An omics evolutionary perspective on phytophagous insect–host plant interactions in Anastrepha obliqua: a review

Phytophagous insects have a close relationship with their host plants. For this reason, their interactions can lead to important changes in insect population dynamics and evolutionary trajectories. Next generation sequencing (NGS) has provided an opportunity to analyze omics data on a large scale, facilitating the change from a classical genetics approach to a more holistic understanding of the underlying molecular mechanisms of host plant use by insects. Most studies have been carried out on model species in Holarctic and temperate zones. In tropical zones, however, the effects of use of various host plants on evolutionary insect history is less understood. In the current review, we describe how omics methodologies help us to understand phytophagous insect–host plant interactions from an evolutionary perspective, using as example the Neotropical phytophagous insect West Indian fruit fly, Anastrepha obliqua (Macquart) (Diptera: Tephritidae), an economically important fruit crop pest in the Americas. Anastrepha obliqua could adopt a generalist or a specialist lifestyle. We first review the adaptive molecular mechanisms of phytophagous insects to host plants, and then describe the main tools to study phytophagous insect–host plant interactions in the era of omics sciences. The omics approaches will advance the understanding of insect molecular mechanisms and their influence on diversification and evolution. Finally, we discuss the importance of a multidisciplinary approach that integrates the use of omics tools and other, more classical methodologies in evolutionary studies.     

Size specific demography of three species of Anastrepha fruit flies

Individuals of three Anastrepha species: A. obliqua, A. ludens, and A. serpentina (Diptera: Tephritidae), were sorted according to pupal weight in cohorts of large and small flies. Demographic parameters and reproductive patterns and heterogeneity were determined for each cohort. Large flies of the three species presented greater expectation of life and gross fecundity rates. A. ludens was the species with the longest life span (expectation of life of large adults was 110 days) and the greatest gross fecundity rates (1597 eggs/female for the large flies). While, A. obliqua had the shortest mean age of reproduction (33 days), and the greatest daily egg production (14 eggs/female/day). Net fecundity was similar in these two. A. serpentina had lower fecundity rates.Reproductive information for each size and each species include: age-by-parity relations, fraction of sexually mature life in which females lay eggs, and frequency distribution of individual egg production. Results demonstrate that even under constant laboratory conditions and using standard artificial hosts, there is a great deal of life history variation among these Anastrepha species and among other tephritid fruit flies.     

Age and host effects on clutch size in the Mexican fruit fly, Anastrepha ludens

We document individual and age-specific variation in reproductive output and clutch size of Anastrepha ludens Loew. (Diptera: Tephritidae). The influence of host size, color, and density on clutch size are also examined. Individual and groups of flies were offered artificial hosts composed of agar spheres wrapped in Parafilm. The gross reproduction rate of individual flies was 1000 eggs/female and 165 clutches/female with a range of 1 to 40 eggs/clutch. Mean clutch sizes for these females ranged from 4.5 to 10.6 eggs/clutch. The number of eggs/clutch laid by females held in groups was highly correlated with host size, ranging from about 4.4 eggs/clutch in 2 cm diameter hosts to 12.7 eggs/clutch in 11 cm hosts. Host color, host density, fly density, and fly age did not affect clutch size. This study suggests that variation among females and host size are the principal determinants of clutch size in A. ludens.

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Résumé L'examen a porté sur l'influence du polymorphisme et des modifications dues à l'âge des mouches sur la fécondité et la taille des pontes de A. ludens Loew (Dipt. Tephritidae). L'étude a concerné aussi l'influence de la dimension, de la couleur et de la densité des hôtes sur la taille des pontes. Des mouches isolées ou par groupes ont reçu des hôtes artificiels formés de sphères d'agar enveloppées dans du parafilm. La fécondité brute de femelles isolées a été de 1000 oeufs/femelle et de 165 pontes/femelle, avec une variation de 1 à 40 oeufs/ponte. La taille moyenne des pontes des différentes femelles isolées s'étalait de 4,5 à 10,6 oeufs/ponte. Le nombre d'oeufs/ponte des femelles groupées était fortement liée à la dimension de l'hôte, s'étalant de 4,4 oeufs/ponte pour des hôtes de 2 cm de diamètre à 12,7 oeufs/ponte pour ceux de 11 cm de diamètre. Ni la couleur et la densité des hôtes, ni la densité et l'âge des mouches n'ont influé sur la taille des pontes. Ces résultats suggèrent que les variabilités du comportement des femelles et de la dimension des hôtes déterminent par priorité la taille des pontes de A. ludens.

     

Sperm allocation and cost of mating in a tropical tephritid fruit fly

Males that copulate repeatedly may suffer from reduced sperm stores. However, few studies have addressed sperm depletion from both the female and male perspective. Here, we show that male Anastrepha obliqua (Diptera: Tephritidae) do not ejaculate all available sperm and are left with mature sperm in the seminal vesicles even after copulating as often as three times in half a day. Ejaculate size was not related to male mating history; time elapsed since the last mating, copulation duration, female thorax length or head width. Larval host origin did not affect the number of sperm stored by females. More sperm was found in the ventral receptacle compared to sperm stored in the three spermathecae. Males apparently do not suffer a cost of mating in terms of longevity, although we cannot rule out other fitness costs. Sperm production in this species may not be as costly as it is for other species. Results suggest that males strategically allocate similar numbers of sperm among successive mates without exhausting sperm reserves for future encounters. We discuss the role that differential sperm storage may have in mediating sperm competition and tie our results to the unique natural history of A. obliqua.     

Quantity and safety vs. quality and performance: conflicting interests during mass rearing and transport affect the efficiency of sterile insect technique programs

The sterile insect technique (SIT) requires production of large quantities of sterile males able to successfully compete with wild males for wild females. During eradication of a pest population, the release of fertile insects or capture of non‐marked released flies can have deleterious effects and trigger costly control measures. These perceived risks encourage program managers to apply high radiation doses and high doses of marking dye. In addition, mass rearing factories are strategically located away from release areas to prevent escape of fertile individuals within eradicated areas, raising the need for lengthy transport. Such is the case for Anastrepha obliqua Macquart (Diptera: Tephritidae) released in mango producing areas of Mexico under an SIT‐based eradication campaign. Here, we examined several standard quality‐control parameters for mass‐reared A. obliqua subjected to various time periods under hypoxia during transport, marked with different doses of fluorescent dye, and subjected to different radiation doses. Such factors were evaluated in isolation and in conjunction. Overall, long periods of hypoxia, high marking doses, and high radiation doses reduced the number of flying adults and increased the number of non‐emerged pupae. Some quality‐control parameters such as number of deformed adults, part‐emerged pupae, and non‐flying adults provided less informative guidance or redundant information of fly performance. Some tests such as mortality under stress and mating propensity in small cages were useless in detecting differences in quality among treatments for parameters evaluated during experiments. We discuss the quantity/safety‐quality/performance conflict during eradication using SIT, propose different strategies according to different stages during eradication (management, suppression, eradication, outbreaks in free areas), where males irradiated at low doses and marked with low doses of dye can be released during early suppression, and examine the pertinence of carrying out different quality‐control tests.     

Effect of Beauveria bassiana on the ovarian development and reproductive potential of Anastrepha ludens (Diptera: Tephritidae)

We investigated the virulence of a native strain of Beauveria bassiana on the mortality, ovarian development, oogenesis, survival, fecundity and fertility of 4-, 8- and 12-day-old Anastrepha ludens females. In the first study, this strain caused 85% mortality in 8-day-old treated females, with a median lethal concentration (LC₅₀) of 3.1×10⁸ (2.1×10⁸–4.7×10⁸) conidia/mL and a median lethal time (LT₅₀) of 6.5 days. In the second study, the ovarian development and oogenesis of A. ludens females treated with 1×10⁹ conidia/mL were monitored daily in sacrificed flies. The fungus infection did not significantly affect ovarian development of the treated females, although there was a delay in vitellogenesis and a reduction in the quantity of mature basal oocytes and oviposition index in these flies. Moreover, the lowest net fecundity was found in 4-, 8- and 12-day-old treated females, and reduced fertility was observed in 4-day-old treated females. An application to test the potential use of this strain under field conditions is discussed.     

Electroantennagrams of Mexican fruit flies to chemicals produced by males

Male-produced chemicals were tested on antennae of the Mexican fruit fly (Anastrepha ludens) (Diptera: Tephritidae) using the electroantennagram technique. Male and female antennae responded equivalently to six chemicals and combinations of the six chemicals. (S,S)-(-)-epianastrephin elicited responses two-three times greater than any of the other chemicals, (S,S)-(-)-anastrephin gave greater responses than (R,R)-(+)-anastrephin, and Z,Z-3,6-nonadienol gave greater responses than Z-3-nonenol. The combination of Z,Z-3,6-nonadienol and Z-3-nonenol elicited a response which was slightly less than the response to Z,Z-3,6-nonadienol alone. The EAG data were highly correlated with behavioral data from earlier experiments.

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Résumé L'étude des substances émises par les mâles d'A. ludens (Diptera, Tephritidae) comprenant 2 paires énantiomériques de lactones épimériques et 2 alcools, a été réalisée à partir d'électroantennogrammes.Les antennes des mâles et des femelles ont répondu de la même façon aux 6 substances examinées séparément, ou combinées 2 à 2, ou toutes ensembles. La (S,S)-(-) épianastréphine, seule ou en combinaison, a induit une réponse significativement de 2 à 3 fois plus importante que n'importe qu'elle autre substance. La (S,S)-(-) anastréphine a induit des EAG deux fois plus importantes que ceux obtenus avec la (R,R)-(+) anastréphine.L'importance des réponses aux 4 lactones est liée à leurs relations structurales.Le (Z,Z)-3,6 nonadiénol a provoqué des réponses 2 fois plus importantes que celles du (Z)-3 nonénol, et la combinaison des 2 alcools a induit une réponse légèrement inférieure à celle obtenue avec le (Z,Z)-3,6-nonadiénol seul.Les résultats en EAG sont très conformes aux observations comportementales d'expériences précédentes.

     

Superparasitism in mass reared Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), a parasitoid of fruit flies (Diptera: Tephritidae)

Superparasitism frequency and its effects on the quality of mass-reared Diachasmimorpha longicaudata (Ashmead) parasitoids were investigated under laboratory conditions. Percentage of adult emergence, sex ratio, survival, fecundity and flight ability of adult parasitoids that emerged from Anastrepha ludens (Loew) pupae with different levels of superparasitism were determined. A high prevalence of superparasitism was observed. The number of scars per pupa, produced by insertion of the parasitoid ovipositor, ranged from 1 to 30, with an average (±SD) of 8.3 ± 6.2. Adult parasitoid emergence decreased as the level of superparasitism increased. However, the fraction of females rose with increasing superparasitism and the flight ability was lower in adults emerging from pupae with only one scar, compared with adults emerging from superparasitized hosts. Female longevity and fecundity were not affected by superparasitism. Our results support the hypothesis that superparasitism in D. longicaudata might be adaptive, since adults emerging from hosts with moderate levels of superparasitism showed the highest percentage of emergence and there were no significant differences in the other quality control parameters tested. Our findings are relevant to the mass rearing process, where the ratio of hosts to parasitoids can be optimized as well as the distribution of eggs deposited in host larvae. This contributes to efficient mass rearing methods for augmentative biological control programs.