymerase chain reaction (PCR)-based molecular gut content analyses to characterize subcortical interactions between M. titillator and members of the SPBG. The half-lives of SPBG DNA were estimated in the laboratory prior to examining these interactions in the field. A total of 271 field-collected M. titillator larvae were analyzed and 26 (9.6?%) tested positive for DNA of members of the SPBG. Of these larvae, 25 (96.2?%) tested positive for I. grandicollis and one (3.8?%) for I. calligraphus. Failure to detect D. terebrans and D. frontalis was likely due to their absence in the field. I. avulsus was present, but primers developed using adult tissues failed to amplify larval tissue. Results from this study support the hypothesis that larval Monochamus spp. are facultative intraguild predators of bark beetle larvae. Additionally, this study demonstrates the capabilities of PCR in elucidating the interactions of cryptic forest insects and provides a tool to better understand mechanisms driving southern pine beetle guild population fluctuations.     

Indirect interactions between a phytopathogenic and an entomopathogenic fungus

Slow growth in herbivores may lead to higher mortality, due to prolonged exposure to natural enemies. A number of studies has tested the 'slow-growth, high-mortality' hypothesis using predators or parasitoids as natural enemies of the herbivore, but the possible role of pathogens is poorly documented. We provide evidence that phytopathogenic infection of a plant enhances the susceptibility of herbivore larvae to a generalist entomopathogen. Larvae of the mustard leaf beetle Phaedon cochleariae grow more slowly when feeding on Chinese cabbage leaves infected by the phytopathogenic fungus Alternaria brassicae than larvae feeding on healthy leaves. Treatment of such larvae feeding on diseased plants with an LD₅₀ of the entomopathogenic fungus Metarhizium anisopliae resulted in 100% mortality, compared with a mortality rate of 54% in the control larvae feeding on uninfected leaves. This is the first demonstration of an interaction between a phyto- and an entomopathogenic fungus.     

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.     

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.     

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.     

Quantifying the ecosystem service of non-native weed seed predation provided by invertebrates and vertebrates in upland wheat fields converted from paddy fields

The extent of post-dispersal weed seed predation in upland wheat fields converted from paddy fields was quantified in Shizuoka Prefecture, central Japan. We investigated the temporal variability in seed predation of Italian ryegrass (Lolium multiflorum Lam.), a non-native winter annual weed in Japan, during summer after the seed shed in both the field interior areas and boundary strips, and estimated the total seed loss due to predation during the summer. Furthermore, the contribution of invertebrates and vertebrates to seed predation was estimated by using exclosures. The total seed loss due to predation during four months (from late June to late October) in the field interior areas and boundary strips was estimated to be 35–43% (the maximum proportion of seed predation per two weeks = 27%) and 42% (25%), respectively. The seed predators in the field interior areas were vertebrates (rodents or birds) and invertebrates (crickets and ground beetles). In contrast, seed predators in the boundary strips were mainly invertebrates (crickets and ground beetles). The results of this study suggest that predators make a substantial contribution in the depletion of post-dispersal seeds of Italian ryegrass in converted paddy fields.     

Defensive responses by a social caterpillar are tailored to different predators and change with larval instar and group size

Gregariousness in animals is widely accepted as a behavioral adaptation for protection from predation. However, predation risk and the effectiveness of a prey's defense can be a function of several other factors, including predator species and prey size or age. The objective of this study was to determine if the gregarious habit of Malacosoma disstria caterpillars is advantageous against invertebrate natural enemies, and whether it is through dilution or cooperative defenses. We also examined the effects of larval growth and group size on the rate and success of attacks. Caterpillars of M. disstria responded with predator-specific behaviors, which led to increased survival. Evasive behaviors were used against stinkbugs, while thrashing by fourth instar caterpillars and holding on to the silk mat by second instar caterpillars was most efficient against spider attacks. Collective head flicking and biting by groups of both second and fourth instar caterpillars were observed when attacked by parasitoids. Increased larval size decreased the average number of attacks by spiders but increased the number of attacks by both stinkbugs and parasitoids. However, increased body size decreased the success rate of attacks by all three natural enemies and increased handling time for both predators. Larger group sizes did not influence the number of attacks from predators but increased the number of attacks and the number of successful attacks from parasitoids. In all cases, individual risk was lower in larger groups. Caterpillars showed collective defenses against parasitoids but not against the walking predators. These results show that caterpillars use different tactics against different natural enemies. Overall, these tactics are both more diverse and more effective in fourth instar than in second instar caterpillars, confirming that growth reduces predation risk. We also show that grouping benefits caterpillars through dilution of risk, and, in the case of parasitoids, through group defenses. The decreased tendency to aggregate in the last larval instar may therefore be linked to decreasing predation risk.     

Diversity of cereal aphid parasitoids in simple and complex landscapes

Structurally complex landscapes may enhance local species richness and interactions, which is possibly due to a higher species pool in complex landscapes. This hypothesis was tested using cereal aphid parasitoids (Hymenoptera, Aphidiidae) by comparing 12 winter wheat fields in structurally complex landscapes (>50% semi-natural habitats; n = 6) and structurally simple landscapes dominated by agricultural lands (>80% arable land; n = 6). Surprisingly, landscape structural complexity had no effect on aphid parasitoid species diversity. In complex landscapes 12 and in simple landscapes 11 species were found; 9 species occurred in both landscape types. Hence, arable fields in high-intensity agricultural landscapes with little non-crop area can support a similar diversity of cereal aphid parasitoids as structurally complex landscapes. This finding suggests that cereal aphid parasitoids may find necessary resources even in simple landscapes, making generalisations concerning the relationship between landscape composition and biodiversity in arable fields difficult.     

Effects of molluscicide baits on field populations of house mice

Two trials were carried out to test the effects of field applications of snail baits on populations of house mice (Mus domesticus) inhabiting cereal-cropping fields during a mouse plague in South Australia. In the first trial, grain based pellets containing 2% w/w active ingredient methiocarb, were laid in trails across fields before crops were sown. The second tested the effect of whole wheat grains treated with 1% w/w methiocarb when broadcast across maturing barley crops. Treatment effects were estimated by comparison with untreated control plots. In the methiocarb-treated wheat trial, comparison was also made with 0.3% w/w strychnine-treated wheat treatments. Methiocarb baiting reduced estimated mouse numbers by 0–46%. Surviving mice did not accept the excess bait material available. In contrast, strychnine-treated wheat reduced estimated mouse numbers by 86–94%. These trials indicate that methiocarb is not likely to be a useful field rodenticide. Furthermore, the consumption of bait by mice is not likely to jeopardise snail control operations. However, methiocarb baits could cause sufficient mortality to pose a threat to rare or endangered granivorous rodents inhabiting agricultural fields.     

Occurrence of phytophagous insects on wild Vigna sp. and cultivated cowpea: comparing the relative importance of host-plant resistance and millet intercropping

The effects of host-plant resistance on cowpea phytophagous insects and their natural enemies under pure and mixed crop conditions was evaluated at Minjibir, Kano State, Nigeria, in 1992–1994 crop seasons. Cowpea Vigna unguiculata cv ‘IT86D-715' (susceptible to insect pests) and a wild Vigna line Vigna vexillata ‘TVnu 72' (resistant to most insect species) were planted alone and in mixtures with millet (Pennisetum glaucum) in plots of 25×25 m.Mixed cropping had limited effect on major insects and natural enemies. Colonies of Aphis craccivora were significantly smaller and there were more adults of Maruca vitrata in crop mixtures than in monocultures. However, flower and raceme infestation by larval M. vitrata, Megalurothrips sjostedti, and Sericothrips sp. were similar in crop mixtures and monocultures. Empoasca sp. populations and seedling infestation by beanfly Ophiomyia phaseoli were also similar in mixtures and monocultures as well as pod damage by M. vitrata and populations of Clavigralla tomentosicollis. Parasitization rates of M. vitrata, C. tomentosicollis and O. phaseoli and predator–prey ratios of spiders and Orius sp. were similar across cropping systems. Host-plant resistance in TVnu 72 drastically reduced insect populations and damage. Grain yield per hill was high in cowpea IT86D-715 and was not affected by intercropping with millet. Grain yield of TVnu 72 was poor and reflected the low yield potential of this accession.Host-plant resistance is an effective means of controlling insect pest damage in cowpea and there is no evidence that high levels of resistance reduced natural biological control.     

Effects of cross-feeding anarchistic and wild type honey bees: anarchistic workers are not queen-like

Unlike normal (wild type) honey bee ( Apis mellifera) colonies, 'anarchistic' colonies are characterised by workers that activate their ovaries in the presence of the queen and brood and by the ability of their workers to lay eggs that evade worker policing. In the Cape honey bee ( A. m. capensis), female larvae can manipulate non- capensis nurse workers such that they receive more larval food and develop into worker-queen intermediates or intercastes. We speculated that, in anarchistic colonies, larvae might produce signals that result in excessive feeding of female larvae. Excessively fed female larvae may then develop into reproductively active workers. In this study we cross-fostered anarchistic and wild type brood and investigated the effect of cross-fostering on the amount of food fed to larvae and on the morphology of the resulting workers. We show that anarchistic larvae do not manipulate wild type nurse workers into feeding them more, nor do anarchistic workers develop into worker-queen intermediates. On the contrary, anarchistic larvae are fed less than wild type larvae and anarchistic workers seem to be poor nurses in that they feed larvae less, irrespective of brood genotype.     

Tracking parasitoids with the stable isotope 44Ca in agroecosystems

Habitat management influences spatial and temporal distribution of parasitoids in farmland. The current work evaluates, for the first time, the potential of a novel marking technique using a calcium stable isotope (⁴⁴Ca) under field conditions. In two subsequent trials, ⁴⁴Ca-enriched Cotesia glomerata parasitoids were released into an organically managed cabbage field in a region known to harbor natural populations of this species. The trap plants infested with Pieris brassicae host larvae were distributed in the trial areas and collected 3 days after parasitoid release. Parasitism by released wasps was determined through calcium isotope analysis of the recovered caterpillars using inductively coupled plasma mass spectrometry (ICPMS). The spatial habitat use by female parasitoids was determined based on marked caterpillars on the trap plants. Both trials yielded relatively consistent results, showing that C. glomerata females dispersed over at least 50 m within 3 days. The total proportion of caterpillars parasitized by the marked wasps amounted to 32.4 and 24.4%, respectively, with no statistically significant difference. The potential of this approach for field investigations on habitat management and biological control is discussed.     

Ecophysiology of dorsal versus ventral cuticle in flattened sawfly larvae

Platycampus larvae are highly cryptic leaf feeders characterised by a dorso-ventrally flattened body, the dorsal integument resembling a shield. Dorsal and ventral cuticles from Platycampus luridiventris were compared by histology and gel electrophoresis. By Azan-staining, a red and a blue layer were distinguished in the dorsal cuticle, while the ventral cuticle showed one, almost uniform blue layer, as in both cuticles of control species. The two cuticles from P. luridiventris had similar amounts and sodium dodecyl sulphate-polyacrylamide gel electrophoresis profiles of soluble proteins, but not insoluble proteins. One insoluble protein (MW ≈ 41 kDa) was visible as a large band in the ventral cuticle only. It is likely that this protein renders the cuticle elastic, and that the dorsal, red layer is the exocuticle, mainly composed of insoluble proteins. We discuss eco-physiological implications of the exocuticle in insects. Further, data from the literature indicate that the defence strategy in P. luridiventris larvae relies on being visually cryptic towards avian predators and tactically cryptic towards arthropod predators and parasitoids. Crypsis in both senses is favoured by the shield effect, itself based on an abnormally thick dorsal exocuticle. Although the larvae are external feeders, they may be considered as hidden from an ecological perspective.     

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.     

Prenatal cannibalism in an insect

Host selection and infection strategies of parasitoids often correlate with high parental investment and low numbers of progeny. In this study, we investigate how additional internal mechanisms might shape brood size and fitness of the offspring. Emblemasoma auditrix is a parasitoid fly in which about 38 larvae hatch simultaneously in utero. After host location, a single larva is deposited into the host, where it rapidly develops and pupates after about 5 days. The search for hosts can take several weeks, and during that time, the larvae arrest their development and remain in the first larval instar. Nevertheless, the larvae increase in weight within the uterus, and this growth correlates to a decrease in the number of larvae, although no larvae are deposited. Thus, our data indicate a first case of prenatal cannibalism in an invertebrate with larvae feeding on each other within the uterus of the adult.     

Bird use of rice field strips of varying width in the Kanto Plain of central Japan

Bird communities in flooded rice strips of different widths were surveyed in 71 fields around Lake Kasumigaura, on the Kanto Plain (central Japan). Strips categorized into four width classes (<50, 50–100, 100–300 and >300 m) and two locations (core >100 and <100 m from edges) were censused from May to July 1998, and mean species number and density of birds were compared. Both density and mean species differed significantly between classes, strips >300 m wide favoring bird diversity and number of marsh and grassland species. Breeding skylarks and fan-tailed warblers hardly occurred in fields adjacent to edges. Strips <50 m wide were not suitable feeding site of egret species (Ardeidae), but supported diurnal activity of black-crowned night herons and species requiring both rice fields and adjacent environment. As a consequence, bird conservation in rice field strips needs to consider both their width and location within the environment.     

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.     

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.     

Flower-visiting behavior of male bees is triggered by nectar-feeding insects

Bees are important pollinators for many flowering plants. Female bees are thought to be more effective pollinators than male bees because they carry much more pollen than males. Males of some solitary bee species are known to patrol near flowers that females visit. Because patrolling males visit flowers to mate or defend their territories, they may function as pollinators. However, the significance of patrolling males to pollination has not been studied. We studied males of a solitary bee, Heriades fulvohispidus (Megachilidae), patrolling near flowers and visiting flowers that attracted nectar-feeding insects, including conspecifics, on the Ogasawara (Bonin) Islands. To test the hypothesis that patrolling male bees may function as pollen vectors, we compared the frequency of visits by H. fulvohispidus to flowers of an endemic plant, Schima mertensiana (Theaceae); comparisons were made among flowers with a dead H. fulvohispidus, a dead beetle, a piece of plastic, and nothing (control flowers). Patrolling H. fulvohispidus more frequently visited flowers with a dead conspecific, a dead beetle, or a piece of plastic than the control flowers. Our experiment demonstrates that nectar-feeding insects (including conspecifics and other insects) enhance the flower-visiting frequency of patrolling H. fulvohispidus males on S. mertensiana flowers. Furthermore, we observed S. mertensiana pollen on patrolling males as well as females, suggesting that male bees may also function as pollen vectors.