Jon I. Nishimoto

Augmentative releases of Diachasmimorpha tryoni (Hymenoptera: Braconidae) to suppress a mediterranean fruit fly (Diptera: Tephritidae) population in Kula, Maui, Hawaii

Abstract Diachasmimorpha tryoni (Cameron), a larval parasitoid, was mass-reared in the laboratory and was used to suppress a wild Mediterranean fruit fly, Ceratitis capitata (Wiedemann), population in a nonisolated area (13 km2) of Kula, Maui, Hawaii. Weekly releases of D. tryoni, averaging 272,000 parasitoids per release, were made from March 10 to June 22, 1988. Trap catches of male C. capitata adults began to decline 8 weeks after the first release, and catches remained low throughout the summer months. However, in the control area of Keokea, adult catches began to increase in April and reached a peak in early July that was similar to that of previous years. The percentage of parasitism of C. capitata by D. tryoni was significantly higher for the six weekly collections of infested peaches in Kula than in the control area of Keokea: an average of 47.0% parasitism in Kula compared with 14.2% in Keokea. Of the total parasitoids, a significantly higher percentage of D. tryoni was recovered in fruit samples from Kula than in those from Keokea. Moreover, the number of C. capitata per fruit was significantly lower in the treated area than in the control area

Capture probability of released males of two Bactrocera species (Diptera: Tephritidae) in detection traps in California.

ABSTRACT The genus Bactrocera (Diptera: Tephritidae) includes ≈70 polyphagous species that are major pests of fruit and vegetable crops. Most Bactrocera species have limited geographic distributions, but several species are invasive, and many countries operate continuous trapping programs to detect infestations. In the United States, California maintains ≈25,000 traps (baited with male lures) specifically for Bactrocera detection distributed over an area of ≈6,400 km2 (2,500 miles2) in the Los Angeles area. Although prior studies have used male lures to describe movement of Bactrocera males, they do not explicitly relate capture probability with fly distance from lure-baited traps; consequently, they do not address the relative effectiveness of male lures in detecting incipient populations of Bactrocera species. The objective of this study was to measure the distance-dependent capture probability of marked, released males of Bactrocera dorsalis (Hendel) and Bactrocera cucurbitae (Coquillett) (methyl eugenol- and cue lure-responding species, respectively) within the detection trapping grid operating in southern California. These data were then used to compute simple probability estimates for detecting populations of different sizes of the two species. Methyl eugenol was the more powerful attractant, and based on the mark—recapture data, we estimated that B. dorsalis populations with as few as ≈50 males would always (>99.9%) be detected using the current trap density of five methyl eugenol-baited traps per 2.6 km2 (1 mile2). By contrast, we estimated that certain detection of B. cucurbitae populations would not occur until these contained ≈350 males. The implications of the results for the California trapping system are discussed, and the findings are compared with mark—release—recapture data obtained for the same two species in Hawaii.

Relationship of sexual maturation rate to response of oriental fruit fly strains (Diptera: Tephritidae) to methyl eugenol

Laboratory-reared and wild, fruit-reared adults of the Oriental fruit fly,Dacus dorsalis Hendel, were tested for response to methyl eugenol at various ages. Virgin laboratory (2, 4, 6, 8, and 10 days old) and wild (7, 11, 15, 19, and 23 days old) flies were released into an outdoor field cage and trapped over a two-day period. Response of males increased with age as ca. 32% and 22% of laboratory and wild males responded at 2 and 7 days of age, respectively, while ca. 93% of both strains responded at 10 and 23 days of age, respectively. These correspond approximately to the ages at which they reach sexual maturity. Female response did not increase with age and fluctuated between 15% and 29% for the laboratory strain and 10% and 45% for the wild strain. The age-related response profiles, when integrated with sexual maturation curves, indicate that one of the major reasons the male-annihilation technique is effective is because methyl eugenol is able to attract 40–50% of male flies prior to the onset of sexual maturation.

Scented Males and Choosy Females: Does Male Odor Influence Female Mate Choice in the Mediterranean Fruit Fly?

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), displays a lek mating system characterized by a high level of female discrimination among potential mates. The basis of female choice is not understood, but recent studies indicate that male exposure to the aroma of certain plant structures or essential oils may increase mating success. In particular, exposure to the aroma of ginger root oil (GRO) enhances male mating frequency, and several sterile-male release programs against C. capitata have incorporated ‘aromatherapy’ (large-scale exposure of pre-release insects to GRO) to increase the effectiveness of control efforts. We investigated the mechanism underlying female preference for GRO-exposed males. Two sets of experiments were conducted. In the first, we monitored female attraction to (1) freshly killed flies, or (2) paper discs that contained hexane extracts from varying treatments. In these tests, females were sighted more often (1) near GRO-exposed than non-exposed males (even when the males were visually concealed) and (2) near extracts from GRO-exposed than non-exposed males. These findings suggest a ‘perfume effect’, whereby female mate choice is mediated by olfactory differences. In the second set, we compared (1) mate choice between intact females and females from which both antennae had been surgically removed, and (2) mating success between intact males and males from which both antennae had been surgically removed before GRO exposure. Intact females preferred GRO-exposed males, whereas females lacking both antennae rarely mated and showed no preference between GRO-exposed and non-exposed males. In the opposite treatment (intact females but surgically altered males), GRO-exposed males lacking both antennae mated as frequently as GRO-exposed intact males. These data suggest that female choice was dependent on olfactory perception of male odor but that male mating success did not depend on olfactory perception of GRO aroma, suggesting, in turn, that GRO conferred a mating advantage through an external phenomenon (possibly alteration of cuticular scent) rather than through internal processing (pheromone synthesis).

Trap capture of three economically important fruit fly species (Diptera: Tephritidae): evaluation of a solid formulation containing multiple male lures in a Hawaiian coffee field.

ABSTRACT Invasive fruit flies (Diptera: Tephritidae) pose a global threat to agriculture through direct damage to food crops and the accompanying trade restrictions that often result. Early detection is vital to controlling fruit flies, because it increases the probability of limiting the growth and spread of the invasive population and thus may greatly reduce the monetary costs required for eradication or suppression. Male-specific lures are an important component of fruit fly detection, and three such lures are used widely: trimedlure (TML), cue lure (CL), and methyl eugenol (ME), attractive to Mediterranean fruit fly, Ceratitis capitata (Wiedemann); melon fly, Bactrocera Cucurbitae (Coquillett); and oriental fruit fly, Bactrocera dorsalis (Hendel), respectively. In California, Florida, and Texas, the two Bactrocera lures are applied to separate species-specific traps as liquids (with a small amount of the insecticide naled added), whereas TML is delivered as a solid plug in another set of traps. Thus, the detection protocol involves considerable handling time as well as potential contact with a pesticide. The purpose of this study was to compare trap capture between liquid male lures and “trilure” wafers that contain TML, ME, raspberry ketone (RK, the hydroxy equivalent of CL), and the toxicant DDVP embedded within a solid matrix. Field studies were conducted in a Hawaiian coffee (Coffea arabica L.) field where the three aforementioned species co-occur, showed that the wafer captured at least as many flies as the liquid baits for all three species. This same result was obtained in comparisons using both fresh and aged (6-wk) baits. Moreover, the wafers performed as well as the single-lure traps in an ancillary experiment in which TML plugs were substituted for liquid TML. Additional experiments demonstrated explicitly that the presence of ME and RK had no effect on captures of C. capitata males and similarly that the presence of TML had no effect on the capture of B. Cucurbitae or B. dorsalis males.

Influence of Methoprene on the Age-Related Mating Propensity of Males of the Oriental Fruit Fly and the Mediterranean Fruit Fly (Diptera: Tephritidae)

ABSTRACT The application of juvenile hormone (or chemical analogs, such as methoprene) to newly emerged adult male fruit flies (Diptera: Tephritidae) represents a promising method to improve the efficiency of the Sterile Insect Technique against economically important species. This procedure has been shown to accelerate male sexual maturity in species with a long pre-copulatory period, and could allow for release of sterile males at younger ages and a greater release rate of sterile males overall. Topical application of methoprene has been shown to enhance male mating competitiveness. The present study investigated the effect of methoprene on maturation speed in males of the oriental fruit fly, Bactrocera dorsalis (Hendel) (a ‘slow’ maturing species) and the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (a ‘fast’ maturing species). For both species, newly emerged males were treated with acetone containing methoprene (treated) or acetone alone (control). The mating propensity of males was then monitored in non-competitive environments with mature females. Contrary to other studies, we found no evidence that methoprene accelerated male sexual activity in either a wild-like or mass-reared strain of B. dorsalis or a mass-reared (genetic sexing strain) of C. capitata. Possible explanations for these results are discussed.

Chilling and flight ability and mating competitiveness of sterile males of the Mediterranean fruit fly

The Sterile Insect Technique (SIT) is widely used to suppress or eradicate infestations of the Mediterranean fruit fly, Ceratitis capitata (Wied.). In large‐scale programs, sterile males are chilled (4°C) to allow their transfer and storage in the aircraft used for the releases. Sterile males may remain chilled for as long as 3 h prior to release. Here, we describe the results of experiments that assessed the effect of chilling on flight ability and mating competitiveness of sterile male Mediterranean fruit flies held under conditions of low (plastic buckets) or high (emergence tower trays) density. Males from both densities were subject to 0 (no chill), 1, or 3 h of chilling at 3 days of age. Chill treatment had no effect on flight ability for males held at low density. However, for males held at high density, chilling for 1 or 3 h significantly reduced flight ability below that observed for the no chill treatment. Consistent with the flight data, chill treatment had no effect on the mating success of males held at low density. However, among males held at high density, 3 h of chilling significantly reduced mating success below levels observed for unchilled males or males chilled for 1 h only in trials conducted 1 day after the cold treatment. An auxiliary experiment revealed that this reduction in mating performance was temporary: in mating trials conducted 3 days after 3 h of chilling, sterile males derived from tower trays had similar mating success as unchilled males. Implications of these findings for Mediterranean fruit fly SIT are discussed.

Release-Recapture of Bactrocera Fruit Flies (Diptera: Tephritidae): Comparing the Efficacy of Liquid and Solid Formulations of Male Lures in Florida, California and Hawaii

ABSTRACT Invasive species of Bactrocera fruit flies (Diptera: Tephritidae), particularly B. dorsalis (Hendel) and B. Cucurbitae (Coquillett), pose serious threats to agricultural crops. Detection relies largely on traps baited with the male lures methyl eugenol (ME), which is attractive to B. dorsalis, and cue-lure (CL) or the related chemicals raspberry ketone (RK) and raspberry ketone formate (RKF), which are all attractive to B. Cucurbitae. Currently, ME and CL are applied as liquids to cotton wicks (along with an insecticide), a procedure involving considerable handling time and exposure to pesticides. Recent studies have shown that traps baited with solid dispensers (plugs or wafers) of male lures, which arrive in sealed envelopes ready for use, catch at least as many Bactrocera males as traps baited with liquid lures. The present study compared captures of B. dorsalis and B. Cucurbitae males in traps baited with liquid lures versus traps baited with lure-bearing solid dispensers in Florida, California, and Hawaii. In the first 2 locations, marked, irradiated males were released at street intersections, and captures were scored at 4 trapping stations 50 m distant along the intersecting streets with various lure/dispenser combinations. In Hawaii, trap catch of wild B. dorsalis and B. Cucurbitae were compared among traps with liquid and solid formulations of the lures. Although several exceptions were observed, the overall finding was that the lure-bearing plugs and wafers captured as many or more Bactrocera males as the liquid application. Consequently, we suggest that solid dispensers could be adopted in area-wide fruit fly surveillance programs without lessening their detection sensitivity to incipient infestations. The use of solid dispensers that contain both ME and RK, in particular, could greatly reduce the number of traps required and result in considerable cost savings.

Does Female Mate Choice Confer Direct Fitness Benefits? Results From a Tephritid Fruit Fly

Abstract The melon fly, Bactrocera cucurbitae (Coquillett), exhibits a lek mating system in which males aggregate on plants, weakly defend leaf territories that lack any resources vital to females, and produce pheromone to attract potential mates. Males are attracted to and feed on the plant-borne compound raspberry ketone (RK) as well as its synthetic analogue, cue lure (CL), and studies have demonstrated that females mate preferentially with males fed these chemicals over males denied them. The objective of the present study was to investigate whether females gained direct fitness benefits by mating with CL-fed males, potentially via CL-mediated modifications in male ejaculate composition and quantity that act to enhance female longevity and reproduction. Mating trials were first performed to re-confirm that CL-feeding conferred a mating advantage to males. Then, having detected an advantage, female survival, fecundity, and fertility were compared between females mated to CL-fed males versus nonfed males. In addition, the incidence and duration of successful egg-to-pupa development were compared between the two groups of females. None of the comparisons suggested that fitness was enhanced by mating with a CL-fed male, and one parameter—fertility or egg hatch rate—showed a potential cost to mating with CL-fed males. Thus, mating with CL-fed males does not appear to confer direct fitness benefits to females. Factors potentially confounding interpretation of this finding are noted, and the possible role of a runaway selection process, mediated via RK or CL consumption, in shaping female mate choice in this species is proposed.

Exposure to the Plant Compound α-Humulene Reduces Mating Success in Male Mediterranean Fruit Flies (Diptera: Tephritidae)

ABSTRACT The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), displays lek mating, where searching females actively choose among aggregated males that produce visual, acoustic, and olfactory signals within the tree canopy. Recent studies demonstrated that treated males exposed to the aroma of particular plant compounds (&agr;-copaene) or oils (orange, manuka, and ginger) gain a mating advantage over control, nonexposed males. The goal of this study was to assess the impact of another plant compound, &agr;-humulene, on the mating success of male C. capitata. Prior work showed that &agr;-humulene was not attractive to either sex but elicited a strong electroantennal response in males. Field cage tests showed that males exposed to the aroma of &agr;-humulene obtained significantly fewer matings than control (nonexposed) males as long as 3 d after exposure. Exposed males exhibited lower signaling (pheromone calling) activity than control males, which presumably contributed to their reduced mating success. Despite this lessened activity, the mortality of treated males after chemical exposure was similar to that observed for control, nonexposed males, suggesting that &agr;-humulene was not a toxic or severely debilitating agent.