Population dynamics of the phytophagous lady beetle,Epilachna vigintioctopunctata,in an eggplant field in Sumatra

From December, 1981 to December 1982, the population dynamics of the phytophagous lady beetle Epilachna vigintioctopunctata (Fabricius ) (Evp) was studied by mark-recapture of adults and the construction of a life table in an eggplant field in Padang, Sumatra, Indonesia.

1. After planting of the host plants, adults of Evp soon colonized and oviposited massively, resulting in a rapid population growth for 1–2 months; thereafter, the population increase slowed due to defoliation. Three–four months thereafter the host plants recovered their leaves, but leaf quality was less suitable for Evp and, as a result, the population remained at a low level during the rest of the study period. Adult population size fluctuated 7–8 fold during the study period.
2. Adult Evp showed a 1∶1 sex ratio.
3. The daily rate of residence, ψ_i, derived by theJolly-Seber formula fluctuated from 0.9 to 1.0.
4. The estimated mean length of residence of adults was 16.5 days (male) and 15.2 (female), but this was probably much shorter than the actual longevity, because the adults were so active that they flew away or dropped off the plants when they were approached or were slightly disturbed.
5. Adults showed a rich variation in elytral spot patterns. The average number of non-persistent spots per elytron was 0.52 in males and 1.08 in females; 23.3% of males and 24.6% of females had confluence(s).
6. The life table shows that parasitism by wasps, which killed 9.7% of eggs and 35.0% of pupae, and starvation by overcrowding contributed most to the total mortality from egg to adult emergence (>98%).
7. The high dispersal power of adults, coupled with their prolonged l_x−m_x schedules was advantageous for exploiting food plants which were variable in space and time.