Evaluating the establishment success of Microctonus aethiopoides (Hymenoptera: Braconidae), a parasitoid of the alfalfa weevil (Coleoptera: Curculionidae), across the northern Great Plains of North America

The alfalfa weevil (Hypera postica (Gyllenhal); Coleoptera: Curculionidae), is a destructive pest of alfalfa (Medicago sativa Linnaeus; Fabaceae) worldwide. The biological control parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae), was successfully introduced, and considered highly effective, in the eastern and mid-western United States of America. Redistribution efforts carried out throughout the 1980s reported initial establishment in the northern Great Plains, however follow-up studies to assess long-term persistence and efficacy are lacking. We resurveyed the counties in which M. aethiopoides had been initially recovered following redistribution in Montana (Flathead and Petroleum counties), Wyoming (Platte County), and South Dakota (Brookings County), to gauge whether this species has become permanently established and, if so, assess levels of parasitism in the field. We collected adult weevils from five fields in each county, and reared them in the laboratory to assess parasitism. Despite rearing more than 1000 weevils, no parasitoids were recovered from any of the locations sampled in our study, suggesting a widespread failure of M. aethiopoides to persist in the region. Thus, M. aethiopoides does not currently appear to be an important biological control agent of alfalfa weevil in the northern Great Plains. More intensive surveys will be required to assess the extent of the distributional limits of this species throughout the region.

Response to clover root weevil outbreaks in South Canterbury, Otago and Southland; the agricultural sector and government working together

Clover root weevil was first discovered in the northern South Island in 2006, and an introduced biocontrol agent the parasitoid wasp Microctonus aethiopoides, was immediately released there in response. As the weevil spread southwards, ongoing releases and natural parasitoid dispersal generally supressed it to economically tolerable levels. However, mild winters in the southern South Island during 2013 and 2014 allowed weevil populations to grow and spread quicker than the parasitoid. This severely impacted white clover production and farm profitability in parts of South Canterbury, Otago and Southland, thus, scientists and industry conducted 18 months of intensive parasitoid releases of ca. 1.1 million parasitised weevils at 6000 sites. The parasitoid rapidly established at all 50 monitored release sites and dispersed from them. The biocontrol agent now occurs at all locations in South Canterbury, Otago, Southland, and elsewhere in New Zealand, where clover root weevil is present. Keywords: biological control, pest spread, parasitic wasp, Sitona obsoletus, Microctonus aethiopoides, South Canterbury, Southland, Otago

Clover root weevil tolerance of clover cultivars

Clover root weevil arrived in New Zealand about 20 years ago causing major loss of productivity as it progressively spread across the whole country. It is now largely controlled by an introduced parasitic wasp biocontrol agent Microctonus aethiopoides (Irish ecotype). However, management of insect pests should not rely on a single mechanism and clovers resistant or tolerant to this weevil would be a useful augmentation for farmers to have. This investigation reports on the suitability of 22 clover cultivars to attack from the weevil. Results have shown that contrary to popular belief, red clovers are not universally less favourable to the weevil than white clovers and usefully, within both species cultivar differences point to the possibility of resistance to this pest. Keywords: Clover root weevil, Sitona obseletus, clover cultivars

lepidus Economic benefits of biological control of Sitona obsoletus (clover root weevil) in Southland pasture

Sitona obsoletus is a serious pasture pest in New Zealand where its rootfeeding larvae reduce white clover cover and nitrogen fixation To maintain production farmers may compensate by increasing inputs The parasitic wasp Microctonus aethiopoides Loan was introduced for biological control of S obsoletus and achieved parasitism rates exceeding 70 In Southland where S obsoletus was first detected in 2010 unusually severe and prolonged infestations during 2013 and 2014 prompted intensive biological control releases in 2014 and 2015 This study evaluated if they were cost effective in 2015 On dairy farms biological control returned 1478/ha/year or 23 million over the 158017 ha On sheep and beef farms the estimated return was 686/ha/year or 47 million over 719854 ha Monte Carlo simulations were used to estimate returns (/ha/year) using plausible ranges of model parameter values and returns were positive in at least 975 of simulations Biological control of S obsoletus has returned a net benefit in Southland

Toxicity of selected agrichemicals to clover root weevil and its parasitoid Microctonus aethiopoides

White clover (Trifolium repens) crops are attacked by various insect pests including Sitona obsoletus (S lepidus) (CRW) Laboratory experiments were conducted to measure the toxicity of eight agrichemicals used against white clover insect pests or for weed control on CRW (parasitised and nonparasitised) and adults of its parasitoid Microctonus aethiopoides Laboratory experiments evaluated insect toxicity through direct contact with the agrichemical spray or via exposure to residues on clover foliage At field rates pymetrozine had the lowest impact on CRW biocontrol but had poor activity against nonparasitised CRW Taufluvalinate provided 60 control of CRW while having reduced impact on M aethiopoides adults (060 mortality) and was considered the best option in the field over the summer period Lambdacyhalothrin and diazinon were the most detrimental to CRW and its biocontrol agent when applied directly and through exposure to residues Diquat and an adjuvant caused some mortality to CRW and parasitoid Field studies are needed to corroborate these results

An Ultrastructural and Fluorescent Study of the Teratocytes ofMicroctonus aethiopoidesLoan (Hymenoptera: Braconidae) from the Hemocoel of Host Alfalfa Weevil,Hypera postica(Gyllenhal) (Coleoptera: Curculionidae)

The braconid waspMicroctonus aethiopoidesLoan is an idiobiont endoparasitoid of alfalfa weevil adultsHypera postica(Gyllenhal). After oviposition and subsequent egg maturation, large trophic cells called teratocytes dissociate from the serosa and are released into the host hemocoel. These teratocytes are present in large numbers and are visible to the naked eye. It is thought that they accumulate host hemocoelic metabolites for later consumption by the parasitoid larvae. We have undertaken a microscopic study of these gargantuan and complex cells at approximately seven months after parasitization. Parasitized adult weevils were dissected into medium and teratocytes were fixed, embedded, and sectioned at 1 μm. Teratocytes were stained with various specific fluorescent dyes for plasma membrane, Golgi, nuclei, lysosomes, mitochondria, and endoplasmic reticulum (ER). The surface of each cell is covered with a dense microvillar layer. Analysis of fluorescent images showed that these cells do not have condensed nuclei. ER was abundant around the nuclear envelope. Lysosomes were positioned around the periphery of the nucleus and the Golgi apparatus was significantly enlarged, being located around the nuclear envelope.

Effect of black legume aphid Aphis craccivora honeydew on survival of the parasitoid Microctonus aethiopoides

The introduced parasitoid Microctonus aethiopoides (Hymenoptera Braconidae) appears to be an effective biocontrol agent for clover root weevil Sitona lepidus Gyllenhal (Coleoptera Curculionidae) in New Zealand pastures As these pastures lack accessible nectar sources hemipteran honeydew may be the most readily available energy source for the parasitoid Experiments were undertaken to compare longevity of newly emerged M aethiopoides adults caged on white clover firstly with and without black legume aphid Aphis craccivora Kock (Hemiptera Aphididae) and then with additional water and sucrose solution treatments Parasitoids with access to aphid honeydew lived significantly longer (mean longevity 81 days) than those with water or no liquid (both 68 days) but not as long as those fed sucrose solution (109 days) Therefore the abundance of aphids commonly present on clovers may enhance M aethiopoides longevity and therefore efficacy in the field especially in mid spring when host availability is very low