Comparative study on the susceptibility of cutworms (Lepidoptera: Noctuidae) to Agrotis segetum nucleopolyhedrovirus and Agrotis ipsilon nucleopolyhedrovirus

The common cutworm (Agrotis segetum) and the black cutworm (Agrotis ipsilon) are serious soil pests of many vegetable and field crops all over the world. We have demonstrated the cross-infectivity of two baculoviruses, A. segetum nucleopolyhedrovirus (AgseNPV) and A. ipsilon nucleopolyhedrovirus (AgipNPV) for these two insect pests. The susceptibility of A. segetum to AgipNPV was confirmed by DNA restriction endonuclease analyses of DNA isolated from virus harvested from infected A. segetum larvae. For an initial comparison of both viruses, partial polyhedrin sequences were amplified by PCR, cloned, and sequenced. Both viruses shared a very similar polyhedrin gene sequence resulting in only three amino acid substitutions. Phylogenetic analyses clearly demonstrated that both viruses belong to NPV group II and are most closely related to a clade consisting of Spodoptera exigua NPV, Spodoptera frugiperda NPV, and Spodoptera littoralis NPV. Since AgipNPV shows high virulence for both cutworm species, it appears to be a suitable candidate as a single biological control agent of A. segetum and A. ipsilon.     

Mortality of Cutworm Larvae Is Not Enhanced by Agrotis segetum Granulovirus and Agrotis segetum Nucleopolyhedrovirus B Coinfection Relative to Single Infection by Either Virus

Mixed infections of insect larvae with different baculoviruses are occasionally found. They are of interest from an evolutionary as well as from a practical point of view when baculoviruses are applied as biocontrol agents. Here, we report mixed-infection studies of neonate larvae of the common cutworm, Agrotis segetum, with two baculoviruses, Agrotis segetum nucleopolyhedrovirus B (AgseNPV-B) and Agrotis segetum granulovirus (AgseGV). By applying quantitative PCR (qPCR) analysis, coinfections of individual larvae were demonstrated, and occlusion body (OB) production within singly infected and coinfected larvae was determined in individual larvae. Mixtures of viruses did not lead to changes in mortality rates compared with rates of single-virus treatments, indicating an independent action within host larvae under our experimental conditions. AgseNPV-B-infected larvae showed an increase in OB production during 2 weeks of infection, whereas the number of AgseGV OBs did not change from the first week to the second week. Fewer OBs of both viruses were produced in coinfections than in singly infected larvae, suggesting a competition of the two viruses for larval resources. Hence, no functional or economic advantage could be inferred from larval mortality and OB production from mixed infections of A. segetum larvae with AgseNPV-B and AgseGV.     

Host range and virulence of five baculoviruses from lepidopterous hosts

The host range and virulence of five insect baculoviruses (two multiply-enveloped nuclear polyhedrosis viruses (MNPVs) from Agrotis segetum and Mamestra brassicae; one singly-enveloped NPV from Plusia gamma and two granulosis viruses (GVs) from A. segetum and Pieris brassicae) were studied for seven lepidopterous pests of temperate agriculture (A. segetum, Agrotis exclamationis, Lacanobia oleracea, M. brassicae, Noctua pronuba, P. gamma and Pieris rapae). None of the viruses killed all species but M. brassicae MNPV failed to infect only P. rapae. The other viruses were restricted to the homologous host, or members of its genus or subfamily. In all examples except A. segetum GV, the median lethal dose for the most susceptible host, was less than 22 virus inclusion bodies and median lethal times for all infections ranged from 5·5 to 16·6 days. The low susceptibility of A. segetum and other noctuids to GV infections is discussed in relation to the structure of inclusion bodies and the nature of the infectious unit in baculoviruses.     

Host suitability and preference studies of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae)

Studies of host suitability and preferences of Trichogramma cordubensis Vargas and Cabello (Hymenoptera: Trichogrammatidae) were performed with eggs of six Lepidoptera (Noctuidae) species: Thysanoplusia orichalcea Fabricius, Peridroma saucia (Hübner), Xestia c-nigrum L., Phlogophora meticulosa (L.), Noctua pronuba (L.), and N. atlantica (Warren). Host suitability was studied by analysing separately the effects of the attacked host species and the influence of the rearing host species on different biological parameters of T. cordubensis. Host preference was analysed by offering eggs of two host species simultaneously to a single female wasp without previous oviposition experience (dual-choice tests). Results show that P. saucia, followed by P. meticulosa were the least suitable hosts for T. cordubensis, since on these species the preimaginal development of the parasitoids was significantly longer and, the number of parasitized eggs as well the number of offspring per female were significantly lower. Contrarily, T. cordubensis parasitized at a higher rate the eggs of the endemic non-target species, N. atlantica. Dual choice tests showed that the option of the first host to be accepted by the wasp was random; however, the mean number of parasitized eggs differed significantly when two host species were offered simultaneously to T. cordubensis, always being the host species with heavier eggs the most parasitized.     

A survey of cutworm attacks in England and Wales, and a descriptive population model for Agrotis segetum (Lepidoptera: Noctuidae)

Surveys of larval populations and numbers of reports of damage showed that from 1945 to 1978 Agrotis segetum was the commonest species of cutworm, causing most damage, to a wide range of crops, from July to October. Attacks varied in extent and severity between years, the most severe damage occurring in 1949 and in 1976. A model has been devised to estimate an index of larval survival to third instar, based on temperature-rate of development relationships and mortality due to daily rainfall. This survival index is highly correlated with year-to-year changes in numbers of reported attacks by A. segetum. The model suggests that weather conditions alone were responsible for the last major cutworm outbreak in 1976.     

Agrotis segetum granulosis virus as a control agent against field populations ofAgrotis ipsilon andA. Segetum [Lep.: Noctuidae] on tobacco,okra, potato and sugar beet in northern pakistan

Agrotis segetum Schiff granulosis virus (AsGV) propagated in Denmark was supplied against naturally occurring cutworm populations (A. ipsilon and to a less extentA. segetum) in experimental field plots of tobacco, okra, potato and sugar beet in northern Pakistan. AsGV doses varied between 4 × 10⁷ and 4 × 10¹¹ capsules per m² plot, and no. of applications between 1 and 3. One treatment with AsGV did not reduce cutworm damage significantly to tobacco seedlings and potato plants. Two treatments with AsGV reduced cutworm damage significantly. In tobacco, reduction was 64–82%, in okra and potato 85% and 77% respectively. Damage in sugar beet was reduced 78%. Three treatments with AsGV dis not reduce damage significantly better than two treatments. AsGV and the chemical insecticides Tamaran and Dieldrin, andBacillus thuringiensis (Thuricide) were about equally effective, reducing damage by 85%, 79%, 87% and 69%, respectively. No difference was found between the efficiency of highly purified AsGV to which activated charcoal was added and partially purified AsGV without charcoal.      

The entomogenous nematode Neoaplectana bibionis as a biological control agent of Agrotis segetum in lettuce

Biological control of the soil-inhabitating larvae (cutworms) of Agrotis segetum Schiff. using the entomogenous nematode Neoaplectana bibionis Bovien was investigated under field conditions. Cutworms were introduced to plots planted with lettuce, Lactuca sativa L. After planting and infection with cutworms the plots were treated with either N. bibionis, the insecticide endosulfan or water. The trials were sited on locations with loamy and sandy soil. Adequate control of cutworms was obtained using 2.5×10⁵ nematodes/m² on sandy soil and 1×10⁶ nematodes/m² on loamy soil. Effects of these treatments with nematodes were equal to the effect of endosulfan.

---

Neoaplectana bibionis ein entomophager nematode zur biologischen bekämpfung von Agrotis segetum an salat

Zusammenfassung Unter Freilandbedingungen wurde die biologische Bekämpfung von Erdraupen (Agrotis segetum Schiff., Lepidoptera, Noctuidae) mit dem entomophagen Nematoden Neoaplectana bibionis Bovien geprüft. Mit Salat bepflanzte Parzellen wurden mit Erdraupen besetzt. Anschliessend wurde auf die Parzellen N. bibionis, das Insektizid Endosulfan oder Wasser ausgebracht. Die Versuche wurden in Gebieten mit lehmigen und sandigen Böden durchgeführt. Für eine ausreichende Bekämpfung der Erdraupen waren auf dem sandigen Boden 2.5×10⁵ Nematoden/m² und auf dem lehmigen Boden 1×10⁶ Nematoden/m² erforderlich. Die Wirkung dieser Behandlungen entsprach der mit Endosulfan.

     

New cell lines derived from the black cutworm, Agrotis ipsilon, that support replication of the A. ipsilon multiple nucleopolyhedrovirus and several group I nucleopolyhedroviruses

New cell lines were recently developed from the embryos of the black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae). A primary culture was initiated from 4-day-old A. ipsilon eggs in ExCell420 medium supplemented with 5% fetal bovine serum. This initial culture produced sufficient cell growth to allow subcultivation and eventually led to the establishment of eight distinct strains. Two of these strains (AiE1611T and AiEd6T) were selected for further characterization. Extracts of these strains were compared to an extract from A. ipsilon eggs by isozyme analysis and shown to be from the same species. Both strains were susceptible to infection by the A. ipsilon multiple nucleopolyhedrovirus (AgipMNPV), as well as to lepidopteran group I NPVs from A. californica, Anagrapha falcifera, Anticarsia gemmatalis, Galleria mellonella, Helicoverpa armigera, Plutella xylostella, and Rachiplusia ou, with large numbers of occlusion bodies produced in most of the inoculated cells. The cell lines did not support the replication of group II NPVs from Helicoverpa zea, Lymantria dispar, and Spodoptera exigua. Both cell lines produced confluent monolayers in plaque assays and supported the formation of plaques upon infection with AgipMNPV and Autographa californica (Ac)MNPV. Twenty AgipMNPV plaques were picked from either AiE1611T or AiEd6T monolayers, and the plaque isolates were serially passaged three times through A. ipsilon cells. Only one isolate from AiE1611T cells exhibited genotypic variation in the form of an altered restriction fragment profile. Our results suggest these new lines can be useful in the study of AgipMNPV and A. ipsilon cellular and molecular biology.     

Does host range influence susceptibility of herbivorous insects to non-host plant proteinase inhibitors?

We examined the influence of proteinase inhibitors on digestive enzymes and development of oriental beetle,Exomala orientalis Waterhouse, European chafer,Rhizotrogus majalis (Razoumowsky),Phyllophaga white grub,Phyllophaga anxia (LeConte), cranberry root grub,Lichnanthe vulpina (Hentz), Japanese beetle,Popillia japonica Newman, Asiatic garden beetle, Maladera castanea (Arrow) (Coleoptera: Scarabaeidae), and the black cutworm,Agrotis ipsilon (Rottemburg) (Lepidoptera: Noctuidae). We demonstrated that all species within our test group had alkaline midguts that contained proteinase activity that could be inhibited,in vitro with serine proteinase inhibitors. Our data suggests that host range may influence the susceptibility to non-host inhibitors. Chronic ingestion of the serine proteinase inhibitor, Kunitz-soybean trypsin inhibitor (STI), significantly reduced proteolytic activityin vivo in those species with relatively specialized feeding habits (i.e., cranberry root grub, Japanese beetle, Asiatic garden beetle, and black cutworm). Chronic ingestion of STI also resulted in reduced larval growth and delayed pupation for black cutworm, and elevated larval mortality for Japanese beetle. However, chronic ingestion of STI did not influence larval survival for those species with relatively generalized feeding habits (i.e., oriental beetle, European chafer). Based on these results, we propose mechanistically-based criteria for selecting proteinase inhibitors for phytochemical defense against herbivorous insects.     

Endophyte infection in perennial ryegrass reduces the susceptibility of black cutworm to an entomopathogenic nematode

Abstract The perennial ryegrass, Lolium perenne, forms a symbiotic relationship with Neotyphodium lolii, a fungus that produces alkaloids. This relationship provides a competitive advantage to the host plant in grassland communities by increasing drought tolerance, and disease and herbivore resistance. Black cutworm, Agrotis ipsilon, is among the few insect species that are able to feed and develop on endophytic perennial ryegrass. Some insects can use plant secondary compounds to defend themselves against predators, therefore we hypothesized that the cutworms fed on endophytic grasses would exhibit greater defense against a lethal endoparasitic nematode, Steinernema carpocapsae. Laboratory experiments involving 4–5th instars support the hypothesis that A. ipsilon feeding on grass clippings from field plots with high (> 90%) incidence of endophyte infected perennial ryegrass are less susceptible to entomopathogenic nematodes than larvae fed grass clippings from plants with little or no incidence of endophyte. Laboratory studies resulted in similar overall mortality after 48 h. Field studies, however, show decreased susceptibility to S. carpocapsae when larvae were confined to areas of endophytic grass (> 75% infected). Early instars (2–3rd) fed on endophyte free grass suffered greater overall mortality at all nematode concentrations than 4–5th instars fed similarly. Early (2–3rd) instars were equally susceptible to nematode attack regardless of food source. Our results indicate that the fungal endosymbionts of grasses can influence the biology of natural enemies of an herbivorous insect.     

Parasitization of granulosis-virus infected and noninfectedAgrotis segetum larvae and the virus transmission by three hymenopteran parasitoids

Apanteles telengai Tobias,Aleiodes gasteratus (Jurine) andCampoletis annulata Tschek parasitized significantly more healthy than granulosis virus (GV)-infectedAgrotis segetum D. & Schiff. larvae. Females of the three parasitoid species that had oviposited previously in GV-infectedA. segetum larvae transmitted the virus to healthyA. segetum larvae in subsequent oviposition.A. telengai andA. gasteratus females also transmitted the GV on unsuccessful oviposition attempts. Male parasites did not transmit the GV.

---

Résumé Apanteles telengai, Aleiodes gasteratus etCampoletis annulata parasitent significativement plus les chenilles saines d'A. segetum que les chenilles infectées par le virus de la granulose. Les femelles des 3 espèces ayant pondu préalablement dans des chenilles contaminées par le virus ont transmis le virus à des chenilles saines lors de pontes ultérieures. Les femelles deA. telengai etA. gasteratus transmettent le virus lors de perforations d'hôtes non suivies de pontes. Les mâles ne transmettent pas le virus.

     

Response of Steinernema carpocapsae Infective Juveniles to the Plasma of Three Insect Species

Exsheathed infective juveniles of Steinernema carpocapsae All strain were attracted to the plasma of three species of insects in agar plate bioassays. Plasma of Pieris rapae crucivora, Spodoptera litura, and Agrotis segetum attracted 88.6%, 80.4%, and 64.4%, respectively, of Steinernema carpocapsae juveniles added to plates. Autoclaved plasma of S. litura larvae attracted more juveniles than saline controls, but less than nonautoclaved plasma. The active agent passed through a 14,000 MW dialysis membrane.     

Leaf biomechanical properties as mechanisms of resistance to black cutworm (Agrotis ipsilon) among Poa species

Biomechanical properties can be important parameters in resistance of plants to herbivorous insects. As plants age, however, there can be dramatic changes in physical defenses that can then influence their susceptibility to insect herbivores. We measured changes in leaf biomechanical properties during ontogeny of Poa species and the relationship of these changes to the development of a generalist herbivore, the black cutworm, Agrotis ipsilon Hufnagel (Lepidoptera: Noctuidae), was investigated. Larvae were reared on two representative age classes, i.e., young (<60 days after planting) and old (>1 year after planting), of foliage in laboratory assays. Foliage generally reaches a peak fracture force between 80 and 109 days after planting depending on grass type. Foliage from old plants was significantly tougher than that of young plants, and black cutworm larvae reared on foliage from young plants gained significantly (ca. four times) more weight than those fed on foliage from old Poa plants. In addition, fracture force has a negative relationship with black cutworm development. Plant fiber, particularly neutral detergent fiber accounted for 65 and 46% of the variation in fracture force and larval development, respectively. These results provide additional insight into how plant ontogeny influences physical defenses to an insect herbivore in a grass system. Likewise, this is seemingly the first study to suggest a mechanism for host plant resistance to black cutworm. Plant fiber may be a useful trait to explore in plant improvement programs in which black cutworm is a primary pest (e.g., managed turfgrass).     

Some pathogenic effects of a species ofPleistophora [Protozoa,Microsporida] forAgrotis exclamationis and other noctuids

Larvae of noctuids were inoculatedper os with spores of a species ofPleistophora isolated fromAgrotis exclamationis (L.). The mean median lethal dose for mainly 3rd instar larvae ofA. exclamationis was 1.38×10⁵ spores per larva accumulating 34 or 35 days after inoculation and the mean slope for the regression of mortality on dose was 0.82. Third instar larvae ofA. exclamationis andSpodoptera frugiperda (J.E. Smith) inoculated with 2.5×10⁴ spores gained weight quicker than uninfected ones until between 8 days (A. exclamationis) and 13 days (S. frugiperda) post-inoculation. Thereafter they grew slower than uninfected individuals. Correspondingly, the feeding rate of inoculated larvae ofA. exclamationis was greater than that of untreated ones until 14 days post-inoculation but thereafter was less. Larvae ofNoctua pronuba (L.)Phlogophora meticulosa L. andSpodoptera littoralis (Boisduval) but notAgrotis segetum (Denis & Schiffermüller) were also susceptible to infection. The species ofPleistophora considered here corresponds toP. schubergi noctuidae (Veremtchuk & Issi) in spore morphology, tissue specificity and host range, except that is was non-infective for the typehostA. segetum. It is probably insufficiently pathogenic for use in the biological control of noctuids.     

Effect of chlorfluazuron and flufenoxuron on development and reproductive performance of the black cutworm,Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae)

The black cutworm, Agrotis ipsilon, is an insect pest with great agricultural importance worldwide. In Egypt, it has acquired resistance against most of the conventional pesticides, particularly organophosphate insecticides, applied against it. Therefore, the present study aimed to investigate the effect of two benzoylureas (chitin synthesis inhibitors) namely chlorfluazuron and flufenoxuron on some developmental and reproductive parameters of Agrotis ipsilon that survived treatment of newly molted fourth instars with the LC₅₀ of these compounds (1.00 and 4.68 mg/L, respectively) using leaf–dip method. These two compounds significantly enhanced the mean larval and pupal durations, whereas they significantly declined the mean percentage pupation, adult emergence, pupal weight, adult longevity, fecundity, and fertility compared to untreated insects. The mean pre-oviposition period was not significantly affected, whereas the mean oviposition period was significantly decreased. Both chlorfluazuron and flufenoxuron significantly decreased the mean total protein, carbohydrate, and lipid content in the ovaries compared to untreated insects, except for insignificant decrease in the total protein in flufenoxuron-treated ones. Additionally, the total ovariolar length was significantly atrophied. In conclusion, chlorfluazuron and flufenoxuron interfere with vitellogenesis of A. ipsilon. Moreover, they could suppress the population size of this insect species by affecting its development and reproductive potential.     

Biological control of tobacco cutworm,Spodoptera litura Fabricius with entomopathogenic nematodes

The efficacies of several entomopathogenic nematodes ofSteinernema andHeterorhabditis spp. were examined against tobacco cutworm,Spodoptera litura Fabricius.H. bacteriophora HY showed 100% mortality after 20 h against 2nd instar of tobacco cutworm. In the case of 3–4th instar,S. carpocapsae PC.,H. bacteriophora HY andS. monticola CR showed 100% mortality after 47 h. In the case of 5–6th instar,S. carpocapsae PC proved more effective than the others. Generally, the number of nematodes harvested increased as their size decreased. Also, the highest number of nematodes was obtained in the 5–6th instar ofS. litura byH. bacteriophora HY, showing about 1.3×10⁶ nematodes per larva.In vitro culturedS. carpocapsae PG showed 100% mortality after 73 h against 5–6th instar tobacco cutworm, indicating that nematodes producedin vitro can be potentially used for the biological control ofS. litura instead of nematodesin vivo.     

特基拉芽孢杆菌XK29挥发物2-甲基丁酸对甘薯长喙壳菌的抑制作用研究

【目的】研究特基拉芽孢杆菌挥发物2-甲基丁酸对甘薯长喙壳菌的抑制作用,评价2-甲基丁酸对甘薯黑斑病的防治效果。【方法】采用I-分隔平皿和气相抑菌体系,研究不同剂量的2-甲基丁酸对甘薯长喙壳菌菌丝生长和孢子萌发的抑制作用;使用乳酸酚棉蓝染色观察2-甲基丁酸对甘薯长喙壳菌显微形态的影响;利用荧光探针钙荧光白和溴化丙锭检测2-甲基丁酸对甘薯长喙壳菌细胞壁结构与细胞膜通透性的影响;使用荧光探针2,7-二氯荧光素二乙酸酯检测甘薯长喙壳菌胞内活性氧含量变化;测定谷胱甘肽含量分析病原菌应对氧化损伤能力的改变;通过线粒体脱氢酶活力和丙酮酸含量的检测,分析2-甲基丁酸对甘薯长喙壳菌线粒体功能和能量代谢的影响;评价2-甲基丁酸在甘薯黑斑病防治中的使用效果。【结果】2-甲基丁酸显著抑制甘薯长喙壳菌菌丝生长和孢子萌发,降低其产孢能力,导致菌丝折叠弯曲并形成不连续的空腔。2-甲基丁酸使甘薯长喙壳菌的细胞壁结构改变,细胞膜通透性增加,胞内活性氧含量升高,谷胱甘肽含量显著降低,使病原菌应对氧化损伤的能力下降,线粒体脱氢酶活力和丙酮酸含量显著降低,诱发线粒体功能障碍,干扰细胞能量代谢,最终导致细胞死亡。此外,2-甲基丁酸对甘薯黑斑病也具有良好的防治作用。【结论】2-甲基丁酸对甘薯长喙壳菌具有显著的抑制作用,可作为安全高效的气相抑菌材料用于新型熏蒸制剂的研发。     

Efficacy and persistence of entomopathogenic nematodes for black cutworm control in turfgrass

Field experiments were conducted in turf maintained under golf course fairway conditions in May, June, and August 2009 and in August and September 2010 to evaluate the ability of entomopathogenic nematodes to control larval populations of the black cutworm, Agrotis ipsilon, on golf courses. Commercial products containing the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema carpocapsae, S. feltiae, and S. riobrave were applied at 1.0 or 2.5×10⁹ infective juveniles per ha against fourth-instar black cutworms. Larval mortality and turf damage were evaluated at 4 and/or 7 days after treatment (DAT). Steinernema carpocapsae was the best performing species due to a combination of high control rates (average 83%), most consistent results (70–90% range), high speed of kill (average 68% at 4 DAT), and prevention of significant turf damage despite very high larval densities at 0 DAT. Efficacy of S. feltiae and H. bacteriophora was often similar to that of S. carpocapsae but overall less consistent. Short-term persistence of the nematodes was evaluated in four turfgrass sites maintained under golf course putting green, fairway, or rough conditions in June and August 2009 by baiting soil samples at 0, 4, 7, and 14 DAT. Relative to recovery immediately after application, at least 50% of S. feltiae and 25% of S. carpocapsae consistently persisted up to 4 days in one of the greens and up to 7 days in some trials. Our finding suggests that S. carpocapsae and S. feltiae may provide adequate black cutworm control in golf course turf under moderate summer temperatures.     

Interactions and effects of multiple biological control insects on diffuse and spotted knapweed in the Front Range of Colorado

Abundances and interactions among biological control insects and their effects on target invasive plants were monitored within the flower heads and roots of diffuse knapweed, Centaurea diffusa, and in spotted knapweed, Centaurea stoebe, along the Colorado Front Range. Flower weevils, (Larinus species) and root-feeders (Cyphocleonus achates and Sphenoptera jugoslavica) were released on knapweed that already supported biological control gall flies (Urophora species). At a single monitoring site, seed production by C. diffusa declined from 4400 seeds m⁻² in 1997 to zero seeds m⁻² on the monitoring sites in 2006, while the flowering stem density of C. diffusa declined from a peak of almost 30 stems m⁻² in 2000 to zero stems m⁻² in 2006. The average abundance of Urophora and Larinus in flower heads fluctuated independently during the 2001–2006 interval, while the relative abundance of C. achates and S. jugoslavica in roots exhibited a weak inverse relationship that appeared driven by climate effects. The relative abundance of insects on a population of C. stoebe was monitored for five years as Larinus species and C. achates became established on spotted knapweed that already supported Urophora species. Spotted knapweed seed production on our monitoring site declined from 4600 seeds m⁻² in 2003 to zero seeds m⁻² in 2006. Unlike C. diffusa, substantial numbers of rosettes of C. stoebe remained present. Larinus consumed almost all Urophora encountered in C. diffusa, and consumed about 40% of the Urophora in co-infested flower heads of C. stoebe (ca. 10–15% of the total Urophora population). No negative correlations between the relative densities of flower head and root-feeding insects were observed. The effects of these insects on target plants have produced results consistent with the ‘cumulative stress hypothesis’ for biological control of Centaurea species.     

The introduction and release of Chiasmia inconspicua and C. assimilis (Lepidoptera: Geometridae) for the biological control of Acacia nilotica in Australia

Two geometrid moths Chiasmia inconspicua and Chiasmia assimilis, identified as potential biological control agents for prickly acacia Acacia nilotica subsp. indica, were collected in Kenya and imported into quarantine facilities in Australia where laboratory cultures were established. Aspects of the biologies of both insects were studied and CLIMEX® models indicating the climatically favourable areas of Australia were developed. Host range tests were conducted using an approved test list of 74 plant species and no-choice tests of neonate larvae placed on both cut foliage and potted plants. C. inconspicua developed through to adult on prickly acacia and, in small numbers, Acacia pulchella. C. assimilis developed through to adult on prickly acacia and also in very small numbers on A. pulchella, A. deanei, A. decurrens, and A. mearnsii. In all experiments, the response on prickly acacia could be clearly differentiated from the responses on the non-target species. Both insects were approved for release in Australia. Over a three-year period releases were made at multiple sites in north Queensland, almost all in inland areas. There was no evidence of either insect’s establishment and both colonies were terminated. A new colony of C. assimilis was subsequently established from insects collected in South Africa and releases of C. assimilis from this new colony were made into coastal and inland infestations of prickly acacia. Establishment was rapid at one coastal site and the insect quickly spread to other infestations. Establishment at one inland area was also confirmed in early 2006. The establishment in coastal areas supported a CLIMEX model that indicated that the climate of coastal areas was more suitable than inland areas.