Carlos Cáceres

Mating Incompatibility Among Populations of the South American Fruit Fly Anastrepha fraterculus (Diptera: Tephritidae)

Abstract Mating compatibility among different populations of the South American fruit fly Anastrepha fraterculus (Wiedemann) was assessed through mating tests in pairwise combinations. Screened cages, inside a greenhouse, containing Citrus limon (L.) trees were used. Mating compatibility was determined using the index of sexual isolation. Most of the populations were noncompatible with each other and thus sexually isolated. Of these, Tucumán (Argentina) and Piracicaba (Brazil) populations showed a lower degree of isolation, whereas the other tested combinations were highly isolated. Full mating compatibility was detected only between two Argentinean (Concordia and Tucumán) and two Peruvian populations (La Molina and Piura + La Molina). Flies were sexually active at different times: Tucumán, Concordia, and Piracicaba populations presented an early morning peak, La Molina and Piura + La Molina were active around midday, and Ibague (Colombia) were active late in the afternoon. Manipulation of light phase conditions to match the times of maximum sexual activity did not increase the compatibility between La Molina and Tucumán. Based on these behavioral results, which confirm morphometric, genetic, and other evidence, the taxonomic revision of this cryptic species complex is warranted. One practical implication is that colonies of this pest to be used in any sterile insect technique approach should be derived from the target population or from a compatible population. Regional efforts should be initiated to determine the distribution of each subgroup and their relationship with each other in terms of compatibility.

Development and Assessment of a Liquid Larval Diet for Bactrocera dorsalis (Diptera: Tephritidae)

Abstract Larvae of Bactrocera dorsalis Hendel (Diptera: Tephritidae), the oriental fruit fly, were reared in a liquid diet without mill feed (a biological bulking agent) on a large scale for the first time. Sponge cloth was used as an inert diet-supporting material. Experiments were conducted to identify the rearing components for factory-scale liquid diet rearing based on the larval duration, pupal recovery, pupal weight, adult emergence, flight ability, mating, egg hatch, sex ratio, egg production, and egging duration. The up-to-date recommended rearing conditions using liquid diet are as follows: formula: basic liquid diet includes sugar (8.99%), yeast (15.06%), nipagen (0.15%), sodium benzoate (0.15%), wheat germ oil (0.15%), citric acid (1.70%), and water (73.81%); tray: lid of pupation fiberglass box; seeding egg density: 2.5 ml; diet volume: 1,250 ml; screen: coarse screen or optional depending on the tray design; water quality: tap water; and additives: 0.15% wheat germ oil or higher. Fruit fly performance from larvae reared in this liquid diet is identical to that from conventional mill feed diet, and preliminary tests show that liquid diet technology can be used at the factory scale.

Effects of the juvenile hormone analogue methoprene and dietary protein on male melon fly Bactrocera cucurbitae (Diptera: Tephritidae) mating success.

The effect of access to dietary protein (P) and the topical application of a juvenile hormone analogue (methoprene (M)) on mating behaviour of male melon fly Bactrocera cucurbitae was assessed in the laboratory and in field cages. Age, dietary protein and methoprene application increased the mating success and influenced the mating behaviour. Treatment with methoprene (M+) to protein-deprived (P-) males had only a modest effect on the acceleration of sexual maturity, but application of methoprene (M+) to protein-fed (P+) males greatly accelerated sexual maturity. Protein diet (P+) increased mating success of males in comparison to protein-deprived (P-) males. Protein and methoprene have a synergistic effect on mating behaviour, since M+P+ treated males exhibit reduced mating latency and achieved higher mating in younger ages than methoprene and/or protein-deprived males. Copulation duration was correlated with nutritional status and M+P+ males copulated longer at the age of advanced sexual maturity than M-P+ males. Our results suggest that in this species with a lek mating system, females discriminate between the males based on their sexual signals, which were influenced by protein in the adult diet, methoprene application and age. The results are discussed in the light of mating competitiveness of precocious treated young males and their relevance to Sterile Insect Technique application against this pest species.

A Novel Liquid Larval Diet and Its Rearing System for Melon Fly, Bactrocera cucurbitae (Diptera: Tephritidae)

Abstract A liquid larval diet and its rearing system for Bactrocera cucurbitae Coquillett fruit fly production were developed. The diet was composed of brewer’s yeast, sugar, antifungal agents (sodium benzoate and nipagen), citric acid, and distilled water. Sponge cloth placed in rearing trays was used as a support substrate for larvae, alleviating the need for the traditional (mill feed) bulking agent. Larval rearing of B. cucurbitae on this diet resulted in ≈20% less pupal production and ≈10% lighter pupal weight than from the control diet, whereas pupal density, adult emergence, adult fliers, and egg hatch showed no significant discrepancies. Pupal recovery increased with yeast concentrations up to 14.2%. Benefits derived from a liquid diet include reduction in postrearing waste, alleviation of (pesticide-free) bulking agent, and reduction in diet ingredient storage and labor. These benefits must be weighed against any reductions in production and size when large-scale mass rearing of fruit flies for use in sterile insect release programs are evaluated.

QUALITY MANAGEMENT SYSTEMS FOR FRUIT FLY (DIPTERA: TEPHRITIDAE) STERILE INSECT TECHNIQUE

Abstract The papers presented in this issue are focused on developing and validating procedures to improve the overall quality of sterile fruit flies for use in area-wide integrated pest management (AW-IPM) programs with a sterile insect technique (SIT) component. The group was coordinated and partially funded by the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture, International Atomic Energy Agency, Vienna, Austria, under a five-year Coordinated Research Project (CRP) on “Quality Assurance in Mass-Reared and Released Fruit Flies for Use in SIT Programmes”. Participants in the CRP from 16 countries came from both basic and applied fields of expertise to ensure that appropriate and relevant procedures were developed. A variety of studies was undertaken to develop protocols to assess strain compatibility and to improve colonization procedures and strain management. Specific studies addressed issues related to insect nutrition, irradiation protocols, field dispersal and survival, field cage behavior assessments, and enhancement of mating competitiveness. The main objective was to increase the efficiency of operational fruit fly programs using sterile insects and to reduce their cost. Many of the protocols developed or improved during the CRP will be incorporated into the international quality control manual for sterile tephritid fruit flies, standardizing key components of the production, sterilization, shipment, handling, and release of sterile insects.

Exploitation of the Medfly Gut Microbiota for the Enhancement of Sterile Insect Technique: Use of Enterobacter sp. in Larval Diet-Based Probiotic Applications

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a pest of worldwide substantial economic importance, as well as a Tephritidae model for sterile insect technique (SIT) applications. The latter is partially due to the development and utilization of genetic sexing strains (GSS) for this species, such as the Vienna 8 strain, which is currently used in mass rearing facilities worldwide. Improving the performance of such a strain both in mass rearing facilities and in the field could significantly enhance the efficacy of SIT and reduce operational costs. Recent studies have suggested that the manipulation of gut symbionts can have a significant positive effect on the overall fitness of insect strains. We used culture-based approaches to isolate and characterize gut-associated bacterial species of the Vienna 8 strain under mass rearing conditions. We also exploited one of the isolated bacterial species, Enterobacter sp., as dietary supplement (probiotic) to the larval diet, and we assessed its effects on fitness parameters under the standard operating procedures used in SIT operational programs. Probiotic application of Enterobacter sp. resulted in improvement of both pupal and adult productivity, as well as reduced rearing duration, particularly for males, without affecting pupal weight, sex ratio, male mating competitiveness, flight ability and longevity under starvation.

Enhancing mating performance after juvenile hormone treatment in Anastrepha fraterculus: a differential response in males and females acts as a physiological sexing system

Methoprene (a mimic of juvenile hormone) treatment can reduce the time required for sexual maturation in Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) males under laboratory conditions, supporting its use as a treatment for sterile males within the context of the sterile insect technique (SIT). We evaluated sexual behaviour, mating competitiveness of methoprene‐treated males, and female readiness to mate after methoprene‐treatment in field cages. The study involved two strains of A. fraterculus from Argentina and Peru, which show several polymorphisms in relation to their sexual behaviour. We also analyzed whether methoprene treatment affected male and/or female behaviour in the same way in these two strains. Methoprene‐treated males were equally competitive with untreated mature males, and became sexually competitive 6 days after emergence (3–4 days earlier than untreated males). In contrast, methoprene did not induce sexual maturation in females or, at least, it did not induce a higher rate of mating in 7‐day‐old females. These results were observed both for the Argentina and the Peru strains. Altogether, our results indicate that methoprene treatment produces sexually competitive males in field cages. In the absence of a genetic sexing system, and when sterile males and females of A. fraterculus are released simultaneously, the fact that females do not respond as do males to the methoprene treatment acts as a physiological sexing effect. Therefore, in the presence of mainly sexually immature sterile females, released sexually mature sterile males would have to disperse in search of wild fertile females, thereby greatly reducing matings among the released sterile insects and thus enhancing sterile insect technique efficiency.

Ongoing speciation within the Anastrepha fraterculus cryptic species complex : the case of the Andean morphotype

The Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) cryptic species complex is currently composed of seven taxonomically recognized morphotypes. Both, pre‐ and post‐zygotic isolation has been documented among four of these morphotypes, revealing that in fact they appear to be distinct biological entities. In order to progress in the full delimitation of species within the complex, we examined reproductive isolation between a Colombian population of the Andean morphotype and populations belonging to four other morphotypes spanning from Mexico to Argentina. Flies from the Andean morphotype exhibited strong pre‐zygotic mating isolation through temporal partitioning of mating activity. Post‐zygotic isolation was observed for crosses of males of all morphotypes and Andean morphotype females, yet most of the F1 hybrid ♂ × F1 hybrid ♀ self‐crosses showed normal levels of fertility, a finding suggesting a nuclear–cytoplasmic interaction according to previous studies. Overall, the Andean morphotype within the complex also appears to be a distinct biological entity. We discuss the implications of these findings for the understanding of speciation mechanisms in the Neotropical genus Anastrepha.

Life History Parameters of Ceratitis capitata (Diptera: Tephritidae) Reared on Liquid Diets

Abstract A liquid diet for rearing Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) was developed. Several yeast-based products were evaluated as diet ingredients, and a combination of whole cell yeast (LBI2240) and hydrolyzed yeast (such as FNILS65) in 1:1–3:1 ratio was selected for use in the study. Larvae reared in a liquid diet with LBI2240:FNILS65 ratios of either 1:1 or 3:1 resulted in the same pupal recovery as to those reared in the conventional mill fee- based control diet. Larvae reared in a liquid diet with whole cell yeast only yielded the lowest pupal production, whereas other parameters such as adult emergence, adult fliers, pupal weight, egg production, and percentage of egg hatch were not affected. In diets fortified with vitamin-fortified yeast (RDA) or glutamine-rich yeast (GSH), there was no enhanced effect on insects, whereas some detrimental effects were observed in some of the parameters measured. A whole cell yeast to hydrolyzed yeast ratio of 3:1 was found to be the most suitable based on quality control parameters measured and cost-effectiveness. This is recommended for use in liquid diets targeting C. capitata mass rearing because the cost of whole cell yeast was 5 times cheaper than that of hydrolyzed yeast. This study also demonstrates that it is possible to rear C. capitata in a liquid diet at a similar cost to mill feed diet and still maintain the same fly quality as that from the conventional control diet.

Mating Compatibility Between Bactrocera invadens and Bactrocera dorsalis (Diptera: Tephritidae)

ABSTRACT n The invasive fruit fly, Bactrocera invadens Drew, Tsuruta & White, is a highly polyphagous fruit pest that occurs predominantly in Africa yet has its origins in the Indian subcontinent. It is extremely morphologically and genetically similar to the Oriental fruit fly, Bactrocera dorsalis (Hendel); as such the specific relationship between these two species is unresolved. We assessed prezygotic compatibility between B. dorsalis and B. invadens using standardized field cage mating tests, which have proven effectiveness in tephritid cryptic species studies. These tests were followed by an assessment of postzygotic compatibility by examining egg viability, larval and pupal survival, and sex ratios of offspring produced from parental and subsequent F1 crosses to examine for hybrid breakdown as predicted under a two-species hypothesis. B. dorsalis was sourced from two countries (Pakistan and China), and each population was compared with B. invadens from its type locality of Kenya. B. invadens mated randomly with B. dorsalis from both localities, and there were generally high levels of hybrid viability and survival resulting from parental and F1 crosses. Furthermore, all but one hybrid cross resulted in equal sex ratios, with the single deviation in favor of males and contrary to expectations under Haldanes rule. These data support the hypothesis that B. dorsalis and B. invadens represent the same biological species, an outcome that poses significant implications for pest management and international trade for sub-Saharan Africa.