Charalampos S. Ioannou

Enhanced mating competitiveness of Ceratitis capitata males following exposure to citrus compounds

Previous work has demonstrated that exposure of males of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), to the scent of sweet orange increases their mating success relative to non‐exposed males. Here, we demonstrate that exposure to the commercial essential oils of bitter orange, mandarin orange, lemon and grapefruit confer to males a significant mating advantage as well. Likewise, exposure to peel‐wounded mandarin oranges and lemons, and to peel‐wounded sweet oranges of the Merlin, Newhole and Naveline varieties, also conferred a significant mating advantage. Exposure to peel‐wounded grapefruits and bitter oranges as well as to sweet oranges of the local Greek variety Xino Artas enhanced mating success, however, not significantly. These results suggest that the chemicals responsible for mating enhancement in C. capitata are present in several citrus fruit species and varieties. In an experiment involving different doses of commercial sweet orange peel oil, males exposed to medium doses of 12.5 or 25 μl achieved significantly higher numbers of matings with virgin females than control males. Lower doses did not increase mating success, whereas higher doses killed a number of males. In another experiment we tested the effect of the seven most abundant individual chemical compounds of citrus oil (some of them also existing in the pheromone of males) and detected compounds with some potential for further trials. In a final experiment we created a mixture of those compounds (geraniol, α‐pinene, limonene, β‐myrcene and linalool) and found that wild or sterile males exposed to it achieved over 70% of all matings when competing with non‐exposed males. Since the mixture did not contain α‐copaene (an expensive compound that is often invoked as responsible for the phenomenon of mating enhancement) our data could lead in a more cost‐effective and efficient implementation of sterile insect technique (SIT) programmes against C. capitata.

Essential oils of citrus fruit stimulate oviposition in the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae)

Female Mediterranean fruit flies (medfly) Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) perceive both qualitative and quantitative aspects of citrus fruit chemistry. However, the behavioural and biological adjustments of this response remain largely unknown. In the present study, the ovipositional responses of gravid female medflies to essential oils (i.e. the most critical resistance factor to medfly infestation) of various citrus fruits are investigated. In dual‐choice (treatment versus distilled water control) experiments, females lay significantly more eggs into pre‐punctured hollow oviposition hemispheres (domes) provided with 1 µL of citrus peel oil from sweet orange, satsuma mandarin, bitter orange, grapefruit and lemon compared with odourless domes. No‐choice tests show a weak effect of lemon essential oils in stimulating oviposition. The female ovipositional response to sweet orange oil (the most active in eliciting oviposition) is dose‐dependent. Additionally, limonene, the most abundant chemical in all citrus oils, stimulates oviposition, whereas linalool, a representative compound of immature citrus fruit associated with high toxicity against immature stages of fruit flies, has a significant deterrent effect. In further no‐choice tests, females lay approximately 23% fewer eggs in limonene (93%) (amount found in orange oil) and 60% fewer eggs in limonene 93% plus linalool 3% (approximately 10‐fold the amount found in orange oil) mixtures, relative to sweet orange oil. The results suggest that the limonene content accounts largely (but not completely) for the ovipositional responses observed in sweet orange oil, whereas high linalool proportions are capable of significantly masking and/or disrupting its stimulatory effects in citrus oils. The importance and practical implications of these findings with respect to understanding how citrus fruit chemistry influences the ovipositional responses of medfly is discussed.

Aromatized to Find Mates: α-Pinene Aroma Boosts the Mating Success of Adult Olive Fruit Flies

Background Contrary to other Tephritidae, female but also male olive flies, Bactrocera oleae release pheromones during their sexual communication. Alpha-pinene, a common plant volatile found in high amounts in unripe olive fruit and leaves has been detected as one of the major components of the female pheromone. However, possible effects of α-pinene and that of other host volatiles on the mating behavior of the olive fly have not been investigated. Methodology Using wild olive flies, reared on olive fruit for 3 generations in the laboratory, we explored whether exposure of male and female olive flies to α-pinene affects their sexual performance. Results Exposure of sexually mature adult olive flies to the aroma of α-pinene significantly increases the mating performance over non-exposed individuals. Interestingly, exposure to α-pinene boosts the mating success of both males and female olive flies. Conclusions This is the first report of such an effect on the olive fly, and the first time that a single plant volatile has been reported to induce such a phenomenon on both sexes of a single species. We discuss the possible associated mechanism and provide some practical implications.

Toxic and hormetic-like effects of three components of citrus essential oils on adult Mediterranean fruit flies (Ceratitis capitata)

Plant essential oils (EOs) and a wide range of their individual components are involved in a variety of biological interactions with insect pests including stimulatory, deterrent, toxic and even hormetic effects. Both the beneficial and toxic properties of citrus EOs on the Mediterranean fruit fly (medfly) have been experimentally evidenced over the last years. However, no information is available regarding the toxic or beneficial effects of the major components of citrus EOs via contact with the adults of the Mediterranean fruit fly. In the present study, we explored the toxicity of limonene, linalool and α-pinene (3 of the main compounds of citrus EOs) against adult medflies and identified the effects of sub-lethal doses of limonene on fitness traits in a relaxed [full diet (yeast and sugar)] and in a stressful (sugar only) feeding environment. Our results demonstrate that all three compounds inferred high toxicity to adult medflies regardless of the diet, with males being more sensitive than females. Sub-lethal doses of limonene (LD20) enhanced the lifespan of adult medflies when they were deprived of protein. Fecundity was positively affected when females were exposed to limonene sub-lethal doses. Therefore, limonene, a major constituent of citrus EOs, induces high mortality at increased doses and positive effects on life history traits of medfly adults through contact at low sub-lethal doses. A hormetic-like effect of limonene to adult medflies and its possible underlying mechanisms are discussed.

The odor of a plant metabolite affects life history traits in dietary restricted adult olive flies

Food quality shapes life history traits either directly or through response of individuals to additional environmental factors, such as chemical cues. Plant extracts used as food additives modulate key life history traits; however little is known regarding such effects for olfactory chemical cues. Exploiting an interesting experimental system that involves the olive fly (Bactrocera oleae) and the plant metabolite α-pinene we asked whether exposure of adults to this compound modulates adult longevity and female reproduction in similar manner in a stressful – dietary (protein) restricted (DR) and in a relaxed- full diet (FD) feeding environment. Accordingly, we exposed males and females to the aroma of α-pinene and measured lifespan and age-specific fecundity in the above two dietary contexts. Our results demonstrate that exposure to α-pinene increased longevity in males and fecundity in females only under dietary restricted conditions. In relaxed food conditions, females exposed to α-pinene shifted high egg-laying towards younger ages compared to non-exposed ones. This is the first report demonstrating that a plant compound affects key life history traits of adult olive flies through olfaction. These effects are sex-specific and more pronounced in dietary restricted adults. Possible underlying mechanisms and the ecological significance are discussed.

Polygyny in the olive fly—effects on male and female fitness

Polygynous males must balance their limited ejaculate resources between current copulations, with putative future ones. Working on olive flies (Bactrocera oleae), our objectives were to determine (a) how males budget sperm to consecutive copulations, (b) what costs consecutive copulations incur, and (c) how male mating history affects female fecundity, fertility, and longevity. We allowed males to copulate with virgin females on successive days and monitored the fertility and fecundity of these females, and the longevity of both sexes. We found that as males gained sexual experience, latency to mate declined significantly, while copula duration increased. The number of sperm stored by females declined according to the sexual history of her mate—as males gained experience, significantly fewer sperm cells were transferred. Mated males suffered a significant longevity cost compared to virgin ones, but this cost was not compounded by additional matings. Male sexual experience affected both female fecundity and fertility. Furthermore, mating with an experienced male incurred a longevity cost to females. We conclude that non-sperm components of the male ejaculate are responsible for reducing female fecundity, fertility, and longevity, and predict that females should prefer to mate with virgin males.

Seasonality of Post-capture Longevity in a Medically-Important Mosquito (Culex pipiens)

The epidemiological importance of the age structure and longevity potential of wild populations of mosquito disease vectors has been known for over 60 years. However, no routine method currently exists that provides reliable insights into the population age dynamics of this medically-important group of insects. In this paper we use a technique originally developed for studying wild fruit fly populations to study the post-capture longevity dynamics in populations of the West Nile virus mosquito Culex pipiens in Greece. This approach, referred to as the captive cohort method, analyzes and interprets the longevity trends in wild-caught Cx. pipiens to infer demographic changes in their field population. Approximately 10 adult females were captured each day from June through November, housed in individual cages in the laboratory, and their remaining longevity recorded. Strong differences were observed in the mean, variation, and extremes of post-capture longevity. Early season (June-July) mosquitoes lived the shortest and late-season the longest with a clear transition period in September. The mean levels of post-capture longevity were quite high at over two months in early season to over 85 days in late season when the vast majority of adults were nulliparous and likely preparing for hibernation. Implications for both basic and epidemiological research on the biodemography of aging in the wild are discussed.

Towards improving sterile insect technique: Exposure to orange oil compounds increases sexual signalling and longevity in Ceratitis capitata males of the Vienna 8 GSS

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a notorious insect pest causing huge economic losses worldwide. The sterile insect technique (SIT) is widely used for its control. Using sexually mature sterilized males of the Vienna 8 (tsl) strain in the laboratory, we explored whether exposure of males to citrus compounds (separately or in a mixture) affects their sexual behaviour and if nutritional conditions and age modulate those effects. Exposed males exhibited increased sexual signalling compared to unexposed ones, particularly when fed a rich adult diet. Interestingly, and for the first time reported in medfly, exposure of Vienna 8 males to a mixture of citrus compounds increases longevity under poor adult diet conditions. We discuss the possible associated mechanisms and provide some practical implications of our results towards improving the effectiveness of SIT.