Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2001
Publication Date: 12/20/2003
Citation: Wheeler, G.S. 2003. Minimal increase in larval and adult performance of the biological control agent oxyops vitiosa when fed melaleuca quinquenervia leaves of different nitrogen levels. Biological Control 26:109-116. Interpretive Summary: The nutritional requirements of weed biological control agents can limit their impact and distribution on the target weed. We studied the survival, growth, development time, and fecundity of the beetle Oxyops vitiosa, a biological control agent of Melaleuca quinquenervia, an invasive weed threatening the south Florida Everglades and neighboring natural areas. The larvae of this weevil are flush-feeders, only feeding on the softest actively growing leaves of the tree. In studies where we fertilized Melaleuca plants at low rates (30 g Osmocote Plus 15-9-12/3 gallon pot) larval survival was half that of larvae fed higher fertilizer rates. This higher mortality at low fertilizer rates is the greatest effect found reducing the weevil's ability to use Melaleuca plants grown under low fertilizer levels. Prepupal, pupal, and adult weights increased when the larvae were fed leaves from the higher fertilizer plants. However, the number of eggs produced was not affected by fertilizer treatments. Therefore, to mass-produce this weevil for biological control of this weed, plants can be grown at a relatively low fertilizer rate (90 g Osmocote Plus 15-9-12/3 gallon pot). Fertilizer rates above this level will have negligible benefit in terms of the number of weevils produced.
Technical Abstract: Leaves from different fertilizer treatments of Melaleuca quinquenervia were fed to neonate and adult Oxyops vitiosa to determine the influence of nutrient levels on insect survival, growth, development, and fecundity. The results indicated that larvae fed the low fertilizer leaves (30 g/pot) had less than one half the survival (30 +/- 5.0 percent) of larvae fed the high fertilizer (90 g fertilizer/pot) leaves (65 +/- 10.4 percent). Additionally, the biomass of prepupae, pupae, and adults were each significantly greater (each 1.1-fold) in larvae fed leaves from the high fertilizer level. However, fecundity was not influenced by these fertilizer treatments. A second experiment determined the effect of 5 fertilizer treatments (30, 90, 135, 180, and 225 g/pot) applied to M. quinquenervia on O. vitiosa larval survival, growth, development and feeding efficiency. These results indicated that slight increases occurred in food consumption and biomass gain when larvae were fed leaves from the lowest and highest fertilizer treatments, respectively. Little if any evidence of compensatory feeding or increased nutrient utilization efficiency was found on the low nitrogen leaves. Thus, these results suggest that in mass rearing activities increased production of weevils will occur in high fertilized (90 g/pot) treatments due to increased larval survival. However, adult fecundity will not be affected by fertilizer treatment. Several qualities of this species contribute to its success as a biological control, namely the adults are long-lived which enables individuals to bridge periods when suitable leaves are available and both larval and adult performance are apparently little-affected by a wide range of nitrogen levels.