PG Thesis

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Subject: search.filters.subject.Morphometrics

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    Biology and predatory potential of rhynocoris marginatus (FAB.) (hemiptera: reduviidae) on insect pests of cowpea
    (Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 2018) Femi Mohasina, M; Smitha, M S
    Insect pests form major threat to cowpea cultivation often causing a yield loss of 30 – 60 per cent. Even though insecticides are the most popular tools for pest management in cowpea their application throughout the crop period is not economically, socially and ecologically advisable. Biological control methods could be an option to reduce the insecticide load on the crop that is often constrained by lack of natural enemies that can effectively control several pests at a time. Members of the predatory family Reduviidae are gaining increased attention due to their broad host range as well as high density responsiveness. Rhynocoris marginatus belonging to the subfamily Harpactorinae of the family Reduviidae (Order: Hemiptera) has been found promising in managing a wide range of insect pests in various legume crop ecosystems. This predator reportedly has preference to lepidopteran caterpillars followed by nymphs and adults of hemipterans, two major insect groups regularly occurring in cowpea. In this context, the work on “Biology and predatory potential of Rhynocoris marginatus (Fab.) (Hemiptera: Reduviidae) on insect pests of cowpea” was carried out in the Department of Agricultural Entomology, College of Horticulture, Vellanikkara. The project aimed to study the biology and predatory potential of R. marginatus on leaf eating caterpillar of cowpea, Spodoptera litura (Fab.); to evaluate the predatory potential of R. marginatus on Aphis craccivora (Koch) and S. litura under caged condition and to study the field efficiency of R. marginatus against insect pests of cowpea. The egg stage recorded an average incubation period of 6.80 ± 0.91 days. It took 32.90 ± 1.81 days to complete nymphal development in five instars. Adult female lived longer than male. The preoviposition period was 14 ± 1.30 days and during the oviposition period of 66.13 ± 6.27 days, it laid 8.60 ± 0.97 batches of egg mass with mean fecundity of 377.20 ± 45.52 eggs. The predatory potential of second, third, fourth and fifth nymphal instars and adult were studied on third instar larvae of S. litura at prey densities, 2, 4, 6, 8 and 10 prey/ predator. Predation had strong correlation with the prey density and stage of the predator. When the number of prey killed by the predator was plotted against the prey density a Holling’s type II functional response curve was obtained. The predatory potential was also assessed against cowpea aphid, A. craccivora and leaf eating caterpillar, S. litura on caged cowpea plants. The third instar nymph of R. marginatus was released on cowpea plants in cages artificially infested with aphid and compared with control. Aphid population in predator released cages were significantly less than that in control. The predator was able to kill all the released third instar larvae of S. litura completely within four days. Field evaluation was carried out by releasing the predator at 30, 50 and 70 days after sowing of the crop. The release of the predator significantly reduced the aphid population on cowpea. The infestation by pod borer Maruca vitrata (Fab.) and pod bug, Riptortus pedestris (Fab.) were negligible. However, the number of pods damaged by pod bug was comparatively less in predator released field. At the same time, the predator had no impact on the population of coccinellid predators in the field.
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    Epilachna beetle complex in vegetables
    (Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1997) Sreekala, S; Ushakumari, R
    Studies on the epilachna beetle complex occuring on selected vegetable crops were carried out at the College of Horticulture, Kerala Agricultural University, Vellanikkara, Thrissur, Kerala during 1995-1997 to establish their taxonomic identities. The morphology, biology and the natural enemy association of these beetles were also studied. Based on the male and female genitalial characters, the epilachna beetles feeding on brinjal, bittergourd and cowpea were identified as Henosepilachna vigintioctopunctata (Fabricius), Henosepilachna septima (Dieke) and Afidenta misera (W eise) respectively. The salient features to distinguish between these three species are the curvature of the apex of sipho which is a part of the male genitalia and the shape of the female genital plates. The apex of sipho is curved outwards with a bluntly rounded tip in both H. vigintioctopunctata and A. misera, while it is curved inwards with a sharply pointed tip in H. septima. A semicircular notch is present on the female genital plates of H. vigintioctopunctata, while there is a slit like notch in H. septima. The notch on female genital plate is absent in A. misera. It was confirmed that the beetles are highly host specific. Henosepilachna vigintioctopunctata showed a strict host restriction to solanaceous plants, while H. septima and A. misera are restricted to a few cucurbitaceous and leguminous plants respectively. There was not much gross morphological variations between the species except for their body size, H. septima being the largest and A. misera the smallest. The different spot variants met within the species by the variations in elytral maculation was found to be a morphological character only. Though the grubs of the three species are similar in external appearance, they can be easily distinguished by the structure and sclerotisation of the scoli on body surface and the details have been discussed. The three species showed similar biological attributes with a life cycle period of 25.25, 2l. 59 and 24.76 days for H. vigintioctopunctata, H. septima and A. misera respectively at 27.6°C and 89.5 per cent relative humidity. Under . field conditions, the grubs and pupae of the three species were parasited by Pediobius foveolatus (Crawford) (Eulophidae:Hymenoptera) and the egg masses were parasitised by Tetrastichus ovu/orum Ferriere (Eulophidae:Hymenoptera).