Influence of snail mucus trails and first snail meal on the behavior of malacophagous sciomyzid larvae

There has been considerable focus on the natural enemies of snails, particularly those of medical and veterinary significance. Much attention has focussed on members of the Family Sciomyzidae (Diptera), the majority of which feed on a range of mollusc species. However, little is known about the influence of first snail meal on subsequent prey choices, an important consideration in biocontrol. We examined neonate larval responses of Ilione albiseta to fresh and aged snail mucus trails of three snail species. Median neonate response rates to aged mucus trails for all three snail species tested were significantly (P < 0.001) weaker than for fresh mucus trails indicating a strategy which enhances the likelihood of reaching prey snail species without expending energy following “cold” trails. More than 78% of first instar larvae, fed on one snail species (Radix peregra or Stagnicola palustris) and subsequently offered a choice of these two snail species for the second snail meal, selected the snail species of the first snail meal suggesting that the first snail meal influences subsequent prey selection. However, the impact of the first snail meal on larval trail-following behavior is less clear-cut. While there may be some preference for the mucus trail of the snail species on which neonate larvae have fed, this does not exclude the larvae from following the mucus trails of other snail species. The results are discussed in the context of the potential use of I. albiseta as a biocontrol agent of vectors of snail borne diseases.