J. Stockel

Delayed mating reduces reproductive output of female European grapevine moth, Lobesia botrana (Lepidoptera: Tortricidae)

Virgin females of Lobesia botrana Denis & Schiffermüller were mated at ages of 1, 3, 5, 8, 12 and 16 days and the effect of mating delay on reproductive output assessed. Delayed mating did not affect female mating success but fertilization was reduced in 16-day-old females. Increased mating delays substantially affected daily oviposition pattern and resulted in a significant reduction of both fecundity and fertility, so that mean number of viable eggs laid decreased from 150 to 22 in 1- and 16-day-old mated females, respectively. Heavier females were more constrained than lighter ones by mating delays and female reproductive efficiency (no. viable eggs/female body weight) was also significantly reduced. Female longevity significantly increased and oviposition period gradually declined with mating delay. The number of viable eggs was positively correlated with both female weight and oviposition period; female longevity and female weight were also significantly correlated. However, the significance of these correlations declined with increased mating delay. Results overall indicated that mating delay drastically reduces female L. botrana reproductive output. The implications of delayed mating of females are discussed from an ecological perspective in relation to L. botrana control using mating disruption.

Physiological factors regulating polyandry in Lobesia botrana (Lepidoptera: Tortricidae)

Abstract. The effects of several physiological factors related to female multiple mating in the monandrous Lobesia botrana Denis and Schiffermuller (Lepidoptera: Tortricidae) were studied under laboratory conditions. Polyandry was assessed observing the induction of re‐calling in previously once‐mated females. Female age at first mating had no effect on induction of re‐calling during practically the whole of the female lifetime, but in older females it was significantly lower. The percentage of re‐calling was negatively correlated with the volume of the spermatophore received, ranging from ≅ 23% with the largest spermatophores to ≅ 75% with the smallest ones. Furthermore, the smaller the spermatophore volume, the earlier the re‐calling was induced, significantly reducing die female refractory period after the first mating. Heavy females showed a significantly higher rate of re‐calling (52.8%) than light ones (37.0%), but no differences were observed when females received only small spermatophores. This finding was explained by die allometric relationship between me female weight and the size of its reproductive system that affects relative replenishment by the spermatophore. Females with a supply of water displayed a significantly higher rate of re‐calling (41.2%) than control females (22.8%), highlighting the effect of adult feeding (or drinking) status on the re‐calling behaviour. The short‐distance presence of virgin males with once‐mated females promoted a re‐calling rate (and subsequent matings) close to 37%, significantly higher than that of isolated females (20%). It is concluded mat re‐calling and polyandry in L. botrana are controlled, as expected, by a number of mating‐derived stimuli, but also to a great extent by other physiological stimuli unrelated to mating. The reproductive strategies in relation to polyandry and the mechanisms controlling female sexual inhibition are discussed.

Heritable variation for female remating in Lobesia botrana, a usually monandrous moth

Abstract The occurrence of heritable variation for polyandry in the usually monandrous moth Lobesia botrana Den. and Schiff. (Lepidoptera: Tortricidae) was studied in the laboratory, using isofemale lines, a selection experiment and F 1 and F 2 crosses between the selected line (S) and an unselected control line (C). We assessed polyandry by observing the frequency of recalling in once mated females (i.e. the frequency of females resuming calling after mating). Polyandry differed significantly between isofemale lines, ranging from 0 to 100% in a normal distribution. Heritability of polyandry ±SE, estimated as a threshold trait using a full-sib design, was h 2 =0.40±0.12. Artificial selection for polyandry resulted in a significant increase from 32 to 65% in which a plateau occurred. Realized heritability in the first and second generations of selection yielded estimates of h 2 =0.41 and h 2 =0.53, respectively. We also found a concomitant, significant increase in matings per female. In the sixth generation (S line), when only females that had mated more than twice were used as parents, polyandry rose again from 65 to 80%. Results from F 1 crosses supported the hypothesis that polyandry was recessive and autosomally inherited. Cavallis joint scaling test confirmed these results, yielding values ±SE of d =0.18±0.03 and h =−0.16±0.05. Observed and expected frequencies of polyandry in F 2 fitted significantly under the hypothesis of a two-loci model. The underlying implications of heritable variation in polyandry in a usually monandrous species are outlined, from an evolutionary perspective, in the context of the adaptive significance of this aspect of insect mating systems. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

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.

DISRUPTION MECHANISMS OF PHEROMONE COMMUNICATION IN THE EUROPEAN GRAPE MOTH Lobesia botrana DEN & SCHIFF. III. SENSORY ADAPTATION AND HABITUATION

Disruption experiments were carried out under vineyard conditions and in the laboratory. Males from laboratory cultures were conditioned in an atmosphere permeated with pheromone (E7 Z9-12Ac), marked externally with fluorescent powder, and released in the middle of vine plots. They were then trapped in a series of traps baited with virgin females or dispensers loaded with various amounts of pheromone. Over 10,000 males were released in these experiments between 19 May and 22 July. Electroantennography tests were used for studying olfactory sensitivity in pheromone-permeated air by measuring the EAG responses of male antennae in constant pheromone air-flows. The conclusion is that both sensory adaptation and central nervous system habituation mechanisms acted simultaneously in air laden with pheromone, but they are probably not relevant when concentrations are of the same order of magnitude as those obtained under field conditions in which mating disruption methods are used for controlling the European grape moth.

Disruption mechanisms of pheromone communication in the European grape moth Lobesia botrana Den. & Schiff. (Lep., Tortricidae) II. Influence of the population density and the distance between insects for males to detect the females in atmosphere impregnated by pheromone

The main consequence of mating disruption in the European grape moth is a decrease of female active space. Two experiments were done in a vineyard in order to evaluate the effect of population density and initial distance between insects on female detection by males.

Artificial selection in pheromone permeated air increases mating ability of the European grape vine moth Lobesia botrana (Lep., Tortricidae)

The existence of L. botrana genotypes more suitable to mating in synthetic pheromone permeated air in olfactometer was investigated by artificial selection through two consecutive generations. The major compound of the female pheromone blend (7E, 9Z)‐7, 9‐dodecadienyl acetate 7E, 9Z DDA was used, the only one commercialized at present both for monitoring and for mating disruption. The adults mated in a mating disruption atmosphere in the parental generation (G1) were reared separately to make up the selected filial generation (G2). Trial was carried out at the doses of 0 (control), 0.5 and 1 μg of 7E, 9Z DDA. In G1 83.33% (50/60 pairs), 18.87% (50/265) and 8.62% (31/360) mated respectively. In the selected generation (G2) 76.67% (46/60), 20.91% (69/330) and 14.38% (64/445) mated respectively. Thus, control mating percentages in both generations were similar. Nevertheless, after selection the increase in mating was significant at 1 μg dose (G = 6.53; d.f. = 1; P < 0.05) but not at 0.5 μg (G = 0.38; d.f. = 1; P > 0.05). On the other hand, selection for increasing mating ability in sex pheromone permeated air at the doses tested, was not linked with a decrease in the dusk time elapsed before mating (mean: 24–30 min). With regard to the controls without pheromone (mean: 10–12 min), matings were significantly delayed (F(5,04) = 18.52; P < 0.01). The differences in response to selection between pheromone doses show the possible effect of the genetic homeostasis. These preliminary results suggest a genetic basis for mating ability and are a complementary hypothesis to explain the lack of an absolute efficiency in control by mating disruption. Finally, the possible factors that could interact and counteract the studied selection pressure are discussed, since resistance to the mating disruption method has not been observed at this time in field conditions.