Abstract
Ascoviruses are double-stranded DNA viruses that are pathogenic to lepidopteran hosts, particularly noctuid larvae. Infection of a larva is characterized by retarded growth, reduced feeding and yellowish body color. In this paper, we reported the growth and development of three major agricultural noctuid insect pests, Helicoverpa armigera (Hübner), Spodoptera exigua (Hübner) and Spodoptera litura (Fabricius), infected with Heliothis virescens ascovirus 3h (HvAV-3h). Using 10-fold serial dilutions (0 to 7) of HvAV-3h-containing hemolymph to infect S. litura larvae, we found no significant difference in larval mortalities from 0 to 103-fold dilutions; however, significant differences were observed at 104-fold dilution and above. Using a 10-fold dilution of HvAV-3h-containing hemolymph to infect H. armigera, S. exigua and S. litura larvae, we found that the growth and development were significantly affected. All infected larvae could not pupate; the survival times of treated H. armigera, S. litura and S. exigua larvae were significantly longer than untreated control larvae. Body weight showed significant difference between treated and untreated control group from day 1 after inoculation in H. armigera and S. exigua, but day 2 in S. litura. Additionally, food intake also showed significant difference between treated and untreated control group from day 2 after inoculation in H. armigera and S. litura, but day 3 in S. exigua.
Highlights
Ascoviruses (AVs), belonging to the family of Ascoviridae, are recently discovered insect-specific viruses with a circular double-stranded DNA genome of 100-199 kbp [1,2,3]
The S. exigua eggs were kindly provided by Dr Yue-Qin Song of Henan University of Science and Technology, the H. armigera larvae were donated by Dr Zhu-Dong Liu of Chinese Academy of Sciences, and the S. litura larvae were collected from a vegetable field near Hunan Agricultural University, Changsha, China
Heliothis virescens ascovirus 3h (HvAV-3h) titration Undiluted HvAV-3h-containing hemolymph did not result in PCR amplification, where 101- and 102-fold dilution showed discernible PCR bands (Figure 1B)
Summary
Ascoviruses (AVs), belonging to the family of Ascoviridae, are recently discovered insect-specific viruses with a circular double-stranded DNA genome of 100-199 kbp [1,2,3] These viruses were first isolated from lepidopteran larvae in the late 1970s [4] and named in the early 1980s [5,6,7]. Once in a laboratory condition, larvae infected by ascovirus are easier to recognize through checking the hemolymph that is milky-white in color, which is opposite to the transparent hemolymph in healthy larvae [7,8]. This infection symptom in larvae is distinguishable from other viruses, such as baculovirus. The virion shape and the hemolymph vesicles aid in ascovirus identification [14]
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