LOSS OF LARVAL PARASITISM IN PARASITENGONINE MITES

Larval Parasitengona are typically parasites, yet at least 29 species of water mites and one species of Trombidiidae forgo larval feeding an d any association with a host. Species with non-feeding larvae are iso lated cases within species groups or genera where the remaining specie s have parasitic larvae. Species without larval parasitism occur in at least 14 genera, eight families and four superfamilies of water mites ; the loss of larval parasitism is presumably polyphyletic, having occ urred at least 21 times. Lineages of water mites with non-feeding larv ae frequently exist in parallel with almost identical populations or s pecies that have parasitic larvae. Thus, there is tremendous potential for studies comparing the relative merits of the two life history str ategies. Comparisons indicate that adults from lineages with non-paras itic larvae produce smaller numbers of larger eggs; the extra nutritio n included in larger eggs permits the larvae to forgo feeding. Non-fee ding larvae frequently have wider dorsal plates but reduced leg length , setal length and sclerotization when compared to parasitic larvae fr om sister lineages. The adults of lineages with non-feeding larvae are frequently smaller in comparison to adults of sister lineages with pa rasitic larvae. There is no apparent pattern in relation to habitat: l ineages lacking larval parasitism occur in streams, temporary ponds an d the littoral and planktonic regions of permanent lakes. (C) 1998 Cha pman & Hall Ltd.