The Effectiveness of Trichogramma chilonis,Trichogramma pretiosum and Trichogramma brasiliense (Hymenoptera: Trichogrammatidae) as Parasitoids of Helicoverpa armigera (Lepidoptera: Noctuidae) on Sunflower (Helianthus annuus) and Redgram (Cajanus cajan)

The performance of three species of trichogrammatids on the pest, Helicoverpa armigera was evaluated in the laboratory and screenhouse conditions in Karnataka, India during 1996-97. Laboratory studies indicated that Trichogramma chilonis and Trichogramma pretiosum were more effective parasitoids of H. armigera than Trichogramma brasiliense. In screenhouse conditions, T. chilonis was the most effective parasitoid of H. armigera eggs on sunflower plants in comparison to the other two trichogrammatid species. When releasing 50?000 per ha on sunflower and redgram, T. chilonis parasitised 50.1 and 11.4% H. armigera eggs, respectively. The position of H. armigera eggs on different plant parts of sunflower had no effect on parasitism by T. chilonis. However, parasitism by the same trichogrammatid among different plant parts of redgram varied significantly. It parasitized 43.4 and 18.7% H. armigera eggs on leaves and flowers, respectively, and significantly fewer, 3.9%, on pods (P<0.05). The growth stage of redgram plants also had an effect on parasitism by T. chilonis, parasitism being extremely low on plants with pods.     

A new species ofTrichogramma [T. Cordubensis n. sp.] [Hym.: Trichogrammatidae], parasitoid ofHeliothis eggs in cotton crops in the sw of spain

Trichogramma cordubensis n. sp. is a parasite ofHeliothis armigera Hb. eggs in cotton crops in western Andalusia. Reproduced onEphestia kuehniella Zeller eggs, it is described morphologically and compared withT. chilonis Ishii andT. evanescens Westwood as both present similarities with this species.T. cordubensis can be distinguished in the male genitalia by the shape of the dorsal expansion of the gonobase and the size, shape and relative position of the median ventral projection. Male antennal setae are longer inT. cordubensis than in the other 2 species. In addition, unlikeT. chilonis andT. evanescens, T. cordubensis is thelytokous at 20°C. in our laboratory, though males and gynandromorphs can be obtained by altering the rearing temperature, this being another difference of this species.     

Recovery of two exotic parasites,Trichogramma brasiliensis [Hym.: Trichogrammatidae] andEucelatoria bryani [Dip.: Tachinidae] fromHeliothis armigera [Lep.: Noctuidae] in tomato fields

Heliothis armigera (Hübner) is a major pest of several crops especially tomato and pulses in India. Indigenous natural enemies likeCarcelia illota Curr.,Campoletis chlorideae Uchida,Trichogramma chilonis Ishii andHexamermis sp are unable to exert adequate control ofH. armigera in tomato. Field trials were conducted with 2 exotic parasites,Trichogramma brasiliensis (Ashmead) andEucelatoria bryani Sabrosky in tomato fields around Bangalore. Both the parasites were recovered fromH. armigera in tomato fields. Field parasitism inH. armigera byT. brasiliensis ranged from 34.6 to 51.3%. WithE. bryani, the parasitism ranged from 0.0 to 8.0%.     

Evaluation of an endosulfan tolerant strain of <Emphasis Type="Italic">Trichogramma chilonis</Emphasis> on cotton

The performance of an endosulfan tolerant strain of Trichogramma chilonis Ishii was evaluated against Helicoverpa armigera (Hübner) eggs on cotton plants in a net house. Under pesticide pressure, the tolerant strain could provide significantly higher parasitism in comparison to the susceptible strain. The parasitoid adult emergence was also significantly higher in the treatment with the tolerant strain in comparison to the susceptible strain, when parasitoids were released within 3 days of endosulfan spraying. Release of the tolerant strain of T. chilonis in conjunction with endosulfan spray application resulted in significantly higher pest mortality in comparison to the endosulfan treatment or release of T. chilonis alone. It could be inferred from the results that T. chilonis should be released only 3 days after endosulfan spray application as during the first 3 days after the spraying, endosulfan provided the required protection and adversely affected the performance of the parasitoid.     

High Susceptibility to Cry1Ac and Low Resistance Allele Frequency Reduce the Risk of Resistance of Helicoverpa armigera to Bt Soybean in Brazil

The Old World bollworm, Helicoverpa armigera (Hübner), was recently introduced into Brazil, where it has caused extensive damage to cotton and soybean crops. MON 87701 × MON 89788 soybean, which expresses the Bt protein Cry1Ac, was recently deployed in Brazil, providing high levels of control against H. armigera. To assess the risk of resistance to the Cry1Ac protein expressed by MON 87701 × MON 89788 soybean in Brazil, we conducted studies to evaluate the baseline susceptibility of H. armigera to Cry1Ac, in planta efficacy including the assessment of the high-dose criterion, and the initial resistance allele frequency based on an F₂ screen. The mean Cry1Ac lethal concentration (LC₅₀) ranged from 0.11 to 1.82 μg·mL⁻¹ of diet among all H. armigera field populations collected from crop seasons 2013/14 to 2014/15, which indicated about 16.5-fold variation. MON 87701 × MON 89788 soybean exhibited a high level of efficacy against H. armigera and most likely met the high dose criterion against this target species in leaf tissue dilution bioassays up to 50 times. A total of 212 F₂ family lines of H. armigera were established from field collections sampled from seven locations across Brazil and were screened for the presence of MON 87701 × MON 89788 soybean resistance alleles. None of the 212 families survived on MON 87701 × MON 89788 soybean leaf tissue (estimated allele frequency = 0.0011). The responses of H. armigera to Cry1Ac protein, high susceptibility to MON 87701 × MON 89788 soybean, and low frequency of resistance alleles across the main soybean-producing regions support the assumptions of a high-dose/refuge strategy. However, maintenance of reasonable compliance with the refuge recommendation will be essential to delay the evolution of resistance in H. armigera to MON 87701 × MON 89788 soybean in Brazil.     

Genetic diversity and demographic history of the Old World Bollworm,Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), in Ethiopia inferred from mitochondrial gene sequences

The Old World bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), is a globally distributed agricultural and horticultural insect pest. Despite the economic importance of this insect in Ethiopia, its genetic diversity and demographic history are poorly understood. We examined the nucleotide variation of the mitochondrial cytochrome c oxidase subunit I (COI) gene fragment of 74 H. armigera individuals from six collection sites in Ethiopia. We recorded 15 COI haplotypes in H. armigera, ten globally shared and five exclusive to Ethiopia (HaET15, HaET14, HaET10, HaET7, and HaET4). Haplotype HaET1 was the most widely geographically distributed and frequent (71.62%). Analysis of molecular variance (AMOVA) revealed a high and significant level of variation within H. armigera populations (θ_ST  = −0.0135). Negative values of the neutrality test and nonsignificant index of mismatch distribution supported the demographic expansion of H. armigera populations in Ethiopia; furthermore, this was also supported by the nonsignificant values of the sum of squared deviations (SSD) and raggedness index (r). The high genetic variation and population expansion of H. armigera have immense implications for devising locally adapted management strategies in area‐wide integrated pest management IPM programs. However, a comprehensive study of H. armigera genetic diversity and population structure using various molecular markers is needed for future confirmation.     

The Potential Distribution of Invading Helicoverpa armigera in North America: Is It Just a Matter of Time?

Helicoverpa armigera has recently invaded South and Central America, and appears to be spreading rapidly. We update a previously developed potential distribution model to highlight the global invasion threat, with emphasis on the risks to the United States. The continued range expansion of H. armigera in Central America is likely to change the invasion threat it poses to North America qualitatively, making natural dispersal from either the Caribbean islands or Mexico feasible. To characterise the threat posed by H. armigera, we collated the value of the major host crops in the United States growing within its modelled potential range, including that area where it could expand its range during favourable seasons. We found that the annual value of crops that would be exposed to H. armigera totalled approximately US$78 billion p.a., with US$843 million p.a. worth growing in climates that are optimal for the pest. Elsewhere, H. armigera has developed broad-spectrum pesticide resistance; meaning that if it invades the United States, protecting these crops from significant production impacts could be challenging. It may be cost-effective to undertake pre-emptive biosecurity activities such as slowing the spread of H. armigera throughout the Americas, improving the system for detecting H. armigera, and methods for rapid identification, especially distinguishing between H. armigera, H. zea and potential H. armigera x H. zea hybrids. Developing biological control programs, especially using inundative techniques with entomopathogens and parasitoids could slow the spread of H. armigera, and reduce selective pressure for pesticide resistance. The rapid spread of H. armigera through South America into Central America suggests that its spread into North America is a matter of time. The likely natural dispersal routes preclude aggressive incursion responses, emphasizing the value of preparatory communication with agricultural producers in areas suitable for invasion by H. armigera.     

Effect of induced tolerance to Bt toxin on the egg size of Helicoverpa armigera and parasitism by Trichogramma pretiosum

Larvae of Helicoverpa armigera (Hübner) can develop a form of Bt tolerance after exposure to sub‐lethal doses of Bt‐toxin subclass Cry1Ac. Increasing levels of tolerance are produced over generations of larval exposure, which are not related to DNA sequence changes, and are largely maternally transmitted. The characteristic of maternal transmission, combined with the importance of egg parasitoids to cotton pest management, raises questions about the effects of Bt tolerance/exposure on the eggs of H. armigera and on some key metrics of egg parasitism. In the present study, the effect of inducible tolerance on eggs of H. armigera and parasitism by Trichogramma pretiosum (Riley) is investigated. First, the volumes of eggs laid by susceptible and tolerant H. armigera females are compared. In addition, the effect of inducible tolerance on egg parasitism is determined by comparing parasitism success, the number of adult wasps emerged per host egg, and the proportion of male and female offspring emerged per host egg. The results obtained suggest that Cry1Ac‐tolerance is associated with increased egg volume, even after just one generation of sub‐lethal exposure. When tolerant H. armigera are freed from ongoing sub‐lethal exposure, a corresponding decrease in egg volume is not detected. Although there is no difference in the percentage of eggs parasitized, there is an increase in the number of emergent parasitoids, especially males, from eggs laid by tolerant H. armigera. These results confirm that maternally‐transmitted Bt tolerance is reflected in the phenotype of the eggs of tolerant offspring, which affects egg parasitism.     

Isolation of microbes associated with field-collected populations of the egg parasitoid,Trichogramma chilonis capable of enhancing biotic fitness

Four bacterial and one yeast species, cultured and identified as Stenotrophomonas maltophilia, Acinetobacter sp., Pseudomonas sp. and Ochrobactrum sp. and the yeast as Metschnikowia reukaufii, were isolated from the internal organs of four collections of field-sourced egg parasitoid, Trichogramma chilonis, obtained as parasitised Helicoverpa armigera eggs. Bacteria were identified through 16 rRNA amplification and sequencing. The single species of yeast was identified through internal transcribed spacer sequences. A single bacterial species could be isolated from each of the four T. chilonis collections; however, all four T. chilonis collections yielded the yeast, M. reukaufii. In order to study the influence of the association of each of the bacterial species and the yeast, microbe-free laboratory-bred populations of T. chilonis were fed with the individual cultures and fitness parameters as parasitisation vigour and female bias were studied in T. chilonis over 10 generations. T. chilonis fed with either S. maltophilia or Acinetobacter sp. and Pseudomonas sp. showed a mean percent increase in female ratio of 26.2%, 30% and 30.3% and mean percent parasitisation of H. armigera eggs significantly increased by 38%, 32.2% and 31.3%, respectively. However, T. chilonis fed with Acinetobacter sp. did not positively influence the two T. chilonis fitness factors. The ubiquitous yeast, M. reukaufii, which could be isolated from all four collections of T. chilonis, could significantly increase both female count and percent parasitism ratio by 22% and 65%, respectively. This study has opened the possibility of modulating the parasitisation fitness of laboratory-bred T. chilonis, prior to field release, using microbes associated with them in the wild.     

Landscape Diversity and Crop Vigor Influence Biological Control of the Western Grape Leafhopper (E. elegantula Osborn) in Vineyards

This study evaluated how the proportional area of natural habitat surrounding a vineyard (i.e. landscape diversity) worked in conjunction with crop vigor, cultivar and rootstock selection to influence biological control of the western grape leafhopper (Erythroneura elegantula Osborn). The key natural enemies of E. elegantula are Anagrus erythroneurae S. Trjapitzin & Chiappini and A. daanei Triapitsyn, both of which are likely impacted by changes in landscape diversity due to their reliance on non-crop habitat to successfully overwinter. Additionally, E. elegantula is sensitive to changes in host plant quality which may influence densities on specific cultivars, rootstocks and/or vines with increased vigor. From 2010–2013, data were collected on natural enemy and leafhopper densities, pest parasitism rates and vine vigor from multiple vineyards that represented a continuum of landscape diversity. Early in the season, vineyards in more diverse landscapes had higher Anagrus spp. densities and lower E. elegantula densities, which led to increased parasitism of E. elegantula. Although late season densities of E. elegantula tended to be lower in vineyards with higher early season parasitism rates and lower total petiole nitrogen content, they were also affected by rootstock and cultivar. While diverse landscapes can support higher natural enemy populations, which can lead to increased biological control, leafhopper densities also appear to be mediated by cultivar, rootstock and vine vigor.     

Systemic Imidacloprid Affects Intraguild Parasitoids Differently

Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) and Campoletis sonorensis (Cameron) (Hymenoptera, Ichneumonidae) are solitary endoparasitoids of the tobacco budworm, Heliothis virescens (Fabricius) (Lepidoptera, Noctuidae). They provide biological control of H. virescens populations in Southeastern US agricultural production systems. Field and greenhouse experiments conducted from 2011–2014 compared parasitism rates of parasitoids that developed inside H. virescens larvae fed on tobacco plants treated with and without imidacloprid. The parasitoids in our study did not have a similar response. Toxoneuron nigriceps had reduced parasitism rates, but parasitism rates of C. sonorensis were unaffected. Preliminary data indicate that adult female lifespans of T. nigriceps are also reduced. ELISA was used to measure concentrations of neonicotinoids, imidacloprid and imidacloprid metabolites in H. virescens larvae that fed on imidacloprid-treated plants and in the parasitoids that fed on these larvae. Concentrations were detectable in the whole bodies of parasitized H. virescens larvae, T. nigriceps larvae and T. nigriceps adults, but not in C. sonorensis larvae and adults. These findings suggest that there are effects of imidacloprid on multiple trophic levels, and that insecticide use may differentially affect natural enemies with similar feeding niches.     

Effects of climate change on different geographical populations of the cotton bollworm Helicoverpa armigera (Lepidoptera,Noctuidae)

The effects of climate change on pest phenology and population size are highly variable. Understanding the impacts of localized climate change on pest distribution and phenology is helpful for improving integrated pest management strategies. Here, the population dynamics of cotton bollworms (Helicoverpa armigera) from Maigaiti County, south Xinjiang, and Shawan County, north Xinjiang, China, were analyzed using a 29‐year dataset at lower latitudes and a 23‐year dataset at higher latitudes to determine the effects of climate change on the population dynamics of H. armigera. The results showed that all generations of H. armigera at both sites showed increasing trends in population size with climate warming. Abrupt changes in phenology and population number occurred after abrupt temperature changes. Climate change had a greater effect on the phenology of H. armigera at higher latitudes than at lower latitudes and led to a greater increase in population size at lower latitudes than at higher latitudes; the temperature increase at higher latitudes will cause a greater increase in the adult moth population size in the future compared to that at lower latitudes; and abrupt changes in the phenology, temperature increase, and population size at lower latitudes occurred earlier than those at higher latitudes. Thus, it is necessary to develop sustainable management strategies for Helicoverpa armigera at an early stage.     

Functional response of Trichogramma chilonis to Galleria mellonella and Chilo sacchariphagus eggs

A biological control programme using inundative releases of Trichogramma chilonis Ischii (Hymenoptera: Trichogrammatidae) reared on Galleria mellonella L. (Lepidoptera: Pyralidae) is currently underway to reduce infestations of Chilo sacchariphagus Bojer (Lepidoptera: Crambidae) in sugarcane, Saccharum spp., on Réunion Island. To assess the potential of the parasitoid as an inundative biocontrol agent, the functional response of three T. chilonis strains was tested with G. mellonella and one strain with C. sacchariphagus host eggs in glass tubes in the laboratory. The shape of the functional response (type II or III) was determined using logistic regression, and attack coefficients and handling times (T_h) were determined using non‐linear least‐square regression. The behaviour of all three strains with G. mellonella host eggs corresponded to a type III response. The St Benoît T. chilonis strain had a significantly shorter estimate of T_h than the St Pierre strain (P<0.05) and may, therefore, be more appropriate as a biocontrol agent. The functional response with C. sacchariphagus host eggs was a type II with the St Benoît T. chilonis strain. More T. chilonis wasps developed per host egg from the larger C. sacchariphagus host eggs (2.9) relative to G. mellonella (1.1). Superparasitism at low host egg densities was, therefore, likely to have been less frequent with C. sacchariphagus. Black eggs were chosen as an estimate of number of eggs parasitized, although they represent the number of eggs where parasitism led to complete pupal development. The low rate of detected parasitism at low host densities with G. mellonella eggs may be due to incomplete pupal development due to superparasitism rather than lack of parasitism, thus explaining the type III functional response.     

A 2-Year Field Study Shows Little Evidence That the Long-Term Planting of Transgenic Insect-Resistant Cotton Affects the Community Structure of Soil Nematodes

Transgenic insect-resistant cotton has been released into the environment for more than a decade in China to effectively control the cotton bollworm (Helicoverpa armigera) and other Lepidoptera. Because of concerns about undesirable ecological side-effects of transgenic crops, it is important to monitor the potential environmental impact of transgenic insect-resistant cotton after commercial release. Our 2-year study included 1 cotton field where non-transgenic cotton had been planted continuously and 2 other cotton fields where transgenic insect-resistant cotton had been planted for different lengths of time since 1997 and since 2002. In 2 consecutive years (2009 and 2010), we took soil samples from 3 cotton fields at 4 different growth stages (seedling, budding, boll-forming and boll-opening stages), collected soil nematodes from soil with the sugar flotation and centrifugation method and identified the soil nematodes to the genus level. The generic composition, individual densities and diversity indices of the soil nematodes did not differ significantly between the 2 transgenic cotton fields and the non-transgenic cotton field, but significant seasonal variation was found in the individual densities of the principal trophic groups and in the diversity indices of the nematodes in all 3 cotton fields. The study used a comparative perspective to monitor the impact of transgenic insect-resistant cotton grown in typical ‘real world’ conditions. The results of the study suggested that more than 10 years of cultivation of transgenic insect-resistant cotton had no significant effects–adverse or otherwise–on soil nematodes. This study provides a theoretical basis for ongoing environmental impact monitoring of transgenic plants.     

新疆北部棉区作物景观多样性对棉铃虫种群的影响

如何从景观尺度上实现对害虫的科学管理已经成为昆虫生态学的研究热点.利用频振式杀虫灯诱集技术,从2007-2009年在新疆北部棉区16-17个农场近240km2作物范围内,监测和评估棉田周边作物景观对棉铃虫种群的影响.结果表明:农业景观多样化显著地影响棉铃虫种群数量,复杂作物系统中(棉花比例＜50％作物面积)棉铃虫成虫数量明显大于简单作物系统(棉花比例≥50％作物面积;棉铃虫种群数量与景观多样性指数(Simpson's Reciprocal Index)呈正相关;同时棉铃虫成虫与加工番茄、玉米和小麦的比例成正相关,但与棉花比例呈负相关.研究结果为转基因棉花抗性管理提供科学依据,同时农田景观多样性指标可作为修正棉区棉铃虫预测模型的重要指标.     

The Influence of Socio-economic,Behavioural and Environmental Factors on Taenia spp. Transmission in Western Kenya: Evidence from a Cross-Sectional Survey in Humans and Pigs

Taenia spp. infections, particularly cysticercosis, cause considerable health impacts in endemic countries. Despite previous evidence of spatial clustering in cysticercosis and the role of environmental factors (e.g. temperature and humidity) in the survival of eggs, little research has explored these aspects of Taenia spp. epidemiology. In addition, there are significant gaps in our understanding of risk factors for infection in humans and pigs. This study aimed to assess the influence of socio-economic, behavioural and environmental variables on human and porcine cysticercosis. A cross-sectional survey for human taeniasis (T. solium and T. saginata), human cysticercosis (T. solium) and pig cysticercosis (T. solium) in 416 households in western Kenya was carried out. These data were linked to questionnaire responses and environmental datasets. Multi-level regression was used to examine the relationships between covariates and human and porcine cysticercosis. The HP10 Ag-ELISA sero-prevalence (suggestive of cysticercosis) was 6.6% for humans (95% CI 5.6%–7.7%), and 17.2% for pigs (95% CI 10.2%–26.4%). Human taeniasis prevalence, based on direct microscopic observation of Taenia spp. eggs (i.e. via microscopy results only) was 0.2% (95% CI 0.05%–0.5%). Presence of Taenia spp. antigen in both humans and pigs was significantly associated with a range of factors, including positive correlations with land cover. The presence of HP10 antigen in humans was correlated (non-linearly) with the proportion of land within a 1 km buffer that was flooding agricultural land and grassland (odds ratio [OR] = 1.09 and 0.998; p = 0.03 and 0.03 for the linear and quadratic terms respectively), gender (OR = 0.58 for males compared to females, p = 0.02), level of education (OR = 0.62 for primary level education versus no formal education, p = 0.09), use of well water for drinking (OR = 2.76 for those who use well water versus those who do not, p = 0.02) and precipitation (OR = 0.998, p = 0.02). Presence of Taenia spp. antigen in pigs was significantly correlated with gender and breeding status of the pig (OR = 10.35 for breeding sows compared to boars, p = 0.01), and the proportion of land within a 1 km buffer that was flooding agricultural land and grassland (OR = 1.04, p = 0.004). These results highlight the role of multiple socio-economic, behavioural and environmental factors in Taenia spp. transmission patterns. Environmental contamination with Taenia spp. eggs is a key issue, with landscape factors influencing presence of Taenia spp. antigens in both pigs and humans.     

Effects of host-egg ages on host selection and suitability of four Chinese Trichogramma species,egg parasitoids of the rice striped stem borer,Chilo suppressalis

The striped stem borer, Chilo suppressalis (Walker), is one of the most economically important rice pests worldwide. However, biological control of this pest using natural-enemy insects has been rarely documented to date. With the objective of screening suitable candidate species for controlling the striped stem borer, we investigated the effect of the age of host eggs on the host selection and suitability by four indigenous Trichogramma species on their native host, C. suppressalis. The results indicated that the differently aged eggs of C. suppressalis were all accepted by T. japonicum, T. dendrolimi and T. chilonis, and there was a clear tendency to parasitize older eggs less under no-choice and choice conditions. The number of parasitized host eggs by T. ostriniae also decreased with the increasing host age in the no-choice test, but more 2-day-old host eggs were parasitized in the choice test. When 0-, 2-day-old eggs were offered, T. dendrolimi, T. japonicum and T. chilonis exhibited similar parasitism ability, whereas T. ostriniae appeared to have a stronger ability to attack the older host eggs (4-day-old). Trichogramma japonicum developed and emerged on parasitized C. suppressalis eggs of all ages tested, while showing a better adaptation to younger host eggs with significantly faster developmental time, higher survival and more female progeny on 0-day-old eggs. No adults for each of the other three Trichogramma species emerged from parasitized 4-day-old host eggs, and they had similar developmental time, survival and female progeny on parasitized 0-, 2-day-old host eggs with an exception of female progeny for T. chilonis. On 0-day-old host eggs, T. japonicum developed faster and T. ostriniae had lower progeny survival than the other three Trichogramma species evaluated, respectively. The current study provides useful information to select suitable Trichogramma species for controlling the striped stem borer, C. suppressalis.     

Importance of host oviposition pattern and plant size for the selection of Trichogramma strains to control the diamondback moth

The aim of this work was to select a candidate strain of Trichogrammatidae (Hymenoptera: Chalcidoidea) to control the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), an important pest of cabbage in Europe. The parasitic efficiency of Trichogramma chilonis Ishii from Japan and Réunion Island, Trichogramma evanescens Westwood from Egypt, Trichogramma ostriniae Pang & Chen from Japan, and Trichogramma semblidis (Aurivillius) from France was studied with sentinel eggs in greenhouse‐grown cauliflower. The percentage of parasitized eggs was measured 1 m from the release point and 3 days after release. Two factors were studied: host‐egg density (three eggs per stem vs. 50 eggs per stem) and plant size (50–100 cm high plants vs. 100–150 cm high plants). Trichogramma evanescens from Egypt achieved the best parasitism. Parasitism efficiency of T. ostriniae from Japan and T. chilonis from Réunion Island was not influenced by egg density. In contrast, parasitism efficiencies of the three other strains were higher at the lower egg density than at the higher egg density. Parasitism efficiency was lower when the plants were bigger, with the exception of T. chilonis from Réunion Island, for which the level of parasitism was not affected by plant size. Thus, T. chilonis from Réunion Island appeared to be the most suitable Trichogramma strain for use in controlling P. xylostella, regardless of the growth stage of the crop. However, T. ostriniae from Japan may also be more suitable for use on cauliflower crops at the early stage of crop development. If potential problems related to the introduction of exotic species are taken into consideration, it is possible to consider the native T. evanescens.     

Population Genetic Structure of the Cotton Bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in India as Inferred from EPIC-PCR DNA Markers

Helicoverpa armigera is an important pest of cotton and other agricultural crops in the Old World. Its wide host range, high mobility and fecundity, and the ability to adapt and develop resistance against all common groups of insecticides used for its management have exacerbated its pest status. An understanding of the population genetic structure in H. armigera under Indian agricultural conditions will help ascertain gene flow patterns across different agricultural zones. This study inferred the population genetic structure of Indian H. armigera using five Exon-Primed Intron-Crossing (EPIC)-PCR markers. Nested alternative EPIC markers detected moderate null allele frequencies (4.3% to 9.4%) in loci used to infer population genetic structure but the apparently genome-wide heterozygote deficit suggests in-breeding or a Wahlund effect rather than a null allele effect. Population genetic analysis of the 26 populations suggested significant genetic differentiation within India but especially in cotton-feeding populations in the 2006–07 cropping season. In contrast, overall pair-wise F _ST estimates from populations feeding on food crops indicated no significant population substructure irrespective of cropping seasons. A Baysian cluster analysis was used to assign the genetic make-up of individuals to likely membership of population clusters. Some evidence was found for four major clusters with individuals in two populations from cotton in one year (from two populations in northern India) showing especially high homogeneity. Taken as a whole, this study found evidence of population substructure at host crop, temporal and spatial levels in Indian H. armigera, without, however, a clear biological rationale for these structures being evident.     

Trichogramma chilonis Ishii: A potential biological control agent of Crocidolomia pavonana in Samoa

Crocidolomia pavonana F. (Lepidoptera: Crambidae) is a major pest of Brassica crops in tropical and sub-tropical regions of Africa, Asia and the Pacific. There are no previous reports of effective natural enemies of the pest across this range but in Samoa an arrhenotokous population of the generalist egg parasitoid Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) frequently attacks it. This is the first record of T. chilonis in Samoa. A three-year field recruitment study showed that although C. pavonana eggs occurred at all times of the year, their abundance was greatest during drier periods. Parasitism of C. pavonana egg masses by T. chilonis was variable (0–87% of egg masses attacked) but the parasitoid was recovered from eggs collected at all times of the year and it is well established in the major Brassica growing regions of the island of Upolu. When partial lifetables were constructed for C. pavonana, the rate of egg disappearance (likely due to predation and the physical effects of rainfall) ranged from 0 to 0.839 and the marginal rate of mortality due to T. chilonis ranged from 0 to 0.474. When it was present, T. chilonis was the major mortality factor affecting C. pavonana eggs in all but one of the recruitment studies. The historical problems surrounding the identity and species status of T. chilonis are discussed and its host range and distribution in the Asia-Pacific region is reviewed briefly. Finally, the potential of this population of T. chilonis for development as a biological control agent of C. pavonana is considered.