Sex Pheromone of the Alfalfa Plant Bug, Adelphocoris lineolatus: Pheromone Composition and Antagonistic Effect of 1-Hexanol (Hemiptera: Miridae)

The sex pheromone composition of alfalfa plant bugs, Adelphocoris lineolatus (Goeze), from Central Europe was investigated to test the hypothesis that insect species across a wide geographical area can vary in pheromone composition. Potential interactions between the pheromone and a known attractant, (E)-cinnamaldehyde, were also assessed. Coupled gas chromatography-electroantennography (GC-EAG) using male antennae and volatile extracts collected from females, previously shown to attract males in field experiments, revealed the presence of three physiologically active compounds. These were identified by coupled GC/mass spectrometry (GC/MS) and peak enhancement as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal. A ternary blend of these compounds in a 5.4:9.0:1.0 ratio attracted male A. lineolatus in field trials in Hungary. Omission of either (E)-2-hexenyl-butyrate or (E)-4-oxo-2-hexenal from the ternary blend or substitution of (E)-4-oxo-2-hexenal by (E)-2-hexenal resulted in loss of activity. These results indicate that this Central European population is similar in pheromone composition to that previously reported for an East Asian population. Interestingly, another EAG-active compound, 1-hexanol, was also present in female extract. When 1-hexanol was tested in combination with the ternary pheromone blend, male catches were reduced. This compound showed a dose-response effect with small doses showing a strong behavioral effect, suggesting that 1-hexanol may act as a sex pheromone antagonist in A. lineolatus. Furthermore, when (E)-cinnamaldehyde was field tested in combination with the sex pheromone, there was no increase in male catch, but the combination attracted both males and females. Prospects for practical application are discussed.

Comparison of the Sex Pheromone Composition of Harmonia axyridis Originating from Native and Invaded Areas

The multicolored Asian lady beetle, Harmonia axyridis (Coleoptera: Coccinellidae), originates from South-East Asia and is now considered as an invasive species at a worldwide scale, with populations encountered in North and South America, Africa, and Europe. Several previous studies suggested that invasive populations display different behavioral and physiological traits, leading to a better fitness than native individuals. H. axyridis sex pheromone was identified recently, but only from individuals established in Europe. In this study, we compare the composition of the female sex pheromone of H. axyridis from two populations: (i) an invasive population in North America, and (ii) a native population in South-East China. We found the females originating from both populations to release in similar proportions the same five pheromonal compounds, namely β-caryophyllene, β-elemene, methyl-eugenol, α-humulene, and α-bulnesene. However, females from the North American strain release all five compounds in larger amount than the Chinese ones. Whether invasive individuals were selected during the process of invasion through their capacity to better call and find sexual partners remains to be confirmed.

Reproductive incompatibility and fitness components in Neoleucinodes elegantalis races (Lepidoptera, Crambidae) from three Solanaceae hosts

Neoleucinodes elegantalis (Lepidoptera, Crambidae) is a Neotropical Solanaceae pest that has evolved into four host races due to host plant association. In this study, prezygotic and postzygotic isolation were evaluated in parental and F1 generations collected from Solanum lycopersicum (S. l), S. quitoense (S. q) and S. betaceum (S. b), representing medium size (S. l, S. q) and large size genitalia races (S. b). 617 adults were obtained in the laboratory and 106 copulated. One spermatophore per female was found in the bursa copulatrix, suggesting monoandry. Crosses between adults mostly occurred assortatively. A third of the female’s eggs laid occurred, but females from ♀S. b x ♂ S. l, ♀S. l x ♂S. b and S. l x S. l did not. In the cross, ♀S. l x ♂ S. q and its reciprocal F1 progeny developed into larvae. Reproductive success only occurred in three crosses: S. q x S. q, ♀ S. q x ♂ S. b and its reciprocal progeny. All the progeny from these crosses reached adulthood. The parental population showed differences in pupae and adult measurements according to host. The results on reproductive isolation obtained here suggest speciation in N. elegantalis due to host race differentiation which is relevant for the improvement of the management of this species, especially when the species has evolved reproductive isolation among races. We suggest that the use of their host plants in sympatry might reduce N. elegantalis densities in the field since hybrids between its races have low survival rates and to evaluate the possibility of pheromone composition differentiation among races given the results on assortative mating obtained here.

Identification and field evaluation of a new blend of the sex pheromone of Hypsipyla grandella

The objective of this work was to identify and carry out a field testing of the sex pheromone composition of the mahogany shoot borer, Hypsipyla grandella, from a population in Southern Brazil. Abdominal glands of H. grandella females were excised and extracted using n-hexane; the gland extracts were analysed by gas chromatography (GC-FID and GC-MS). Wind-tunnel and electrophysiology experiments were conducted to evaluate the role of gland compounds in the mating behavior of H. grandella males. In the field, pheromone traps containing the identified pheromone were tested. In addition to the two previously identified compounds - (9Z,12E)-tetradecadien-1-ol and (9Z,12E)-tetradecadienyl acetate -, in insects from Central America populations, two additional compounds were identified in the blend: (9Z)-tetradecen-1-ol and (9Z)-tetradecenyl acetate. Gas chromatography-electroantennographic analyses showed that these four components elicited antennal responses from conspecific males. Wind tunnel bioassays using different amounts of the components Z9-14:OH, Z9,E12-14:OH, Z9-14:OAc, and Z9,E12-14:OAc, elicited male responses similar to the response to conspecific calling females. When the binary and quaternary mixtures were tested in field conditions, males were attracted to the traps containing the quaternary mixture. The new pheromone blend identified in H. grandella males has a great potential to be exploited as a monitoring tool or control measure in the field.

Variación en la captura de machos de Neoleucinodes elegantalis Guenée (Lepidoptera: Crambidae) usando feromonas sexuales comerciales en tres hospederos solanáceos

Neoleucinodes elegantalis Guenée (Lepidoptera: Crambidae) represents the most damaging pest of the Solanaceae family. Current studies have demonstrated that the species has differentiated into four races according to variations in female genitalia, wing morphometrics and sequencing of the cytochrome Oxydase (CO1) mitochondrial gene. The number of males captured in Colombia and Ecuador were registered using traps baited with two sex pheromone: Neolegantol ® and P228. These pheromones were synthesized using natural female pheromones collected in Solanum lycopersicum L. plantations in Venezuela. In Colombia, the number of male catches was significantly higher for Neolegantol ® than for P228 and this number was significantly higher on S. lycopersicum followed by S. quitoense and S. betaceum. The haplotype net obtained with the CO1 gene produced two main clusters: one cluster was comprised by specimens from S. lycopersicum and S. quitoense plants (both with medium sized female genitalia) and the other cluster by specimens from S. betaceum (large sized genitalia). The Neolegantol® pheromone was also tested in Ecuador, however, insignificant number of males were attracted. Results suggest that pheromone composition or concentration, host biotypes and geographic location are relevant to monitor populations of N. elegantalis. Further studies of the species should concentrate on establishing the pheromone composition and concentration among the four biotypes.

Male white grub beetles prefer the pheromone composition of young females in the field

Females of the white grub beetle, Dasylepida ishigakiensis, release both (R)- and (S)-2-butanol as sex pheromones, but the males are only attracted to (R)-2-butanol. In laboratory-reared females, the proportion of the (R)-isomer decreased significantly as their calling opportunities increased and as they aged. We examined whether such qualitative changes also occur in field populations. We collected virgin females from the field and then trapped and analysed the volatiles emitted during their first and second callings. The ratio of (R)- to (S)-2-butanol (R/S) was 78:22 at the first calling, but shifted to 39:61 at the second calling. While investigating the composition of the female pheromones, the question arose as to whether the male preferences change in response to the shift in female pheromone composition. To answer this question, we observed the behaviour of young and old males in response to various R/S ratios as lures in the laboratory and in the field. In the flight tunnel assay of laboratory-reared individuals, young males touched female models with a 9:1 R/S ratio lure less than those with pure (R)-2-butanol; however, older males touched the two groups with equivalent frequency. In the field trap test, older males were much more attracted to (R)-2-butanol-scented lures. When we tested using lures with the same amount of (R)-2-butanol but added different amounts of the (S)-isomer, we found that increased levels of (S)-2-butanol resulted in lower attractiveness to males. (S)-2-butanol was confirmed to have an inhibitive activity in the attractiveness of (R)-2-butanol.