Maria A. Minor

Effects of multiple matings on reproductive fitness of male and female Diaeretiella rapae

Mating frequency and the amount of sperm transferred during mating have important consequences on progeny sex ratio and fitness of haplodiploid insects. Production of female offspring may be limited by the availability of sperm for fertilizing eggs. This study examined multiple mating and its effect on fitness of the cabbage aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Female D. rapae mated once, whereas males mated with on average more than three females in a single day. The minimum time lag between two consecutive matings by a male was 3 min, and the maximum number of matings a male achieved in a day was eight. Sperm depletion occurred as a consequence of multiple mating in D. rapae. The number of daughters produced by females that mated with multiple‐mated males was negatively correlated with the number of matings achieved by these males. Similarly, the proportion of female progeny decreased in females that mated with males that had already mated three times. Although the proportion of female progeny resulting from multiple mating decreased, the decrease was quicker when the mating occurred on the same day than when the matings occurred once per day over several days. Mating success of males initially increased after the first mating, but then males became ‘exhausted’ in later matings; their mating success decreased with the number of prior matings. The fertility of females was affected by mating with multiple‐mated males. The study suggests that male mating history affects the fitness of male and female D. rapae.

Influence of summer irrigation on soil invertebrate populations in a long-term sheep irrigation trial at Winchmore (Canterbury)

Abstract Soil invertebrates have limited defences against moisture stress but little is understood of how irrigation influences their community. This paper investigates the influence of five summer irrigation schedules on earthworms over a 15-month period in a long-term pasture irrigation study. The influence of the two extreme rates of irrigation on other soil invertebrates was also examined. The effects of frequent drought periods under dryland pasture favoured small and short-lived nematodes and oribatids. During wetter months, earthworm abundances were similar between dryland and irrigated treatments, while earthworms tended to migrate down the soil profile and aestivate in response to soil water deficits during summer. The higher abundance of earthworms in the summer months under irrigation may partly explain the lower soil carbon found under irrigation, due to enhanced rates of soil organic matter turnover, despite higher primary production and inputs of carbon. It is thus important to consider irrigation schedules not only to optimise plant growth, but also to optimise the invertebrate community and its activity.

Mating or ovipositing? A crucial decision in the life history of the cabbage aphid parasitoid Diaeretiella rapae (M’Intosh)

1. The reproductive fitness of a parasitoid depends on its mating and ovipositing success. Virgin haplodiploid females can reproduce, but produce only males, and may diminish fitness by producing more male offspring than required. Therefore, females must decide on whether to mate or oviposit first.

Influence of phosphorus inputs and sheep treading on soil macrofauna and mesofauna in hill pastures

Abstract Earthworm abundance increased and Oribatida abundance decreased on a Brown soil with increasing inputs of phosphorus (P) fertiliser and sheep stocking rates. To determine if the same response to increasing management intensity is found in Allophanic soil, samples were collected from a long-term sheep-grazed trial with two contrasting management regimes, low and high intensity. As pastures on the Allophanic soil became more productive and were grazed with more sheep, there was a tendency for earthworm abundance to increase and oribatid abundance to decrease. Both these trends were consistent with those on the Brown soil, supporting the potential of earthworms and Oribatida as biological indicators. Oribatid mites, which produce nutrient rich faecal pellets, were positively correlated with porosity. The higher earthworm abundances in more intensive sheep grazed pastures may have a positive influence on ecosystem services such as air and water movement, and organic matter incorporation.

Effects of Cushion Plants on High-Altitude Soil Microarthropod Communities: Cushions Increase Abundance and Diversity of Mites (Acari), but not Springtails (Collembola)

ABSTRACT Cushion plants in alpine ecosystems act as nurse species, which modify and alleviate environmental conditions and positively influence the diversity and abundance of other organisms. Soil fauna in alpine environments should benefit from nurse plant facilitation, but this has not been investigated. We compared diversity, abundance, and community structure of soil microarthropods (Collembola, Oribatida, Mesostigmata, Prostigmata, Endeostigmata, and Astigmata) under cushion plants and in adjacent open microsites in high altitude patterned ground landscapes in New Zealand. We investigated how cushion plants influence environmental factors, and how environmental factors and species traits contribute to microarthropod community structure. The results show that cushion plants are a key in maintaining the biodiversity of soil microarthropods in the high alpine. Cushion plants maintain higher moisture and organic matter content in the soil, provide productive and structurally complex habitat, and mitigate disturbance. Abundance and species richness of Oribatida, Mesostigmata, and Prostigmata were higher under cushion plants. In contrast, abundance of Collembola was higher in open microsites, while their species richness similar in and out of cushions. Oribatida assemblages were dominated by small asexual species, indicating a disturbed environment. Oribatida community structure was significantly related to the microhabitat in two out of three mountain ranges. Collembola assemblages were similar in and out of cushions. Higher soil moisture and organic matter content under cushion plants were significant in explaining patterns in microarthropod assemblages, although high percentage of variability was not explained by environmental variables. There was no effect of cushions on soil temperatures. Species identity of the cushion plant did not influence abundance, species richness, or community assemblages of mites and springtails; however, some species were associated with either Dracophyllum or Raoulia cushions.

Effects of dairy cow treading pressures and food resources on invertebrates in two contrasting and co-occurring soils

It is often difficult to compare the effects of land use on soil invertebrates across different soil types, as management practices are often adjusted to compensate for soil differences. A mosaic of two contrasting and co-occurring soils offered a unique opportunity to examine the influence of common management practices on soil invertebrates (macrofauna, mesofauna, and nematodes). Treatments established on a well-structured Andosol soil and co-occurring poorly structured Gleysol included a legume-based pasture grazed at 2.3 cows/ha and nitrogen (N) fertilised pastures grazed at 3 and 3.8 cows/ha, with the 3.8 cows/ha treatment also receiving maize supplementation. Low abundance (<13 000 individuals/m2) and diversity (four species) of Oribatida was a feature of both soils, reflecting the low porosity of the two contrasting, co-occurring pastoral soils, despite the Gleysol soil being more susceptible to treading than the Andosol. The lack of difference might reflect the ongoing disturbance from livestock treading on both soils. Nematode trophic groups behaved most predictably across both soils, with plant-feeding and bacterial-feeding nematodes increasing with the use of N fertiliser. Despite potentially more organic material available for incorporation into the soil profile with increasing inputs of N fertiliser and use of feed supplement, lower abundances of anecic earthworms, Collembola, and Oribatida are reported. Both direct and indirect effects of livestock treading on the decomposer community in intensive systems might be factors limiting the incorporation of organic matter from the soil surface into the profile to sustain soil carbon.

New taxa and record of mite family Microdispidae (Acari: Heterostigmata) from alpine New Zealand

ABSTRACT A new monotypic genus Paraphyllodispus Khaustov and Minor gen. nov. (Acari: Pygmephoroidea: Microdispidae) with type species P. vulgaris sp. nov., and new species Phyllodispus undulatus Khaustov and Minor sp. nov. and Microdispus (Microdispus) montanus Khaustov and Minor sp. nov. are described from alpine zone (1600–1900 m a.s.l.) of the Central Otago region of the South Island of New Zealand. Dolichodispus angustus (Krczal, 1959) is also recorded from New Zealand for the first time.

Austrodontella monticola sp. nov., a new species of Collembola from montane New Zealand.

Collembola were collected from soil in the alpine belt (1600-1900 m a.s.l.) of the Southern Alps of New Zealand. A list of species found is provided. Austrodontella monticola sp. nov., the third species of a Odontellidae genus with a southern distribution is described. The other two species in the genus occur in southern Australia and in the Indian Ocean sector of the Subantarctic respectively. Notes on A. trispina (Womersley, 1935), the type species of the genus, are provided.

The oribatid mite genus Macrogena (Acari, Oribatida, Ceratozetidae), with description of two new species from New Zealand

Abstract Two new species of oribatid mites of the genus Macrogena (Oribatida, Ceratozetidae) are described from alpine soils of the South Island of New Zealand. Macrogena brevisensilla sp. n. and Macrogena abbreviata sp. n. differ from all species of this genus by the tridactylous legs and by the comparatively short interlamellar setae, respectively. New generic diagnosis and an identification key to the known species of Macrogena are provided.

Influence of soil faunal communities on nitrogen dynamics in legume-based mesocosms

Soil invertebrates play an important part in nutrient supply. It has been suggested that invertebrates have the greatest influence on nitrogen (N) availability in soils of low N fertility, and therefore invertebrates may be less important in pastoral systems with high N inputs. The influence of invertebrates on N cycling, and the fate of 15N-labelled plant litter, in a low- or high-N environment and in a soil with low or high bulk density were explored by the introduction of different elements of the invertebrate community in constructed soil ryegrass–white clover mesocosms. At high bulk density and low N, the N made available by invertebrates resulted in higher plant growth, without any increases in N losses to the environment. At high N, where pasture growth was not limited by N, the N made available by invertebrates increased both herbage N% and the amount of N in leachate. More of the 15N-labelled plant litter decomposed in high-N than low-N mesocosms. Invertebrates increased the plant uptake of surface-applied 15N plant litter. The influence of invertebrates was dependent on bulk density, suggesting that invertebrates in compacted soils improved soil structure and N availability. This mesocosm study highlights the important role of invertebrates in N supply across a range of soil conditions.