The effect of vine phenological stage during larval feeding on the reproductive output of Lobesia botrana (Denis & Schiffermüller) adults was assessed. Larvae were reared under field conditions on vine inflorescences, unripe or ripe berries simulating the first, second and third insect generations respectively. The resulting adults showed significant differences in body weight, longevity and reproductive output as measured by oviposition period, total fecundity and reproductive efficiency (viable eggs/body weight) for females, and spermatophore number and volume of the first spermatophore for males. Viable egg number was positively correlated with female body weight for all treatments but male reproductive efficiency (spermatophores/body weight) was not. The reproductive output of females from larvae reared on a standard semisynthetic diet was comparable to that of females reared on ripe berries whereas males showed a higher reproductive output when reared on semisynthetic diet. These results clearly show that data obtained from insects reared on artificial diet cannot be extrapolated to 'fieldderived' adults. The results suggest that the variation in L. botrana reproductive output due to the larval food source should be taken into account as a potential factor affecting insect population dynamics. It is suggested that different intervention thresholds, such as those based on pheromone catches, may be needed for each of the three moth generations, to compensate for the increased fecundity and potential to cause larger amounts of crop damage of later generations.
This study compares the sensitivity of different phenological stages of grapevine cultivars to infestation by larvae of the European grapevine moth, Lobesia botrana Den. et Schiff.
The fructiferous organs of six cultivars: Cabernet Franc, Merlot, Cabernet Sauvignon, Sauvignon, Semillon and Müller Thurgau were infested at 5–10 days intervals from the beginning of the vegetative period, with a constant number of newly hatched L. botrana larvae (five per organ). After the larvae reached the fifth instar, the fructiferous organs were cut and each grape analysed according to the damage. Each organ was classified into one of three groups: I — no damage; II — traces of probing activity and III — traces of feeding activity.
At the beginning of the vegetative period (stages D and E) the percentage of fructiferous organs with traces of feeding activity is relatively low (20–35% dependent on cultivar). From stage F onwards the number of bunches with traces of feeding activity progressively increases, reaching a maximum at stage H (78–93%). In all cultivars tested a period was clearly observed when the fructiferous organs were significantly (ANOVA procedure, P< 0.0001) unsuitable for infestation by freshly hatched larvae, and this corresponded to phenological stages I and J (8–35% of bunches with traces of feeding activity). The phenological stages following stage until harvest were again suitable for development of the larvae (50–95% of bunches in the group III), but with greater individual alter variability than observed for stages from F to H.
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.
Disruption nzechanisnzs o f pkeronmie comn?unication in the Europrun grape niotli Lohesia hotruna Den. et Schiff: ~ I Respectii,r ro1e.s of'conipetition, camouflage ?f:fetnale signcils and modification of'pheronzonal signalThe mechanisms implied in confusion were studied by experiments in vineyard using the technique of males released and captured, completed in laboratory by tests in the olfactometer. The following results were found: (1) The sex behaviour of males was not inhibited by the presence of a source of synthetic pheromone up to the dose of 500 mg. (2) The main mechanism was the competition between females and source of synthetic pheromone. This competition was more and more favourable to the dispenser when the dose of pheromone increased. (3) It was also a camouflage of the smelling trail of the females. That caused a decrease of active space in which the males were able to locate the females. This effect was got for high doses only. (4) Addition of minor compounds of natural pheromone to synthetic products had no influence on competition and camouflage.
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