THE RELATION BETWEEN DISPERSAL AND SURVIVAL OF LOBESIA-BOTRANA LARVAEAND THEIR DENSITY IN VINE INFLORESCENCES

Dispersal and survival of Lobesia botrana Den. & Schiff. (Lepidoptera: Tortricidae) larvae in a simulated first generation and the relations hip with their density on vine inflorescences were studied under field conditions. Artificial infestations with neonate larvae were conducte d at densities of 5, 10, 15, 20 and 25 individuals per vine infloresce nce. Larvae had a considerable dispersal capacity on the vine espalier and were able to reach several inflorescences around those artificial ly infested. Dispersal downwards (63.1%) was significantly more freque nt than upwards (36.9%), probably because larvae move down the vine pl ant using silk threads. However, the fact that there was upwards dispe rsal provides evidence that larvae are capable of active locomotion up wards on the vine plant structure. Mean distances covered by larvae ra nged between 10 and 30 cm, with a maximum as far as 45 cm. The longest displacements were not associated with the downward dispersal. The ma ximum distance covered by larvae was positively correlated with larval density. Mean distance and larval density were not correlated, but me an distances covered at high larval densities were significantly highe r 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 dispersa l, 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 wh ether damage thresholds are reached in an integrated pest management p rogram.