M.R. McNeill

Transportation of nonindigenous species via soil on international aircraft passengers’ footwear

The potential for transported soil to harbour and spread nonindigenous species (NIS) is widely recognised and many National Plant Protection Organisations (NPPOs) restrict or prohibit its movement. However, surprisingly few studies have surveyed soil while it is in transit to provide direct support for its role in accidental introductions of NIS. Moreover, there are few border interception records for soil organisms because they are neither easily detected nor routinely isolated and identified. Better data would improve evaluations of risks from soil transported via different pathways, enable targeting of management resources at the riskiest pathways, and support development of new risk management methods. We surveyed organisms present in soil that had been removed from footwear being carried in the baggage of international aircraft passengers arriving in New Zealand and recorded high incidences, counts and diversities of viable bacteria, fungi, nematodes and seeds, as well as several live arthropods. These included taxa that have not been recorded in New Zealand and were therefore almost certainly nonindigenous to this country. In each gram of soil, there was an estimated 52–84% incidence of genera that contain species regulated by New Zealand’s NPPO, which suggests many were potentially harmful. Variation in the incidences and counts of soil organisms with sample weight, footwear type and season at the port of departure indicated it may be possible to develop methods for targeting management resources at the riskiest footwear. Comparisons with previously published data supported the hypothesis that survival of soil organisms is greater when they are transported in protected (e.g. in luggage) rather than unprotected environments (e.g. external surfaces of sea containers); this offers opportunities to develop methods for targeting management resources at the most hazardous soil pathways.

Host specificity testing and suitability of a European biotype of the braconid parasitoid Microctonus aethiopoides as a biological control agent against Sitona lepidus (Coleoptera: Curculionidae) in New Zealand

Abstract The European biotype of the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae) is being considered for release against Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) in New Zealand. Host specificity was evaluated in the laboratory using both endemic and introduced weed biological control curculionid species, with 12 no-choice and three choice experiments carried out comparing the S. lepidus and test weevils. Two further no-choice tests used the Moroccan M. aethiopoides biotype to compare attack rate between European and Moroccan M. aethiopoides, the latter released in 1982 to control the lucerne pest S. discoideus. Across all experiments, total parasitism of S. lepidus was 69% compared with 15% for the test weevils. European M. aethiopoides was able to develop in the native weevils Irenimus aequalis, Nicaeana cervina, Catoptes cuspidatus, Protolobus porculus and Steriphus variabilis with parasitism rates of 13, 28, 2, 7 and 8%, respectively. These levels were significantly less than those in the corresponding S. lepidus control. Total parasitism of I. aequalis and C. cuspidatus increased significantly in the presence of S. lepidus than recorded under no-choice conditions. The presence of European M. aethiopoides caused minor, if any, test weevil mortality prior to the onset of prepupal emergence and there was no significant reproductive suppression in parasitoid-exposed test weevils. Parasitism of the introduced weed control agent R. conicus by European M. aethiopoides was significantly lower (1.1%) compared to the Moroccan biotype (47.5%). Based on these and other experiments, should the European M. aethiopoides be released as a biological control agent of S. lepidus, its ecological impacts are likely to be less severe than those already exhibited by the Moroccan M. aethiopoides.

Linear patterns of dispersal and build up of the introduced parasitoid Microctonus hyperodae (Hymenoptera : Braconidae) in Canterbury, New Zealand

The dispersal of Microctonus hyperodae Loan, an introduced parasitoid of the South American grassland pest Listronotus bonariensis Kuschel, was measured in Canterbury, New Zealand. Considering all directions, the mean annual dispersive increment was 1.9 ± 0.9 km year –1 as measured in the winters of 1993, 1994 and 1995. The parasitoid’s ground distribution suggested that its movement was biased towards the south-west indicating probable wind-borne dispersal. The overall relatively low rate of dispersal was thought to be related to the inhibitory effects of M. hyperodae parasitism on L. bonariensis flight. A generalized linear model fitted to percentage of L. bonariensis parasitized took a simple form, with a quadratic increase in weevil infection, that with time, gradually decreased. The build-up of parasitism at the release site was significantly greater than the rates at the other sites measured in this study ( P c . 140 km 2 .

The potential of parasitoid strains in biological control: Observations to date on Microctonus spp. intraspecific variation in New Zealand

Abstract Over the last 15 years New Zealand researchers have been actively involved in the classical biological control of forage weevil pests. In the 1980s, the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) was successfully suppressed by the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae). Since 1990, an additional programme has been developed to examine the impact of the recently introduced parasitoid Microctonus hyperodae (Hymenoptera: Braconidae) on New Zealands worst ryegrass pest, the Argentine stem weevil ( Listronotus bonariensis (Kuschel)). The imported M. hyperodae founder populations were collected from a wide range of ecoclimatic zones. During both of the programmes, the importance of ecotypes has become increasingly apparent. The New Zealand M. aethiopoides population revealed phenological patterns quite different from those observed in Mediterranean Europe, North America and Australia. As a result of these observations, part of the current research into M. hyperodae has been developed specifically to explore ecotypic variation and its implications. This contribution reviews progress to date in researching ecotypic differences and comments on the potential of ecotypes in classical biological control, with particular reference to recently developed DNA-based techniques.

Modeling Embryo Development of Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) Under Constant Temperature

Abstract The alfalfa root weevil, Sitona discoideus (Coleoptera: Curculionidae), is an important pest of alfalfa. The developmental rates of the embryo development were recorded at eight constant temperatures ranging from 8.5 to 30°C. Using 10 models (1 linear and 9 nonlinear), we evaluated the relationship between constant temperature and developmental rate. Embryo development was shortest (8.5 d) and longest (69 d), at 28 and 8.5°C, respectively. The threshold temperature (T0) and the thermal constant (K) were estimated using linear regression to be 4.7°C and 207.7 DD, respectively. The two most efficient nonlinear models, the Lactin and the Sharp and DeMichele, gave estimates of Tmin and Tmax of 4.4 and 3.9 and 30.0 and 30.9°C, respectively. This information has potential application in predicting the suitability and optimal time of release of an egg parasitoid of S. discoideus.

Curculionoidea (Insecta: Coleoptera) of New Zealand agricultural grassland and lucerne as potential non‐target hosts of the parasitoids Microctonus aethiopoides Loan and Microctonus hyperodae Loan (Hymenoptera: Braconidae)

Abstract The parasitoids Microctonus aethiopoides Loan and Microctonus hyperodae Loan (Hymenoptera: Braconidae) have been introduced into New Zealand to control the adult stage of the forage pests Sitona discoideus and Listronotus bonariensis (Coleoptera: Curculionidae), respectively. These parasitoids have been chosen to examine the environmental impact of introduced biological control agents on native and non‐target species. A survey of the Curculionoidea fauna of pasture, lucerne, and modified native grassland in parts of the southern South Island, Canterbury, and the northern North Island of New Zealand, where these parasitoids are present, was carried out in order to identify Curculionoidea with taxonomic and ecological affinities with the target hosts, and hence, potential non‐target hosts. At a total of 155 sites, 85 species of Curculionoidea were identified, of which 64 (75%) were native species. Three tribes in the subfamily Brachycerinae (broad‐nosed weevils) accounted for 61 species, and 7 trib...

Phenology of native weevils (Coleoptera: Curculionidae) in New Zealand pastures and parasitism by the introduced braconid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae).

Abstract The phenology of native brachycerine weevil species at seven pasture sites in Otago, Canterbury and Waikato was studied by regular quantitative sampling of adults. Weevils were identified to species, and dissected to record reproductive status and parasitism by introduced braconid parasitoids in the genus Microctonus. Climatic data assisted in the interpretation of some population density patterns. Weevil population density was estimated for periods of two to five years at the selected sites. Species in the Entimini (species of Irenimus and Nicaeana) were generally univoltine, with adults emerging in winter‐spring. The main period of reproductive activity was spring, and parasitism by Microctonus aethiopoides reached its highest incidence in January. Low level parasitism of native weevil species by M. aethiopoides was detected at all sites, and by M. hyperodae at two sites. At one site in Otago, parasitism by M. aethiopoides was higher and could have affected the population density of Irenimus aemulator (Broun) and Nicaeana sp. Most parasitism occurred after the main reproductive period of weevils in spring, but a putative second generation in some species might be more affected by parasitoid attack. A native rhytirhinine species, Steriphus variabilis, differed from the entimines because adults emerged in autumn and spring, and may be bivoltine. Mechanisms of M. aethiopoides parasitism of non‐target species in the field are discussed.

Effect of host condition and photoperiod on the development of Microctonus hyperodae Loan, a parasitoid of the Argentine stem weevil (Listronotus bonariensis (Kuschel))

Abstract Microctonus hyperodae, a euphorine parasitoid of Listronotus bonariensis, was found to enter photoperiodically induced diapause independently of the seasonally determined reproductive condition of its host. Indications were that the critical daylength may be c. 12.3: 11.7 L:D, which represents a photoperiod of 13.6: 10.4 L:D.

Characterization of olfactory receptor neurons for pheromone candidate and plant volatile compounds in the clover root weevil, Sitona lepidus

Antennal olfactory receptor neurons (ORNs) for pheromone and plant volatile compounds were identified and characterized in male and female clover root weevil, Sitona lepidus (Gyllenhal), using the single sensillum recording technique with five pheromone-related compounds, and 40 host and non-host plant volatile compounds. Overall, seven different types of olfactory sensilla containing specialized ORNs were identified in each sex of S. lepidus. Among them, three different types of sensilla in the males and two types in the females housed ORNs specialized for pheromone-related compounds. The ORNs in males were specialized for 4-methyl-3,5-heptanedione or one or more of four stereoisomers of 5-hydroxy-4-methyl-3-heptanone. In contrast, female sensilla did not contain ORNs sensitive to 4-methyl-3,5-heptanedione while they contained ORNs sensitive to and specialized for the stereoisomers of (4S,5S)-5-hydroxy-4-methyl-3-heptanone. In addition to the pheromone-related ORNs, four types of olfactory sensilla contained ORNs responsive to plant volatile compounds in male S. lepidus, and five types in females. Most of the ORNs identified in S. lepidus showed a high degree of specificity to specific volatile compounds although some of the active compounds showed overlapping response spectra in the ORNs across different types of sensilla. The most active plant volatile compounds were the four green leaf volatile compounds, (E)-2-hexenol, (Z)-2-hexenol, (Z)-3-hexenol and (E)-2-hexenal, and isomers of two monoterpenols, (±)-linalool and (±)-α-terpineol, all eliciting strong responses from relatively large numbers of ORNs in male and female S. lepidus. Our study indicates that S. lepidus has a set of highly sensitive and selective ORNs for pheromone and plant volatile compounds. Further work is needed to elucidate the behavioral implications of these findings.

Evidence of density-dependent oviposition behaviour by Listronotus bonariensis (Coleoptera: Curculionidae) in Canterbury pasture

Argentine stem weevil ( Listronotus bonariensis ) (Kuschel) is a pasture pest of Lolium spp. in New Zealand and is the target of a classical biological control programme using the parasitoid Microctonus hyperodae Loan. However, laboratory experiments have indicated a strong density-dependent egg laying response which may have important implications for the biological control effort. Two field experiments were conducted using a manipulated range of weevil densities within 2.0–2.4 m –2 field enclosures and oviposition activity measured by weekly sampling of grass tillers within the enclosures. In both experiments, density had no effect on general oviposition behaviour although the percentage of tillers found to be infested with eggs increased significantly at higher densities. In experiment 1, L. bonariensis exhibited strong density-dependent oviposition with a significant decline in eggs/tiller/female with increasing adult density. An initial population of five L. bonariensis m −2 oviposited 32 times more eggs/tiller/female than 200 L. bonariensis m −2 . By comparison, density-dependent oviposition was absent in experiment 2 with eggs/tiller/female comparable for all densities. The dramatic difference between the two experiments in the expression of density-dependent oviposition was attributed to prevailing spring temperatures during the sampling interval, which in the second experiment were much cooler and delayed the onset of egg laying. It is probable that in experiment 2, oviposition was not regulated by density-dependent cues but limited by temperature and age related mortality in the adult population. The mechanism for density-dependent oviposition, its occurrence in the field and impact on the effectiveness of the parasitoid M. hyperodae are discussed.