A COMPARISON OF UNIVOLTINE AND MULTIVOLTINE EUROPEAN CORN BORER (OSTRINIA NUBILALIS HÜBNER): LIFE HISTORY CHARACTERS, BT TOXIN SUSCEPTIBILITY, PARASITOID IMPACT, AND POPULATION PATTERN

Open Access
Author:
ZAMAN, MD. FARUQUE UZ
Graduate Program:
Entomology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 21, 2007
Committee Members:
  • Edwin George Rajotte, Committee Chair
  • Dennis D Calvin, Committee Chair
  • David A Mortensen, Committee Member
  • Liwang Cui, Committee Member
  • Douglas V Sumerford, Committee Member
Keywords:
  • European corn borer
  • Parasitoid
  • Ecotype
  • Life History
  • Univoltine
  • Multivoltine
Abstract:
Abstract: Among the various stalk boring insect attacking corn in the U.S., European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), alone is responsible for a $1.85 billion annual loss. Soon after its discovery (1914) the insects displayed ecotype or voltine diversity. ECB management and its cost may be influenced by the ecotype pattern within a region. Since 1996, the commercial use of transgenic corn hybrids reduced the uses of synthetic insecticides in corn fields dramatically. However, wider uses of Bt corn poses the risk of resistance development and threatens parasitoids of ECB. Several Integrated Resistance Management (IRM) practices were introduced to minimize this threat, but the lack of understanding of the biology and population dynamics of geographic ecotypes of ECB may hinder the success of the IRM program. This dissertation studies were design to compare life history parameters, Bt toxin susceptibilities, parasitoid impacts, and population patterns between univoltine and multivoltine ecotypes collected from Pennsylvania, USA. From 2002-2005 post-diapause ECB were field collected in central, north, and south Pennsylvania. Various populations were reared through several generations in the laboratory to determine differences between univoltine and multivoltine ecotypes. These research included life history parameters, Bt susceptibility and parasitoid impacts. Co-occurring univoltine ECB required higher degree-days to complete its life cycle than bivoltine ECB. Post-diapause univoltine pupal weights were significantly higher than multivoltine pupal weights, whereas the pupal weights of non-diapause ECB (F1) reared in controlled environmental conditions were not significantly different. This suggests a non-genetic basis of weight gain. No variation was observed in reproductive parameters. No significant mortality differences were found between univoltine and multivoltine ECB when subjected to Cry1Ab and Cry1F Bt toxins. A 1.5- to 2- fold increase in susceptibility for the LC50, LC95, and LC99 was observed in univoltine exposed to Cry1Ab. Sub-lethal effects were not significant for Cry1Ab, however, severe growth inhibition was observed in ecotypes when exposed to Cry1F toxin. These minor variations in susceptibility are unlikely to affect resistance. Four years of field and laboratory study strongly suggested that M. cingulum emergence was completely synchronized with the spring emergence of the multivoltine ecotype. Post-diapause univoltine populations face almost no impact from M. cingulum parasitism. Sex ratio differences observed in over-wintered ECB populations in the presence or absence of M. cingulum parasitism suggested differential parasitism between male and female larvae. Overall, experimental outcomes from this research suggested that in areas of co-occurrence, variation in ECB ecotypes is due to the synergistic effects of seasonal degree days, host plant stage, and perhaps parasitoid pressure. Further genetic structure studies of multi ecotype populations across several geographic areas may elucidate the general applicability of these findings.