| Based on the study on the effect of Microplitis pallidipes (Szepligeti) on host selectivity of Spodoptera exigua Hiibner and Prodenia litura (Fabriciu), quadratic regression rotating combination design was adopted to study the combined effects of temperature and photoperiod on parasitic rate and sex ratio of M. pallidipes, and to confirm the effect of different density of parasitoids, the age of parasitoids and host diet on the parasitism of M. pallidipes, the effect of extra-nutrition and temperature on the longevity of parasitoids, and further the changes of the growth and development of host, biochemical metabolism as well as hostimmunity of host were determined after host was parasitized by M. pallidipes. This research results not only serve to strengthen the understanding of host-parasitoid interaction in theory, bot also provided paradigm and guide for mass reproduction of M. pallidipes as well as for field application. The main results are as follows:1. The effect of M. pallidipes on host selectivityBreeding host had apparent effect on host selectivity of M. pallidipes which has preference to attacking breeding host larvae; M. pallidipes was easier to search S. exigua and more liked to attack S. exigua whether the breeding host was S. exigua or P. litura, but there was no significant difference between the parasitic rates of S. exigua and P. litura, which indicated that both S. exigua and P. litura were suitable for breeding hosts.2. The effect of ecological factors on the parasitism of parasitoidsQuadratic regression rotating combination design was adopted to model the effects of temperature and photoperiod on the parasitic rate, cocoon rate, emergence rate and sex ratio of M. pallidipes. According to the simulating result, the optimal conditions for mass propagation was temperature28℃and photoperiod L:D=12h:12h.Ages of parastitoids, density of hosts and host plants conspicuously limited parasitic efficacy. As the increase of post-emergence, the activity of parasitoids decreased, parasitic rate was more lower, and the parasitoids of one-day, two-day, three-day and four-day age have the parasitic rate of83.890%,82.510%,76.984%and 66.327%respectively; when the ratios of parasitoids to hosts were1:30,1:40and1:50, the parasitic rates were63.892%,60.549%and81.311%respectively, which had no significant effect on sex ratio, and meanwhile the ratio1:50was most beneficial for parasitoids to parasitize host larvae; after feeding soybean, taro, cabbage, or green vegetable leaves, the parasitic rate was82.390%,75.810%,73.550%and66.390%respectively, and soybean leaves were the best host diet which sex ratio is0.449approaching the most ideal of0.5.3. the effect of extra-nutrition and temperature on the longevity of parasitoidsQuadratic regression model for the goal function of adult parasitoid longevity was constructed, which simulating results indicated that the effect of temperature on the longevity of adult parasitoids was greater than photoperiod; the adult longevity shortened as the increase of temperature, while increased as the increase of photoperiod. Among the18～38℃, the adult longevity shortened as the increase of temperature, but extra-nutrition and fresh water could significantly extended adult longevity; at18℃conditions of feeding10%honey water, the longest longevity of male and female was17.05d and15.44d respectively; at38℃conditions of not feeding any materials, the shortest longevity of male and female was1.70d and1.95d respectively.4. The effect of M. pallidipes on the growth and development of hostAfter S. exigua was parasitized by M. pallidipes, body length, body width and head capsule width and body weight of S. exigua were all significantly lower than that of controls, and at the late parasitic time, all the increasing rates of body weight of host larvae slowed down. When late second-to initial third-instar host larvae were parasitized, both the periods of third and fourth larvae periods were prolonged, but the host larvae could not continue to normally develop and meanwhile the parasitoids immediately died towards egression when the host larvae developed to the late fourth-instar.5. The effect of M. pallidipes on the host biochemical metabolismWithin the observation time (from the first to the fifth day) of S. exigua being parasitized, the lipids content in parasitized host larvae was constantly significantly higher than that of non-parasitized larvae (control), but the fat content in host larvae decreased gradually; the total carbohydrates free in the host hemolymph of parasitized larvae were significantly more than that in controls but the significant difference just occurred at the2nd and the5st day after host larvae was parasitized; the protein content in parasitized host larvae was all significantly lower than that in controls at the1st, the4th and the5th day after host larvae was parasitized, while there were no significant difference at any other observation time. The free amino acids in the host hemolymph of parasitized larvae were significantly more than that in controls, and threonine, cystine, glutamic acid and proline in the host hemolymph of parasitized larvae were also significantly more than that in controls.6.The effect of M. pallidipes on the host protective enzyme systemWithin the observation time (from the first to the fifth day) of S. exigua being parasitized, the activities of three protective enzymes (SOD、CAT、POD) in the host hemolymph of parasitized larvae were all higher than that of controls respectively, and the values of SOD in the host hemolymph of parasitized larvae from the1st to the5th day were0.41,0.47,0.58,0.82, and2.65U/mg respectively, the values of CAT were2.377,2.291,1.625,2.846, and3.842U/mg.min respectively, and the values of POD were2.377,3.618,3.077,5.236, and14.781U/mg.min respectively.7. The effect of M. pallidipes on host immune systemThe number of total hemocytes and granular cells in the host hemolymph of parasitized larvae were both less than those of controls; within the observation time (from the first to the sixth day) of S. exigua being parasitized, the number of plasmacytes first decreased then increased while granular cells gradually decreased in the host hemolymph of parasitized larvae, which change tendency was not identical to controls.The black change rate in the host hemolymph in controls reached to100%, while that in parasitized host larvae conspicuously decreased; with the increase of observation time, the black change rates gradually decreased which were all significantly lower than that in controls respectively at the2nd-to-5th day after host were parasitized.The change tendency of the activities of phenoloxidases in host hemolymph in treatments and controls was the same with the5days after host were parasitized; the activities of phenoloxidases in parasitized host hemolymph gradually increased from the1st to the3rd day after host were parasitized, but slightly decreased at the4th day and increased at the5th day; the values of the activities of phenoloxidases in host hemolymph in treatments from the1st to the5th day were all lower that in controls respectively, and there were the significant difference between the treatments and controls from the2nd to the5th day.At the1st-to-2nd day after host were parasitized, the activities of lysozyme in host hemolymph in treatments increased, but decreased at the3rd-5th day; the change tendency of the activities of lysozyme in host hemolymph between treatments and controls was a bit difference, the values of the activities of lysozyme in treatments were significantly higher than that in controls at the3rd-to-4th day after host were parasitized, but there were no significant difference at any other observation time between treatments and controls. |
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