The relation between dispersal and survival of Lobesia botrana larvae and their density in vine inflorescences

Dispersal and survival of Lobesia botrana Den. & Schiff. (Lepidoptera: Tortricidae) larvae in a simulated first generation and the relationship with their density on vine inflorescences were studied under field conditions. Artificial infestations with neonate larvae were conducted at densities of 5, 10, 15, 20 and 25 individuals per vine inflorescence. Larvae had a considerable dispersal capacity on the vine espalier and were able to reach several inflorescences around those artificially infested. Dispersal downwards (63.1%) was significantly more frequent than upwards (36.9%), probably because larvae move down the vine plant using silk threads. However, the fact that there was upwards dispersal provides evidence that larvae are capable of active locomotion upwards on the vine plant structure. Mean distances covered by larvae ranged between 10 and 30 cm, with a maximum as far as 45 cm. The longest displacements were not associated with the downward dispersal. The maximum distance covered by larvae was positively correlated with larval density. Mean distance and larval density were not correlated, but mean distances covered at high larval densities were significantly higher than at low densities. At higher larval densities, the proportion of larvae which established in the artificially infested inflorescences decreased whereas the proportion of dispersing individuals increased. However, as a result of the balance between establishment and dispersal, larval survival did not differ significantly among larval densities (26–44%). The results obtained suggest that larval dispersal must be taken into account when preimaginal stages are sampled to determine whether damage thresholds are reached in an integrated pest management program.