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Two species from the genus Microctonus Wesmael (Hymenoptera: Braconidae) have been introduced into New Zealand as biocontrol agents of pest weevils in pasture. Both parasitoids have similar life cycles and co-exist in pasture along with their respective weevil hosts. However, winter parasitism rates by M. hyperodae Loan are low in comparison to the Irish biotype of M. aethiopoides’ Loan. Population studies at two Waikato sites over three consecutive seasons of parasitoid activity showed that M. aethiopoides recovered from near extinction each spring and built up to effective levels by winter because hosts were available continuously throughout summer and autumn. In contrast, M. hyperodae began each season at higher larval populations and parasitism levels than M. aethiopoides, but populations and parasitism levels declined during late summer and early autumn due to low host availability. The contrast between species is consistent with the high levels of endophyte-conferred pest-resistant grass in the pastures, which impacts strongly on M. hyperodae’s host weevil abundance during summer but has no effect on M. aethiopoides’ host weevils which feed only on clovers. It was accentuated by a warming climate with the now regular occurrence of a third host generation after most M. hyperodae adult activity had ceased.

Background Yersinia entomophaga is an entomopathogenic bacterium that is active against scarab beetles, among other insects. In New Zealand, the African black beetle, Heteronychus arator (Coleoptera: Scarabaeidae), is a major pest of pastures and arable crops but very few control options exist and no insecticides are registered for use in established pastures. Results In laboratory bioassays, H. arator adults were susceptible to a bait containing Y. entomophaga at low doses. This bait was more effective against H. arator adults during spring than autumn in small-scale field plots (320 mm diameter). A large-scale field trial (40 × 40 m plots) reduced adult numbers substantially: approximately twice as many beetles were captured in pitfall traps from untreated plots compared with plots treated with the Y. entomophaga bait at 70 kg ha-1 . This single bait application in spring also reduced subsequent larval populations in summer. Conclusions Heteronychus arator is a difficult pest to manage using chemical insecticides. This biopesticide with Y. entomophaga as the active ingredient offers a new solution for New Zealand pastures, with potential for application to other crops affected by H. arator and for control of other pests. © 2020 Society of Chemical Industry.

The lack of plant biodiversity in New Zealand pastoral ecosystems may limit the abundance and diversity of generalist parasitoids and predators, predisposing these ecosystems to pest outbreaks. To test this hypothesis, patches of turf were established in existing pasture during spring 2016. Four treatments of increasing plant complexity were established, commencing with ryegrass alone, and increasing exponentially up to eight species of forage plant per patch. In the summer of 2017, insects were collected from the patches and control plots using suction to assess whether or not plant diversity had influenced the abundance and diversity of lacewings and parasitic Hymenoptera aggregating in the patches. Plant species richness had no impact on lacewing abundance but fewer parasitic Hymenoptera were recovered from the ryegrass-only plots compared with more species rich plots. Also, a wider range of parasitoid families were represented in the more diverse plant treatments compared with the less diverse treatments. Such diversity may have beneficial impacts on the stability of pasture ecosystem and the risk of pest outbreaks.

The African black beetle (Heteronychus arator F.) is a pest of pastures in the North Island of New Zealand. Except during dispersal activity, adult beetles live in the soil and feed at the base of grass stems during spring and fall and to a lesser amount over-winter. Larvae develop over summer months feeding on the grass roots. We tested three life-stages of H. arator (first and third instar larvae and adults) for susceptibility to the four entomopathogenic nematode (EPN) species present in New Zealand: Steinernema carpocapsae, Steinernema feltiae, Heterorhabditis bacteriophora and Heterorhabditis zealandica. All H. arator stages were found to be susceptible to EPN, but different life-stages varied in susceptibility to EPN species. Based on our laboratory assays, we chose to target adult beetles using S. carpocapsae. We ran three field experiments, one in spring and two in fall but the EPN did not reduce beetle numbers in any experiments. Field temperatures were cool, but within the stated thermal niche breadth of S. carpocapsae for killing hosts. Sampling on nematode-treated plots revealed several susceptible lepidopteran larvae clearly infected with S. carpocapsae but no infected H. arator. We tested the hypothesis that the effective niche breadth for killing hosts may vary with host-susceptibility. We studied the temperature response of S. carpocapsae against Galleria mellonella and H. arator at 12.5, 15, 18, 20 and 25 °C. While S. carpocapsae caused significant mortality of G. mellonella at all temperatures, no H. arator mortality was seen at 12.5 or 15 °C despite using a high nematode rate and incubating for two weeks. Our data highlight the importance of testing susceptibility of different insect life stages at the temperatures likely to be encountered in the field following nematode application.

Classical biological control of insects has a long history of success, with high benefit–cost ratios. However, most attempts to introduce a biological control agent have been unsuccessful, largely because the agent does not establish in the new environment. This perspectives paper discusses the possibility that even successful biological control may eventually fail, although records show that this is far from a common event. A documented example of eventual biological control failure is discussed and the prospect for future failures analyzed. Part of this analysis is based on an introduced weevil pest in New Zealand and its successful parasitoid biological control agent. The potential fragility of this host–parasitoid relationship is considered, as well as why it may indeed be starting to show signs of instability; this is particularly from the point of view of New Zealand’s often species-poor agricultural ecosystems.

New Zealand pastures are host to a range of native and exotic invertebrates. Many of these are pests that feed on the sown plant species, often causing plant death and deterioration in the productivity and persistence of the sward. While most research has focused on pest biology and control, studies of plant productivity show dramatic acute (short-medium term) and chronic (longterm) effects. For example, grass grub has been reported to cause 50% losses to ryegrass swards and Argentine stem weevil can cause a 20% loss of productivity, but the long term effects through loss of the sown species and changes in composition can be even more severe. Insect damage can be exacerbated by other biotic (e.g. weed invasion, grazing animals, plant pathogens) or abiotic factors (e.g. climate, soil fertility) to further reduce plant persistence. Some biotic and abiotic factors may interact with insect pests to have positive effects on pasture persistence, e.g. biocontrol agents that reduce pest density or addition of fertiliser to enable plants to recover from insect damage. For many pasture pests, knowledge of their ecology is based on research from over 20 years ago that, while still valid, needs to be updated to account for modern intensive pasture management practices, such as intensive grazing with a lack of reseeding, and new cultivars. To improve pasture persistence, integrated research programmes are needed that examine the relative importance of all factors contributing to plant survival and develop strategies to mitigate their effects. Keywords: Argentine stem weevil, black beetle, clover root weevil, drought, grass grub, grazing pressure, manuka beetle, nematodes, pasture persistence, pasture quality, pasture yield, porina, soil fertility, striped chafer.

The effects of larval herbivory by clover root weevil (CRW, Sitona lepidus) on seven white clover (Trifolium repens) and two red clover (Trifolium pratense) progenies from plants showing tolerance of CRW in field trials were tested in two controlled glasshouse experiments. CRW larvae recovered from red clover plants were, on average, fewer (6.3 larvae/g root dry weight) and shorter (5.7 mm/g root dry weight) than those from white clover (16.7 larvae, 7.1 mm length).This confirmed previous findings that red clover is an inferior host for this pest. In the first experiment, progeny of four of the white clover selections for CRW tolerance showed high tolerance (shoot dry weights −2.9% to +3.1% different from their respective weevil-free controls) compared with a 13–24% shoot weight loss for two white clover cultivars. These results confirm field trial observations that there is variation for CRW tolerance in white clover and also that CRW tolerance is hereditable in at least some populations. The se...

The effects of root herbivory at five densities of Sitona lepidus larvae (overall means between 4 and 333 larvae m‐2) were assessed over 2 years on newly established perennial ryegrass‐white clover swards in a small plot trial. Initial larval establishment in autumn 2003 was positively related to clover content in plots, and there was no significant impact on clover herbage yield in the first year. Nodule damage in winter 2003 increased with larval density, and results suggested an overcompensatory response in nodule production. A 34–35% reduction in clover yield between highest and lowest S. lepidus densities was recorded for both cultivars in the second year, with greatest losses in spring 2004. This coincided with reductions in clover root and stolon weights. Plant parasitic nematodes and grass grub larvae were most abundant in the plots with lowest weevil numbers. These results confirm field observations that S. lepidus is a major pest of pastures.

Populations of adult clover root weevil (Sitona lepidus) can infl ict signifi cant numbers of their distinctive feeding notches on the leaves of white clover (Trifolium repens) plants. However, it is assumed that because white clover is bred for defoliation, the damage on established plants has little impact. Two experiments were undertaken to quantify the daily leaf consumption levels of adult weevils, and how this varied with weevil size and sex, clover cultivar and previous leaf damage. Overall, adults consumed between 0.75 and 1.2 mg dry matter/day depending on cultivar and sex. Sexual differences were observed between two contrasting clover cultivars, with females consuming more Grassland Prestige and males Grasslands Kopu. Clover dry matter loss through adult feeding was estimated at about 50 kg/ha from early summer until midwinter in the Waikato, the period of peak adult activity.

Clover root weevil adults collected from the field were held in four contrasting temperature, moisture and feeding regimes for a period of 10 weeks. Temperature was the main factor, inducing changes in adult wing muscle development and egg production. Egg production from females held in the ‘moist winter’ regime (10 °C, 8:16 h light:dark, moist conditions, ample food) increased linearly with time, with 90% of females fully reproductive at 10 weeks. In contrast, when held in the ‘hot drought’ regime (20 °C 16:8 h light:dark, dry conditions, intermittent food), the oviposition rate decreased logarithmically, with 32% of females fully reproductive at 10 weeks. Overall, adult mortality was lower in the ‘moist’ regimes (17%) than the ‘drought’ regimes (29%). Wing muscle development differed between regimes, ranging from 4% of adults with fully developed wing muscles in the ‘moist winter’ regime to 35% in the ‘hot drought’ regime. Clover root weevils are likely to oviposit throughout winter in most of New Zealand, but warm, dry summers will prevent a summer larval generation.

The chitinase inhibitor/insect ecdysis inhibitor allosamidin and eight allosamidin analogues have been synthesised from simple carbohydrate starting materials. Allosamidin was assayed against Tineola bisselliella (Hummel) larvae and all nine compounds were examined for their effects on the development of larvae of Lucilia cuprina (Wiedemann). High larval mortality compared to controls resulted when T. bisselliella and L. cuprina larva were exposed to allosamidin. The (1→3) linked regioisomer, the dimeric analogue and the gluco-configurated dimeric analogue of allosamidin all showed high activity against L. cuprina larvae. The regioisomer, the (1→3) linked isomer and its dimeric analogue, as well as the monomer allosamizoline and its regioisomer, were inactive. These new in-vivo results are consistent with known in-vitro insect chitinase inhibition data, in that greatest larval mortality was exhibited by the best inhibitors.

A modified serum‐based bioassay was used to screen plant extracts and assess compound activity against newly hatched larvae of the Australian sheep blowfly Lucilia cuprina. Larval instar mortality and physical appearance were recorded after exposure for 24 h to the treatments. Extracts from New Zealand gymnosperms shown to have activity against L. cuprina larvae were: Podocarpus totara; P. acuteafolius; Dacrycarpus dacrydioides; Halocarpus bidwillii; H. biformis; H. kirkii; Lagarostrobos colensoi; Lepidothamnus intermedius; L. laxifolius; Phyllocladus tricho‐manoides; P. glaucus, and Agathis australis. The phytoecdysones 20‐hydroxyecdysone, 5,20‐dihydroxyecdysone, and ponasterone A inhibited larval moulting. Dyshomoerythrine, dacrysterone, and nagilactone C were insecticidal, with the latter also retarding growth at sublethal rates.

This study focuses on three main groups of organisms: soil invertebrates, biological control agents (BCAs) and pollinators. These groups play key roles in agricultural systems, and have the potential to be used, moved or manipulated for the benefit of agriculture. Soil invertebrates are a key component of agricultural landscapes. They participate in essential soil processes that maintain healthy productive soils in the face of changing environmental conditions. Reducing the diversity of a community of soil invertebrates reduces its beneficial functions and services, with drastic ecological effects such as long-term deterioration of soil fertility and agricultural productive capacity. The introduction of a keystone species may have detrimental or beneficial effects depending on the context. The interaction between soil invertebrates and soil microorganisms is critical: the activities of soil invertebrates regulate microbial activity in soils, and micro-organisms enter into intimate relationships with soil invertebrates to help them degrade highly complex compounds such as cellulose. Different groups of invertebrates provide biological control of crop pests. In many situations, they form the basis of, and tools for, the integrated pest management (IPM) approach. Given that the losses caused by pre- and post-harvest pests can be very substantial, the potential benefits of using invertebrates as BCAs are vast, but as yet only partially tapped. The potential for soil invertebrates to assist in this function is still largely unknown. Pollination services by animals, especially by insects, are among the most widespread and important processes that structure ecological communities in both natural and agricultural landscapes. An estimated 60-90% of the world's flowering plants - including a range of economically important species - depend on insects for pollination. Crop pollination used to be (and often still is) provided by wild pollinators spilling over from natural and semi-natural habitats close to crop fields. This service has generally been free and therefore has received little attention in agricultural management. If wild pollinators are lacking or additional pollination is required, as is the case in many intensive agricultural production systems, farmers in some developed countries can buy or rent managed honeybees or sometimes other species (e.g. bumblebees, alfalfa leafcutter bees and alkali bees). Both options - i.e. use of wild species and managed bees - have recently come under pressure, a development that is sometimes referred to as the 'pollination crisis'. Of the interactions and overlaps between these key groups, that between soil invertebrates and BCAs is the most important, and further research is needed to evaluate the scope and impact of manipulation of the soil ecosystem to conserve or encourage beneficial BCAs. © CAB International 2012., This review is based in part on a report that the authors prepared for the Commission on Genetic Resources for Agriculture (CGRFA at FAO, Rome) on climate change and invertebrate genetic resources for food and agriculture [117]. We thank Kim-Anh Tempelman and colleagues at the CGRFA for their interest, support and encouragement in preparing that report. We also thank Fabian Haas (icipe, Kenya) who contributed a case study as indicated; Joop van Lenteren (Wageningen University, The Netherlands) and several anonymous scientists of the CGRFA and FAO who reviewed parts of a draft of the report from which this review was derived; and Rebecca J. Murphy (United Kingdom) and Dafydd Pilling (FAO) for editorial inputs to that report.