Arthropod Natural Enemies of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in India

Helicoverpa armigera Hubner Lepidoptera: Noctuidae is one of the most serious insect pests in the Old World. In India, it causes substantial losses to legume, fibre, cereal oilseed and vegetable crops. This paper reviews the literature on the biology, ecology, efficacy, rearing and augmentation of endemic parasitoids and predators, as well as exotic parasitoids introduced and released in India. It also provides updated lists of H. armigera natural enemies native to India. In addition, reports of augmentative releases of Trichogramma spp., the most extensively studied natural enemy of H. armigera are summarized.     

常规棉花粉和转Cry1Ac+CpTI棉花粉对拟澳洲赤眼蜂繁殖和存活的影响

在室内评价了常规棉花粉和转Cry1Ac CpTI棉(Bt棉)花粉通过不同处理方式作为食物源对拟澳洲赤眼蜂Trichogrammaconfusum寿命、寄生卵数、子代羽化数和性比等繁殖和存活特征的影响。共设计7个饲喂处理,即不饲喂(UNFED)、水(W)、水 常规棉花粉(W P)、水 Bt棉花粉(W BtP)、10%蜂蜜水(H)、10%蜂蜜水 常规棉花粉(H P)和10%蜂蜜水 转Bt棉花粉(H BtP)。在提供或不提供米蛾Corcyracephalonica卵条件下,经W P或W BtP饲喂的雌蜂寿命与W或UNFED间无显著差异,但均显著短于H和H P或H BtP饲喂的雌蜂,而经H P或H BtP饲喂的雌蜂寿命又均显著长于经H饲喂的雌蜂(p<0.05)。比较每雌寄生卵数和子代羽化数来看,各处理明显分为3类,即UNFED、W、W P和W BtP为最低,H为居中,H P和H BtP为最高。比较每雌子代性比来看,各处理也明显分为3类,即H、H P和H BtP为最低,W P和W BtP为居中,UNFED和W为最高。饲喂W P和W BtP的雌蜂寿命、寄生卵粒数、子代羽化数和性比分别与W BtP和H BtP饲喂间无显著差异(p<0.05)。因而,棉花花粉需与蜂蜜组合才能成为拟澳洲赤眼蜂实现其最大存活和繁殖力的食物;Bt棉花粉对拟澳洲赤眼蜂无影响。     

Collection of Trichogramma Westwood (Hymenoptera: Trichogrammatidae) from tropical northern Australia: a survey of egg parasitoids for potential pest insect biological control in regions of proposed agricultural expansion

Abstract  Trichogramma limit pest damage to crops by killing the developing embryo of their insect host at the egg stage. Their impact on the potentially insecticide resistant species, Helicoverpa armigera (Hübner), is considered integral to the resistance management plan for transgenic cotton production in the Ord River Irrigation Area in northern Western Australia. The dominant species of egg parasitoid in Ord River Irrigation Area cotton crops is the introduced Trichogramma pretiosum (Riley). Surveys of similar northern Australian regions earmarked for agricultural expansion revealed that T. pretiosum has been introduced, or has adventitiously dispersed, to all developing agricultural regions of northern Australia. Several previously unsequenced species were collected during surveys in more pristine habitats. Trichogramma pretiosum demonstrates an apparent ability to supersede native Trichogramma species and is perhaps favoured by agricultural expansion.     

Oviposition Behaviour and Reproductive Performance of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) Reared in Artificial Diet

Biotypes of Trichogramma australicum were reared on artificial diet "A", Helicoverpa armigera (Hübner) (natural host) eggs and Sitotroga cerealella (Olivier) (factitious host) eggs. We evaluated the quality of these biotypes by comparing their oviposition behaviour and reproductive performance on H. armigera eggs. Female T. australicum reared in vitro accepted H. armigera eggs for oviposition and displayed similar behavioural components of oviposition to females reared on natural hosts. However, handling time during oviposition in H. armigera eggs by females from in vitro rearing was significantly longer than handling time of females reared on the natural host because the females needed a significantly longer time for host feeding. In vitro reared females produced significantly more progeny and parasitised more H. armigera eggs than the females reared on S. cerealella. Improvements to the artificial diet for T. australicum may reduce handling time of the in vitro reared females and increase the female population. These improvements may include changes in nutrient content and size of the artificial eggs.     

Do sympatric Trichogramma species parasitize the pest insect Helicoverpa armigera and the beneficial insect Chrysoperla carnea in different proportions?

Parasitism of two host species by five Trichogramma species (Hymenoptera, Trichogrammatidae) was studied in the laboratory. The host species were: i) the bollworm Helicoverpa armigera Hübner (Lepidoptera, Noctuidae), an important pest of many crops in the tropics and subtropics, and ii) one of its natural enemies, the lacewing Chrysoperla carnea Stephens (Neuroptera, Chrysopidae), a predator often used as a biological control agent. The proportion of H. armigera eggs parasitized from the total number of parasitized hosts differed between Trichogramma species. The average number of parasitized eggs per female in 24 h by Trichogramma pintoi and T. bourarachae was 10 of H. armigera and about 0.5 of C. carnea. For the other three Trichogramma species (T. cordubensis, T. evanescens and T. turkestanica) these averages varied from 6 to 11 H. armigera eggs and from 3 to 4 C. carnea eggs. Total adult offspring production, contacts with hosts, secondary clutch size and sex-ratio of each Trichogramma species were determined as well. The results show that sympatric Trichogramma may parasitize target and non-target species in different proportions. If this difference corresponds to the field situation, simple laboratory tests could be performed to select not only efficient biogical control agents, but also species which are the least detrimental to non-target hosts.     

Constraints on the use of Trichogramma Egg Parasitoids in Biological Control Programmes in India

The use of Trichogramma (Hymenoptera: Trichogrammatidae) egg parasitoids for the biological control of several insect pests, including the pod borer Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), is being promoted in India. Several companies supply these parasitoids to farmers, but no evaluation of product quality has been made. Low product quality is recognized as being one of the most important reasons for the failure of these biocontrol agents. In this study, Trichogramma chilonis Ishii egg-cards were obtained from eight producers in southern India. Product quality was evaluated using the following parameters: number of eggs/card, percentage parasitism, percentage emergence, progeny sex ratio and percentage of deformed females. In addition, producers were asked for the average values of these parameters in their production systems and for their recommendations for the use of T. chilonis to control H. armigera in cotton. The quality of the egg-cards was highly variable and was much lower than that stated by the producers. The recommended frequency and interval of releases, and the number of parasitoids to be released, differed greatly among producers. The low product quality results in up to 85% fewer parasitoids being released than is recommended by the producer. The effect of the low product quality and the highly variable release recommendations on applied biological control programmes is discussed. Suggestions for more effective use of Trichogramma spp. are given.     

Development of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) in Helicoverpa (Lepidoptera: Noctuidae) host eggs

Abstract Morphological studies of development of the egg parasitoid Trichogramma australicum Girault in the cotton bollworm, Helicoverpa armigera (Hübner), were conducted to provide benchmarks for assessing developmental rates in both natural hosts and artificial diets. Observations of living embryos and histological sections show that embryos proceed rapidly through cleavage and blastoderm formation and show a characteristic pinching or rotation 8 h after deposition. Eggs progressively increase in volume, primarily by increasing in diameter at the widest point. At 29 ± 1°C the duration of the egg stage is 22−24 h, the larval stage 27 h, the prepupal stage 50−52 h, and pupa 85 h. Larvae undergo dramatic shape changes as they ingest food but do not show signs of larval moults, reinforcing observations that there is only one larval instar. Criteria for staging the embryonic and postembryonic development in natural hosts will be used for future studies aimed at developing and refining artificial diets for Trichogramma.     

Structure of the gut contents of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) larvae fixed in situ in eggs of its host Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract Trichogramma australicum larvae develop most rapidly in younger eggs of its host, the pest lepidopteran Helicoverpa armigera . To establish how the developmental stage of the host affects the diet of T. australicum , larvae were fixed in situ in eggs of H. armigera of different ages and the structure of the egg contents and parasitoid gut contents examined histologically. Larvae feeding on newly laid host eggs contain primarily yolk particles in their gut, while larvae feeding on older hosts contain necrotic cells and yolk particles. The gut of T. australicum larvae does not contain organised tissue remnants, indicating that larvae feed primarily by sucking food into their pharynx and feed best on a mixture of particulate semisolids in a liquid matrix. Secretory structures of T. australicum larvae that could be involved in modifying the host environment were examined. The hindgut is modified to form an anal vesicle with a number of attributes suggesting that it may be a specialised secretory structure. The paired salivary glands open to the exterior via a common duct.     

Trichogramma egg parasitism of Helicoverpa armigera on pigeonpea and sorghum in southern India

Trichogramma spp. (Hymenoptera: Trichogrammatidae) only rarely parasitize eggs of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on pigeonpea (Cajanus cajan (L.) Millspaugh), while on other plants including sorghum (Sorghum bicolor (L.)) high parasitism levels of this host are found. In this study two strategies designed to increase the parasitoid activity on pigeonpea were tested in the field: intercropping pigeonpea with sorghum and mass-releasing T. chilonis Ishii. Neither strategy led to an increase in parasitism. On pigeonpea, H. armigera oviposited >74.8% of its eggs on calyxes and pods. Parasitism levels in host eggs collected from different plant structures varied significantly with 3.6, 0.3, and 40.7% of eggs on calyxes, pods, and leaves parasitized. Earlier studies have shown that calyxes and pods possess long glandular and non-glandular trichomes, and are covered by sticky trichome exudates which inhibit parasitoid searching behaviour. Parasitism levels between 27.9 and 100% were recorded from host eggs on the intercropped sorghum. Trichogramma chilonis was the dominant parasitoid species. The mean clutch size was 2.03, but up to six parasitoids emerged per egg. Progeny sex ratio (% females) decreased with clutch size, from 63.1% at a clutch size of one to 46.0% at a clutch size of five. Sticky trap catches showed that while the parasitoid population in sorghum increased when H. armigera started ovipositing, the population within pigeonpea did not benefit from either a high parasitoid population in sorghum or a high host egg density on pigeonpea. During one of five seasons studied, however, high parasitism levels (up to 73%) were recorded on pigeonpea. During this season, H. armigera oviposited on pigeonpea plants in the vegetative growth stage and a high proportion of eggs were collected from leaves. Parasitism levels were positively correlated with the percentage of eggs collected from leaves. This study shows that the parasitization efficiency of Trichogramma spp. on pigeonpea depends mainly on the location of the host eggs. This explains why parasitism levels of H. armigera eggs on pigeonpea did not increase when intercropped with sorghum or after mass-releasing T. chilonis.     

Effects of physiological condition and experience on oviposition behaviour of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) on eggs of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

We produced an ethogram for and investigated effects of physiological condition and experience on oviposition behaviour for Trichogramma australicum on Helicoverpa armigera eggs. The data, coupled with the ethogram, have enabled the establishment of standard behavioural categories which can be used to assess acceptability of H. armigera eggs to T. australicum reared in vitro or in eggs of other species. Physiological and experiential conditions were investigated using females of three different ages (0–24, 24–48 and 48–72 h old), two types of sexual states (mated and unmated) and two types of ovipositional experience (naive and experienced). Durations of host finding, host examination, and post-ovipositional re-examination were reduced by oviposition experience and were shorter in younger females (0–48 h old). Oviposition experience reduces the duration of the drilling and percentage of females host-feeding. Being mated and young reduces the host examination time in subsequent oviposition bouts. Only ovipositionally inexperienced females host-feed before oviposition and host-fed more frequently than experienced individuals after oviposition. Host-feeding needs consideration for optimal culture.     

Laboratory fecundity as predictor of field success in Trichogramma carverae (Hymenoptera: Trichogrammatidae)

Laboratory fecundity assessments are routinely used to determine the quality of commercially reared Trichogramma egg parasitoids before release for pest control, but there is little information on the relevance of this trait to the field success of Trichogramma. Herein, we characterize the parasitism success of strains of Trichogramma carverae Oatman & Pinto in the laboratory on a factitious (Sitotroga cerealella Olivier) and a natural (Epiphyas postvittana Walker) host. Differences in fecundity of the strains in the laboratory were consistent with a heritability of approximately 10%, allowing ranking of the strains from highest to lowest fecundity. The strains with particularly high and low fecundities were tested for successful parasitism in the field. Results of the field releases show that strain differences in laboratory fecundity did not influence field performance. The implications of this result for fecundity as a quality indicator for commercial stocks are discussed.     

Temperature-dependent Development of Four Egg Parasitoid Trichogramma Species (Hymenoptera: Trichogrammatidae)

Trichogramma species have been successfully utilized for biocontrol of several lepidopteran pests worldwide. The development, survival and progeny production of two Kenyan species' Trichogramma bournieri Pintureau & Babault and Trichogramma sp. nr. mwanzai Schulten & Feijen (collected from Kenya), Trichogramma evanescens Westwood (Germany) and Trichogramma chilonis Ishii (India) was studied at four constant temperatures (13, 18, 25 and 34°C) with the 011 aim of assessing the relative biotic potential of the two native species for 011 biocontrol of Helicoverpa armigera and Plutella xylostella in Kenya. The study was conducted at the Institute 011 for Biological Control (BBA), Darmstadt, Germany. The Trichogramma species tested showed variations 011 in fertility, developmental time, percent emergence, progeny production and sex ratio 011 at the four temperature regimes. Fertility decreased as temperature increased from 25 to 34°C. 011 T. chilonis and T. evanescens completed development at all temperatures tested, but T. 011 bournieri and T. sp. nr. mwanzai failed to complete development at 13°C. The developmental 011 period for all the species decreased as the temperature increased. The duration of development from 011 oviposition to adult emergence varied from 8 days to 12 weeks shorter at 34°C than at 011 13°C for T. chilonis and T. evanescens . For the various temperatures tested, a linear model was 011 satisfactory for egg to adult development at P = 0.05 for T. chilonis and T. evanescens . The 011 lower temperature thresholds for development and duration in degree-days were 8.83°C and 188 for 011 T. chilonis and 9.23°C and 192 for T. evanescens , respectively. For all temperatures tested, 011 T. sp. nr. mwanzai had the highest preimaginal survivorship. Adult emergence was lower at 13°C and 34°C than at 011 18 and 25°C. The highest fertility (mean ±SE) (50.37 ±2.32 adult 011 female -1 ) and progeny production (44.03 ±2.02 adult female -1 ) was recorded at 25°C for 011 T. evanescens . Sex ratio was biased towards female at all temperatures in T. bournieri and T. chilonis . 011 At all temperatures tested, T . sp. nr. mwanzai produced more males than females. For all species tested, 011 favourable parasitism was between 18 and 25°C. The results from this study will be useful for mass rearing purposes as well as for future field release programmes.     

A laboratory comparison of four Trichogramma species (Hymenoptera: Trichogrammatidae) as potential biocontrol agents for the carob moth,Ectomyelois ceratoniae (Lepidoptera: Pyralidae)

Four Trichogramma species were recovered in the field from eggs of carob moth, Ectomyelois ceratoniae (Lepidoptera: Pyralidae). The oviposition rates of Trichogramma oleae, Trichogramma cacoeciae, Trichogramma evanescens and Trichogramma bourarachae were compared when presented either E. ceratoniae or Ephestia kuehniella (Lepidoptera: Pyralidae). T. oleae and T. bourarachae did not parasitise either species of Lepidoptera.     

First report of parasitism of the Trichogramma bruni Nagaraja (Hymenoptera: Trichogrammatidae) in eggs of urbanus proteus (L.) (Lepidoptera: Hesperiidae) in snap beans (Phaseolus vulgaris) ( L.)

Aiming to verify the presence of eggs parasitoids of the genus Trichogramma, for using in the biological control of insects pests, were collected eggs from long tailed skipper butterfly, a lepidopteran defoliator of snap beans, which presented eggs with parasitism characteristics (dark eggs). The eggs were taken to the laboratory were 44.9% of parasitism was verified. Viability was 96.3%, with an average of 6.6 individuals per egg and a sexual ratio of 0.93. Male specimens were identified as Trichogramma bruni Nagaraja. It is the first report of parasitism in this host and culture.     

Naturally occurring egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) in a pomegranate orchard in Tunisia

Four Trichogramma species were found in a pomegranate orchard in Gabès, an arid region of Tunisia, from parasitized eggs of Ectomyelois ceratoniae Zeller (Lepidoptera: Pyralidae), an economically important insect pest. Identification based on assessment of male genitalia and internal transcribed spacer 2 ( ITS 2) sequences showed that they were T. bourarachae Pintureau and Babault, 1988, T. oleae Voegelé and Pointel, 1979, T. cacoeciae Marchal, 1927 and T. evanescens Westwood, 1833. Trichogramma evanescens is reported for the first time in Tunisia. Trichogramma cacoeciae was the largely dominant species in the analyzed samples, whereas T. bourarachae was present in a minor portion of 1.38%. The implications of these results for attempts at controlling E. ceratoniae are discussed.     

M-PCR： a powerful method for rapid molecular identification of Trichogramma wasps （Hymenoptera： Trichogrammatidae）

Two species-specific primers were designed depending on ITS2 sequence variation of 37 Trichogramma wasps, and these primers were applied to establish an assay,multiplex PCR (M-PCR), for molecular diagnosis of two important Trichogramma wasps,T. confusum and T. dendrolimi, in China. Multiplex-PCR results showed that only target species produced two PCR products, one product of ITS2 region species-specific amplification and one product of its ITS 1 region universal amplification, but other species produced only one ITS1 universal PCR product. Using this method, the target Trichogramma species can be distinguished from other Trichogramma species. Molecular identification based on M-PCR has particular value over morphological technology and other approaches, such as normal molecular and biochemical methods. Furthermore, because M-PCR assay can avoid false negative results, which frequently happen in PCR reaction, this method will be much more accurate and useful for Trichogramma identification, and can be developed as an easy and rapid diagnostic kit applied in the identification and quality monitoring of Trichogramma mass products both in the factory and in the field. Such an easy and rapid diagnostic kit will be valuable in the application of Trichogramma species as a biological control.     

The effect of temperature and humidity on the bionomics of six African egg parasitoids (Hymenoptera: Trichogrammatidae)

The life table statistics of six native Kenyan species/strains of Trichogramma and Trichogrammatoidea were established using a factitious host Corcyra cephalonica, Stainton (Lepidoptera: Pyralidae), at eight different temperatures (10, 15, 20, 25, 28, 30, 32 and 35 degrees C) and two humidity levels (40-50 and 70-80%). The objective was to select insects with superior attributes for augmentative release against lepidopteran pests in horticultural crops. Both temperature and humidity affected developmental time and life table parameters of the parasitoids but temperature played a more critical role. Developmental time was inversely related to temperature. The intrinsic and finite rates of increase increased with temperature up to 30 degrees C. Both net reproduction rate and intrinsic rate of increase were higher at the lower humidity. Temperature inversely affected generation time of parasitoid strains regardless of the relative humidity. Two strains of Trichogramma sp. nr. mwanzai collected from both low and medium altitudes and Trichogrammatoidea sp. nr. lutea from the mid-altitudes, were better adapted to both low and high temperatures than the other strains, as indicated by the high intrinsic and net reproductive rates, at both humidity levels. These three strains appear to be promising candidates for augmentation biocontrol against the African bollworm Helicoverpa armigera in Kenya.     

Using COI gene sequence to barcode two morphologically alike species: the cotton bollworm and the oriental tobacco budworm (Lepidoptera: Noctuidae)

Due to limited morphological difference, the two closely related sister species, the cotton bollworm, Helicoverpa armigera (Hübner) and the oriental tobacco budworm, H. assulta (Guenée) (Lepidoptera: Noctuidae), are very difficult to distinguish, especially at the larvae stage. Recently, DNA sequence has been widely used as a bio-barcode for species identification. In this study, we attempted to distinguish H. armigera and H. assulta using the mitochondrial cytochrome C oxidase subunit I gene (COI) gene sequence as the barcode. We determined a 658 bp segment of the COI gene for 28 individuals of H. armigera, 8 individuals of H. assulta, and 10 individuals of Mamestra brassicae (as the outgroup) in Yunnan Province, southwest of P. R. China, together with one H. assulta and two H. armigera reported sequences from GenBank. Twenty-three haplotypes were identified in all 49 samples. As expected, network analysis of the haplotypes of the three species presented a clustering pattern consistent with the respective species status. Haplotypes of the same species differed from each other by no more than three nucleotide substitutions. However, each haplotype of H. armigera differed from that of H. assulta by at least 22 nucleotide substitutions. Both species differed from M. brassicae by more than 50 nucleotide substitutions. 17 unique diagnostic nucleotides were also used to discriminate the two species. The finding of large COI sequence differences between H. armigera and H. assulta suggested that it could be used to distinguish the two morphologically alike species and be employed for quick species identification during pest control.     

Rapid antibody-based field test to distinguish between Helicoverpa armigera (Lepidoptera: Noctuidae) and Helicoverpa punctigera (Lepidoptera: Noctuidae)

Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) are the two most important insect pests of cotton production in Australia and require application of insecticides to control them. H. armigera has developed resistance to several insecticides but H. punctigera has not. Cost-effective management of insecticide resistance requires that growers be able to determine the proportion of H. armigera eggs or young larvae present on their crop before applying insecticides. This is impossible visually. We generated two monoclonal antibodies that reacted with the insect protein "lipophorin" and were capable of discriminating individuals of the two species at all life-stages. The antibodies were incorporated into a rapid test kit that was tested under field conditions over two growing seasons. Results obtained with the kit agreed closely with those obtained by rearing larvae through to second instar.     

Wolbachia在玉米螟赤眼蜂内的三重感染

Wolbachia是一类广泛存在于节肢动物体内的共生菌。玉米螟赤眼蜂Trichogramma ostriniae是我国玉米田间的优势赤眼蜂种, 据报道, 赤眼蜂种内有Wolbachia感染。本文利用Wolbachia的16s rDNA和wsp基因引物通过PCR方法对玉米螟赤眼蜂的野生种群进行了调查, 发现以wsp基因为鉴定依据, 检测的所有个体都感染了3种Wolbachia ［wOstGDAa (GenBank accession no. EU157103), wOstGDAb (GenBank accession no. EU157104) 和 wOstGDB (GenBank accession no. EU157105)］。本文首次报道了野生赤眼蜂种群内Wolbachia的三重感染率几乎为100%。根据本研究的结果, 可以推测当不同种赤眼蜂寄生同一寄主时, Wolbachia可能会在不同赤眼蜂种间进行横向传播。