Effect of larval density on growth, development and reproduction of potato tuber moth, Phthorimaea operculella
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Key Words:Phthorimaea operculella, density, growth, development, reproduction
Abstract: The effect of larval density (5, 10, 15, 20, 25 and 30 larvae/tuber) on the growth, development and reproduction of offspring of the potato tuber moth Phthorimaea operculella Zeller was investigated under laboratory conditions. The results show that larval density significantly affected growth, development and reproduction. The duration of larval (7.1- 9.1 d), and pupal (8.8-9.9 d) stages, and adult female and male life spans (6.7-11.6 d, 6.4-12.9 d, respectively), was longer at higher larval densities. Larval survival (70.3%-93.3%) and pupal emergence (69.8%-91.7%) were significantly lower at higher larval densities. Pupal weight (9.2- 11.4 mg), the number of eggs per female (136.8-166.0) and the ratio of females∶males (0.54-2.17) decreased with increasing larval density. Increased larval density also affected the life history of offspring; offspring of insects raised at high larval densities had longer egg (3.0 -4.4 d), larval (6.2 -10.8 d), pupal (8.1- 10.0 d), and adult stages (female = 7.4 -11.8 d, male = 6.6 -10.5 d), and a longer overall generation time (24.4-36.1 d). However, they also had lower hatching (73.1%-79.0%), larval survival (55.0%-96.8%), pupal emergence (63.3%-93.3%) and overall survival (25.6%- 75.1%). The offspring of insects raised at high larval densities had lighter pupae (8.9-9.9 mg), a lower female∶male ratio (0.45-2.20) and fewer eggs per female (93.5-155.6). The index of population trend (Ⅰ) decreased from 76.43-7.44 with increasing larval density. The optimal density of potato tuber moths was 1 larvae/ 13.0-26.0 g tuber.