Search

Housefly, Musca domestica is used as an alternate host to rear a eulophid, Nesolynx thymus (Girault), a pupal parasitoid of the tachinid fly, Exorista bombyci s (Louis) which in turn is an endolarval parasitoid of Bombyx mo ri (L.). An attempt was made to evaluate the host factors like pupal size, age and exposure periods of N. thymus for developing robust mass multiplication methods. The host size had significant effect on mean parasitism by N. thymus . Mated females of N. thymus when exposed to host pupae of varying size, revealed that mean per cent parasitisation was significantly higher (74%) in large sized pupae having a volume of 263.89 mm3. Regarding host age, 24 - 48 h old host pupae had higher level of parasitism (65%) by N. thymus . The parasitism rate declined with an increase in host age after 72 h. In field evaluation, release of N. thymus at weekly interval resulted in the reduction of housefly population as evinced from the higher parasitism (56 %) of the sentinel cards placed in the treated poultry sheds. The information on host factors generated will help to enhance the mass multiplication of parasitoid for the release of which would aid to bring down the M. domestica population in poultry and dairy units.

The present study was conducted to collect and identify the species of trichogrammatids from eggs of lepidopteran pests infesting the diverse cropping systems in the country. A total of 28 plant species were inspected for the collection of lepidopteran eggs either through collection of insect eggs or by placing sentinel egg cards. The species such as Trichogramma chilonis Ishii, T. achaeae Nagaraja and Nagarkatti, T. danausicida Nagaraja, Trichogrammatoidea bactrae Nagaraja and Tr. armigera Manjunath were recorded naturally occurring with 12 species of lepidopteran insect pests. In nature, the parasitism rate varied from 5.35 to 82.25% by the associated trichogrammatids. A total of 596 sentinel trap cards were placed in the agricultural, vegetables, fruits crops, and grasses on the bunds of fields to trap the egg parasitoids present in the different habitat. Through sentinel cards, three species, viz. , T. chilonis , T. achaeae and Tr. bactrae were found inhabit the vegetables and ornamental crops. The percentage of adult emergence from the sentinel trap cards ranged from 70.59 to 100.0%. Natural parasitism of Tr. bactrae recorded for the first time on the eggs of Lampides boeticus L. infesting wild species of Crotalaria . In addition, the natural parasitism of Tr. armigera and Tr. bactrae on the eggs of L. boeticus laid on either cultivated or wild relatives of Crotalaria in undisturbed habitat had higher natural parasitism due to their bright yellow flower attracts parasitoids to parasitize the eggs and conserve these egg parasitoids. Recently, natural parasitism of Trichogramma sp. was recorded on invasive fall armyworm, Spodoptera frugiperda (J.E. Smith) infesting maize in Karnataka. Based on the present work, there could be choice of selecting right species which occur naturally on individual crops.

A field trial was conducted in a farmer’s field by integrating biocontrol agents, a multiple insecticide tolerant strain (MITs), Trichogramma chilonis and formulation of Bacillus thuringiensis (NBAIR BtG4) with reduced insecticidal spray as a biocontrol-based IPM compared to insecticidal application as a farmer’s practice, for the management of the diamondback moth (DBM), Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) infesting cabbage. Six T. chilonis releases of 100,000 parasitized eggs ha− 1 were applied. Along with parasitoid release, a liquid formulation of B. thuringiensis (2%) was applied after third and fifth releases of T. chilonis. The number of P. xylostella larvae were significantly reduced in the field treated with biocontrol-based IPM as compared to farmer’s practice after 30 and 45 days after treatment. After the 45 days, the holes on cabbage leaves were 2.2/plant in the field treated with biocontrol, opposed to 8.0 holes per plant were recorded in the farmer’s practice filed. Only 7% of cabbage head damage was recorded in the field treated with biocontrol, whereas, in farmer’s practice field, those were 32.2%. The cost-benefit analysis showed that integrating these biological control agents along with a reduced number of insecticidal sprays could reduce DBM population and percent head damage with an eventual increase in the yield.

Trichogrammatids (Hymenoptera: Trichogrammatidae) are the most important egg parasitoids widely used in different biocontrol programs worldwide. Since there are several species, strains, and ecotypes available, correct identification is the first step for successful biological control programs. Morphological identification remains complex due to subtle difference in male genetalia, therefore alternative molecular techniques were employed for rapid and reliable identification of this group of parasitoids. Furthermore, many of the field collected specimens are females, which are not identifiable using morphological keys. This study was carried out to unravel the discrimination success in the two molecular marker loci cytochrome oxidase I (COI) and internal transcribed spacer-2 (ITS-2) region of trichogrammatids. In achieving these objectives, the single specimen of 22 trichogrammatids belonging to 19 species were subjected to DNA extraction, PCR amplification, and sequencing. Additionally, we obtained homologous sequences from GenBank and sequences in BOLD database to understand internal relationships between the trichogrammatids. Bayesian inference phylogenetic analysis conducted with 84 and 76 sequences of COI and ITS-2 loci respectively and studied discrimination among the different species. Based on trees in comparison, we observed that there was a total of 10 and 6 out of 19 species correctly discriminate with COI and ITS-2 respectively. Our result revealed that the ITS-2 gene was less divergent than the COI gene in the majority of species and failed to differentiate all terminal clades. Therefore, we recommend that COI is suitable as the primary DNA barcode locus in trichogrammatids. Overall, we suggest that COI gene has higher discrimination power and can be considered as an appropriate molecular marker for species identification in trichogrammatids.

BACKGROUND: Genetically engineered corn (Bt corn) expressing Bacillus thuringiensis Berliner insecticidal protein Cry1Ab is a biotechnological option being considered for management of lepidopteran corn pests in India. As a resistance management practice it was essential to determine the sensitivity of multiple populations of the stalk borer Chilo partellus (Swinhoe), pink borer Sesamia inferens (Walker) and the cob borer Helicoverpa armigera (Hubner) to Cry1Ab protein through bioassays. The insect populations were collected during growing seasons of Rabi 2005 (October 2005 to February 2006) and Kharif 2006 (May to September 2006). RESULTS: Multiple populations of the three lepidopteran corn pests were found to be susceptible to Cry1Ab. Median lethal concentrations (LC50) ranged between 0.008 and 0.068 µg Cry1Ab mL−1 diet for 18 populations of C. partellus (across two seasons), between 0.12 and 1.99 µg mL−1 for seven populations of H. armigera and between 0.46 and 0.56 µg mL−1 for two populations of S. inferens. CONCLUSION: Dose–response concentrations for lethality and growth inhibition have been determined to mark baseline sensitivity of multiple populations of key lepidopteran corn pests in India to Cry1Ab protein. These benchmark values will be referenced while monitoring resistance to Cry1Ab should Bt corn hybrids expressing Cry1Ab be approved for commercial cultivation in India. Copyright © 2010 Society of Chemical Industry

Host-insect and host-plant associated differentiation of genetically divergent microbiota were recorded from economically important egg parasitoid collected from 26 locations in India, Trichogramma chilonis constituted 86.8% of the populations collected. It was recorded from 14 host-insects, 14 different crops and weed plants from 12 states. Nine species of yeast were recorded from parasitoid from 5 host-insects with Wickerhamomyces anamalus was isolated from 36.4% samples and highest numbers were recorded from parasitoid collected on sugarcane. Bacillus cereus, Pseudomonas sp. and Stenotrophomonas maltophilia from T. chilonis constitute 64.3% of bacterial diversity based on their 16S rDNA sequences. For taxonomic identification using 16s rDNA and ITS sequences, we performed taxonomic classification of total 33 ITS isolates against UNITE Fungal ITS database and assigned taxonomy hierarchy to the sequences. Also, a total of 13 isolates 16s rDNA sequences were taxonomically assigned against RDP 16s rDNA database using RDP Naive Bayesian rRNA Classifier Version 2.1. Most of the species are correctly identified in the respective species members with high confidence threshold value support.

ITS-2-RFLP method was employed to distinguish 12 different trichogrammatids consisting of indigenous and exotic species such as Trichogrammatoidea armigera and Tr. bactrae , Trichogramma achaeae , T. chilonis , T. japonicum , T. embryophagum , T. pretiosum (Thelytokous Form—TF), T. brassicae , T. dendrolimi , T. evanescens and T. mwanzai . ITS-2 region was amplified; complete ITS-2 sequences of nine species were deposited in Genbank. The size of the amplified product ranged from 500 to 900 bp. Restriction enzyme digestion of ITS-2 region showed different banding profiles for these 12 species. Dichotomous keys using the size of the ITS-2 product and the restriction fragment length polymorphism for the enzymes (EcoRI, MseI, MvaI, and TaqI) allowed quick species identification of these trichogrammatids.

The eggs of the factitious host insect, Corcyra cephalonica (Stainton), are used for production of several natural enemies in many countries across the world. Trichogramma spp. are used widely for the biological control of lepidopterous pests on various crops in more than 30 countries covering a total area of 3.2 million ha of agricultural and forest land. A novel and simple technique for storage of eggs of C. cephalonica by vacuum packing at 500 Hg−1 and stored at 8 ± 1 °C in refrigerator was developed to enhance egg viability for production of Trichogramma species, and assessed and compared with the traditional method. The percent parasitism of vacuum packed eggs was 100.0–75.0% after storing for 7–42 days and declined to 10.0% after 70 days storage compared to 100.0, 50.0, 40.0 and 5.0% parasitism after 7, 14, 21 and 28 days, respectively, in the traditional method. The percent emergence from parasitized eggs was identical in both vacuum and non-vacuum packed eggs indicating suitability of vacuum packing eggs. The percent females ranged 50.0–59.0% in vacuum-packed eggs and 48.4–55.8% in non-vacuum packed eggs. Vacuum packing enhanced storability of C. cephalonica eggs by 3- to 4-fold as compared to the traditional method of storage.