Chemical Ecology of Neuroptera

Replenishment of Drosophila Male Pheromone After Mating

Insect exocrine gland products can be involved in sexual communication, defense, territory labelling, aggregation and alarm. In the vinegar fly Drosophila melanogaster the ejaculatory bulb synthesizes and releases 11-cis-Vaccenyl acetate (cVa). This pheromone, transferred to the female during copulation, affects aggregation, courtship and male-male aggressive behaviors. To determine the ability of male flies to replenish their cVa levels, males of a control laboratory strain and from the desat1 pheromone-defective mutant strain were allowed to mate successively with several females. We measured mating frequency, duration and latency, the amount of cVa transferred to mated females and the residual cVa in tested males. Mating duration remained constant with multiple matings, but we found that the amount of cVa transferred to females declined with multiple matings, indicating that, over short, biologically-relevant periods, replenishment of the pheromone does not keep up with mating frequency, resulting in the transfer of varying quantities of cVa. Adult responses to cVa are affected by early developmental exposure to this pheromone; our revelation of quantitative variation in the amount of cVa transferred to females in the event of multiple matings by a male suggests variable responses to cVa shown by adults produced by such matings. This implies that the natural role of this compound may be richer than suggested by laboratory experiments that study only one mating event and its immediate behavioral or neurobiological consequences.

Novel pheromone-mediated reproductive behaviour in the stag beetle, Lucanus cervus

The iconic European stag beetle (Lucanus cervus) (Coleoptera: Lucanidae) is one of the largest terrestrial beetles in Europe. Due to decreasing population numbers, thought to be a consequence of habitat loss, this beetle has become a near-threatened species across much of Europe, and a reliable monitoring system is required to measure its future population trends. As part of a programme aimed at conserving UK populations, we have investigated the chemical ecology of the beetle, with a view to developing an efficient semiochemical-based monitoring system. Such a scheme will be beneficial not only in the UK but across the European range of the species, where the beetle is of conservation concern. Here, we report on a surprising discovery of a male-produced pheromone, which provokes initial sexual receptivity in females, and which has not been previously identified in the animal kingdom. Furthermore, we assign sex pheromone function to a previously described female-specific compound.

Defensive spray by a semiaquatic osmylid larva (Insecta: Neuroptera) for both aquatic and terrestrial predators

Chemical secretions are an effective means by which insects can deter potential enemies. Several terrestrial insects spray these liquids directionally toward enemies, but little is known about spraying behavior in aquatic and semiaquatic insects. The larvae of Osmylus hyalinatus (Neuroptera: Osmylidae) are semiaquatic, inhabiting the edges of small streams and ponds where they encounter multiple enemies on land and in water. The larvae of this osmylid sprayed a hyaline liquid from the anal opening if disturbed in either air and water, although the spray appeared slightly viscous in water. The liquid was stored in the posterior half of the hindgut and sprayed directionally toward an artificial stimulus. Spraying allowed the larvae to escape biting by ants, and to repel them in 90% of encounters. Spraying caused the regurgitation of 71% and 60% of all larvae swallowed by terrestrial frogs and aquatic newts, respectively. Aquatic fishfly larvae released 30% of captured larvae due to spraying. Most of the larvae that repelled ants or were regurgitated by amphibians survived, but those released by fishfly larvae were killed by heavy biting with the mandibles. This is the first report of effective liquid spraying by insects in water, and also within the order Neuroptera.

Attraction of Chrysotropia ciliata (Neuroptera, Chrysopidae) Males to P-Anisaldehyde, a Compound with Presumed Pheromone Function

In a field-trapping experiment with plant volatiles, we observed notably high attraction of green lacewing (Chrysotropia ciliata) males to the compound p-anisaldehyde. Based on this finding, we initiated the present study to elucidate this phenomenon and to investigate the chemical ecology of C. ciliata. Scanning electron microscopy revealed elliptical glands abundantly distributed on the 2nd to 6th abdominal sternites of C. ciliata males, whereas females of the species completely lacked such glands. No p-anisaldehyde was found in extractions of body parts of C. ciliata. Methyl p-anisate and p-methoxybenzoic acid were identified exclusively in the extract from abdominal segments 2–8 of males. Field-trapping experiments revealed no attraction of C. ciliata to either methyl p-anisate or p-methoxybenzoic acid. In contrast, males showed marked attraction to p-anisaldehyde in the field and antennae showed strong responses to this compound. Headspace collections in the field from living insects in their natural environment and during their main daily activity period indicated that p-anisaldehyde was emitted exclusively by C. ciliata males. Our overall results suggest that p-anisaldehyde might serve as a male-produced pheromone that attracts conspecific C. ciliata males. Here, we discuss hypotheses regarding possible mechanisms involved in regulation of p-anisaldehyde production, including involvement of the compounds methyl p-anisate and p-methoxybenzoic acid, and the potential ecological function of p-anisaldehyde in C. ciliata.

Electrophysiological and behavioral responses of Bradysia odoriphaga (Diptera: Sciaridae) to volatiles from its Host Plant, Chinese Chives (Allium tuberosum Rottler ex Spreng)

Bradysia odoriphaga Yang et Zhang is a serious belowground pest of Chinese chives (Allium tuberosum). Our previous studies have indicated that B. odoriphaga females prefer to oviposit near the roots of Chinese chives rather than the roots of other plants, and that the performance (longevity and fecundity) of B. odoriphaga offspring was better on Chinese chives than on Lettuce (var. ramosa Hort.), Onion (Allium cepa) and Potato (Solanum tuberosum) but little is known about how the volatiles released by Chinese chives affect the host-finding and oviposition behaviors of B. odoriphaga. Here, we used gas chromatography-mass spectrometry and determined that Chinese chives releases the following volatiles: methyl allyl disulfide, β-myrcene, cis-ocimene, diallyl disulfide, nonane, n-dodecane, n-tetradecane, and n-hexadecane; quantities released were highest for methyl allyl disulfide and diallyl disulfide. In addition to eliciting strong responses in females in electroantennography assays, the latter two sulfur compounds and their mixtures attracted females in Y-tube olfactometer assays. The addition of methyl allyl disulfide, diallyl disulfide, or a mixture of the two compounds at a 1:5 ratio to chive plants increased oviposition when compared to control plants. These results indicate that methyl allyl disulfide and diallyl disulfide, either alone or in combination, influence the host-seeking behavior of B. odoriphaga.

New perspectives for simultaneous attraction of Chrysoperla and Chrysopa lacewing species for enhanced biological control (Neuroptera: Chrysopidae)

Green lacewings (Chrysopidae) are important predators of many soft-bodied pest insects, for instance aphids. Previous studies reported attraction of Chrysoperla carnea species-complex to a ternary floral bait. The larvae of these lacewings are important generalist predators in agroecosystems, however adults are non-predatory, they feed on pollen, nectar or honeydew. Squalene, a plant originated compound was previously reported to be attractive to the nearctic Chrysopa nigricornis. In the current study squalene was tested alone and in combination with the ternary bait in field experiments in Hungary. In our experiments, traps baited with squalene attracted predatory males of Chrysopa formosa. Traps baited with squalene and the ternary floral bait attracted adults of both C. formosa and C. carnea complex lacewings. To our knowledge this is the first report of a bait combination attractive to both Chrysoperla and Chrysopa species. This finding is of special interest considering the remarkably different feeding habits of the adults of these lacewings. Potential perspectives in biological control are discussed.

Pest Management Systems and Insecticide Tolerance of Lacewings (Neuroptera: Chrysopidae)

Lacewings (Neuroptera: Chrysopidae) are part of the beneficial fauna found in citrus orchards under both organic and conventional pest management. Due to their importance, knowledge about susceptibility of these predators to insecticides is a key element for their use as biological control agents. We studied the inter- and intraspecific susceptibility of the following lacewing species to bifenthrin, chlorpyrifos, and imidacloprid: Ceraeochrysa cincta (Schneider) (Neuroptera: Chrysopidae), Ceraeochrysa cubana (Hagen), Ceraeochrysa paraguaria (Navás), and Chrysoperla externa (Hagen). Different concentrations of these insecticides were sprayed on first instar larvae of these lacewing species from six orchards (three organic and three conventional), and LC50s were estimated. Development and reproduction of the most common lacewing, C. cincta, from both organic and conventional management systems were also studied. Lacewings from conventional management areas do not always have greater tolerance to insecticides. Chrysoperla externa was the most susceptible species to insecticides. Ceraeochrysa cincta displayed the highest LC50 and its populations from the conventional system showed lower egg hatching but shorter egg and larval developmental time. Adults collected from orchards managed conventionally lived longer, exhibited a higher population growth rate and a reduced doubling time. Ceraeochrysa cincta was the more tolerant species to insecticides better coping with systems that rely on chemical control as the main pest management tactic used.

Attraction of the Green Lacewing Chrysoperla comanche (Neuroptera: Chrysopidae) to Yeast

Many adult Chrysoperla comanche (Stephens) green lacewings were caught in traps baited with live yeast cultures during tests designed to catch olive fruit flies. All 13 yeast species tested were more attractive than the industry-standard dried torula yeast (Cyberlindnera jadinii; syn. Candida utilis). Live C. jadinii culture attracted significantly more lacewings than the inactive dried-pellet form of the same yeast species, demonstrating that volatiles from live yeast cultures attract adults of this lacewing. Odor profiles for two of the highly active yeasts tested herein (Lachancea thermotolerans and Solicoccozyma terrea) were similar to that for Metschnikowia pulcherrima, a yeast species isolated earlier from the gut diverticulum of Chrysoperla rufilabris. A new Metschnikowia species (M. chrysoperlae), along with two new Candida spp. that were recently realigned to one of the Metschnikowia clades (M. picachoensis and M. pimensis), were also identified from the diverticulum of C. comanche. Thus, one clade of Metschnikowia yeasts that commonly occur in floral nectar appears to exhibit mutualistic symbioses with Chrysoperla green lacewings. Both male and female C. comanche adults were attracted in the present study, and we speculate that males have exploited this symbiosis by offering Metschnikowia-laden regurgitant, including attractive volatiles, to females ('mating trophallaxis') as a nuptial gift.

Mating system, age, and reproductive performance in Tenuisvalvae notata, a long-lived ladybird beetle

The long-lived polygynandrous ladybird beetle Tenuisvalvae notata (Mulsant) found in Brazil was evaluated in the laboratory for the effects of multiple mating and aging on its reproductive performance. This species is native to South America and is an important predator of mealybugs. Specifically studied were partner choice, female reproductive success, adult longevity, male virility, and offspring development. Young (5-10 days old) and older virgin females (95-100 days old) were subjected to either a single mate or multiple mating with the same or different males of various mating status (virgin or previously mated once, twice, and thrice). Results revealed a preference in both genders to mate with previously known partners. Additionally, younger females had higher fecundity and greater longevity when mated only once in comparison to those mated multiple times. Fecundity, fertility, and offspring development were similar across the treatments regardless of the number of mating or male mating history. Fecundity and fertility decreased throughout the oviposition period regardless of mating treatment.

Uptake of plant-derived specific alkaloids allows males of a butterfly to copulate

Certain butterflies utilize plant-acquired alkaloids for their own chemical defense and/or for producing male sex pheromone; a trait known as pharmacophagy. Males of the danaine butterfly, Parantica sita, have been reported to ingest pyrrolizidine alkaloids (PAs) as adults to produce two PA-derived sex pheromone components, viz. danaidone (major) and 7R-hydroxydanaidal. We found, however, that not all PAs that can be precursors for the pheromone serve for mating success of males. Here we show that although the sex pheromone is regarded as a requisite for successful mating, uptake of specific PA(s) (lycopsamine-type PAs) is also imperative for the males to achieve copulation. The increase in the levels of two biogenic amines, octopamine and/or serotonin, in the brain and thoracic ganglia of males fed with specific PA(s) suggested that these alkaloids most likely enhance male mating activity. The results can present new evidence for the evolutionary provenance of pharmacophagous acquisition of PAs in PA-adapted insects.

Field Trapping of Predaceous Insects With Synthetic Herbivore-Induced Plant Volatiles in Cotton Fields

Nine herbivore-induced plant volatiles (HIPVs) and one methyl jasmonate were field-tested for their attractiveness to the main predators in cotton fields of North China in 2 yr. The main predators including ladybird beetles (Propylaea japonica (Thunberg), Harmonia axyridis (Pallas)), green lacewings (Chrysoplera sinica (Tjeder), Chrysopa spp.), predatory bugs (Geocoris pallidipennis (Costa), Orius spp., Nabis spp.) and spiders (Misumenops tricuspidatus (Fabricius), Erigonidium graminicolum (Sundevall)) were investigated. Two-way ANOVA indicated that the volatile compound, year, and the volatile compound × year interaction affected the behavioral responses of predators. It was found that indole significantly attracted the ladybird beetle P. japonica, H. axyridis. Linalool could attract P. japonica. Green lacewing C. sinica was significantly attracted by α-pinene and β-pinene, whereas indole significantly attracted Chrysopa spp. Methyl jasmonate and α-pinene showed significant attraction to small-flower bug Orius spp. In addition, the attraction of α-humulene to C. sinica, attractiveness of β-pinene to Orius spp. and Chrysopa spp., were observed only in one of the two years. However, the big-eyed bug G. pallidipennis, damsel bug Nabis spp., spiders M. tricuspiata and E. graminicolum did not respond to any of the tested HIPVs. These results are discussed with respect to possible applications of a synthetic attractant for main predators in cotton fields.

Conspecific and Heterogeneric Lacewings Respond to (Z)-4-Tridecene Identified from Chrysopa formosa (Neuroptera: Chrysopidae)

Green lacewings (Chrysopidae) are predators of soft-bodied pest insects and are among the most important biological control agents in crop protection. Chrysopa spp. are of special importance since, unlike most green lacewing species, adults are also predatory. The current study was undertaken in search of Chrysopa formosa compounds with semiochemical activity. Using coupled gas chromatography-electroantennography (GC-EAG), head and thorax extracts of C. formosa elicited EAG responses to a compound subsequently identified by coupled GC/mass spectrometry, microchemistry, chemical synthesis and GC peak enhancement as (Z)-4-tridecene. In field experiments, this compound decreased attraction of adult C. formosa to (1R,4aS,7S,7aR)-nepetalactol and that of Chrysoperla carnea species-complex to a ternary floral lure, with the inhibitory effect found to be dose-dependent. Our results suggest that (Z)-4-tridecene may serve as a general warning signal among multiple green lacewing species. Perspectives for potential practical applications are discussed.

Pharmacophagy in green lacewings (Neuroptera: Chrysopidae: Chrysopa spp.)?

Green lacewings (Neuroptera: Chrysopidae) are voracious predators of aphids and other small, soft-bodied insects and mites. Earlier, we identified (1R,2S,5R,8R)-iridodial from wild males of the goldeneyed lacewing, Chrysopa oculata Say, which is released from thousands of microscopic dermal glands on the abdominal sterna. Iridodial-baited traps attract C. oculata and other Chrysopa spp. males into traps, while females come to the vicinity of, but do not usually enter traps. Despite their healthy appearance and normal fertility, laboratory-reared C. oculata males do not produce iridodial. Surprisingly, goldeneyed lacewing males caught alive in iridodial-baited traps attempt to eat the lure and, in Asia, males of other Chrysopa species reportedly eat the native plant, Actinidia polygama (Siebold & Zucc.) Maxim. (Actinidiaceae) to obtain the monoterpenoid, neomatatabiol. These observations suggest that Chrysopa males must sequester exogenous natural iridoids in order to produce iridodial; we investigated this phenomenon in laboratory feeding studies. Lacewing adult males fed various monoterpenes reduced carbonyls to alcohols and saturated double bonds, but did not convert these compounds to iridodial. Only males fed the common aphid sex pheromone component, (1R,4aS,7S,7aR)-nepetalactol, produced (1R,2S,5R,8R)-iridodial. Furthermore, although C. oculata males fed the second common aphid sex pheromone component, (4aS,7S,7aR)-nepetalactone, did not produce iridodial, they did convert ∼75% of this compound to the corresponding dihydronepetalactone, and wild C. oculata males collected in early spring contained traces of this dihydronepetalactone. These findings are consistent with the hypothesis that Chrysopa males feed on oviparae (the late-season pheromone producing stage of aphids) to obtain nepetalactol as a precursor to iridodial. In the spring, however, wild C. oculata males produce less iridodial than do males collected later in the season. Therefore, we further hypothesize that Asian Chrysopa eat A. polygama to obtain iridoid precursors in order to make their pheromone, and that other iridoid-producing plants elsewhere in the world must be similarly usurped by male Chrysopa species to sequester pheromone precursors.