N. J. Holliday

Interaction of a solitary larval endoparasitoid, Microplitis mediator, with its host, Mamestra brassicae: host acceptance and host suitability

Abstract:  Microplitis mediator (Haliday) (Hym., Braconidae) is an important parasitoid of early instar larvae of the European cabbage moth, Mamestra brassicae L. (Lep., Noctuidae). In the laboratory, we examined attack responses of female M. mediator to the first three larval instars of M. brassicae. Females were presented with M. brassicae larvae either one individual at a time in a no‐choice experiment, or three individuals, one from each instar, simultaneously in a choice experiment. Whether or not there was choice, naïve female parasitoids attacked a high proportion of larvae and did not discriminate among instars. In the no‐choice experiment, attacked larvae were reared, and parasitoid cocoons were produced from about 76% of larvae attacked as first and second instars, but from only 19% of larvae attacked as third instars. Dissections of attacked larvae from the choice experiment showed that about 79% of attacks on first and second instars resulted in oviposition compared with only 49% for third instars. When given choice, frequency and number of attacks on first instar larvae increased with increasing parasitoid experience. Our results suggest that first and second instar larvae of M. brassicae are suitable hosts for M. mediator, but that third instar larvae are suboptimal both because oviposition attempts were frequently unsuccessful and because immature parasitoids failed to complete development. Nevertheless, naïve attacking parasitoids exhibited minimal discrimination among instars, although experienced parasitoids most frequently attacked first instar larvae. The host selection behaviour of M. mediator is discussed in the context of optimal foraging theory and implications for biological control.

Oviposition and Diapause Behavior in Colorado Potato Beetle (Coleoptera: Chrysomelidae) Populations from East Central Minnesota and the Valley of the Red River of the North

Abstract Oviposition and diapause behavior were compared among populations of Colorado potato beetle, Leptinotarsa decemlineata (Say), from six locations in 1994 and 1995. Locations ranged from Winnipeg, Manitoba (49° 49′ N), to Rosemount in east central Minnesota (44° 44′ N). Newly emerged first summer generation adults were held in field cages at each location for 7–14 d, then observed for 7 d in the laboratory for frequency of oviposition and frequency of burrowing behavior associated with diapause. Females from the Red River Valley seldom oviposited and although frequency of burrowing varied among locations it was independent of field and laboratory conditions. Under long-day laboratory conditions, 9–15% of females from east central Minnesota oviposited with frequency dependent on photoperiod experienced in the field, the critical photoperiod was 15.8 h. Under long-day laboratory conditions, 18–52% of beetles from east central Minnesota burrowed with frequency dependent on cumulative temperatures experienced in the field. Cool conditions were associated with higher frequencies of burrowing. Beetles from Rosemount exhibited identical responses under short-day and long-day laboratory conditions. In contrast, under short-day conditions, beetles from Big Lake did not oviposit and frequency of burrowing was not dependent on field conditions. We concluded that there is local geographic variation in Colorado potato beetle populations not only between the Red River Valley and east central Minnesota, but also among the different locations within these two areas.

Behavioral responses of Colorado potato beetle larvae to combinations of temperature and insolation, under field conditions

In short‐term field trials at combinations of ambient temperature (°C) and insolation (W·m−2), larval Colorado potato beetles (Leptinotarsa decemlineata [Say] [Coleoptera: Chrysomelidae]) were observed after their release on the adaxial surface of leaflets on potato plants (Solanum tuberosum L. Solanaceae). The larvae either began feeding or moved under the leaflet; mean interval from release to expression of these behaviors (2.9 ± 0.05 min [n = 358]) was independent of air temperature and insolation. Proportion of larvae moving under the leaflet increased logistically with both air temperature and insolation. A 1 W·m−2 change in insolation (P) evoked the same effect on this proportion as a 0.0838 °C change in air temperature (Ta), so the two quantities were combined as T* = Ta + P · 0.0838 °C/(W·m−2), which has units of °C. The proportion of larvae moving under the leaflet increased logistically with T*.

Spatial patterns of Trybliographa rapae parasitism of Delia radicum larvae in oilseed rape and cauliflower

Trybliographa rapae (Westwood) is an important parasitoid of Delia radicum (L.). Parasitism of D. radicum larvae by T. rapae in relation to host density on canola (oilseed rape) and cauliflower roots was examined at 10 field sites in Germany and Switzerland. For roots with host larvae, the proportion of roots with one or more parasitized hosts increased with increasing host density. However, for these infested roots, the parasitism of individual larvae was not consistently related to host density. When considering only roots on which there were parasitized larvae and the opportunity for multiple attacks, the proportion of larvae that were parasitized decreased with increasing host density in the field locations, and in a cage study under controlled conditions. A model of patch‐finding and number of attacks by female parasitoids suggests that patch‐finding is density‐dependent, but that low attack rate and interference effects limit numbers of attacks to three or less per visit to a host patch; the reduced number of attacks per visit leads to the inverse relationship of larval parasitism with host density in the host patches visited. The interplay of the density‐dependent and inversely density‐dependent processes appears to be responsible for the inconsistency of density dependence of overall larval parasitism in this and previous studies. In the laboratory, adult female T. rapae parasitized hosts at ≤4 cm deep in soil, but not at 6 cm deep. From the depth distribution of larval feeding sites in the field, we infer that between 4% and 20% of Delia larvae may be in a physical refuge from T. rapae parasitism, which may have a stabilizing influence on the host–parasitoid interaction.

Defensive Secretions of the Carabid Beetle Chlaenius cordicollis: Chemical Components and their Geographic Patterns of Variation

The defensive secretion of the ground beetle Chlaenius cordicollis is predominantly 3-methylphenol. Adult C. cordicollis were collected in Pennsylvania and Manitoba and induced to discharge defensive secretion in a vial. The headspace was sampled by solid phase microextraction, and samples were analyzed by gas chromatography–mass spectrometry. Five alkylphenolic compounds were detected: all beetles secreted 3-methlyphenol, 2,5-dimethylphenol, and 3-ethylphenol, and most beetles from each locality secreted detectable amounts of 2,3-dimethlyphenol and 3,4-dimethylphenol. In about 80% of beetles, we detected small amounts of the alkoxyphenolic compounds 2-methoxy-4-methylphenol and 2-methoxy-5-methylphenol. Multivariate compositional analysis of relative peak areas of alkylphenolic compounds revealed geographic variation and sexual dimorphism in defensive secretions. Compared with samples from Manitoba, relative peak areas of samples from Pennsylvania were lower for 2,3-dimethylphenol and higher for 3-methylphenol. Sexual dimorphism was detected only in Manitoba where, compared with samples from males, relative peak areas for samples from females were higher for 2,5-dimethylphenol and lower for 3-ethylphenol. This is the first report of geographic variation in defensive secretions of carabid beetles, and it demonstrates the need for knowledge of patterns of variation before characterizing the defensive secretions of a species as a whole.

Multiple equilibria of the Escherichia coli chaperonin GroES revealed by mass spectrometry

Nanospray time‐of‐flight mass spectrometry has been used to study the assembly of the heptamer of the Escherichia coli cochaperonin protein GroES, a system previously described as a monomer–heptamer equilibrium. In addition to the monomers and heptamers, we have found measurable amounts of dimers and hexamers, the presence of which suggests the following mechanism for heptamer assembly: 2 Monomers ↔ Dimer; 3 Dimers ↔ Hexamer; Hexamer + Monomer ↔ Heptamer. Equilibrium constants for each of these steps, and an overall constant for the Monomer ↔ Heptamer equilibrium, have been estimated from the data. These constants imply a standard free‐energy change, ΔG0, of about 9 kcal/mol for each contact surface formed between GroES subunits, except for the addition of the last subunit, where ΔG0 = 6 kcal/mol. This lower value probably reflects the loss of entropy when the heptamer ring is formed. These experiments illustrate the advantages of electrospray mass spectrometry as a method of measuring all components of a multiple equilibrium system.

Can mustard seed meal increase attacks by Aleochara spp. on Delia radicum in oilseed rape

Abstract Responses to mustard seed meal of two parasitic beetles, Aleochara bipustulata and A. bilineata, were assessed by measuring levels of parasitism of Delia radicum puparia and of root damage to oilseed rape, and by pitfall trapping of the beetles. Levels of parasitism and trap catches of A. bipustulata were higher in meal-treated plots than in untreated control plots; however, there were no significant effects on A. bilineata, numbers of D. radicum in roots or on levels of root damage. Olfactometry confirmed the absence of response by A. bilineata and showed that A. bipustulata is attracted to volatiles released by dry or wet mustard seed meal. From GC–MS, the most abundant volatiles from mustard seed meal were limonene and structurally-similar compounds. These results are discussed with respect to mechanism of attraction, the host finding cues used by the major parasitoids of D. radicum, and the value of mustard seed meal for enhancing biological control.

Defensive secretions of larvae of a carabid beetle

Secretions of an eversible gland on the metathorax of larvae of Chlaenius cordicollis Kirby (Coleoptera: Carabidae) are investigated by headspace analysis using solid phase microextraction followed by gas chromatography‐mass spectrometry (GC‐MS). Larvae from Manitoba, Canada and Pennsylvania, U.S.A., are sampled. Nine presumed defensive compounds are detected when the gland is everted, and this represents the first characterization of defensive secretions of larvae of a carabid beetle. With the exception of a single component (2‐methoxy‐4‐methylphenol), these compounds are distinct from those found in the defensive secretion of adult C. cordicollis. However, seven are more oxidized versions of the alkylphenolic compounds secreted by adult beetles: three hydroquinones (hydroquinone, methylhydroquinone and 2,3‐dimethylhydroquinone) and four quinones (p‐benzoquinone, toluquinone, 2,3‐dimethylquinone and ethyl‐p‐benzoquinone). An additional alkoxyphenol (2‐methoxy‐4‐ethylphenol) is also detected. Two patterns of composition are observed: in one, p‐benzoquinone and hydroquinone are undetectable and the ratio of toluquinone : 2,3‐dimethylquinone is 1 : 4.6 ± 0.6 (mean ± SE); in the other, all nine compounds are detectable and the ratio of toluquinone : 2,3‐dimethylquinone is 1 : 1.0 ± 0.2. These differences in pattern do not appear to be related to geographical source, sex or age of the larvae.

Spring Emergence of Canadian Delia radicum and Synchronization with Its Natural Enemy, Aleochara bilineata

Abstract To characterize time of spring emergence following post-diapause development, Delia radicum (L.) (Diptera: Anthomyiidae) from Saskatchewan, Manitoba, and southwestern Ontario were collected in fall, maintained over winter at 1 °C, then transferred to higher constant temperatures until adult emergence. At each location there were “early” and “late” phenotypes. Truncated normal models of temperature dependency of development rate were fitted for each phenotype from each location. We provide the first evidence of geographic variation in the criteria separating these phenotypes. Separation criteria and models for early and late phenotypes at the two prairie locations, approximately 700 km apart, were indistinguishable, but differed from those for Ontario. Prairie phenotypes developed more slowly than Ontario phenotypes, and more prairie individuals were of the late phenotype. Poor synchronization of spring emergence could impair predation of D. radicum eggs by adult Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae). Aleochara bilineata from Manitoba were reared and development rates modelled as for D. radicum. Models of development rates for the two species, when combined with simulated soil temperatures for two prairie locations, suggest that emergence of adult A. bilineata is well synchronized with availability of D. radicum eggs in prairie canola.

An elm bark beetle bioassay for residual efficacy of chlorpyrifos and cypermethrin used for the control of Dutch elm disease in Manitoba

Abstract The basal 1 m of the elm trunks were treated with 0.48% (active ingredient, Al) Dursban aqueous solution (chlorpyrifos) or 0.1% (Al) Ripcord aqueous solution (cypermethrin) for control of overwintering native elm bark beetle, Hylurgopinus rufipes, the vector of Dutch elm disease, Ophiostoma (Ceratocystis) ulmi, at Beaudry Provincial Park, near Winnipeg, Manitoba, Canada. A simple and effective bioassay method was developed to determine insecticidal persistence against the native elm bark beetle. Beetles reared in naturally infested elm logs were confined to the surface of elm bark circles taken from the treated trees. Bark circles were cut at various times after treatment using a cordless hole saw and stored at ‐ 32°C until the beetles were available. Mortality/morbidity data for the two treatments were suitable for use in the comparison of the action of the two insecticides over a two‐year period.