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Title:	Effect of Nosema sp. on the reproductive biology, histopathology, host plant preference of Plutella xylostella and on parasitism rate of its parasitoid, Cotesia vestalis
Authors:	Kermani Nadia Mohamed (P48197)
Supervisor:	Idris Abd Ghani, Prof. Dr.
Keywords:	Microsporidium Nosema Parasitoid Nosema.
Issue Date:	18-Jun-2015
Description:	The effects of the microsporidium, Nosema sp on the reproductive biology, histopathology and oviposition behavior of diamondback moth (DBM) Plutella xylostella L. (Lepidoptera: Plutellidae) were investigated before incorporate it in IPM. The effectiveness of Nosema sp. as an important pathogen of DBM can be influenced by various factors, particularly temperature. To investigate the effect of temperature on NB infection of DBM larvae, second-instar larvae was infected with five different spore concentrations at 15°, 20°, 25°, 30° and 35°C and RH of 65% and light dark cycle (L:D) of 12:12. Larval mortality was recorded at every 24 h intervals until the larvae died or pupated. Results showed that the spore concentrations had a significant negative effect (P < 0.05) on larval survival at all temperatures and more pronounced (92% mortality) at 35°C. Histological observations showed that Nosema preferentially infected the adipose tissue and epithelial cells of the midgut, resulting in marked vacuolization of the cytoplasm suggesting that Nosema damaged the midgut epithelial cell. Four hosts were selected to examine adult oviposition preference for both untreated and Nosema-infected DBM. The host plants were leaves of Brassica juncea, B. chinensis, B. oleracea and B. rapa. The DBM performance (larvae hatched, pupae developed, adults emerged and developmental time for each stage) parameters were also conducted using mean values for each host plant and the results showed that it varied between plants. For untreated DBM, rape plants were the most preferred for oviposition, and more eggs were laid by DBM on rape than either green mustard or pak choi while oviposition was lowest on cabbage. However, the infected-DBM exhibited no significant difference in egg laying preference between rape, green mustard and pak choi with low number of egg laid, irrespective of host plants. Interestingly, Nosema-infected DBM adults showed an unattractive egg laying behaviour on cabbage. The interactions between pathogens and the parasitoids and/or predators may affect their roles in regulating host population and in this case is the DBM. Parasitism rate of Cotesia vestalis (CV) (Haliday) (Hym., Braconidae), one of the major parasitoid of DBM, on Nosema-infected DBM could indirectly inflict a negative influence on the CV role in management of DBM in Malaysia. Effects of DBM infected with different NB spore concentrations on the percentages of parasitism of FI CV and their F2 progeny was studied. Results showed that CV had higher parasitism rate on non-infected than on Nosema-infected DBM larvae. In Nosema-infected DBM, the CV had smaller pupal size, decreased percent emergence and fecundity, prolonged development period and negatively affecting its morphometrics compared to the control. In conclusion, results of this study revealed that the Nosema might not be suitable to be integrated with parasitoids such as CV in DBM management programs. However, detailing field study need to be conducted to get definite answers whether or not Nosema could be used along with the parasitoid in an integrated DBM management,Kesan mikrosporaadia, Nosema sp. terhadap biologi pembiakan, hispatologi dan kelakuan oviposisi rama-rama belakang intan (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae) dikaji sebelum digunakan dalam pengurusan perosak bersepadu (PPB). Keberkesanan Nosema sebagai patogen yang penting bagi DBM boleh dipengaruhi oleh pelbagai faktor, terutamanya suhu. Kesan suhu terhadap infeksi Nosema pada larva DBM dikaji dengan menggunakan larva DBM instar kedua yang dijangkiti dengan lima kepekatan spora Nosema sp. yang berbeza pada suhu 15°, 20°, 25°, 30° dan 35°C pada kelembapan relatif 65% dan kitaran terang-gelap (T:G) 12:12. Kematian larva yang direkod pada setiap 24 jam sela masa sehingga ia mati atau menjadi pupa menunjukkan bahawa kepekatan spora memberi kesan negatif yang signifikan (P < 0.05) kepada kemandirian larva pada semua suhu dengan kesan ketara (92% kematian) pada 35°C. Pemerhatian secara histologi menunjukkan bahawa Nosema menjangkiti terutamanya tisu adipos dan sel epitelium usus tengah yang menyebabkan pemvakulan bertanda pada sitoplasma dan ini menunjukkan bahawa Nosema merosakkan sel epitelium usus tengah. Untuk ujian oviposit memilih bagi kedua-dua larva DBM kawalan dan dirawat, empat tumbuhan perumah telah diguna iaitu sawi, Brassica juncea, sawi putih, B. chinensis, kubis, B. oleracea dan pak choi, B. rapa. Nilai min bagi parameter prestasi DBM (kemunculan larva, penghasilan pupa, kemunculan dewasa dan tempoh perkembangan setiap peringkat) didapati berbeza pada tanaman perumah yang berbeza. Bagi DBM yang tidak dirawat, sawi menjadi pilihan utama bagi oviposisi apabila lebih banyak telur dihasilkan berbanding pada sawi putih dan pak choi. Oviposisi paling rendah adalah pada kubis. Walau bagaimanapun, DBM yang dijangkiti tidak menunjukkan perbezaan yang signifikan dalam pemilihan oviposisi antara sawi, sawi putih dan pak choi disamping penghasilan telur yang sedikit. Menariknya, DBM dewasa yang dijangkiti Nosema kurang menunjukkan perlakuan bertelur pada kubis. Hubungan di antara pathogen dan parasitoid dan/atau pemangsa dapat mempengaruhi peranan masing-masing dalam mengawal populasi perumah, DBM. Kadar parasitisme Cotesia vestalis (Haliday) (Hym., Braconidae), salah satu parasitoid utama DBM, pada DBM yang dijangkiti Nosema mungkin memberi kesan negatif secara tidak langsung kepada peranannya dalam pengurusan DBM di Malaysia. Kesan DBM yang dijangkiti kepekatan spora Nosema sp. yang berbeza terhadap peratusan parasitisme progeni F1 dan F2 C. vestalis dikaji. Keputusan ujian tanpa pilihan menunjukkan bahawa kadar parasitisme adalah lebih tinggi pada larva DBM yang tidak dijangkiti Nosema. Cotesia vestalis daripada DBM yang dijangkiti Nosema menunjukkan saiz pupa yang lebih kecil, peratusan kemunculan dan kesuburan yang rendah, tempoh perkembangan yang lebih panjang selain wujud kesan negatif dari segi morfometrik berbanding kawalan. Kesimpulannya, kajian ini menunjukkan bahawa Nosema mungkin tidak sesuai untuk diintegrasikan bersama parasitoid seperti C. vestalis dalam program pengawalan DBM. Namun kajian seterusnya di ladang akan membantu memberi keputusan yang lebih tepat dan jitu samada Nosema boleh diguna bersama dengan parasitoid atau pemangsa DBM dalam sistem pengurusan DBM bersepadu.,Ph.D
Pages:	185
Call Number:	QL368.M5 K446 2015
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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