Quantity does matter: How feces are used for host stage selection by granary weevil parasitoid Lariophagus distinguendus

The present paper examiner the mechanisms of host stage selection in Lariop hagus distinguendus, a larval parasitoid of the granary weevil Sitophilus g ranarius endophytic in wheat grain. The amount of host feces accumulating i n interested grains was on average, 0.2. 0.3, 1.5, and 4 mg for first, seco nd, third, and fourth instars, respectively. A maximum of 9 mg feces was Fo und in grains with fourth instars. In bioassays with female parasitoids. on ly a little drumming and drilling behavior was observed on grain models tre ated with feces extract equivalent to 0.2 mg and 0.4 mg frees. Most drummin g and drilling occurred on models with extracts equivalent to 4 and 8 mg fe ces. These results correspond to literature data demonstrating that older h ost larvae (Fourth instars) are preferred for oviposition. Thus, host stage selection in L. distinguendus is apparently achieved by assessing the quan tity uf Feces present in infested grains.