Behavioural Acceptability of Sitona lepidus (Coleoptera: Curculionidae) to the Parasitoid Microctonus aethiopoides (Hymenoptera: Braconidae) Using the Pathogenic Bacterium Serratia marcescens Bizio

Microctonous aethiopoides Loan has been introduced into New Zealand to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) a pest of clover ( Trifolium spp.), has recently established in New Zealand. Laboratory experiments to test the potential of M. aethiopoides to parasitize S. lepidus has resulted in very low levels of parasitism. To investigate whether there were behavioural or physiological barriers to successful parasitism, two experiments were conducted using the insect pathogenic bacterium. Serratia marcescens Bizio as a marker for parasitoid ovipositor penetration. Firstly, M. aethiopoides 'treated' with S. marcescens were exposed to weevils and rapid weevil mortality was used to indicate ovipositor penetration. Up to 50% mortality of S. lepidus occurred, which was comparable with mortality observed in the permissive host Listronotus bonariensis . Dissection of S. lepidus exposed to parasitoids treated with distilled water showed that ca. 21% contained parasitoid eggs of which 98% were nonviable. In the second experiment, exposure periods of 24, 48 and 72 h to S. marcescens -treated parasitoids produced an increase in S. lepidus mortality of 14, 28 and 38%, respectively. There was 3% successful parasitoid development in weevils exposed for 72 h to parasitoids treated with distilled water. M. aethiopoides has been shown to develop successfully in a wide range of non-target weevil species both in the laboratory and field. Possible reasons for poor survival of M. aethiopoides immature stages in S. lepidus are discussed.     

Biology of Coeloides sordidator (Hymenoptera: Braconidae), a Possible Candidate for Introduction Against Pissodes strobi (Coleoptera: Curculionidae) in North America

Various aspects of the biology of Coeloides sordidator, an ectoparasitoid of pine weevils of the genus Pissodes, were studied. When reared in the laboratory on P. castaneus, females preferred to oviposit on third and fourth instar larvae in galleries, but ovipositions were also observed on second instars and prepupae. Pupae were not accepted as hosts. At 23°C and a 16 h day length, pre-imaginal development lasted 15-20 days. For each parasitoid population tested, between 8 and 28% of the individuals diapaused as prepupae in cocoons. The rate of diapause was not influenced by the photoperiod during larval development. In contrast, diapause was induced by a short day photoperiod on parents before and during oviposition and by low temperatures during the larval stage. Diapause termination was achieved by cold storage at 2°C for at least 8 weeks. Rearing of C. sordidator on P. castaneus under natural conditions showed that in the Swiss Jura it is mainly univoltine, with less than 10% of the parasitoids emerging for a second generation. When C. sordidator females were offered healthy P. castaneus larvae and larvae parasitized by the braconid endoparasitoid Eubazus semirugosus, there was no evidence that they were able to discriminate between healthy and parasitized hosts. The potential of C. sordidator as a biological control agent against the North American species P. strobi is discussed.     

Virus-like particles in the ovaries of Microctonus aethiopoides Loan (Hymenoptera: Braconidae): comparison of biotypes from Morocco and Europe

Virus-like particles (MaVLP) have been discovered in the ovarial epithelial cells of the solitary, koinobiont, endoparasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) introduced to New Zealand originally from Morocco to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). MaVLP have been found in all females examined. It has been suggested, although not demonstrated, that like many other such VLP found in parasitoids, MaVLP might play a role in host immunosuppression. Since another biotype of M. aethiopoides from Ireland has been proposed for introduction to control the white clover pest, Sitona lepidus Gyllenhal, in New Zealand, it was considered that females from this biotype warranted transmission electron microscope examination for VLP. No VLP were observed in ovarian tissues of specimens collected from three different locations in Ireland. Similarly, none were found in M. aethiopoides sourced from France, Wales, and Norway. These observations are discussed in relation to quarantine host specificity tests with the Irish biotype, which found that the host range of the Irish biotype is likely to be less extensive than that of the Moroccan biotype already in New Zealand.     

Evidence of Host Discrimination by Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae), a Parasitoid of the Argentine Stem Weevil Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae)

Microctonus hyperodae is a solitary endoparasitoid of the Argentine stem weevil, Listronotus bonariensis. Early investigation into the biology of the parasitoid indicated that there was no discrimination between parasitized and unparasitized hosts. However, dissection data from two experiments were analyzed according to three mathematical models. Model I was based on the Poisson distribution and assumed random selection of hosts. The host discrimination model (model II) assumed that parasitized hosts had reduced attractiveness to searching parasitoids. A competition model (model III) made the assumption that competition between the early immature parasitoid stages led to premature mortality, which was not accounted for in the dissection results. The dissection data indicated statistically significant departure from the Poisson model. Results from the laboratory experiment indicated that host discrimination explained the results more accurately than parasitoid larval competition. Models II and III both provided adequate fits to the field data, although the departure from the observed data was greatest for the competition model. Both intra- and inter-ecotypic host recognition were evident, and there was some indication that clonal recognition took place. This is the first evidence of host discrimination by a member of the genus Microctonus. It has provided further indication of the success of M. hyperodae as a biological control agent.     

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.     

A Morphometric Method to Assist in Defining the South American Origins of Microctonus hyperodae Loan (Hymenoptera: Braconidae) Established in New Zealand

In 1991, Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae), collected from eight diverse South American locations, was released in New Zealand as a biological control agent of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). Equal numbers of each South American geographical population of this thelytokous endoparasitoid of adult hosts were released in New Zealand. A morphometric method described in this paper provided a means of classifying M. hyperodae adults as originating from either east or west of the Andes. Analysis revealed that, on average, specimens collected in Chile had significantly more antennal segments, narrower stigmas and longer radial cells than those collected in Brazil, Uruguay and Argentina. Significant differences between populations originating from each side of the Andes were also recorded in the dimensions of metasomal tergum one and basitarsus three. The morphometric method should, therefore, assist in defining the origins of M. hyperodae established in New Zealand. This information will be used in attempts to ascertain the importance of climate matching and host-parasitoid co-evolution to the outcome of the L. bonariensis biological control programme.     

South American Origins of Microctonus hyperodae Loan (Hymenoptera: Braconidae) Established in New Zealand as Defined by Morphometric Analysis

Eight South American geographic populations of the thelytokous parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae) were released in New Zealand in 1991 to assist in the suppression of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). With one exception, parasitoids from each South American geographic population were released in equal numbers at each New Zealand release site. It was postulated that the South American geographic population(s) best suited to the conditions encountered at each New Zealand release locality would eventually become prevalent there. A morphometric analysis of adult parasitoids of known South American origins, reported previously, allowed M. hyperodae derived from west of the Andes (i.e. two collection sites in Chile) to be distinguished from parasitoids derived from east of the Andes (i.e. three collection sites in Argentina and one each in Brazil and Uruguay). Parasitoids derived from a fourth site in Argentina (S. C. de Bariloche) could not be clearly discriminated from either the 'east of the Andes' or 'west of the Andes' categories. A morphometric analysis of M. hyperodae adults collected from five of the New Zealand release sites from 1992-1994 is presented in this contribution. The analysis indicated that parasitoids derived from east of the Andes were significantly more prevalent than expected. The possible reasons for the initial success in New Zealand of one or more east of the Andes populations include the greater fecundity of M. hyperodae collected in Uruguay and the likelihood that M. hyperodae from east of the Andes co-evolved more recently with the stock from which New Zealand's L. bonariensis was founded.     

Field parasitism of nontarget weevil species (Coleoptera: Curculionidae) by the introduced biological control agent Microctonus aethiopoides Loan (Hymenoptera: Braconidae) over an altitude gradient

The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate nontarget parasitism by M. aethiopoides over an altitudinal sequence from the target host habitat (alfalfa) into native grassland. Three locations were selected for the study, and at each, the alfalfa growing in the valley floor was sampled annually for parasitism of the target pest that ranged between 17 and 78%. At progressively higher altitudes, three further grassland sites at each location were sampled monthly during spring to autumn for up to 6 yr. Weevil densities were estimated, species identified, and dissections carried out to determine reproductive status and parasitism. Almost 12,000 weevils were collected during the study, which were identified as 36 species in total from the three locations. Eight weevil species were found to be parasitized, including S. discoideus, the target host that was found at all sites. Parasitism of nontarget species was approximately 2% overall but varied with location, site, and season. Substantial nontarget parasitism was found at only one of the locations, with up to 24% parasitism of a native weevil, Nicaeana fraudator Broun (Coleoptera: Curculionidae), recorded. Another species, Irenimus egens (Broun) (Coleoptera: Curculionidae), was also found at this location at similar population densities but was attacked far less by M. aethiopoides. Results are discussed in relation to weevil phenology.     

Geographic Variation in Egg Load of Microctonus hyperodae Loan (Hymenoptera: Braconidae) and its Implications for Biological Control Success

Eight South American geographic populations of the parthenogenic, proovigenic, koinobiont parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae: Euphorinae) were introduced to New Zealand to assist management of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). Geographic variation in fecundity has been suggested as a reason for the populations' differential successes in establishing in New Zealand. This study investigated whether geographic variation in fecundity was due to corresponding variation in pre-oviposition egg load (other possible sources of fecundity variation include searching efficiency, egg survival and female longevity). Variation in egg load accounted for that in fecundity, but also showed that the variation in fecundity was not as great as it had first appeared. Geographic variation in egg load did not explain the pattern of population establishment observed in New Zealand. Egg load was proportional to parasitoid size and this relationship was stronger in populations originating from west, rather than east, of the Andes. A new method for making parasitoid eggs visible is described.     

Antennal sensilla of the adult alfalfa weevil,Hypera postica (Gyllenhal) (Coleoptera : Curculionidae)

Sensilla on the antennae of adult alfalfa weevils, Hypera postica (Gyllenhal),were studied with scanning and transmission electron microscopes to determine the sensilla structure and possible chemo- and mechanoreceptive functions for food detection.Five types of sensilla trichodea (s.t.) occur (length 35 – 135 μm); s.t. I (71 – 135-μm long)are thick-walled without radial pores and s.t. II (50 – 75-μm long), the most abundant s.t., are multiporous. Bifurcated and trifurcated types (75 –85 -μm long) also occur. Five types of sensilla basiconica (s.b.) are present and include s.b. I (26 – 50-μm long), a fluted uniporous type with a rugose surface and encircling ledges; s.b. II (15 – 35-gm long), a common multiporous type with many longitudinal grooves; and s.b. IV (4 – 7-μm long), which are 3 apical, short pegs. Sensilla styloconica occur in a small band among the s.b. type II. One or 2 epidermal gland ducts are adjacent to most s.t. and some s.b.     

Alternatives to key factor analyses for assessing the population dynamics of Hypera postica (Coleoptera: Curculionidae)

Key factors are those causes that are most responsible for the observed changes in population density between generations. Stage-frequency of alfalfa weevil was modeled using Manly-1997 model. Multiple decrement life table parameters from an 8 year-field study were analyzed using traditional and λ contribution methods. In traditional method, the key factor was determined as k _LII, the death of period-two larvae from all mortality factors, whereas in λ contribution method, the key factor was determined as b _2&3, oviposition rate of females per square meter. These differences result directly from the sensitivity of the population growth rate, λ, to variation of both k and b in various stages of the weevil. Among all mortality factors, only k _LI-Z, the death of period-one larvae from the entomopathogenic fungus, Zoophthora phytonomi (Arthur) Batko (Zygomycetes: Entomophthoraceae), k _LII and k _LII-Z, the death of period-two larvae from Z. phytonomi, acted in a density dependent fashion. Remaining factors were independent of population densities affected. Using λ contribution method, life table approach still remains a major way of studying the dynamics of field populations for applied ecologists and population managers.     

Parasitism of the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and non-target weevils by Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in south-eastern Australia, with an assessment of the taxonomic affinities of non-target hosts of M. aethiopoides recorded from Australia and New Zealand

Abstract  The braconid parasitoid Microctonus aethiopoides Loan has been released in Australia and New Zealand for biological control of the lucerne pest Sitona discoideus Gyllenhal. In New Zealand, the parasitoid attacks a number of endemic weevil species. A survey of Curculionoidea found in and near lucerne in south-eastern Australia was carried out to investigate whether similar non-target parasitism was occurring, and to relate this to levels of parasitism found in the target host, S. discoideus . Some of the original M. aethiopoides release sites were particularly targeted in the survey of 25 sites in Victoria, New South Wales and South Australia. Almost 2500 weevils were collected, of which over 90% were S. discoideus , with the remaining 197 other weevils comprising 29 species found at 15 of the 25 sites. Parasitism of S. discoideus by M. aethiopoides occurred at 12 lucerne sites, with levels ranging from 0 to 25%. A single incidence of parasitism of a species of an Australian native weevil Prosayleus sp. by M. aethiopoides was recorded. No parasitism of any other weevil species was observed. The taxonomic affinities between Sitona and native Australian and New Zealand weevils are discussed, concluding that non-target host range in M. aethiopoides may be determined more by ecological factors than by taxonomic affinities among its hosts.     

Digestive amylase and pectinase activity in the larvae of alfalfa weevil Hypera postica (Coleoptera: Curculionidae)

The alfalfa weevil Hypera postica is a serious economic pest in most alfalfa grown in many countries worldwide. Digestive α-amylase and pectinase activities of larvae were investigated using general substrates. Midgut extracts from larvae showed an optimum activity for α-amylase against starch at acidic pH (pH 5.0). α-Amylase from larval midgut was more stable at mildly acidic pH (pH 5–6) than highly acidic and alkaline pH. The enzyme showed its maximum activity at 35°C. α-Amylase activity was significantly decreased in the presence of Ca²⁺, Mg²⁺ and sodium dodecylsulfate. On the contrary, K⁺ and Na⁺ did not significantly affect the enzyme activity. Zymogram analysis revealed the presence of one band of α-amylase activity in in-gel assays. Pectinase activity was assayed using agarose plate and colorimetric assays. Optimal pH for pectinase activity in the larval midgut was determined to be pH 5.0. Pectinase enzyme is more stable at pH 4.0–7.0 than highly acidic and alkaline pH. However, the enzyme was more stable at slightly acidic pH (pH 6.0) when incubation time increased. Maximum activity for the enzyme incubated at different temperatures was observed to be 40°C. Optimum pH activity for α-amylase and pectinase is not completely consistent with the pH prevailing in the larval midgut. This is the first report of the presence of pectinase activity in H. postica.     

Host selection and reproductive success of French and Moroccan populations of the parasitoid, Microctonus aethiopoides (Hymenoptera: Braconidae)

French and Moroccan populations of the parasitoid Microctonus aethiopoides Loan were studied in the laboratory for their host selection, mating behavior, and reproductive success. The French strain, collected on Hypera postica (Gyllenhal), although capable of parasitizing and producing viable offspring on Sitona weevils, preferred Hypera weevils, its known target host. The Moroccan strain, collected on Sitona discoideus Gyllenhal, exhibited host specificity for Sitona. A partial reproductive isolation was observed between the two strains. Moroccan females mated more frequently with French males than did French females with Moroccan males. The pre-copulation time for mating pairs of opposite strains was significantly longer than that for mating pairs of the same strain. There was no significant difference in copulation time nor in larval and pupal duration between French and Moroccan strains. In summary, the French and Moroccan strains of M. aethiopoides are clearly separable by biological, behavioral, and morphometric traits and the preferred host for Hypera is the French strain and Sitona for the Moroccan strain. Consequently, geographic location and host source become important when considering this parasitoid as a potential biological control agent.     

Efficacy of the parasitoid,Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) against Myzus persicae (Sulzer) (Hemiptera: Aphididae) infesting rapeseed-mustard

Efficacy of Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) was determined by studying its biological and behavioural attributes on the aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). Total developmental duration of the parasitoid was longer in younger instars compared to that in older instars of aphid. Host age negatively affected the oviposition period and fecundity of the ovipositing parasitoid. Survival of the immatures was higher in older than the younger instars of the aphid. Sex ratio for the parasitoid was female-biased. Longevity of female parasitoid was higher while parasitizing aphid nymphs of younger age groups (1–2 days old) compared to that of older age groups (4–5 days old). Parasitoid showed a higher preference towards second instar of M. persicae both in choice and no-choice tests. Results on mutual interference revealed that per capita searching efficiency decreased from 0.91 to 0.07 as parasitoid densities increased from 1 to 8. Logistic regression exhibited a type II functional response for D. rapae. The estimated values of search-efficiency (a) and handling time (T_h) were 0.038 h⁻¹ and 1.59 h, respectively. The maximum parasitization rate was 15.08. This investigation suggests that D. rapae could be an effective candidate for augmentative biological control of M. persicae which infests several plant species of economic importance.     

Global genetic diversity,lineage distribution,and Wolbachia infection of the alfalfa weevil Hypera postica (Coleoptera: Curculionidae)

The alfalfa weevil (Hypera postica) is a well‐known example of a worldwide‐distributed pest with high genetic variation. Based on the mitochondrial genes, the alfalfa weevil clusters into two main mitochondrial lineages. However, there is no clear picture of the global diversity and distribution of these lineages; neither the drivers of its diversification are known. However, it appears likely that historic demographic events including founder effects played a role. In addition, Wolbachia, a widespread intracellular parasite/symbiont, likely played an important role in the evolution of the species. Wolbachia infection so far was only detected in the Western lineage of H. postica with no information on the infecting strain, its frequency, and its consequences on the genetic diversity of the host. We here used a combination of mitochondrial and nuclear sequences of the host and sequence information on Wolbachia to document the distribution of strains and the degree of infection. The Eastern lineage has a higher genetic diversity and is found in the Mediterranean, the Middle East, Eastern Europe, and eastern America, whereas the less diverse Western lineage is found in Central Europe and the western America. Both lineages are infected with the same common strain of Wolbachia belonging to Supergroup B. Based on neutrality tests, selection tests, and the current distribution and diversification of Wolbachia in H. postica, we suggested the Wolbachia infection did not shape genetic diversity of the host. The introduced populations in the United States are generally genetically less diverse, which is in line with founder effects.     

Host Age Choice for Oviposition in Pauesia juniperorum (Hymenoptera: Braconidae: Aphidiinae) and its Effect on the Parasitoid's Biology and Host Population Growth

Pauesia juniperorum has been selected as a potential agent for the biological control of Cinara cupressivora, an important introduced pest of conifers in Africa. As part of the pre-introductory assessment studies, selection of different host age categories for oviposition was studied in choice and no choice experiments. The duration of development and adult size of parasitoid progeny developing in different host age categories were compared. The effects of parasitism on survival and reproduction of five categories of the apterous morph of the host ranging in age from 3-15 days was also studied. The age of hosts had a significant influence on the degree with which different categories were parasitized. Host defensive behaviour, which increased with age, influenced the outcome of attempts by the parasitoid to oviposit. The effect was greater in older hosts, but in young hosts their small size was more important in enabling aphids to escape parasitism. The duration of development decreased while adult size increased with age of hosts. This demonstrated that fitness attributes of P. juniperorum were affected by larval ontogeny with older/larger hosts being more optimal. The ability of the parasitoid to exploit hosts of varying age was suggestive of a high degree of phenotypic plasticity which is potentially of adaptive value. Hosts parasitized before they were 9-days-old became mummies without reproducing. Those that were 9 days or older achieved part of their reproductive capacity before dying. Thus, the impact of P. juniperorum is markedly reduced when attacking older hosts.     

Field Efficacy of Entomopathogenic Nematodes against the Sugar-beet Weevil Temnorhinus ( = Conorrhynchus ) mendicus Gyll. (Coleoptera: Curculionidae)

In 1992 and 1993, the field effectiveness of Heterorhabditis sp. (NL-HL81 strain), H. bacteriophora (HP 88 strain) and Steinernema carpocapsae ('All' strain) against the larvae of Temnorhinus mendicus Gyll. was assessed. The biological tests were compared with two chemical treatments (cypermethrin or deltamethrin) and one untreated control. In 1992, S. carpocapsae gave better results than Heterorhabditis sp. in reducing the percentage of infested roots, as compared with the untreated sample and the chemical one; similarly, the irrigated control gave the best results. In 1993, three concentrations of entomopathogenic nematodes (EPNs) were tested: 0.250 106 infective juveniles (IJs) m - 2, 0.125 106 IJs m - 2 and 0.075 106 IJs m - 2. The different numbers of EPNs did not give very different results from each other; however, H. bacteriophora at 0.075 106 IJs m - 2 was the least effective. In general, cypermethrin was more effective than deltamethrin, but one treatment with EPNs followed by irrigation was always more effective than two chemical applications.     

Sub-lethal Effects of the Insecticides Pirimicarb and Dimethoate on the Aphid Parasitoid Diaeretiella rapae (Hymenoptera: Braconidae) When Attacking and Developing in Insecticide-Resistant Hosts

The effectiveness of parasitoids as biological control agents can be constrained by insecticide use, not only through direct mortality but also as a result of sublethal effects. Several pest aphids have become resistant to a range of insecticides and a resistant strain of Myzus persicae was used in laboratory experiments to investigate sublethal effects of the insecticides pirimicarb and dimethoate on the parasitoid Diaeretiella rapae . Both insecticides produced sublethal effects on D. rapae when the parasitoid attacked and developed in aphids that had been dipped in insecticide solutions. Dimethoate affected oviposition behaviour; females were apparently repelled by residues on the surface of dipped aphids, thus reducing their attack rate and hence the number of mummies produced. Also, the reproductive performance of parasitoids that had developed in pirimicarb-dipped aphids appeared to be adversely affected, in comparison with parasitoids that emerged from uncontaminated hosts, and this was reflected both in lower mummy production and lower attack rates. Pirimicarb, but not dimethoate, affected the sex ratio of the offspring of D. rapae that had developed in dipped aphids, causing a significant increase in the proportion of males. This only occurred when the male parent had developed in a pirimicarb-dipped aphid, suggesting that the effect involves male sterility or mating behaviour, although they appeared to mate normally. These sublethal effects are potential constraints on the efficiency and effectiveness of D. rapae as a biological control agent of aphid pests, but to assess fully their potential impact further studies need to be done using more realistic extended laboratory and semi-field techniques.     

Evaluation of Steinernema carpocapsae Weiser for Control of Carrot Weevil Adults, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae), in Organically Grown Carrots

Under controlled conditions, application of Steinernema carpocapsae using a baiting method consistently reduced the oviposition of Listronotus oregonensis adults at all moisture regimens. At 80 and 95% relative humidity, soil applications at 10 4 infective juveniles (IJs) cm-2 and 10 5 infective stages (400 IJs cm-2) per pot reduced the survival and oviposition of L. oregonensis adults; soil applications were ineffective at relative humidity lower than 80%. When timed correctly, soil application at the rate of 2 105 IJs/linear meter of row (4.4 109 IJs ha-1) reduced damage by up to 59%.