Directed search pattern of a leafminer parasitoid among mines of host larvae

Parasitoids have developed a variety of searching strategies to maximize their searching efficiency. To increase the efficiency, leafminer parasitoids first search for host mines, which are linear and visually conspicuous, and then search for host larvae situated at the end of the mines by tracking the mines. We hypothesized that the leafminer parasitoids have the ability of directional orientation toward larvae as opposed to orienting randomly and tested this hypothesis by using the leafminer Liriomyza trifolii (Burgess) (Diptera; Agromyzidae) and its parasitoid Hemiptarsenus varicornis (Girault) (Hymenoptera: Eulophidae). Direct observations of parasitoid behavior revealed that female parasitoids mostly selected the correct direction immediately after mine encounter. However, they did not select correctly when the host had been parasitized, or when the point of the mine encounter was far from the host larva, suggesting the possibility of sound-based search. Curiously, the success of encounter rates was not influenced by the directions that the female had selected. This was because the female turned to the correct direction during her search even after selecting the wrong direction. Thus, female H. varicornis can recognize which end of the mine the target larva lays upon mine encounter or during the foraging bout. The importance of the ability of recognizing the correct direction by the parasitoid and the possible mechanism involved in this ability is discussed.