Tritrophic effects of leaf nitrogen on Liriomyza trifolii (Burgess) and an associated parasitoid Chrysocharis oscinidis (Ashmead) on bean

Significant differences in developmental times of Liriomyza trifolii (Burgess) males and Chrysocharis oscinidis (Ashmead) males and females were found in response to percent nitrogen levels in bean foliage. These changes represented differences in developmental times of 4.5% in L. trifolii males and 2.7% in C. oscinidis females and occurred over the ranges of nitrogen examined (L. trifolii 2.76-6.27% leaf N; C. oscinidis 2.67-6.52% leaf N). Although pupal weights of L. trifolii larvae reared on leaves with various nitrogen levels increased significantly as leaf nitrogen increased, L. trifolii fecundity was not significantly affected by nitrogen in the leaves upon which the females developed. It appears that larval food acquisition of the female has less effect on fecundity than does adult food acquisition. Parasitoids were allowed to feed and oviposit on L. trifolii reared on leaves with differing nitrogen levels. Fecundity of adult C. oscinidis (averaged 69 progeny per female over a 10-day period) was significantly highest at the 4.88% leaf nitrogen level. Similar to the shortest developmental time, fecundity was enhanced at this level and adversely affected at the other levels. C. oscinidis sex ratio averaged 1:1.23 (male:female); no significant differences in sex ratio were found among nitrogen treatments. Total progeny production of adult C. oscinidis, allowed to feed and oviposit on L. trifolii larva reared on leaves with differing nitrogen levels, may increase by as much as 40%. These changes in fecundity are highly significant and could greatly affect pest/parasitoid populations in both agroecosystems and mass rearing programs. (C) 1996 Academic Press, Inc.