DNA barcoding of large oak-living cerambycids: diagnostic tool, phylogenetic insights and natural hybridization between Cerambyx cerdo and Cerambyx welensii (Coleoptera: Cerambycidae)

Three large saproxylic cerambycids with different pest/legal status co-occur in the Iberian oak woodlands, Cerambyx welensii (Cw), Cerambyx cerdo (Cc) and Prinobius myardi (Pm): Cw is an emerging pest, Cc is a protected but sometimes harmful species and Pm is a secondary/minor pest. A precise taxonomic diagnosis is necessary for research, management or protection purposes, but may be problematic mainly because Cw and Cc larvae are morphologically indistinguishable. To resolve this constraint, we genotyped adults, larvae and eggs collected over a wide geographical range using the mitochondrial barcoding of the cytochrome c oxidase subunit I (COI). A Neighbour-Joining tree phylogram revealed three distinct clusters corresponding to Cw, Cc and Pm. We further first sequenced for Cw and Cc two mitochondrial (12S rRNA and 16S rRNA) and one nuclear (28S rRNA) gene fragments. For the first two genes, interspecific divergence was lower than in COI, and for the 28S (lower mutation rate), the two species shared identical haplotypes. Two approaches for species delimitation (General Mixed Yule Coalescent (GMYC), Barcode Index Number (BIN)) confirmed the species distinctiveness of Cc and Cw. The Bayesian COI gene tree showed a remarkable genetic divergence between Cc populations from Iberia and the rest of Europe. Such divergence has relevant taxonomic connotations and stresses the importance of a wide geographical scale sampling for accurate DNA barcoding species identification. Incongruities between morphology/lineage and COI barcodes in some individuals revealed natural hybridization between Cw and Cc. Natural hybridization is important from a phylogenetic/evolutionary perspective in these cerambycids, but the prevalence of (and the behavioural/ecological factors involved in) interspecific cross-breeding remain to be investigated.

Reproductive biology of the great capricorn beetle, Cerambyx cerdo (Coleoptera: Cerambycidae): a protected but occasionally harmful species

Cerambyx cerdo (Cc) is a protected saproxylic beetle in Europe, although it is increasingly reported as an oak 'pest'. Cc ecological features are relatively well known, but, its reproductive biology is still poorly understood. Hence, we investigated the reproductive traits of Cc under laboratory conditions. In females, body length was 44.1 ± 0.9 mm, 28-53 (mean ± SE, range); fecundity 143 ± 11 eggs, 33-347; fertility 78 ± 1%, 65-93; oviposition period 44 ± 3 days, 13-128 and longevity 59 ± 5 days, 16-157. Fecundity was positively correlated with female size, longevity and oviposition period. Daily fecundity was 3.5 ± 0.2 eggs/day, 0.9-6.5 showing a fluctuating synovigenic pattern with a slight decreasing trend over time. Egg length was 3.74 ± 0.01 mm, 2.3-6.0 and egg volume 5.45 ± 0.04 mm3, 2.4-9.6. Egg size was correlated with female size, but, the relative size of eggs was larger in smaller females. Incubation time was 13.5 ± 0.1 days, 7-28. Hatching was superior in larger eggs and neonate size was positively correlated to egg volume. Females were polyandrous (up to 19 matings), but, multiple mating did not enhance fecundity or fertility. In males, body length was 41.8 ± 0.8 mm, 29-53 and longevity 49 ± 3 days, 9-124. Male longevity was unrelated to body size. Males were polygynous (up to 16 matings) and mating number did not affect male longevity. Overall, females were larger and lived longer than males. Cc reproductive traits are compared with those other Cerambycidae, especially with the congeneric pest Cerambyx welensii. Our data may be valuable to improve the protection/management measures of Cc in dehesa woodlands and other oak forests.

Reproductive traits and number of matings in males and females of Cerambyx welensii (Coleoptera: Cerambycidae) an emergent pest of oaks

The longhorn beetle Cerambyx welensii is an emerging pest involved in oak decline episodes, whose damage is increasingly reported in dehesa open woodlands. Knowledge of the reproductive biology of C. welensii is a crucial goal due to its new pest status. In this study, we assess the reproductive traits of both sexes in the laboratory (25°C and 60% relative humidity ). In females, body length was 44.9 ± 0.9 mm (mean ± SE), fecundity 132 ± 12 eggs, fertility 70 ± 1 %, longevity 70 ± 3 days, preoviposition period 2 ± 0.2 days, oviposition period 44 ± 3 days and postoviposition period 19 ± 3 days. Fecundity was positively correlated with female size, longevity and oviposition period. Daily fecundity was 3.0 ± 0.2 eggs/day and showed a fluctuating synovigenic pattern with a slight decreasing trend over time. Egg length was 4.24 ± 0.01 mm and egg volume 8.14 ± 0.04 mm3. Egg size was correlated with female size but the relative size of eggs was larger in smaller females. Incubation time was 13.9 ± 0.1 days and hatching did not depend on egg size. Neonate size was positively correlated with egg length. Females were polyandrous (more than 20 lifetime matings) but multiple mating did not increase fecundity, fertility or longevity. In males, body length was 43.7 ± 0.6 mm and longevity 52 ± 3 days. Unlike with females, longevity was positively correlated with male size. Males were polygynous (up to 30 lifetime matings) but mating history did not affect male longevity. Rather to the contrary, long-lived males mated more times because they had more mating chances. Lastly, C. welensii reproductive traits were compared with those other Cerambycidae species and discussed from an adaptive perspective. Our data will be useful to improve management of C. welensii in order to prevent or mitigate its impact in dehesa woodlands and other oak forests.

Polyandry-fecundity relationship in insects: methodological and conceptual problems

Polyandry is perhaps the most puzzling component of mating systems because the fitness benefits for females of mating with more than one male during lifetime are poorly understood. The occurrence and extent of polyandry varies considerably both among and within species, and a positive association between polyandry and fecundity is widespread but not universal. The scenario is further complicated because the scientific literature on this issue includes studies that are often inconclusive or contradictory even for the same target species. A previous meta-analysis detected the crucial importance of two usually neglected aspects that potentially bias the interpretation of primary studies about the polyandry-fecundity relationship: the methodological approach--experimental or descriptive--and the polyandry concept itself--realized or potential. In this paper, we experimentally test the effect of these aspects with the moth Lobesia botrana. We used an innovative protocol in which the experimental and the descriptive methods were conducted simultaneously on the same target population and the results were then interpreted from the perspective of both concepts of polyandry. The results clearly showed that 1) the conclusions about the polyandry-fecundity relationship were strongly dependent on the methodological approach used and 2) the concept of polyandry invoked by the researcher was a confounding effect that potentially biases data interpretation. We suggest that greater attention must be paid to intraspecific variation among females in their propensity to remate. The differentiation in experimental studies between potentially polyandrous and monandrous phenotypes could greatly improve our knowledge about the maintenance of female mating polymorphism in most species and the adaptive significance of polyandry.

First Report of Fusarium Wilt of Flue-Cured Tobacco Caused by Fusarium oxysporum f. sp. batatas in Spain

Tobacco (Nicotiana tabaccum L.) is among the most important crops in La Vera Region (Cáceres, west-central Spain) where, since 2001, flue-cured tobacco plants showing typical symptoms of a vascular disease associated to the cyst nematode (Globodera tabacum) complex have been frequently observed (2). Symptoms observed were wilting, yellowing, and drying of the leaves, usually on one side of the plant; stunted and distorted leaves with curved midribs due to the unequal growth; and brown vascular discoloration of stems and midribs. Several diseased plants were collected during the summers of 2003 and 2004, and F. oxysporum was consistently isolated from sections of necrotic midribs. To confirm the pathogenicity of F. oxysporum isolates, plants of flue-cured tobacco (cv. Ct-681) were inoculated. Since Fusarium wilt of tobacco may be caused by F. oxysporum f. sp. vasinfectum or F. oxysporum f. sp. batatas (1), plants of cotton (cv. Acala) and sweet potato (cvs. Nemagold and Nancy Hall) were also inoculated to determine the forma specialis designation. Twenty plants per cultivar and isolate were inoculated with six isolates at the two to four true-leaf stage by pouring into the substrate 200 ml of a conidial suspension (1 × 10⁵ CFU/ml). After inoculation, plants were incubated in a growth chamber at 28°C (day) and 24°C (night) with a 16-h photoperiod. All six F. oxysporum isolates were pathogenic to tobacco and sweet potato, but there were differences among isolates in time from inoculation to appearance of first disease symptoms (7 to 15 days after inoculation in tobacco and sweet potato) and also in disease severity 30 days after inoculation (60 to 100% wilt or mortality in tobacco and 50 to 100% in sweet potato). F. oxysporum was reisolated from stems of inoculated plants. No disease symptom was observed in cotton plants 60 days after inoculation, and F. oxysporum was not reisolated from them. Results of inoculation on the differential hosts indicated that disease symptoms in tobacco were caused by F. oxysporum f. sp. batatas. To our knowledge, this is the first report of F. oxysporum f. sp. batatas causing disease in flue-cured tobacco in Spain. References: (1) G. M. Armstrong and J. K. Armstrong. Phytopathology 58:1242, 1968. (2) G. Espárrago and I. Blanco. Plant Dis. 86:1402, 2002.

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.

Polyandry in Lepidoptera: a heritable trait in Spodoptera exigua Hübner

The genetic basis as well as the mode of inheritance of polyandry in Spodoptera exigua Hübner was studied in the laboratory by using a simple divergent selection experiment followed by F1 reciprocal crosses, F2 and backcrosses. There was an effective response to artificial selection for high (H line) and low (L line) female mating frequency with significant separation of the lines by the second generation of selection. The mean female mating frequency in the parental generation (1.57 matings per female) reached plateaus of 2.50 and 1.25 matings per female in the H and L lines, respectively, after six generations of selection. Selection response becomes saturated at about 90% and 25% levels of polyandry (percentage females re-mating) in the H and L lines, respectively, and consequently mono- and polyandric pure strains were not obtained. Polyandry levels in offspring from the H and L lines and their hybrids in F1, F2 and backcrosses consistently indicate that female mating frequency was more or less proportional to the relative amounts of genes derived from the H and L lines. Such a clear pattern of hybrid responses, together with the gradual selective changes under artificial selection, suggests the involvement of a polygenic system. Female mating frequencies from progeny of the two reciprocal F1 crosses were not significantly different, which suggest that the trait was autosomally inherited. Moreover, female mating frequency of F1 (pooled) progeny was not significantly different from the mid-parental value, which suggest no dominance. The computation of the Cavalli's joint scaling test consistently confirmed these results yielding values of d = 0.51 +/- 0.10 and h = 0.12 +/- 0.21. The broad sense heritability estimate was H2 = 0.73. It is concluded that polyandry in S. exigua is a polygenic, autosomal heritable trait and that additive genetic variance is available for selection for female mating frequency. The implications of the genetic basis of polyandry are briefly discussed in the context of current theories about this crucial insect mating system.