Predation by Podisus maculiventris (Hemiptera: Pentatomidae) on Plutella xylostella (Lepidoptera: Plutellidae) larvae parasitized by Cotesia plutellae (Hymenoptera: Braconidae) and its impact on cabbage

Biological control offers potentially effective suppression of the diamondback moth (DBM), Plutella xylostella, a serious pest of Brassica crops. Little is known of whether multiple natural enemies have additive, antagonistic, or synergistic effects on DBM populations. No-choice and choice tests were conducted to assess predation by Podisus maculiventris on DBM larvae parasitized by Cotesia plutellae and unparasitized larvae. In no-choice tests, P. maculiventris preyed on greater numbers of parasitized than unparasitized larvae and greater numbers of young larvae than old larvae. In choice tests with early third instar DBM, there was no difference in predation between parasitized or unparasitized larvae. However, in choice tests with older prey, P. maculiventris preyed on more parasitized than unparasitized larvae. Two field studies were conducted to test if this predator and parasitoid have additive, antagonistic or synergistic effects on DBM populations and plant damage in cabbage (Brassica oleracea var. capitata). In 2002, DBM populations were significantly lower in the presence of C. plutellae but not in the presence of P. maculiventris. There was not a significant interaction between the natural enemies. Plant damage was reduced only with C. plutellae. In 2003, DBM populations were significantly lower in the presence of C. plutellae and P. maculiventris, although the combination of natural enemies did not lead to a non-additive interaction. Plant damage was unaffected by the presence of either natural enemy. Because of its greater predation on parasitized larvae, P. maculiventris could be an intraguild predator of C. plutellae. Yet, their overall combined effect in the field was additive rather than antagonistic.     

Characteristic of parasitism of diamondback moth by two larval parasites

Laboratory and greenhouse studies were conducted to investigate the suitability of 2 hymenopterous parasites,Diadegma eucerophaga Horstmann andApanteles plutellae Kurdjumov for introduction to control diamondback moth (DBM),Plutella xylostella (L.), a destructive pest of crucifers in tropical to subtropical Southeast Asia. Parasitism byD. eucerophaga was high at temperature range of 15°C to 25°C and that ofA. plutellae, at 20°C to 35°C. Both parasites were active in searching for host and oviposited only during photophase. No parasitism was observed during darkness. WhereasA. plutellae could parasitize all instars of DBM larvae,D. eucerophaga parasitized only the first 3 instars and failed to parasitize the 4^th. Parasitism byD. eucerophaga was greater when DBM larvae were feeding on common cabbage (Brassica oleracea var.capitata L.), than on cauliflower (B. oleracea var.italica L.), broccoli (B. oleracea var.botrytis L.) or Chinese cabbage [Brassica campestris L. ssp.pekinensis (Lour) Olsson].A. plutellae parasitism was greater when DBM larvac were feeding on Chinese cabbage than on common cabbage, cauliflower or broccoli. Storage of pupae at 0°C and 4°C to 6°C for up to 2 weeks reduced emergence ofD. eucerophaga adults more than that ofA. plutellae. A non-selective insecticide, deltamethrin, was toxic to adults of both parasites but selective ones such asBacillus thuringiensis, teflubenzuron, and pirimicarb were not. Pupae were more tolerant than adults to insecticides. The insecticide-resistant Luchu strain and susceptible laboratory strain of DBM suffered an equal level of parasitism by both parasites.      

闭弯尾姬蜂与菜蛾盘绒茧蜂寄生菜蛾幼虫时的种间竞争

在室内25℃下,以菜蛾3龄初幼虫作寄主,研究了菜蛾盘绒茧蜂Cotesia plutellae和半闭弯尾姬蜂Diadegma semiclausum的种间竞争。当寄主供2种蜂同时产卵寄生时,2种蜂各自的寄生率与其单独寄生时无显著差异,合计寄生率比一种蜂单独存在时有所提高,但差异不显著。2种蜂均能产卵寄生已被另一种蜂寄生了的寄主幼虫。当寄主被2种蜂寄生的间隔时间很短（少于10 h）时,所育出的蜂绝大部分（80%以上）为绒茧蜂;当寄主先被绒茧蜂寄生,并饲养2天以上再供弯尾姬蜂寄生时,所育出的全为绒茧蜂;当寄主先被弯尾姬蜂寄生,并饲养2天以上再供绒茧蜂寄生时,寄主幼虫绝大部分不能存活,只有少部分能育出寄生蜂,且多为弯尾姬蜂。当2种蜂的幼虫存在于同一寄主体内时,2种蜂的发育均受到另一种蜂的抑制;绒茧蜂1龄幼虫具有物理攻击能力,能将弯尾姬蜂卵或幼虫致死。这些结果表明,菜蛾盘绒茧蜂与半闭弯尾姬蜂在同一寄主中发育时,前者具有明显的竞争优势。     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Studies on the characteristics of parasitism ofPlutella xylostella (Lep.: Plutellidae) by a larval parasiteDiadegma semiclausum (Hym.: Ichneumonidae)

Laboratory experiments were conducted to study the characteristics of parasitism of diamondback moth,Plutella xylostella (L.), a worldwide pest of crucifers, by a larval parasite,Diadegma semiclausum Hellén. Results showed that the greater the host larval density, the lesser was the percentage of larvae parasitized. The area of discovery decreased with increasing parasite density, but k-value remained practically unchanged. Parasitism reduced food consumption in parasitised larvae. No difference was observed in duration of larval instars between the parasitized and healthy larvae. As the frequency of superparasitism increased, the proportion of production of female progeny also increased. Presence of parasite larva within the host larva deterred superparasitism greater than the presence of parasite egg. Presence of larva of eitherD. semiclausum or another larval parasite,Cotesia plutellae Kurdjumov, within host larva deterred multiparasitism by either species greater than the presence of egg of either parasite species.Diadegma semiclausum was much more aggressive thanC. plutellae in parasitisingP. xylostella larvae.     

An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes

An adjustable action threshold that uses estimates of larval parasitism of Helicoverpa armigera (Hübner) in individual fields was assessed over three consecutive years in processing tomatoes in Hawke’s Bay, New Zealand. Tomato fields were monitored weekly for levels of infestation by H. armigera larvae. When infestation levels became of concern, either approaching or exceeding the standard action threshold of one larva per plant, collections of 30+ representative larvae were made. These larvae were measured and reared individually at 30 °C, and after 4 days rates of parasitism were estimated visually. From these data, spray recommendations were made using a formula that adjusted the action threshold to allow for mortality from parasitism. At harvest, damage assessments were made to validate these recommendations. Results showed that estimates of parasitism after 4 days were accurate predictors of final assessments of parasitism. Overall parasitism during the three seasons was 71%, confirming that the original threshold, which relies on about 50% parasitism, needed revision. The dominant parasitoid was Cotesia kazak, reared from 91% of all parasitized larvae over the 3 years. Microplitis croceipes and the self introduced polyphagous parasitoid Meteorus pulchricornis were reared from 4% and 5% of the parasitized larvae respectively. In 16 of 17 fields examined, the adjustable threshold kept fruit damage at harvest below the tolerated level of 5%. The single crop with excessive damage had only 0.5% fruit damage above this level. This adjustable threshold, which varied in this study from 1–8.3 larvae per plant, has been incorporated into an updated IPM programme and contributed to a 95% reduction in insecticide use.     

Selecting the right parasitoid for the environment in classical biological control programmes: the case of Diadegma semiclausum (Hymenoptera: Ichneumonidae) and Plutella xylostella (Lepidoptera: Plutellidae) in the Kofele highland of Ethiopia

The careful selection of parasitoids with a track record of success in similar environmental conditions may increase the likelihood of effective biocontrol. Diamondback moth (DBM) population and level of parasitism were assessed for three years prior to the release of Diadegma semiclausum (Hellén) in June 2008. Thereafter, the DBM population and severity of crop damage and the occurrence of D. semiclausum and indigenous DBM parasitoids were monitored by monthly surveys during the main production season of June to December for three years. Before release, DBM numbers fluctuated between 4.2 and 11.2 per plant and parasitism ranged between 6.5 and 24.7%. DBM density declined to 2.8, 0.9 and 0.7 per plant whilst parasitism levels increased successively to 21, 39 and 38% in 2008, 2009 and 2010, respectively. A significant shift in parasitoid guild was observed after D. semiclausum release: it comprised 18.6, 80.3 and 88.6% of total parasitism in the first, second and third year, respectively. The decline of DBM density following the release of the introduced parasitoid and its establishment will ensure production of Brassica spp. without pesticide use against DBM in the affected area.     

Role of a parasitoid with a low fecundity,Praestochrysis shanghaiensis (Hymenoptera: Chrysididae), in the population dynamics of its host

1. Analysis of life tables of the oriental moth, Monema flavescens, obtained for 8 generations over 4 years, disclosed that the cocoon parasitoid, Praestochrysis shanghaiensis, acted as a density-disruptive factor.
2. The density of the host cocoon remained stable (max./min.=3.2), whereas that of the host adult varied (max./min.=14.3) although both showed similar fluctation patterns.
3. Stability of the host population was associated with the density-dependence in the ratio of first generation cocoons to overwintered generation moths, which was the key factor for the rate of change throughout the year. Chrysidid parasitism among the first generation cocoons ranged from 37.7 to 70.1%, and that among the second generation cocoons from 16.7 to 63.2%, each showing an inverse density-dependence and acting as the main determinant (key-factor) of the between-year variation in the density of the adult moths.
4. The density-dependence of the rate of change from overwintered generation adults to first generation cocoons was so strong that the parasitism on the second generation hosts had not effect on the cocoon density of the first generation. On the other hand, the density-dependence of the rate of change from first generation adults to second generation cocoons was weak, and the parasitism on the first generation hosts became the key factor for the between-year variation of the second generation cocoons.
5. It is suggested that the stability of the parasitoid-host system will be disrupted without three parasitism-restricting factors: asynchrony in the parasitoid attack on the second generation hosts, high mortality among parasitoid larvae of the second generation, and the high proportion of those first generation parasitoids that enter diapause. These factors are considered to be effective only in cooler parts of the distribution of the parasitoid.

     

Transient transcription of a putative RNase containing BEN domain encoded in Cotesia plutellae bracovirus induces an immunosuppression of the diamondback moth, Plutella xylostella

A polydnavirus, Cotesia plutellae bracovirus (CpBV), possesses segmented genome located on chromosome(s) of an endoparasitoid wasp, C. plutellae. An episomal viral segment (CpBV-S3) consists of 11,017 bp and encodes two putative open reading frames (ORFs). ORF301 shows amino acid sequence homologies (28-50%) with RNase T2s of various organisms. It also contains BEN domain in C-terminal region. ORF302 is a hypothetical gene, which is also found in other bracoviruses. Both genes were expressed in larvae of Plutella xylostella parasitized by C. plutellae. Their expressions were detected in all tested tissues including hemocyte, fat body, gut, and epidermis. To analyze effects of these genes on the parasitism, the segment of CpBV-S3 was injected to nonparasitized larvae of P. xylostella, in which the two genes were expressed at least for 4 days post-injection. The larvae injected with CpBV-S3 exhibited significant immunosuppression, such as reduction in total hemocyte population and impairment in nodule formation behavior of hemocytes in response to bacterial challenge. Each gene expression in the treated larvae was inhibited by co-injecting respective double strand RNA (dsRNA) specific to each ORF. Injection of dsRNA of ORF301 could rescue the immunosuppression of the viral segment-treated larvae, while dsRNA specific to ORF302 did not. These results suggest that a putative RNase fused with a BEN domain encoded in CpBV-S3 plays a parasitic role in inducing host immunosuppression in the parasitism.     

Performance of Microplitis tuberculifer (Hymenoptera: Braconidae) parasitizing Mythimna separata (Lepidoptera: Noctuidae) in different larval instars

The solitary parasitoid Microplitis tuberculifer (Wesmael) is an important biological control agent of various lepidopteran pests in Asia. We examined the preference of M. tuberculifer for different instars of its common host, Mythimna separata (Walker), host instar effects on parasitoid development, and the consequences of parasitism in different stages for growth and consumption of host larvae. The wasp successfully parasitized the first four larval instars of M. separata, but not the fifth, which appeared to be behaviorally resistant. First and second instars were parasitized at higher rates compared to thirds and fourths in no-choice situations, ostensibly due to longer handling times for the latter, but second instars were most preferred in a choice test that presented all stages simultaneously. Although later instar hosts yielded heavier cocoons, the fastest parasitoid development was obtained in second instars. Lower sex ratios were obtained from first instars as females appeared to lay a smaller proportion of fertilized eggs in small hosts. Both weight gain and food consumption of parasitized larvae were reduced significantly within 24 h of parasitism, regardless of the stage parasitized, and final body weights were less than 10% those of unparasitized larvae. Thus, M. tuberculifer has good potential as a biological control agent of M. separata, successfully parasitizing the first four larval instars and dramatically reducing plant consumption by the host in all cases.     

Natural parasitism of the diamondback moth,Plutella xylostella (L.) (Lep.: Plutellidae) by a larval parasitoid wasp,Diadegma anurum on different cauliflower cultivars

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), is the most serious pest of cauliflower fields in central Iran and its control is primarily based on pesticide sprays. Over the past years, a number of new pesticide compounds were introduced onto the market and some of them may cause adverse effects on natural populations of parasitoids associated with DBM. Excessive use of insecticides against the pest did not produce satisfactory results but has caused concerns about environmental pollution and increased pest resistance to chemicals. This research aims to study natural parasitism of pest on different cauliflower cultivars in the fields of south of Tehran. Dominant species of parasitoids include Diadegma anurum, Cotesia plutellae and Oomyzus sokolowskii. The highest parasitism rate was observed by D. anurum that was recorded on Buris cultivar (19.92?±?1.06) and White cloud cultivar (16.20?±?1.49) and the lowest parasitism rate was observed on Snow crown cultivar (3.42) and SG cultivar (5.00) during the season.     

Application of synthetic herbivore‐induced plant volatiles causes increased parasitism of herbivores in the field

We previously reported that Cotesia vestalis (Hymenoptera, Braconidae), a parasitoid of diamondback moth (DBM) (Plutella xylostella; Lepidoptera, Plutellidae) larvae, was attracted to volatiles from crucifer plants infested by moth larvae kept in a desktop acrylic box, and that a blend of four DBM‐induced plant volatiles was responsible for this attraction. In this study, using a specially designed dispenser to release the four compounds, we demonstrated that the wasp was attracted to intact komatsuna plants (Brassica rapa var. perviridis). The experiments were performed in a climate‐controlled room, which was approximately 1000 times larger than the acrylic box used previously. Similarly, using the dispenser in the field, C. vestalis females were attracted to intact komatsuna plants with the dispenser from a distance of three metres. We also examined the effect of the volatile blend on the incidence of parasitism of DBM larvae in the field. Three small containers containing DBM‐infested komatsuna plants with dispensers, and three control containers containing only infested plants (control) were arranged in two lines running perpendicular to a komatsuna field in which both DBM larvae and C. vestalis populations were maintained, at distances of 12, 30 and 70 m. The results showed that the incidence of DBM parasitism was significantly higher in containers containing dispensers than in the control containers, suggesting that the blend could potentially be applied to DBM control in agroecosystems.     

Field confirmation of a mechanism causing synergism between Bacillus thuringiensis and the gypsy moth parasitoid, Apanteles melanoscelus

In 16-ha plots aerially sprayed with single and double applications of Bacillus thuringiensis, percentage parasitism by A. melanoscelus and the number of A. melanoscelus cocoons under burlap strips were higher than in comparable untreated plots in the same area. Strong correlations occurred between percentage parasitism and caterpillar size, with plots having the smallest caterpillars being the most heavily parasitized. However, these parameters were also negatively correlated with number of caterpillars per plot. The increased numbers of parasitoid progeny, i.e., cocoons, found in treated plots showed that corresponding increases in percentage parasitism could not be due simply to improved parasitoid: host ratios. Evidence strongly suggests that the retarding effect of B. thuringiensis infection kept gypsy moth larvae small enough in the treated plots to permit A. melanoscelus females to parasitize relatively large numbers of caterpillars.     

Occurrence of Diadegma semiclausum,a parasitoid of diamondback moth in lowlands of Syria

The parasitoid, Diadegma semiclausum (Hymenoptera: Ichneumonidae) is one of the most effective parasitoids of diamondback moth (DBM) in the highlands (> 1600 m above sea level) of Asia. A Diadegma population from the lowland areas of Homs, Syria (about 203–487 m above sea level) was examined to determine if it differs at the species-level from the D. semiclausum and other Diadegma populations present in different countries using molecular diagnostic tools. Phylogenetic analysis based on the neighbor-joining method using the mitochondrial cytochrome oxidase I (COI) and the nuclear internal transcribed spacer 2 (ITS2) sequences grouped the Homs (Syria) Diadegma population with D. semiclausum populations from other countries. The results suggest that D. semiclausum occurs in the lowland conditions in Homs (Syria), where the temperature is higher. The Homs (Syria) strain did not show any variations in the parasitism when the parasitized host (DBM) larvae were exposed to varying temperatures for 24 h. It could not survive when the parasitized DBM larvae were continuously reared at 35 °C; however it inflicted significantly higher parasitism when the parasitized DBM larvae were reared at day and night temperatures of 35 °C and 20 °C, respectively. Preliminary results indicate that the D. semiclausum strain from Homs (Syria) possesses some level of heat tolerance, which could be exploited for successful management of DBM in the tropical lowlands.     

Cotesia orobenae (Hymenoptera: Braconidae), a Gregarious Endoparasitoid of Evergestis rimosalis (Lepidoptera: Pyralidae), and Hyperparasitoids in Virginia Brassica Crops

Cotesia orobenae Forbes (Hymenoptera: Braconidae) is a gregarious endoparasitoid of the cross-striped cabbageworm (Evergestis rimosalis Guenée) (Lepidoptera: Pyralidae), a minor pest of Brassica crops in Virginia. Cocoons of C. orobenae were collected, weekly, from field plots of broccoli and cabbage crops in Whitethorne, Montgomery County (VA) during 1989 and 1990. Counts were also made of the eggs and larvae of E. rimosalis to determine the pest′s seasonality. In January 1991, C. orobenae cocoons were collected from the held plots to see if C. orobenae overwinters within cocoons. In May 1993, trap plants bearing E. rimosalis larvae were placed among the field plants weekly to determine if C. orobenae adults are present and ovipositing early in the season. Field counts of E. rimosalis eggs and larvae in 1990 indicated the occurrence of three generations off. rimosalis from June to October, but parasitism of larvae on trap plants by C. orobenae in May 1993 suggested that the parasitoid is present in mid-May. C. orobenae oviposits in first through third instar E. rimosalis and the resulting larvae feed internally on the developing host, exit the fourth (last) instar host, and spin cocoons in a loose mass. Mean brood size of 118 C. orobenae field-collected cocoon masses was 9.2 ± 4.4 cocoons per mass. Out of 1085 cocoons, adult C. orobenae emerged from 77%, hyperparasitoids emerged from 7%, and nothing emerged from 16%. Females accounted for 73% of the emerging C. orobenae adults. Data from field-collected cocoons suggest that C. orobenae enter diapause in late September and overwinter in cocoons. Six pupal hyperparasitoids were recovered: Isdromas lycaenae (Howard) (Ichneumonidae); Conura (=Spilochalcis) torvina (Cresson) and Conura (=Spilochalcis) albifrons (Walsh) (Chalcididae); Hypopteromalus tabacum (Fitch), Catolaccus cyanoideus Burks, and Trichomalopsis viridescens (Walsh) (Pteromalidae).     

Seasonal parasitism and biological characteristics of Habrobracon hebetor (Hymenoptera: Braconidae) – a potential larval ectoparasitoid of Helicoverpa armigera (Lepidoptera: Noctuidae) in a chickpea ecosystem

Seasonal parasitism of Habrobracon hebetor (Say) on Helicoverpa armigera (Hübner) in chickpea was studied for three consecutive years. Parasitism by H. hebetor on larvae of H. armigera reached 12.3%. The parasitoid maintained reproductive activity on H. armigera from February to April coinciding with pod formation and maturation stages of the crop. In laboratory assays, we investigated the suitability of larval instars of H. armigera to the parasitoid H. hebetor. This parasitoid attacked third to sixth instars, though fourth and fifth instar larvae were found most suitable with 100% parasitism and development to adults. Parasitoid developmental time was longest in fifth instar (9.1 days) compared to other instars (8.1–8.9 days). Fifth instar larvae resulted in highest numbers of cocoons and adult emergence. In addition, suitability of seven lepidopteran species to H. hebetor was investigated. Corcyra cephalonica, Galleria mellonella and H. armigera were the most suitable hosts with 100% parasitism and development to adults. It was followed by Maruca vitrata and Autographa nigrisigna with 60–76.7% and 40–70% parasitism and parasitoid developmental success, respectively. Though there was 23.3% parasitism, there was no parasitoid development in Spodoptera litura. No parasitism was recorded in Spilarctia obliqua. Development of H. hebetor was most rapid in C. cephalonica (8.7 days), and longest in G. mellonella (9.3 days). Parasitoids that developed on these hosts resulted in highest numbers of cocoons and adult emergence. The parasitoid could be exploited for the biological control of H. armigera in a chickpea ecosystem.     

Inhibition of larval recruitment of ARmandia sp. (Polychaeta: Opheliidae) by established adults of Pseudopolydora paucibranchiata (Okuda) (Polychaeta : Spionidae) on an intertidal sand flat

Inhibition of larval settlement by a dense assemblage of established adults was examined by observing natural and experimental abundance patterns of two polychaete species on an intertidal sand flat in west Kyushu, Japan. A cage left for 43 days in the field in spring-summer brought about a remarkable increase in the within-cage density of adults of the tube-building spionid polychaete Pseudopolydorapaucibranchiata (Okuda) as compared with the density in an uncaged plot (× 52). In contrast, the densities of juveniles of the burrowing opheliid polychaete Armandia sp. showed an inverse trend (× $\text{1}\text{22}$). The attractiveness of the within-cage sediment for settling larvae of Armandia (cage-induced artifact) was assessed in a laboratory experiment: given an alternative choice between the sediments from the cage and the uncaged plot, Armandia larvae produced by artificial fertilization showed no substratum-preference. In another laboratory experiment, it was confirmed that Pseudopolydora paucibranchiata adults at a density of only $\text{1}\text{30}$ of that in the cage exerted a great lethal effect (probably ingestion) on Armandia larvae. These two results strongly support the hypothesis that the low density of Armandia juveniles in the cage was induced not through avoidance of the cage sediment by the larvae themselves but through inhibition of recruitment by the dense assemblage of established Pseudopolydora paucibranchiata adults in the cage. Moreover, the natural abundance pattern of Armandia juveniles in summer could partly be explained in relation to spatial and temporal changes in the density of Pseudopolydora paucibranchiata adults.     

Status of Charidotis pygmaea (Coleoptera: Chrysomelidae) as a Biological Control Agent of Lantana montevidensis (Verbenaceae) in Australia

The establishment of the leaf-feeding beetle Charidotis pygmaea Klug and its potential to control Lantana montevidensis (Sprengel) Briquet, a serious pasture weed of central and southern Queensland, Australia, were assessed. C. pygmaea was collected in Brazil from Lantana fucata Lindley, a plant morphologically similar to L. montevidensis. Over 40,000 beetles were released over 3 years by use of caged and uncaged techniques at 25 sites throughout southeast and central Queensland. At 6 of the sites where detailed and frequent monitoring occurred, no adults were found 6 months after the release. At another 2 sites, adults were present for only 12 months. Only a small number of eggs were laid at any single site and few larvae completed development to the adult stage. No signs of insect activity were found at any site after 24 months. Comparative laboratory and experimental field plot trials with both the weedy (field host) and the ornamental (glasshouse host) forms of L. montevidensis did not show significant differences in insect performance. Assessment of nitrogen, phosphorous, potassium, and water contents, leaf hairiness, and leaf toughness of both the weedy and the ornamental forms of L. montevidensis grown under glasshouse and field plot conditions did not show differences between the two plant forms. There were, however, differences in the percentage of adults that developed in the glasshouse trials compared to the field plot trials (55% vs 5%). Field observations in Brazil showed that C. pygmaea was found only on L. fucata and L. tiliifolia Chamisso and was not seen on L. montevidensis growing in the same region. Climate matching with CLIMEX showed that most areas in Australia where L. montevidensis is a major problem are not climatically similar to the collection sites of C. pygmaea in Brazil. Whereas populations of C. pygmaea can be maintained on L. montevidensis under glasshouse conditions, it performs poorly on that species under field conditions. Unsuitable climatic conditions and an incompatible target plant are the most likely factors affecting the poor performance of C. pygmaea. Consequently, field releases of the agent in Australia have ceased and C. pygmaea is not recommended as a biological control agent for L. montevidensis in Australia.     

Reproductive isolation and differentiation between five populations of Cotesia plutellae (Hymenoptera: Braconidae), parasitoid of Plutella xylostella (Lepidoptera: Plutellidae)

Many taxa used in biological control may be composed of several population units reproductively isolated to various degrees. Yet, the introductions of non-compatible populations may result in a depression of intended biological control. Cotesia plutellae has been widely used as a biological control agent of the diamondback moth, Plutella xylostella. However, not all introductions and augmentations were successful. With the aim to develop markers of compatibility for this species, we studied the reproductive compatibility between five populations (South Africa, Benin, Martinique, Reunion, and Taiwan) and analyzed its statistical relationship with three morphological characters (antennae and body length and antennae/body ratio), one molecular character (sequence of a cytochrome b fragment) and the Wolbachia infection status. This study shows that C. plutellae populations formed two interbreeding groups. The antenna/body length ratio of females, the ratio between male and female body length, one non-silent base pair substitution observed in cytochrome b sequences, and Wolbachia infection status differentiate these groups and were all good predictors of reproductive compatibility. Our results suggest also that genetic factors independent from Wolbachia are needed to fully explain reproductive isolation between C. plutellae populations. We conclude that C. plutellae is a single species composed of at least two partially incompatible population aggregates. Diagnostic markers were proposed for the prediction of the level of reproductive compatibility between populations which can be used for further biocontrol introductions.     

Interaction between Neoaplectana carpocapsae (Nematoda: Steinernematidae) and Apanteles militaris (Hymenoptera: Bracondiae), a parasitoid of the armyworm, Pseudaletia unipuncta

The DD-136 strain of Neoaplectana carpocapsae adversely affected the development of immature stages of Apanteles militaris, a gregarious internal parasitoid of the armyworm, Pseudaletia unipuncta. The adverse effect of the nematode-bacterium complex was indirect, i.e., the infection by the nematode killed the host before A. militaris could complete its development. However, if armyworms containing 10- or 11-day-old A. militaris were exposed to dauer juveniles in Petri dishes, 48.1 and 94.4%, respectively, produced normal cocoons. If hosts containing 9- or 10-day-old A. militaris were fed dauer juveniles, 42.6 and 73.4% of the armyworms, respectively, produced A. militaris which formed normal cocoons. Cocoon-spinning A. militaris larvae were infected by the nematode. After cocoon formation was completed, the dauer juveniles could not penetrate the cocoon and infect the pupa. However, pupae in cocoons which had been deliberately cut open at one end became infected. A. militaris adults were infected when exposed to dauer juveniles in Petri dishes. After 3 days of exposure to dauer juveniles, 25.0, 44.2, and 7.0% of the adults in three trials were alive, whereas 100, 100, and 96.7% of the control adults were alive. Examination of dead adults in the nematode treatment showed that 67.6% contained nematodes. N. carpocapsae developed and reproduced in unparasitized armyworms, in armyworms containing 9-day-old A. militaris, and in those from which A. militaris had emerged. Production of dauer juveniles was significantly higher in unparasitized armyworms and in armyworms containing 9-day-old A. militaris than in those from which A. militaris had emerged.