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Keywords:

  • guava fruit fly;
  • hydrolysed yeast;
  • Oriental fruit fly;
  • sterile insect technique;
  • Tephritidae

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. References

The objective of this extensive series of experiments, involving more than 2800 field cage tests with potted mango trees, was to assess pre-release supplements to enhance the mating success of sterile male Bactrocera dorsalis and Bactrocera correcta. We examined the effects of different pre-release diets and methyl eugenol (ME), both independently and in combination. Tests were carried out more than 15 and 18 days for B. dorsalis and B. correcta, respectively, each day increasing the age of sterile flies. To evaluate the effect of different pre-release diets on males, no-choice mating tests were conducted with sterile males of increasing age and mature sterile females. Sterile males fed up to 2 days of age on sugar–yeast hydrolysate combinations achieved significantly more matings than males fed only water in B. dorsalis and more matings than males fed only sugar, only yeast hydrolysate or only water in B. correcta. To examine the effect of ME on mating performance, 2-, 3-, 4- or 5-day-old sterile males were given or not given access to ME for 1 h, followed by the sugar–protein diet until the day of the mating test. Mating performance tests were carried out with ME-exposed and non-exposed sterile males competing with mature wild males for wild females. Results showed a significant mating advantage of ME-exposed over non-exposed sterile males, although at younger ages they were still less competitive than wild males. The interaction of sugar–yeast hydrolysate diet and ME as pre-release treatments for 2- and 3-day-old sterile males was assessed in terms of male sexual competitiveness. Overall, the combination showed an additive effect on increased mating success in B. dorsalis sterile males when competing a wild males for wild females, while in B. correcta males the drastic improvement in mating success was mainly linked to the ME exposure.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. References

Methyl eugenol (ME) (1,2-dimethoxy-4-(2-propenyl)benzene) is a strong attractant that induces compulsive feeding in males of the Oriental fruit fly, Bactrocera dorsalis (Hendel) (Hee and Tan 2005, 2006), which is an economically important tephritid fruit fly (Diptera: Tephritidae). Methyl eugenol is a naturally occurring phenyl-propanoid found as a plant secondary metabolite and a component of essential oils in more than 200 species of plants from 32 families (Shelly and Dewire 2000; Tan 2000; Hee and Tan 2005). Consumption of ME by males of B. dorsalis has been shown to enhance male mating performance (Tan and Nishida 1996, 1998; Shelly et al. 2010). It has also been shown that teneral males provided with protein (yeast hydrolysate), but then protein deprived when mature, were less competitive when compared to males with access to a diet that included protein throughout the maturation period but achieved a significantly higher percentage of matings than males never provided protein (Shelly et al. 2005). Also, in most of the experiments conducted with Mediterranean fruit fly, Ceratitis capitata (Wiedemann), males reared on protein diet (hydrolysate yeast and sugar) showed a significant mating advantage over competitors feeding on the standard sugar diet (Niyazi et al. 2004; Yuval et al. 2007).

The Oriental fruit fly and the guava fruit fly, Bactrocera correcta (Bezzi), are two key pests of fruit production causing significant yield losses, quality degradation and interference with international trade of fresh fruit. The sterile insect technique (SIT) has been used in Thailand as part of suppression programmes against these two major pest species (Orankanok et al. 2007). Difficulties in the expanded application of this technology are related to expanding from pilot areas to a regional- or country-wide level. Besides, substantial improvements are needed to increase sterile male performance to apply the SIT in a more cost-effective way.

Unfortunately, the procedures inherent to mass-rearing large numbers of sterile males and their post-factory handling reduce male mating competitiveness (Orankanok et al. 2007). As a result, the local research team in Thailand invested great efforts to assess different pre-release sterile fly management methods to improve sterile male mating. Our objective was to optimize the age of release of sterile flies, after exposing them to different pre-release treatments and periods, to improve routine release conditions of the SIT fruit fly suppression programme against these two pest species. In this study, the results of an extensive number of field cage experiments evaluating the supply of protein-enriched adult diets and ME exposure, independently and in combination, are presented and discussed.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. References

Insects

Wild B. dorsalis and B. correcta flies were originally obtained from infested guava fruits (Psidium guajava L.) collected in Nong Suar district, Pathumthani province, Thailand. Fruits were maintained in containers with a layer of sand on the bottom to serve as pupation medium. Pupae were collected, and subsequent generations were reared under laboratory conditions. The flies used in the experiments were 2–5 generations removed from the wild (and were thus semi-wild but are referred to as wild to simplify the language). For testing purposes, wild flies were separated by sex within 48 h after emergence and maintained in separate plastic cages (30 by 30 by 45 cm) at about 2000 flies per cage. The flies were provided with adult diet [sugar and yeast hydrolysate (P+ 3 : 1)] and water-agar ad libitum. Wild males (W♂) were tested in all experiments at the constant age of 23 days (B. dorsalis) and 34 days (B. correcta), while wild females (W♀) at the constant age of 21 days (B. dorsalis) and 37 days (B. correcta). These ages were selected based on preliminary tests that assured the sexual maturation of the wild flies. Wild males were never exposed to ME.

Sterile flies of both fruit fly species used in the experiments were obtained from the Pathumthani, Thailand, mass-rearing facility. They were irradiated by a Gammacell 220 irradiator (Nordion, Ottawa, ON, Canada) 2 days before emergence at a dose of 80 and 90 Gy, respectively, for B. dorsalis and B. correcta. Before irradiation, the pupae were marked with fluorescent dye and maintained at 25°C and ca 70% RH. Sterile males (S♂) and females (S♀) were separated by sex within 24 h after emergence. Sexes were maintained in separate cages as described earlier for wild flies with provision of the adult diet but allowed to feed on ME according to the specific treatment.

Field cage experiments

A randomized complete block design was conducted simultaneously using a maximum of 25 octagonal field cages (each side being 120 cm wide and 270 cm high). Each field cage contained one potted mango tree (Mangifera indica L.) approximately 250 cm tall. This allowed five simultaneous replications for 3–5 treatments for each experiment. The experiments were conducted at Pathumthani in the vicinity of the mass-rearing facility according to the protocol for the mating performance field cage test (FAO/IAEA/USDA 2003) with some adaptations as described below. Male flies were released into cages at 15:45–16:00 h and wild females (W♀) 1 h later at 16:45–17:00 h (sunset was at 18:30). Temperature, RH and light intensity in the cages were recorded at the time of male release and every half hour thereafter. For each detected mating pair, the initiation time was recorded, and the pair was collected and observed for about 5 min to observe that the couple did not separate. Three field cage mating experiments, for a total of 2805 field cage tests, were conducted for B. dorsalis and B. correcta, each more than 15- and 18-day periods, respectively.

Experiment 1: Effect of pre-release diet

Five treatments, with different adult food regimes, provided during the first 2 days of adult life, were tested (i) water-agar (A); (ii) sugar (P); (iii) sugar and yeast hydrolysate in a 3 : 1 ratio by weight (P+ 3 : 1); (iv) sugar and yeast hydrolysate in a 2 : 1 ratio by weight (P+ 2 : 1); and (v) yeast hydrolysate alone (P only). The respective diets were provided before and after the separation of sexes (within 24 h of emergence) together with water until sterile males reached the age of 2 days (current release age of the flies at the Thailand SIT programme, Orankanok et al. (2007)). Thereafter, the protein–sugar standard adult diet (P+ 3 : 1) and water-agar were provided continuously until the day of the mating test. That same diet (P+ 3 : 1) was provided to the females used in the experiment. The adult food was provided in a Petri dish, which was replaced every 2 days until the implementation of the field cage tests. For each species, we performed five replications (field cage tests) for each of the five treatments of a given test day and conducted tests more than 15 days for B. dorsalis (375 replications in total) and 18 days for B. correcta (450 replications in total).

Bactrocera dorsalis

Daily, 50 sterile males from the 53rd generation of the mass-rearing colony were introduced into each of the five field cages (one treatment per cage). Sterile males tested were of increasing age during the 15 test days (2 + n days old; n = 1–15), and the 50 males from the respective treatments were placed with 50 virgin sexually mature sterile females (S♀) of constant age (12 days).

Bactrocera correcta

Daily, 50 sterile males from the 21st generation of the mass-rearing colony were introduced into each of the five field cages (one treatment per cage). Sterile males tested were of increasing age during the 18 test days (2 + n days old; n = 1–18), and the 50 males from the respective treatments were placed with 50 virgin sexually mature sterile females (S♀) of constant age (17 days).

Experiment 2: Effect of ME exposure

Sterile fruit flies used originated from the 32nd and 34th generations of mass-reared B. dorsalis and B. correcta, respectively. After emergence, sterile males were provided with water-agar only placed on top of the screened holding cage. For each of the treatment ages (sets) of 2, 3, 4 or 5 days, sterile males were separated into two groups, one not exposed to ME (S♂ME) and the second exposed to ME (S♂ME+). The ME was supplied for 1 h from 8:00 to 9:00 (1 ml on a 12.5-cm2 filter paper) at each respective male treatment age. After ME exposure or non-exposure, protein-rich (P+ 3 : 1) adult diet was provided to all flies tested in this experiment. The adult food was provided in a Petri dish, which was replaced every 2 days until the implementation of the field cage tests. For each species, we performed five replications (field cage tests) for each of the four exposure ages (sets) and conducted tests more than 15 days for B. dorsalis (300 replications in total) and 18 days for B. correcta (360 replications in total).

Bactrocera dorsalis

The test was conducted daily more than 15 days of increasing sterile males age for each of the four male exposure ages (2 + n, 3 + n, 4 + n and 5 + n days, with n = 1–15 days). In each field cage, 50 sterile non-ME-exposed males (S♂ME), 50 sterile ME-exposed males (S♂ME+) and 50 W♂ (23 days old) were released. The three types of males were competing for 50 virgin and sexually mature W♀ (21 days old).

Bactrocera correcta

The same procedure was followed as for B. dorsalis, except that the number of test days was n = 1–18, and the wild flies were tested when W♂ were 34 and W♀ were 37 days old, respectively.

Experiment 3: Combined pre-release diet feeding and ME exposure

Two pre-release diets were tested; sugar only (P) and sugar and yeast hydrolysate (P+ 3 : 1) and ME exposure (ME+) or no exposure (ME) were assessed in this series of field cage tests. Sterile males were provided with one of the two pre-release diets before and after the separation of sexes (within 24 h of emergence) continuously until 2 or 3 days old, followed by ME exposure (for 1 h) or no exposure at the age of 2 or 3 days. Thereafter, the standard adult diet (P+ 3 : 1) and water ad libitum were provided to the males until the mating test that started 1 day after the ME exposure and continued more than 15 and 18 test days for B. dorsalis and B. correcta, respectively. Mating competitiveness experiments were conducted as a 2-by-2 factorial randomized complete block design that included the following four treatments (for each of the ages of exposure to ME, 2 or 3 days old): PME; PME+; P+ME and P+ME+. Five replicates (field cage tests) were conducted for each of the four treatments and two ages of ME exposure more than 15 or 18 test days for B. dorsalis and B. correcta, respectively. Therefore, a total of 600 and 720 replications (cages) were run for B. dorsalis and B. correcta, respectively.

Bactrocera dorsalis

For each age of exposure to ME and test day (2 + n or 3 + n; n = 1–15 test days), 50 S♂ from one of the four treatments were introduced into each field cage to compete with 50 mature W♂ (23 days old) for 50 virgin mature W♀ (21 days old).

Bactrocera correcta

The procedure was the same as for B. dorsalis, except that tests spanned 18 days. For each age of exposure to ME and test day (2 + n and 3 + n; n = 18 test days), 50 S♂ from one of the four treatments were introduced into each field cage to compete with 50 mature W♂ (34 days old) for 50 virgin mature W♀ (37 days old).

Statistical analyses

The percentages of matings achieved by each male treatment group in experiments 1 (with a sex ratio of one male : one female) and 2 (with a sex ratio of three males : one female) were calculated by dividing the number of matings of each treatment by the total number of possible matings (all female matings). For experiment 3 (with a sex ratio of two male : one female), the assessment of the male sexual competitiveness is given as the relative sterile index (RSI) where SW: sterile male × wild female matings and WW: wild male × wild female matings (FAO/IAEA/USDA 2003):

  • image

The data (after arcsine transformation) were analysed using the programme IRRI STAT for analysis of variance (anova), and the performance was compared by Duncan’s multiple range test. The number of mating pairs is shown in terms of mating percentages (specifically, the RSI for experiment 3). For each of the three experiments, results were computed for each day more than 15 and 18 test days for B. dorsalis and B. correcta, respectively; in addition, the average percentages of mating achieved for each treatment over all days for each experiment were compared.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. References

Experiment 1: Effect of pre-release diet

Bactrocera dorsalis

During the early test days, mating percentages were low and variable as a majority of sterile males were not sexually mature (table 1). From test day 4 onward, S♂ of all the treatments, except from the water-agar (A), performed similarly with one another in achieving matings. Summarizing over the total test period for B. dorsalis, mean percentages of mating pairs achieved by S♂ fed during the first 2 days on different pre-release diets (including P only) were significantly higher than those achieved by S♂ fed only water-agar (A) during this initial period (fig. 1a).

Table 1. Percentages of matings achieved by young sterile males (S♂) of Bactrocera dorsalis exposed up to the age of 2 days to the following food regimes: (A) water-agar; (P) sugar; (P+ 3 : 1) sugar and yeast hydrolysate ratio 3 : 1; (P+ 2 : 1) sugar and yeast hydrolysate ratio 2 : 1; and (P only) no sugar, and mating on test days 2+n, where n = 1–15, with sexually mature sterile females (S♀, with the P+ 3 : 1 adult diet regime). Five replications of field cage tests were carried out for each treatment and test day
TreatmentTest days (n)
123456789101112131415
  1. Means followed by a common letter within each column are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

A0.00a1.60a2.80b5.20c8.40b7.20b6.80b16.80b23.60b23.20b24.80b23.20b23.60b25.60b22.80b
P0.00a0.00c4.40a20.40a38.00a40.80a29.60a47.60a49.60a42.40a38.40a39.20a45.20a51.60a34.80a
P+ 3 : 10.00a0.80b6.00a22.40a36.80a33.60a27.20a61.20a52.40a41.20a41.20a39.60a36.00a50.40a36.40a
P+ 2 : 10.00a1.20b3.60b17.20ab33.20a40.80a27.20a57.20a53.60a46.80a46.00a38.40a44.00a46.80a36.00a
P only0.00a1.20ab2.00c12.40a37.20a36.80a26.00a56.80a48.00a47.20a52.40a48.80a48.00a51.20a36.40a
image

Figure 1.  Average percentage of matings achieved by sterile males (S♂) of Bactrocera dorsalis (a) and Bactrocera correcta (b) with access to different pre-release diets until 2 days old [water-agar (A); sugar (P); sugar and yeast hydrolysate ratio 3 : 1 (P+ 3 : 1); sugar and yeast hydrolysate ratio 2 : 1 (P+ 2 : 1); and yeast hydrolysate alone (P only)], followed by a sugar–protein diet (P+ 3 : 1) until the day of testing, when placed with virgin mature sterile females (S♀) more than 15 and 18 test days, respectively. Means followed by a common letter, for each species, were not significantly different at the 5% level of confidence by Duncan’s multiple range test.

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Bactrocera correcta

From testing days 2–6, S♂ of the three treatments containing protein performed significantly better than males fed on the other two diets lacking protein (A and P). The S♂ that received only sugar and water (P) recovered by test day 7 and after that did not differ significantly from the treatments that contained protein (table 2). Averaging treatments over the total test period for B. correcta, S♂ fed P+ 3 : 1 and P+ 2 : 1 diets during the first 2 days achieved significantly more matings than the S♂ fed the other pre-release diets (fig. 1b).

Table 2. Percentages of matings achieved by young sterile males (S♂) of Bactrocera correcta exposed up to the age of 2 days to the following food regimes: (A) water-agar; (P−) sugar; (P+ 3 : 1) sugar and yeast hydrolysate ratio 3 : 1; (P+ 2 : 1) sugar and yeast hydrolysate ratio 2 : 1; and (P only) no sugar, and mating on test days aged 2 + n, where n = 1–18, with sexually mature sterile females (S♀, with the P+ 3 : 1 adult diet regime). Five replications of field cage tests were carried out for each treatment and test day
TreatmentTest days (n)
123456789101112131415161718
  1. Means followed by a common letter within each column are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

A0.00a0.00b0.00c1.60c2.60c4.40c6.40b8.40b9.20b8.00b8.80b9.20b10.80c10.80b8.00b4.80d8.40b2.40b
P0.00a0.40b4.00b4.40b9.60b15.20b18.00a23.20a26.40a28.00a32.00a34.40a36.80b25.60a19.20a12.00a13.20a8.80a
P+ 3 : 10.00a1.60a5.60a12.00a18.00a19.20ab23.20a30.40a31.60a35.60a35.20a39.60a53.20a24.80a19.20a10.40ab13.20a10.00a
P+ 2 : 10.00a1.60a5.60a8.80a20.40a21.60a25.20a28.40a32.40a35.20a33.60a36.40a49.60a30.00a18.40a6.00cd11.60ab7.60a
P only0.00a2.00a7.20a8.80a12.40b16.00ab18.80a23.60a32.00a30.00a33.60a32.40a39.20ab28.80a16.00a8.00bc12.40a8.00a

Experiment 2: Effect of ME exposure

Bactrocera dorsalis

For each of the ages of exposure, S♂ME+ consistently achieved significantly more matings than S♂ME of the same age. With advancing test age, S♂ME+ obtained increasingly higher percentages of matings (table 3) that were significantly different from S♂ME. Over the total 15 days of observations, mating percentages of increasingly older S♂ME+ males showed a clearly enhanced mating performance compared to S♂ME. For S♂ME+ exposed to ME at the age of 2 days, there was no significant difference in matings achieved to W♂ on test days 6, 8, 10, 14 and 15. For S♂ME+ exposed to ME at the age of 3, 4 or 5 days, the first days with no significant difference to W♂ was on the test days 4, 4 and 2 after ME exposure, respectively (table 3).

Table 3. Percentages of matings achieved by young sterile males (S♂) of Bactrocera dorsalis exposed (ME+) or not exposed (ME) to ME at exposure ages 2, 3, 4 or 5 days, and competing on test days 2 + n, 3 + n, 4 + n or 5 + n, where n = 1–15, with mature (23 days old) wild males (W♂) for matings with virgin mature (21 days old) wild females (W♀). Five replications of field cage tests were carried out for each treatment, test day and set (exposure age)
Type of fliesTest days (n)
123456789101112131415
  1. ME, methyl eugenol.

  2. For each set of males, means followed by a common letter in each column are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

Set of male 2 + n days old
 W♂42.80a37.60a29.60a36.80a35.60a26.00a30.80a26.00a28.40a14.00a47.20a20.80a29.60a28.00a26.00a
 S♂ ME−4.80c6.40c3.60c4.40c6.40c5.20b9.60c11.60b8.00c8.00bb8.40c12.40c10.00c15.60b18.80b
 S♂ ME+12.40b15.60b17.20b15.20b24.40b24.40a21.20b30.40a18.40b14.00a21.60b11.60b20.40b24.40a27.60a
Set of male 3 + n days old
 W♂37.20a35.20a34.00a23.60a24.40a28.40a35.60a33.60a29.60a20.80a44.00a26.00a38.80a34.80a26.00a
 S♂ ME−3.20c6.00c7.60c5.60b4.40b5.20b7.20b14.00b6.40c3.20b7.20c10.40b9.60c15.20c16.80b
 S♂ ME+16.80b14.80b25.20b28.40a26.80a25.60a31.20a29.20a17.60b15.20a23.60b14.00ab21.60b18.00bc22.00ab
Set of male 4 + n days old
 W♂43.60a39.20a38.40a25.20b25.60b21.60a23.20a36.80a41.20a16.80a46.80a26.80a31.20a35.60a28.40a
 S♂ ME−5.60c10.00c10.00c5.60c9.60c6.40b9.60b11.60b9.20c4.40b10.40c8.80b11.60c10.00c12.40b
 S♂ ME+18.40b27.20b29.60b34.40a34.80a28.00a30.00a28.80a20.00b13.60a21.60b9.60b17.60b24.80b24.00a
Set of male 5 + n days old
 W♂42.00a34.40a37.60a24.40a30.40a33.60a23.20a34.00a33.20a18.80a46.00a24.00a32.40a36.80a34.80a
 S♂ ME−6.80c9.20b7.20b8.80b7.60b6.00c12.40b10.00b8.00b6.00b9.60c11.60b14.40b15.60b13.60b
 S♂ ME+23.20b38.00a38.00a30.40a30.40a22.00b25.20a31.60a16.40b15.20a23.60b7.60b14.00b20.00b18.00b

Average results summarizing the whole 15-day test period showed that B. dorsalis S♂ME+ exposed at 2 days of age showed the lowest percentage of mating but were not significantly different to those of S♂ME+ exposed when males are 3 days old, while S♂ME+ exposed at 4 and 5 days of age showed significantly higher percentages of mating (fig. 2a). As an overall result, one can conclude that ME exposure increases the mating performance of B. dorsalis and that the exposure is recommended when males are 4–5 days old.

image

Figure 2.  Average percentage of matings achieved by sterile males (S♂) of Bactrocera dorsalis (a) and Bactrocera correcta (b) exposed to methyl eugenol (ME+) or not treated (ME) at age 2, 3, 4 or 5 days and competing for matings with mature wild males (W♂) of constant age (23 days for B. dorsalis and 34 days for B. correcta) for mature wild females of constant age (21 days for B. dorsalis and 37 days for B. correcta), over a test duration of 15 and 18 days (n), respectively. Five replications were carried out for each treatment, exposure age (set) and age after exposure (test day). Means followed by a common letter are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

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Bactrocera correcta

The percentages of matings achieved by all sets of S♂ME+ exposed to ME when 2, 3, 4 or 5 days old were for a majority of the test days and set of males significantly higher than those achieved by S♂ME over all of the 18 test days and were not significantly different to W♂ between test days 6 and 14 (table 4). Average results summarizing the whole test period showed that among B. correcta S♂ME+, those exposed to ME when 2 and 3 days old were significantly more successful in achieving matings with wild females than those exposed when 5 days old (fig. 2b). From this experiment, one can conclude that ME exposure increases the mating performance of B. correcta, although the exposure is recommended when males are 2–4 days old.

Table 4. Percentages of matings achieved by young sterile males (S♂) of Bactrocera correcta exposed (ME+) or not exposed (ME) to ME at exposure ages 2, 3, 4 or 5 days, and competing on test days 2 + n, 3 + n, 4 + n or 5 + n, where n = 1–18, with mature (34 days old) wild males (W♂) for matings with virgin mature (37 days old) wild females (W♀). Five replications of field cage tests were carried out for each treatment, test day and set (exposure day)
Type of fliesTest days (n)
123456789101112131415161718
  1. ME, methyl eugenol.

  2. For each set of males, means followed by a common letter in each column are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

Set of male 2 + n days old
 W♂11.60a11.20a8.80a5.60a20.80a6.00a12.00a6.00a8.800a5.20ab8.40a8.00a9.60a4.80a9.60a10.40a10.40a10.00a
 S♂ ME−0.80c0.00c0.80b0.00b5.20c1.60c2.40b1.20b3.60b4.00b3.20b1.60b2.80b1.20b0.80b2.00c2.80b2.40c
 S♂ ME+5.20b1.60b2.80b3.20ab10.40b11.60a13.20a10.00a11.60a9.60a8.40a6.00a6.00a6.00a8.40a6.00b6.80a4.40b
Set of male 3 + n days old
 W♂10.00a9.60a10.80a15.20a19.60a11.60a12.80a1.60b6.80b5.60a4.80a4.00a5.20a11.60a14.40a15.60a11.20a10.00a
 S♂ ME−0.80c0.80c0.40c1.20b4.00c3.60b4.00b1.20b3.20b6.40a3.20a2.00a2.40a2.40b0.00c4.80c3.60b3.60b
 S♂ ME+5.60b5.20b4.80b2.40b12.80b11.20a12.40a6.40a12.00a7.60a6.80a5.20a6.40a7.60a6.00b9.20b4.00b5.20b
Set of male 4 + n days old
 W♂13.20a13.60a11.2018.00a25.20a10.40b10.80a2.80ab7.60b6.00a4.00a7.60a7.20a2.80a14.80a8.00a5.60a8.40a
 S♂ no ME−0.80c1.20c0.80b0.80b6.80c2.00c2.40b0.40b2.80c8.00a5.20a1.20b2.80b1.20a0.00b2.40b1.60b2.40b
 S♂ +ME+4.80b4.80b4.40b3.20b10.40b14.40a12.80a6.00a14.00a9.60a6.80a5.20a5.20ab2.80a2.00b4.80ab3.60ab4.80ab
Set of male 5 + n days old
 W♂8.00a12.80a9.60a10.80a16.80a8.80a14.80a8.80a6.80a6.80a5.60a4.80a4.40a4.40a10.00a6.40a5.60a8.00a
 S♂ ME−2.80b0.40b1.60b2.00c4.80c1.60b2.40c1.60b2.80c5.20a3.20a1.60a2.80a2.00a0.00b2.40b0.40b1.60b
 S♂ ME+4.80ab2.80b4.40b5.60b10.00b10.40a10.80b7.20a11.60a8.00a4.80a4.80a5.20a3.20a6.80a6.00a1.20b4.00b

Experiment 3: Combined pre-release diet feeding and ME exposure

Bactrocera dorsalis

When analysing by test day after ME exposure, P+ME+ sterile B. dorsalis males achieved significantly higher matings with wild females than the S♂ subject to the other treatments, being almost always the ones that had higher RSI values for both day 2 and day 3 exposure ages (table 5), reaching at much younger ages RSI levels close to those obtained by the fully mature 23-day-old W♂. As an overall result, averaging treatments over the whole test period showed that an additive interaction of protein in the pre-release diet and ME exposure increased the male mating competitiveness (RSI) significantly compared to males pre-release feeding on diets without yeast hydrolysate or ME exposure (fig. 3a).

Table 5. Relative sterility index (RSI) achieved by young sterile males (S♂) of Bactrocera dorsalis after having been provided a (P) or (P+) pre-release diet after emergence continuously until 2 and 3 days old when exposed (ME+) or not exposed (ME) to ME, and then competing on test days 2 + n or 3 + n, where n = 1–15, with mature (23 days old) wild males (W♂) for mating with virgin mature (21 days old) wild females (W♀). Five replications of field cage tests were carried out for each treatment, test day and set (exposure age)
TreatmentTest days (n)
123456789101112131415
  1. ME, methyl eugenol.

  2. For each set of males, means followed by a common letter in each column are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

Set of male 2 + n days old
 P−ME−0.00c0.09b0.16c0.22b0.19b0.32bc0.25c0.33c0.35c0.39b0.34b0.37ab0.29b0.22c0.37b
 P−ME+0.06b0.13b0.10d0.26b0.35a0.30c0.34b0.35bc0.37c0.43ab0.37ab0.38ab0.28b0.20c0.34b
 P+ME−0.09b0.20a0.22b0.37a0.36b0.36ab0.43a0.40ab0.45b0.46a0.41a0.32b0.35a0.34a0.39ab
 P+ME+0.18a0.23a0.29a0.37a0.38a0.40a0.41a0.44a0.51a0.44ab0.42a0.41a0.32ab0.28bc0.42a
Set of male 3 + n days old
 P−ME−0.10b0.20b0.19a0.33b0.30b0.31b0.34b0.46b0.44ab0.43a0.39a0.32b0.35b0.26a0.25b
 P−ME+0.13b0.20b0.19a0.32b0.31b0.32bc0.33b0.44bc0.39b0.40a0.38a0.36b0.28c0.20b0.30ab
 P+ME−0.12b0.22ab0.24a0.37ab0.34ab0.32bc0.35b0.45bc0.41ab0.40a0.40a0.38b0.31bc0.28a0.25b
 P+ME+0.21a0.26a0.24a0.43a0.37a0.43ab0.42a0.53ab0.47a0.45a0.42a0.44a0.47a0.30a0.34ab
image

Figure 3.  Average Relative of Sterility Index (RSI) achieved by sterile males (S♂) of Bactrocera dorsalis (a) and Bactrocera correcta (b) after feeding on pre-release diets with (P+) or without (P) protein and with (ME+) or without (ME) methyl eugenol exposure at the age of 2 or 3 days (set) when competing for matings with mature wild males (W♂) of constant age (23 days for B. dorsalis and 34 days for B. correcta) for mature wild females of constant age (21 days for B. dorsalis and 37 days for B. correcta), over a test duration of 15 and 18 days, respectively. Five replications were carried out for each treatment, exposure age (set) and age after exposure (test day). Means followed by a common letter are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

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Bactrocera correcta

For B. correcta, the consistency of the significantly better performance of the ME+S♂, with or without a protein-enriched pre-release diet, was even more drastic for test days and ages of exposure to ME (table 6). For many test days, ME exposure was so effective that ME+S♂ achieved, starting with test days 4–5, RSI values above those obtained by the fully mature 34-day-old W♂. Averaging treatments over the total observation period, ME+ sterile B. correcta males performed significantly better than the ME males, independent of the pre-release diet; their average RSI values exceeded 0.5 for all ME+S♂ (both exposure ages), being on average even more successful than W♂ (fig. 3b).

Table 6. Relative sterility index (RSI) achieved by young sterile males (S♂) of Bactrocera correcta after having been provided a (P) or (P+) pre-release diet from emergence continuously until 2 or 3 days old when exposed (ME+) or not exposed (ME) to ME, and then competing on test days 2 + n or 3 + n, where n = 1–18, with mature (34 days old) wild males (W♂) for mating with virgin mature (37 days old) wild females (W♀). Five replications of field cage tests were carried out for each treatment, test day and set (exposure age)
TreatmentTest days (n)
123456789101112131415161718
  1. ME, methyl eugenol.

  2. For each set of males, means followed by a common letter in each column are not significantly different at the 5% level of confidence by Duncan’s multiple range test.

Set of male 2 + n days old
 P−ME−0.00a0.00c0.02c0.16b0.26b0.30c0.33bc0.39b0.46b0.44b0.45b0.39d0.46b0.43bc0.37b0.46b0.25s0.25a
 P−ME+0.00a0.09b0.31a0.40a0.56a0.51b0.37b0.65a0.61a0.63a0.67a0.66b0.57a0.61a0.57a0.55a0.45a0.25a
 P+ME−0.00a0.03c0.11b0.20b0.24b0.22d0.27c0.35b0.49b0.42b0.49b0.53c0.42b0.39d0.41b0.45b0.35b0.24a
 P+ME+0.00a0.24a0.29a0.40a0.60a0.67a0.71a0.65a0.60a0.69a0.67a0.75a0.64a0.48b0.64a0.45b0.39ab0.30a
Set of male 3 + n days old
 P−ME−0.00b0.09b0.11c0.22c0.2c40.32b0.31b0.47b0.44b0.45c0.47c0.39b0.40c0.41c0.44b0.35b0.33b0.29a
 P−ME+0.00b0.26a0.35a0.55a0.55a0.54a0.53a0.54a0.63a0.60b0.59b0.58a0.61a0.60a0.59a0.50a0.32b0.26a
 P+ME−0.00b0.13b0.18b0.30b0.22c0.29b0.31b0.30b0.40b0.45c0.55b0.47b0.49b0.34d0.41b0.47a0.31b0.24a
 P+ME+0.16a0.33a0.40a0.53a0.47b0.47a0.56a0.56a0.61a0.69a0.70a0.60a0.58a0.49b0.46b0.44a0.41a0.27a

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. References

The results obtained in the three experiments for the two Bactrocera species differed considerably, reflecting different biologies and ecological requirements. While there were no significant differences in terms of mating performance among the four pre-release diets that involved the incorporation of protein (P, P+ 3 : 1; P+ 2 : 1 and P only) when fed to young sterile B. dorsalis males, for B. correcta sterile males fed the P+ 3 : 1 or the P+ 2 : 1 diet resulted in mating percentages that were significantly higher than P and P only fed sterile males. These experiments showed that sterile males of B. dorsalis and B. correcta provided only water-agar as a pre-release diet during this critical initial period obtained very low mating success, achieving 50% less mating pairs than young sterile males exposed to an improved pre-release diet.

Young sterile males of B. dorsalis and B. correcta exposed at the age of 2, 3, 4 or 5 days to ME manifested a mating competitiveness significantly higher than that of non-ME-exposed males but were competitively inferior to mature wild males, at least at younger ages. Nevertheless, including ME exposure in the pre-release diet of teneral sterile males is advantageous because ME-exposed sterile males were able to compete at an earlier age with mature wild males.

Results also showed an additive effect of interaction of protein-rich diet and ME exposure on higher mating success of B. dorsalis and a clear effect of ME exposure for B. correcta, confirming the potential of this approach to improve operational SIT application against both species.

The addition of the protein to the pre-release diet, as shown previously by Shelly et al. (2005), significantly increases the mating performance of the B. dorsalis and B correcta males. Young males fed only agar and water during this critical early period never recovered, while those with access to only sugar, or protein without sugar, took some time after the switch to a full diet (P+ 3 : 1) to recover and perform at the same level as the males that received sugar–protein during the initial 2 days. This is in line with data for many other trepritids, like Anastrepha suspensa (Loew), showing that sugar is a key to fuel the metabolism and therefore also essential for male maturation and sexual performance (Teal et al. 2004).

Methyl eugenol is a strong attractant for male B. dorsalis that when ingested can significantly enhance and advance the mating performance of sterile males when competing with wild males for wild females (Hee and Tan 2006; Shelly et al. 2010). Our findings for B. dorsalis are in line with these and other studies (Obra and Resilva 2013), clearly showing the advantage of a carefully timed pre-release ME exposure, not only for the well-studied B. dorsalis, but for B. correcta as well. To obtain the benefits of ME feeding in sterile males, there is a need to hold the flies for 1–2 days longer before exposure and release in the field. Even though this would entail additional cost and sterile fly holding space, the benefits of improved sterile male performance would be even larger.

Independent and interactive effects of pre-release diet and ME exposure represent the benefits in terms of mating success by young sterile male B. dorsalis and B. correcta. For the optimal implementation of our findings from these experiments and the requirements of an ongoing field operations of a fruit fly SIT suppression programme, we recommend including sugar–yeast hydrolysate at a ratio of 3 : 1 into each adult holding container from fly emergence at least until 2–3 days of age or even later if flies can be held longer before release to improve the sterile male performance in the field. Furthermore, in the morning of the release day, sterile flies should be exposed for 1 h to ME, at a rate of 1 ml/2000 flies. From the viewpoint of operating an fly emergence and release facility, providing sugar/yeast hydrolysate into holding containers is practicable, while large-scale ME feeding methods still need to be developed, although some proposals have already been made (see Tan and Tan 2013).

Besides improving sterile male mating performance, ME exposure of sterile males before release can represent an additional major advantage. Shelly (1994) demonstrated that males previously fed on ME have a low incidence of repeat feeding, while male annihilation treatment (MAT), involving the deployment of ME-treated toxic baits, is an effective method used to eliminate wild males before they are able to mate and produce offspring. The simultaneous release of ME fed sterile males and MAT application appears possible, resulting in the ‘replacement’ of wild males by sterile males (Robinson and Hendrichs 2005), as a consequence increasing much the sterile-to-wild male sex ratios and thus greatly enhancing the effectiveness of the SIT.

Clearly, this research effectively impacts the improvement in sterile male performance in B. dorsalis and B. correcta. These extensive experiments are widely applicable to efforts to suppress Bactrocera fruit fly in an environment-friendly way by incorporating an SIT component into the area-wide integrated management programmes against these pest insects.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. References
  • FAO/IAEA/USDA, 2003. Manual for product quality control and shipping procedures for sterile mass-reared tephritid fruit flies, Version 5.0. IAEA, Vienna, Austria.
  • Hee AKW, Tan KH, 2005. Bioactive fractions containing methyl eugenol-derived sex pheromonal components in haemolymph of the male fruit fly Bactrocera dorsalis (Diptera: Tephritidae). Bull. Entomol. Res.95, 615620.
  • Hee AKW, Tan KH, 2006. Transport of methyl eugenol-derived sex pheromonal components in the male fruit fly, Bactrocera dorsalis. Comp. Biochem. Physiol. C Toxicol. Pharmacol.143, 422428.
  • Niyazi N, Lauron CR, Shelly TE, 2004. Effect of probiotic adult diets on fitness components of sterile male Mediterranean fruit flies (Diptera: Tephritidae) under laboratory and field cage conditions. J. Econ. Entomol.97, 15701580.
  • Obra GB, Resilva SS, 2013. Influence of adult diet and exposure to methyl eugenol in the mating performance of Bactrocera philippinensis. J. Appl. Entomol. 137(Suppl. 1), 210216.
  • Orankanok W, Chinvinijkul S, Thanaphum S, Sitilob P, Enkerlin WE, 2007. Area-wide integrated control of oriental fruit fly Bactrocera dorsalis and guava fruit fly Bactrocera correcta in Thailand. In: Sterile insect technique, principles and practice in area-wide integrated pest management. Ed. by Dyck VA, Hendrichs J, Robinson AS, Springer, Dordrecht, The Netherlands, 517526.
  • Robinson AS, Hendrichs J, 2005. Prospects for the future develoment and application of the sterile insect technique. In Sterile insect technique, principles and practice in area-wide integrated pest management. Ed. by Dyck VA, Hendrichs J, Robinson AS, Springer, Dordrecht, The Netherlands, 727760.
  • Shelly TE, 1994. Consumption of methyl eugenol by male Bactrocera dorsalis (Diptera: Tephritidae): low incidence of repeat feeding. Fla. Entomol.77, 201208.
  • Shelly TE, Dewire AM, 2000. Flower-feeding affects mating performance in male oriental fruit flies Bactrocera dorsalis. Ecol. Entomol.25, 109114.
  • Shelly TE, Edu J, Pahio E, 2005. Influence of diet and methyl eugenol on the mating success of males of the Oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae). Fla. Entomol.88, 307313.
  • Shelly TE, Edu J, McInnis DO, 2010. Pre-release consumption of methyl eugenol increases the mating competitiveness of sterile males of the Oriental fruit fly, Bactrocera dorsalis, in large field enclosures. J. Insect Sci.10, 8.
  • Tan KH, 2000. Behaviour and chemical ecology of Bactrocera flies. In: Area-wide control of fruit flies and other insect pests. Ed. by Tan KH, Penang, Penerbit Universiti Sains Malaysia, Pulau Pinang, Malaysia, 647656.
  • Tan KH, Nishida R, 1996. Sex pheromone and mating competition after methyl eugenol consumption in the Bactrocera dorsalis complex. In: Fruit fly pests: a world assessment of their biology and management. Ed. by McPheron BA, Steck GJ, St Lucie Press, Delray Beach, FL, 147153.
  • Tan KH, Nishida R, 1998. Ecological significance of male attractant in the defence and mating strategies of the fruit fly pest, Bactrocera papayae. Entomol. Exp. Appl.89, 155158.
  • Tan LT, Tan KH, 2013. Automated tephritid fruit fly semiochemical mass feeding structure: design, construction and testing. J. Appl. Entomol. 137(Suppl. 1), 217229.
  • Teal PEA, Gavilanez-Slone JM, Dueben BD, 2004. Effects of sucrose in adult diet mortality of males of Anastrepha suspensa (Diptera: Tephritidae). Fla. Entomol.87, 487491.
  • Yuval B, Maor M, Levy K, Kaspi R, Taylor PW, Shelly TE, 2007. Breakfast of champions or kiss of death? Survival and sexual performance of protein-fed, sterile Mediterranean fruit flies (Diptera: Tephritidae)Fla. Entomol.90, 115122.

This article was published online on 21 October 2011. The references for Obra and Resilva (2013) and Tan and Tan (2013) have now been updated to show the correct citation details for J. Appl. Entomol. Vol. 137, Suppl. 1.