Effect of a Probiotic-Enriched Diet on Sexual Competitiveness, Pheromone Emission, and Cuticular Hydrocarbons of Sterile and Fertile Anastrepha ludens (Diptera: Tephritidae)

The sterile insect technique has been used for the eradication or control of numerous tephritid fruit flies. However, mass-rearing and sterilization can affect the microbiota and sexual performance of male tephritid fruit flies. Despite the addition of postteneral protein food which contributes to the enhancement of the sexual performance of mass-reared males, in some cases, they are less competitive than their wild counterparts. Alternatively, the addition of probiotics may improve the sexual performance of mass-reared sterile males. In this study, we evaluated the effect of a postteneral Lactobacillus casei-enriched diet on the sexual competitivity, pheromone emission, and cuticular hydrocarbons of mass-reared sterile and fertile Anastrepha ludens (Loew) (Diptera: Tephritidae) males. Flies were fed either with sugar, standard diet (sugar and protein, 3:1), sugar + probiotic, or standard diet + probiotic. The addition of the probiotic improved the sexual competitivity of fertile and sterile males that were devoid of protein but led to a negative effect on males fed with a standard diet. As compared to males that were fed with the standard diet + probiotic/only sugar, the males fed with the standard diet or those fed on sugar + probiotic displayed a higher number of mating instances. Sterile males that fed on sugar + probiotic had a higher relative amount of anastrephine, epianastrephine, n-methyl octacosane, and 2-methyl triacontane than those fed on sugar only. Overall, these compounds were common in the treatments where males had the best sexual performance. Our results suggest that the probiotics offer nutritional advantages to males whose food lacks protein.

Combined Effects of Methoprene and Metformin on Reproduction, Longevity, and Stress Resistance in Anastrepha ludens (Diptera: Tephritidae): Implications for the Sterile Insect Technique

Survival and mating success are traits of quality in mass-reared sterile males. Thus, studying the trade-offs between these traits may help to improve process in the sterile insect technique (SIT). Here, we tested the hypothesis that modifying individual metabolism, especially of energetic reserves, may reduce the negative impact of an early reproduction on the survival of Anastrepha ludens flies. Appling metformin (a drug used to treat type II diabetes) that improves insects' survival, through dietary restriction mimicry, and methoprene (a juvenile hormone analogue) that accelerates the age to reproduction in insects, we explore the dynamic of this trade-off. We fed A. ludens flies with metformin, methoprene, or a mixture of metformin-methoprene for five consecutive days. We determined the effect of these treatments on the fecundity and fertility (number of eggs and percentage of hatching) of females, on sexual maturation and mating success of males, and on the survival of both sexes. The results showed that the acceleration in sexual maturation by the action of methoprene significantly reduced survival in both sexes of two different fly strains. However, adding metformin to the diet buffered this negative effect, without reducing the mating propensity compared with the males treated only with methoprene. The response to metformin was sex-specific since females responded to high doses of the substance, whereas males responded better to low doses. These results suggest that trade-offs between survival and reproduction do not necessarily depend on energy reserves but they are intrinsically related to metabolic regulation and hormonal control.

Impact of Metarhizium robertsii on Adults of the Parasitoid Diachasmimorpha longicaudata and Parasitized Anastrepha ludens Larvae

Biological control of the Mexican fruit fly, Anastrepha ludens, is mainly carried out by releasing parasitoids, such as Diachasmimorpha longicaudata, and by applying entomopathogenic fungi (EPF), such as Metarhizium anisopliae, Beauveria bassiana, or Isaria fumosorosea, which can be applied to the soil or dispersed using infective devices. The combined use of two or more biocontrol agents could improve A. ludens control, but IGP between natural enemies, if it occurs, may have negative effects. We evaluated the effects of EPF on D. longicaudata. First, we determined the susceptibility of adults of D. longicaudata to strains of EPF (Metarhizium robertsii strain V3-160 and M. anisopliae strain MAAP1). We also evaluated the infection of these two fungi on A. ludens larvae parasitized by D. longicaudata. Finally, we determined sub-lethal effects on adults of D. longicaudata that emerged from larvae that had been exposed to low concentrations of M. robertsii. Both fungi caused moderate mortality to D. longicaudata adults. There were no adverse effects on the longevity of parasitoids that emerged from parasitized larvae exposed to M. robertsii. Based on these results, we argue that M. robertsii has the potential to be used for biocontrol of A. ludens, with limited risk to D. longicaudata adults.

Distinctive egg-laying patterns in terminal versus non-terminal periods in three fruit fly species

The specific objective of this study was to use a logistic regression model for determining the degree to which egg laying patterns of individual females at the end of life (i.e., terminal segments) in each of three different fruit fly species could be distinguished from the egg-laying patterns over a similar period in midlife (i.e., non-terminal segments). Extracting data from large-scale databases for 11-day terminal and 11-day non-terminal segments in the vinegar fly (Drosophila melanogaster), the Mexican fruit fly (Anastrepha ludens) and the Mediterranean fruit fly (Ceratitis capitata) and organizing the model's results in a 2 × 2 contingency table, we found that: (1) daily egg-laying patterns in fruit flies can be used to distinguish terminal from non-terminal periods; (2) the overall performance metrics such as precision, accuracy, false positives and true negatives depended heavily on species; (3) differentiating between terminal and non-terminal segments is more difficult when flies die at younger ages; and (4) among the three species the best performing metrics including accuracy and precision were those produced using data on D. melanogaster. We conclude that, although the reliability of the prediction of whether a segment occurred at the end of life is relatively high for most species, it does not follow precisely predicting remaining life will also be highly reliable since classifying an end of life period is a fundamentally different challenge than is predicting an exact day of death.

Genetic and Ecological Relationships of Anastrepha ludens (Diptera: Tephritidae) Populations in Southern Mexico

Knowledge of the influence of evolutionary factors that promote either the differentiation or cohesion of pest insect populations is critical for the improvement of control strategies. Here, we explore the extent to which genetic differentiation occurs between populations of the Mexican fruit fly, Anastrepha ludens, in association with four plant hosts (Citrus sinensis, C. paradisi, Mangifera indica and Casimiroa edulis) in the Soconusco region of Chiapas (Mexico). Using variants from six enzymatic loci, we obtained measures of genetic diversity for three sample arrangements: (1) by sex per locality, (2) by locality and (3) by host. The extent of genetic differentiation in populations was assessed using the Analyses of Molecular Variance (AMOVA) method for each array of samples, and moderate to high levels of genetic variation were observed between the sexes, as well as among localities and host plants. A Bayesian approach was then used to assess any population structure underlying the genetic data we obtained, but this analysis showed no significant structuring due to locality or host plant. We also considered whether the observed genotypic frequencies in male and females matched those expected under a hypothesis of random mating. Here we found significant deviations from expected genotypic frequencies, suggesting that sexual selection is acting on these populations. Overall, our results indicate that sexual selection, along with the presence of some heterogeneity in environments provided by both geographical factors and availability of host plants, has influenced the evolution of pest populations in this region of Mexico. Implications for area-wide pest management strategies are discussed.

Behavioral Responses and Pupa Development Patterns After Hypoxia or Anoxia in a Desiccation-Resistant Anastrepha ludens Strain

The aim of this study was to experimentally test for adult cross-resistance to hypoxia or anoxia in a desiccation-resistant population of Anastrepha ludens Loew. We compared desiccation resistant flies with unselected (control) flies by measuring the effect of pre-emergence hypoxia on some fitness parameters (emergence, flight ability, copulation success, latency to copulation, copulation duration, ovary size). Anoxia effects were determined using eye color changes during pupa development and fly emergence after re-oxygenation. Both strains were negatively affected in all measured parameters when exposed to hypoxia for more than 48 h. However, after hypoxia, control flies showed, in general, shorter latency to mate and longer copula duration than desiccation-resistant flies. Anoxia-induced arrest of pupa development, whereas returning to normoxia conditions induced resumption of development. Anoxia period length (longer than 72 h) increased mortality to 100% in the control line, whereas the desiccation-resistant line survived even at 120 h of anoxia. Thus, pre-release hypoxia must not exceed 24 h in order to maintain insect quality independently of fly type.

Slow Larvae Mutant and Its Potential to Improve the Pupal Color-Based Genetic Sexing System in Mexican Fruit Fly, (Diptera: Tephritidae)

For many years, an area-wide fruit fly control campaign against the Mexican fruit fly, Anastrepha ludens (Loew) has been implemented in some regions of Mexico and Texas, using the sterile insect technique (SIT) as its principal component. To improve the efficiency of the SIT, a genetic sexing strain based on black pupae mutation (bp) was developed for A. ludens, namely, 'Tapachula-7' (Tap-7 genetic sexing strains [GSSs]). This strain was introduced into the AW-IPM program recently and allows male-only releases for SIT applications. Here, we report the genetic and biological characterization of a new mutation, slow larvae (sl), which was introduced to the original translocation of the Tap-7 GSS resulting in two new GSS (slow-7 and Tap/slow-7). In both GSSs, the translocated wild-type males emerge from brown pupae that develop faster than females. The females are homozygous for sl mutation in the slow-7 GSS and homozygous for sl and bp mutations in the Tap/slow-7 GSS, reaching larval maturity 2 d after most of the wild-type males, allowing the separation of most males during pupariation. The potential use of the slow-7 and Tap/slow-7 GSSs in mass rearing and large-scale population suppression programs is discussed.

Structural Differences in the Digestive Tract Between Females and Males Could Modulate Regurgitation Behavior in Anastrepha ludens (Diptera: Tephritidae)

With the aim of understanding the mechanisms involved in the regurgitation behavior of tephritid flies, we performed a structural study of the digestive system of the economically important fruit-fly pest, Anastrepha ludens (Loew) using optical, scanning electronic microscopy (SEM) and transmission electron microscopy (TEM), plus a feeding assay. Most structures studied are similar to those previously reported in other adult dipterans, but, importantly, we found sexual differences in some structures that apparently affect regurgitation. We report for the first time sexual differences in the crop duct nerve and large numbers of dense core vesicles within the nerve bundle. Male nerve bundles are bigger and have more secretory vesicles than female ones. The close proximity to the muscles of both the crop lobes and duct suggest that these vesicles (i.e., possibly neurosecretions) might help modulate the muscles regulating regurgitation. The salivary glands are connected to the crop via tracheae, however, SEM/TEM studies failed to find any direct structural connection. Results of the feeding assay indicate that, independently of food type (sucrose or protein) and age, males regurgitate significantly more than females. Regurgitation behavior may also play an important role in capturing bacteria in the environment, and possibly help adults eliminate ingested toxicants such as insecticides. Our findings shed light on an interesting phenomenon that has important practical implications.

Directional selection to improve the sterile insect technique: Survival and sexual performance of desiccation resistant Anastrepha ludens strains

The sterile insect technique (SIT) is an effective, environmentally friendly method for insect control whose success depends on the sexual performance and survival of sterile males. These two parameters are influenced by environmental conditions of target areas, and releasing insects with a higher tolerance to stressful environments can improve SIT efficiency. Directional selection can be used to produce insect strains with higher tolerance to extreme environmental conditions, such as low humidity, for extended periods. We evaluated, under field cage conditions, the sexual competitiveness, sexual compatibility, and survival of strains of Anastrepha ludens (Loew) selected for desiccation resistance to determine the value of directional selection as a possible approach to enhance SIT efficiency. Fly strains (selected and unselected and those mass-reared) were exposed to stressful conditions of low humidity and food and water deprivation for 24 hr before test. As a control, mild conditions without the stressors were used. No differences in sexual competitiveness and sexual compatibility between selected, nonselected, and mass-reared strains were observed when previously exposed to mild conditions. Thus, selection for desiccation resistance does not modified negatively the sexual performance. However, when insects were exposed to stressful conditions, males of selected strains sexually outperform mass-reared males. Additionally, selected strains presented higher survival than mass-reared flies. The approach to integrate directional selection with other technologies in the SIT as well as the implications of using a desiccation-selected strain in the current pest management program is discussed.

Selection by mating competitiveness improves the performance of Anastrepha ludens males of the genetic sexing strain Tapachula-7

The sexual performance of Anastrepha ludens males of the Tapachula-7 genetic sexing strain, produced via selection based on mating success, was compared with that of males produced without selection in competition with wild males. Mating competition, development time, survival, mass-rearing quality parameters and pheromone production were compared. The results showed that selection based on mating competitiveness significantly improved the sexual performance of offspring. Development time, survival of larvae, pupae and adults, and weights of larvae and pupae increased with each selection cycle. Differences in the relative quantity of the pheromone compounds (Z)-3-nonenol and anastrephin were observed when comparing the parental males with the F4 and wild males. The implications of this colony management method on the sterile insect technique are discussed.

Comparative Responses of Anastrepha ludens and Anastrepha obliqua (Diptera: Tephritidae) to the Synthetic Attractant BioLure

The responses of wild and sterile Anastrepha ludens (Loew) and Anastrepha obliqua (Mcquart) fruit flies to the synthetic attractant BioLure were determined by electroantennography (EAG), in field cage tests using MultiLure traps, and by release-recapture field experiments using sterile flies. In EAG bioassays, no differences were found between species, sexes, sterile and wild flies. There were only specific differences and interactions in dose responses. More A. ludens than A. obliqua individuals were captured in multilure traps in field cage test. In A. ludens, there was not significant difference between the number of females and males captured, whereas in A. obliqua more females than males were caught. Age showed a bimodal response in both species and both sexes, with peaks at 4 and 14 d old. In the release-recapture experiments, there were significant differences between species, sexes, and orchards and among the days after release. More individuals of A. ludens than A obliqua were recaptured. Only in A. obliqua the difference between the sexes was significant, with a 3.60:1 female:male ratio. Orchard conditions affected the recapture rate, but in both orchards the largest number of flies recaptured occurred during the first day after release (46 and 88% in each orchard). Our results show that the response to this synthetic lure is species-specific and contribute to better interpret trapping data.

Population Dynamics of Anastrepha ludens (Loew) (Diptera: Tephritidae) on Citrus Areas in Southern Tamaulipas, Mexico

An analysis of adult population fluctuation of Anastrepha ludens (Loew) was performed in southern Tamaulipas, Mexico from 2008 to 2011. The aim was to analyze population dynamics of A. ludens and its relationships with climatic factors in the citrus region of Llera, Tamaulipas, Mexico. Population densities were weekly examined to identify variation through the year and study period. Four periods were identified according to population size, amplitude, host availability and season of the year. The correlation between population density vs. rainfall and temperature (average, minimum and maximum) was determined by linear and multiple regression analyses. Simple linear regression analysis showed that population density with minimum temperature and rainfall was the most consistent correlation, whereas in multiple regression analysis, rainfall and maximum temperature showed more consistency. A seasonal association between the availability of commercial host, climatic variation, and population peaks of A. ludens was determined. This study may have practical implications for the design of specific control strategies, monitoring, and infestation prevention based on different phases of the pest through the year. This strategy, along with the area-wide approach implemented by the Plant Protection Service may lead to an optimization of material, financial and human resources.

A New Adult Diet Formulation for Sterile Males of Anastrepha ludens and Anastrepha obliqua (Diptera: Tephritidae)

A new adult diet formulation was evaluated for sterile Anastrepha ludens (Loew) and Anastrepha obliqua (Macquart) males at the emergence and release facility of fruit flies in Mexico. The formulation consists of hydrolyzed protein, sugar, juvenile hormone analogue methoprene, and water. The proportion of the ingredients between the solute (4% hydrolyzed protein and 96% sugar) and solvent (10% methoprene and 90% water) was 5:1. This new formulation was called the 1:24 formulation. The main objectives of this study were to develop a simple way to supply the 1:24 formulation to adults and to compare the sexual performance of these flies with the performance of flies fed a standard diet (called the Mubarqui formulation) used at the emergence and release facility of fruit flies in Mexico. The preparation, time, and cost also were evaluated. The results showed no significant differences in the sexual behaviors of the males (number of males mating, number of males calling, mating latency, and mating duration) between the 1:24 formulation and the Mubarqui formulation. However, the cost and the required preparation time are much lower for the 1:24 formulation process than for the Mubarqui formulation process. Based on these results, we recommend the 1:24 formulation as an additional adult diet option in the handling of sterile flies. Its application is practical and does not require changes in packaging systems. The contribution of our findings and their potential application to the improvement of the sterile insect technique are discussed.

Regional-Scale Spatio-Temporal Analysis of Anastrepha ludens (Diptera: Tephritidae) Populations in the Citrus Region of Santa Engracia, Tamaulipas, Mexico

Large citrus areas in Tamaulipas are affected by Anastrepha ludens (Loew) populations. Here we report the findings of a spatio-temporal analysis of A. ludens on an extended citrus area from 2008-2011 aimed at analyzing the probabilities of A. ludens infestation and developing an infestation risk classification for citrus production. A Geographic Information System combined with the indicator kriging geostatistics technique was used to assess A. ludens adult densities in the spring and fall. During the spring, our models predicted higher probabilities of infestation in the western region, close to the Sierra Madre Oriental, than in the east. Although a patchy distribution of probabilities was observed in the fall, there was a trend toward higher probabilities of infestation in the west than east. The final raster models summarized the probability maps using a three-tiered infestation risk classification (low-, medium-, and high risk). These models confirmed the greater infestation risk in the west in both seasons. These risk classification data support arguments for the use of the sterile insect technique and biological control in this extended citrus area and will have practical implications for the area-wide integrated pest management carried out by the National Program Against Fruit Flies in Tamaulipas, Mexico.

Phylogeographic Structure in Anastrepha ludens (Diptera: Tephritidae) Populations Inferred With mtDNA Sequencing

Anastrepha ludens (Loew) (Diptera: Tephritidae), the Mexican fruit fly, is a major pest of citrus and mango. It has a wide distribution in Mexico and Central America, with infestations occurring in Texas, California, and Florida with origins believed to have been centered in northeastern Mexico. This research evaluates the utility of a sequence-based approach for two mitochondrial (COI and ND6) gene regions. We use these markers to examine genetic diversity, estimate population structure, and identify diagnostic information for A. ludens populations. We analyzed 543 individuals from 67 geographic collections and found one predominant haplotype occurring in the majority of specimens. We observed 68 haplotypes in all and see differences among haplotypes belonging to northern and southern collections. Mexico haplotypes differ by few bases possibly as a result of a recent bottleneck event. In contrast to the hypothesis suggesting northeastern Mexico as the origin of this species, we see that specimens from two southern collections show high genetic variability delineating three mitochondrial groups. These data suggest that Central America is the origin for A. ludens. We show that COI and ND6 are useful for phylogeographic studies of A. ludens.

Sexual Competitiveness of Anastrepha ludens (Diptera: Tephritidae) Males Exposed to Citrus aurantium and Citrus paradisi Essential Oils

Males of the Mediterranean fruit fly (Ceratitis capitata (Wiedemann)) display increased mating competitiveness following exposure to the odor of certain host and nonhost plants, and this phenomenon has been used in the sterile insect technique to boost the mating success of released, sterile males. Here, we aimed to establish whether males of the Mexican fruit fly (Anastrepha ludens (Loew)) gain a mating advantage when exposed to the aroma of two preferred hosts, grapefruit (Citrus paradisi Macfadyen) and bitter orange (Citrus aurantium L.). Under seminatural conditions, we observed that, in trials using wildish males (from a young laboratory colony started with wild flies) exclusively, exposure to the aroma of bitter orange had no effect on male mating success but exposure to the odor grapefruit oil increased male mating success significantly. In a separate test involving both exposed and nonexposed wildish and mass-reared, sterile males, although wildish males were clearly more competitive than sterile males, exposure to grapefruit oil had no detectable effect on either male type. Exposure to oils had no effect on copulation duration in any of the experiments. We discuss the possibility that the positive effect of grapefruit essential oils on wildish male competitiveness may have been linked to exposure of females to grapefruit as a larval food, which may have imprinted them with grapefruit odors during pupal eclosion and biased their response as adults to odors of their maternal host.

Female receptivity in Anastrepha ludens (Diptera: Tephritidae) is not modulated by male accessory gland products

In numerous insects, accessory gland products (AGPs) transferred from males to females during mating are responsible for female sexual inhibition, but these products can be affected by male condition. Here, we investigated the effect of AGPs on female receptivity of the Mexican fruit fly Anastrepha ludens (Loew), and the effect of male and female strain, male irradiation, AGP dose and sexual activity period on the effectiveness of these AGPs in inhibiting female remating. Injections of aqueous extracts of male accessory glands into the abdomen of females did not reduce their receptivity either at 0.2 or 0.8 male equivalent. Females injected with AGPs behaved like virgin females and not as mated females. Neither male origin, female origin (wild versus mass-reared), nor male irradiation (sterile versus fertile males) had an effect in inhibiting female remating. Also, injections of glands obtained during the sexual calling period of males, or obtained during the morning when males are not sexually active had no effect on female remating behavior. Mated mass-reared females were more likely to remate than wild females. We conclude that inhibition of female sexual receptivity of A. ludens is mediated by factors other than AGPs, such as the number of sperm stored by females, the stimulus of copulation per se or more probably, mediated by a combination of factors. More research is needed to elucidate the role of AGPs in this species.

Superparasitism in the Fruit Fly Parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) and the Implications for Mass Rearing and Augmentative Release

Superparasitism, a strategy in which a female lays eggs in/on a previously parasitized host, was attributed in the past to the inability of females to discriminate between parasitized and non-parasitized hosts. However, superparasitism is now accepted as an adaptive strategy under specific conditions. In fruit fly parasitoids, superparasitism has mainly been studied as concerns the new association between Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) and the Mexican fruit fly Anastrepha ludens (Loew) (Diptera: Tephritidae), wherein this phenomenon is a common occurrence in both mass rearing and field conditions. Studies of this species have shown that moderate levels of superparasitism result in a female-biased sex ratio and that both massreared and wild females superparasitize their hosts without detrimental effects on offspring demographic parameters, including longevity and fecundity. These studies suggest that superparasitism in this species is advantageous. In this paper, we review superparasitism in D. longicaudata, discuss these findings in the context of mass rearing and field releases and address the possible implications of superparasitism in programs employing augmentative releases of parasitoids for the control of fruit fly pests.