Effects Of Cotesia Plutellae Polydnaviruses On The Development And Immune System Of The Host Plutella Xylostella Larvae

The host (Plutella xylostella L.) -- parasitoid (Cotesia plutellae) system was used to evaluate the effects of Cotesia plutellae polydnaviruses (CpBV) on the larval development and immune system of the host Plutella xylostella in this study. Effects of pseudoparasitism on the development of host larvaeWe found that there were some different effects between on the early 3th (one-day old) and later 4th (three-day old) instar larvae of Plutella xylostella after pseudoparasitized by Cotesia plutellae. The weight of later 4th instar host larvae after pseudoparasitized increased more slowly than that of the early 3th instar. All of the pseudoparasitized 3th instar host larvae could not span their cocoons while there were 85% of the pseudoparasitized 4th instar larvae could span their cocoons. The 3th instar host larvae pseudoparasitized by the parasitoid were more easily affected by other viruses than those pseudoparasitized 4th instar larvae. Microscopy examinations revealed that the spermary of 3th and 4th instar host larvae were both suppressed in volume growth, and their color both became lighter, but spermary of 4th instar host larvae was more severely affected. Midguts of both the early 3th and later 4th instar larvae were decomposed after pseudoparasitism, and some of them were tinged with red spots, and furthermore, the midguts of early 3th instar larvae of Plutella xylostella are more likely to be marked with red spots than those of later 4th instar larvae.Effects of Cotesia plutellae polydnaviruses on partial tissues of the host Plutella xylostella larvaeMicroinjection and microscopy examination revealed that CpBVs affect the development of larval tissues, such as spermary, prothoracic gland and mid-gut. After infected by CpBVs, the spermary was suppressed in volume growth and eventually partially decomposed, its color became lighter gradually until transparent at the final stage;the prothoracic gland shrank after infected by CpBVs in 12 h;the midgut was also stunted, and decomposed, its color was changed from green (normal) to yellow;some red spots appeared on midgut of 20% individuals, and trachea on midgut shrank at the same time. SDS-PAGE analyses showed that there were a number of proteins in normal spermary, prothoracic gland and mid-gut: nearly 20 protein bands from spermary with the 78.8 kDa band most clear and 66.2, 43.4, 34.83, 30.0 and 28.58 kDa protein bands relatively clear;more than 10 protein bands from midgut with 63.7 kDa band most clear and 79.39, 54.7, 41.1, 30.7 and 28.9 kDa protein bands relatively clear;also more than 10 protein bands from prothoracic gland with 81.2 and 55.76kDa proteinbands relatively clear. After infected by CpBVs, the numbers of proteins in above three tissues decreased significantly, especially for spermary only one band visible;all bands almost became paler distinctly, suggesting that the concentration of proteins also decreased after infected by CpBVs, but.one band (81.2 kDa) from prothoracic gland was more clear than that from normal one, suggesting that its concentration increased after CpBV infection. The bioassay indicated that the esterase activity in midgut declined distinctly after infected by CpBVs.Effects of Cotesia plutellae polydnaviruses on immune system of host Plutella xylostella larvaeCpBVs were injected into Plutella xylostella larvae in order to evaluate the effects of CpBVs on the host immune system. SDS-PAGE analyses showed that there were only a few protein bands presented for the haemolymph injected with CpBVs in 18h while there were more than 20 protein bands visible for haemolymph injected with CpBVs in 5d, and after that the number of protein bands started to decrease. The encapsulations of haemocytes were totally inhibited until 30h after injection with CpBVs. The activity of PO started to reduce when the host haemolymph was injected with CpBVs in 18h, but resumed in 150h. The melanization of the host haemolymph started to be partially inhibited when the host haemolymph was injected with CpBVs in 18h, but totally inhibited in 72h. Effects of parasitism by Cotesia plutellae on the immune system and development of habitual and non-habitual hostsThree larval lepidopteran species were used in this study to test the effects of parasitism by Cotesia plutellae on the immune response of the habitual and non-habitual hosts. Here we demonstrate that although C. plutellae could parasitize the larvae of P. xylostella, Spodoptera litura and Pieris rapae, but the parasitoid could only develope well in P. xylostella larvae. The results showed that the effects of parasitism on non-habitual hosts were less than those of habitual host. The growth and development of P. xylostella, and the encapsulations of its haemocytes and the melanization of its haemolymph were inhibited after parasitized by C. plutellae whereas there was almost no effect on the growth and deveopment or on immune response of S. litura larvae after parasitism, indicating that the parasitoid-associated factors (such as CpBVs and venom) of C. plutellae could hardly affect thenon-habitual host, S. litura. In contrast, P. rapae (one species is further from P. xylostella in taxonomic relatedness as compared with 5". litura) showed some limied immune response to the parasitism of C. plutellae in the first 2-3 days. The encapsulations of haemocytes and the melanization of haemolymph of P. rapae larvae were inhibited. However, after 2-3d all of these effectsdisappeared while the effects of parasitism on the growth and development still retianed, showing half of Pieris rapae larvae could not pupate.