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 and any association with a host. Species with non-feeding larvae are isolated cases within species groups or genera where the remaining species 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 occurred at least 21 times. Lineages of water mites with non-feeding larvae frequently exist in parallel with almost identical populations or species that have parasitic larvae. Thus, there is tremendous potential for studies comparing the relative merits of the two life history strategies. Comparisons indicate that adults from lineages with non-parasitic larvae produce smaller numbers of larger eggs; the extra nutrition included in larger eggs permits the larvae to forgo feeding. Non-feeding larvae frequently have wider dorsal plates but reduced leg length, setal length and sclerotization when compared to parasitic larvae from sister lineages. The adults of lineages with non-feeding larvae are frequently smaller in comparison to adults of sister lineages with parasitic larvae. There is no apparent pattern in relation to habitat: lineages lacking larval parasitism occur in streams, temporary ponds and the littoral and planktonic regions of permanent lakes. © Rapid Science Ltd. 1998