Characterization and Growing Development of Spodoptera exigua (Lepidoptera: Noctuidae) Larvae Infected by Heliothis virescens ascovirus 3h (HvAV-3h).

Abstract

Spodoptera exigua (Hübner) is a very serious worldwide pest capable of causing severe economic losses in numerous agricultural crops. The need for an effective, highly virulent, pathogenic microorganism for use as a biological control agent against S. exigua larvae is particularly important. Heliothis virescens ascovirus 3 h (HvAV-3h)-containing hemolymph with a titer of 9.58 × 10(12) genome copies per ml was used to inoculate S. exigua larvae per os with a 1.06 × 10(10) dosage per larva for the first- to second instar and 9.58 × 10(9) genome copies per larva for the third- to fifth instars. Intrahemocoelic injections were also used with a dosage of 1.53 × 10(9) genome copies per larva for third- to fifth instar. The postinjection mortality, body weight, and food intake of the S. exigua larvae were observed and recorded. The corrected mortality rates for the first- through fifth instar inoculated per os were 21.88 ± 0.98, 22.22 ± 4.00, 8.89 ± 4.01, 6.66 ± 3.33, and 8.89 ± 2.94%, respectively. The early instars were significantly easier to infect with virus compared to the later instar. The corrected mortality of the third, fourth, and fifth instars inoculated by injection was 96.58 ± 3.42, 98.83 ± 1.17, and 97.78 ± 2.22%, respectively. Compared to the healthy larval population, survival time of the diseased larval population was considerably extended. In addition, food intake was greatly reduced, and the body weight remained fairly constant in the third- and fourth instar. The body weight declined in the fifth instar corresponding to a reduction in food intake.