Tim Holler

Food sources for adult Diachasmimorpha longicaudata , a parasitoid of tephritid fruit flies: effects on longevity and fecundity

We report the results of a study on potential food sources of the widely distributed Indo‐Australian braconid fruit fly parasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). Adults sustained life on diets of fruit juice or fruit pulp, a homopteran and its associated honeydew, or extrafloral nectary secretions. Longevities on all these foods and fecundity on fruit juice were comparable to those achieved on the honey that is typically provided in mass‐rearing programs. Certain of the flower species Bidens alba (L.), Spermacoce verticillata L., Lobularia maritima (L.) Desv., Brassica nigra (L.), Lantana camara L., their nectar or pollen, provided a diet that resulted in longer maximum life spans than water alone. Unlike some tephritid flies, the braconid did not feed on fresh bird feces or leaf‐surface exudates. Feeding by D. longicaudata on wounded host fruits of tephritid flies suggests that adult parasitoids would not need separate forays for adult food and oviposition sites, as these occur in the same locations. We conclude that an inventory of adult foods may help target inundative releases of D. longicaudata and lead to improvements in diets used for mass rearing.

COLONIZATION OF FOPIUS CERATITIVORUS, A NEWLY DISCOVERED AFRICAN EGG-PUPAL PARASITOID (HYMENOPTERA: BRACONIDAE) OF CERATITIS CAPITATA (DIPTERA: TEPHRITIDAE)

Abstract Fopius ceratitivorus Wharton is a recently discovered braconid parasitoid of the Mediterranean fruit fly (= medfly), Ceratitis capitata (Wied.). Unlike other parasitoids previously used in medfly biological control, F. ceratitivorus was originally collected from medfly in its purported region of origin, east Africa. Shipments of Ceratitis spp. pupae from Kenya to a newly constructed quarantine facility in Guatemala yielded both F. ceratitivorus and its congener F. caudatus (Szèpligeti). Only the former species was successfully colonized through the use of medfly infested coffee berries. In the process of colonization it was determined that F. ceratitivorus oviposited into the eggs and recently hatched larvae of medflies and completed development in the hosts’ puparia. This is a relatively rare behavior among fruit fly parasitoids and, because tephritid eggs near the surface of fruits are particularly vulnerable to attack, one that might contribute to its success as a biological control agent.

Biogeography of Braconid Parasitoids of the Caribbean Fruit Fly (Diptera: Tephritidae) in Florida

Abstract The geographic distribution of three braconid parasitoids of the Caribbean fruit fly, Anastrepha suspensa (Loew), was determined by collecting host fruit throughout central and southern Florida. Diachasmimorpha longicaudata (Ashmead) was most abundant in southern Florida, occurring at higher latitudes along the Atlantic and Gulf coasts. Distribution of this species was negatively related to variance of monthly temperatures. This suggests that D. longicaudata may be dependent on a relatively constant supply of hosts. Doryctobracon areolatus (Szepligeti) was the dominant species at the majority of interior locations, but it was uncommon or absent along both coasts. Utetes anastrephae (Viereck) was widespread but usually less common than the other species. Parasitism levels of both D. areolatus and D. longicaudata were positively related to density of common guava, Psidium guajava L., trees. Parasitism levels of both D. longicaudata and U. anastrephae were positively related to numbers of A. suspensa captured in McPhail traps. Abundance of D. areolatus was inversely related to that of both D. longicaudata and U. anastrephae. The absence of D. areolatus in southeastern Florida, where it was originally established, suggests that a process of competitive displacement may have occurred. Parasitoid distribution is consistent with the hypothesis that D. areolatus is a superior searcher and D. longicaudata is a superior intrinsic competitor.

The Effects of Chilling on the Fecundity and Life Span of Mass-reared Parasitoids (Hymenoptera: Braconidae) of the Mediterranean Fruit Fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

Suppression of Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann), populations may be achieved through the mass-rearing and augmentative aerial release of opiine braconid parasitoids. Typically, aerial release techniques require up to one hour of chilling of adult parasitoids at temperatures as low as 3.5°C prior to their dissemination. Such chilling potentially could affect the subsequent performance of the insects. Among three species of the genus Diachasmimorpha longicaudata (Ashmead), tryoni (Cameron), and krausii (Fullaway) there was little or no affect of chilling in the laboratory on female longevity, production of daughters, or offspring sex ratio. This is consistent with previous experiments that found chilling to have no discernable effect on the short-term mortality of D. tryoni or on its ability to take flight immediately after aerial release. While there was little effect of chilling on longevity and fecundity in a species from another opiine genus, Fopius arisanus (Sonan), exposure to low temperatures did result in a significantly more male-biased offspring sex ratio.

USE OF HOST FRUIT CHEMICAL CUES FOR LABORATORY REARING OF DORYCTOBRACON AREOLATUS (HYMENOPTERA: BRACONIDAE), A PARASITOID OF ANASTREPHA SPP. (DIPTERA: TEPHRITIDAE)

Abstract Doryctobracon areolatus (Szepligeti) (Hymenoptera: Braconidae) is a common parasitoid of Anastrepha spp. (Diptera: Tephritidae). An efficient method of laboratory rearing incorporates chemicals from pear fruits into oviposition units. Production for the F1 and F2 generations was 12.1 and 9.3 progeny per female, respectively. Mean daily progeny production by F2 females was between 1-2 progeny per female for almost all ages from 9 to 22 days. A bioassay was designed to determine the source of chemical cues used for host location. Parasitoids were given a choice between two oviposition units: a positive control containing all possible cues, and a treatment unit with cues derived from either the host fly, host fruit, both, or none. The number of females active on each oviposition unit was recorded. This experiment demonstrated that chemical cues derived from the host fruit, probably the peel, are involved in host location.

The Distributions of the Caribbean Fruit Fly, Anastrepha suspensa (Tephritidae) and Its Parasitoids (Hymenoptera: Braconidae) within the Canopies of Host Trees

In the area of LaBelle, Florida (Hendry County), the Caribbean fruit fly, Anastrepha suspensa (Loew), is commonly attacked by three braconid parasitoids, Doryctobracon areolatus (Szepligeti), Diachasmimorpha longicaudata (Ashmead), and Utetes anastrephae (Viereck). Fruits from fifteen individual trees of four species, Surinam Cherry (Eugenia uniflora L.), Cattley guava (Psidium cattleianum Sabine), guava (P. guajava L.), and loquat (Eriobotrya japonica [Thunb.]), were systematically sampled in order to determine the distribution of A. suspensa and its parasitoids within the trees canopies. Fruits infested by A. suspensa were lighter than infested ones in P. guajava. This may be due to the presence of the larvae. There was no evidence that A. suspensa preferred to oviposit in fruits at particular heights above ground or distances from canopy edges. Fruits containing larvae parasitized by U. anastrephae were significantly lighter than those containing larvae parasitized by either D. areolatus or D. longicaudata, and it was not present in P. guajava, the species with the heaviest fruits. There were no differences, either overall or within host tree species, among the heights above ground or distances from canopy edges of fruits containing larvae parasitized by any of the three braconids. Niche similarity in D. areolatus and D. longicaudata may be due to the absence of a shared evolutionary history. Both are recent introductions to Florida, but while D. areolatus is a neotropical species, D. longicaudata is from the Indo-Philippine region. Thus, there has been little opportunity for divergence. Knowledge of the distributions within tree canopies of the pest-fly, and of its natural enemies, may lead to improvements in its biological control.

Efficacy of Tower Medfly Eclosion Systems

A 16-repetition experiment was conducted to evaluate the performance of the “tower” system for eclosion of sterile medflies, Ceratitis capitata (Wiedemann). This system has now replaced the PARC system previously used in Florida S.I.T. programs. In addition to testing the efficacy of these eclosion systems, as compared to the PARC system, quality control was also monitored and evaluated. No significant differences were found between either system in regards to C. capitata yield, weight or flight ability (p=0.05). Based on these comparative trials, the tower eclosion system appears to be an efficient alternative to the PARC system.

Release of Sterile Mediterranean Fruit Flies, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), Using an Automated Ground Release Vehicle

A trial was conducted in Tampa, Florida to test an automated ground release machine as an alternative to aerial methods for release of sterile Mediterranean fruit flies, Ceratitis capitata (Wiedemann). Twenty-four Jackson traps baited with trimedlure at three release sites yielded lower than expected numbers of ground released Medflies. Recaptures per trap ranged from 2.8 (±0.7 S.E.) to 6.8 (±1.7 S.E.). Average recovery of sterile flies at each site for all releases combined (144 observations) was similar, 3.4 (±0.5 S.E.), 4.4 (±0.5 S.E.), 4.5 (±0.5 S.E.) for sites 1, 2 and 3 respectively. There was a significant reduction in flight ability from 67.5 (±2.1 S.E.) to 53.6 (±2.9 S.E.)%, from the time of pre-chilling to when immobilized flies were released after 2.5 h in the release container. Further tests are needed to determine what mortality factors may influence recovery and how the automated ground release machine compares to the aerial release method.

Evaluation of Irradiated Caribbean Fruit Fly (Diptera: Tephritidae) Larvae for Laboratory Rearing of Doryctobracon areolatus (Hymenoptera: Braconidae)

ABSTRACT We report here that it is possible to rear D. areolatus on irradiated A. suspensa larvae without adversely affecting sex ratio and overall parasitoid emergence and with no adult A. suspense emergence. There was no difference in emergence of D. areolatus adults from irradiated versus non-irradiated hosts (72.4 ± 1.9% vs. 73.0 ± 1.9%), and no difference in sex ratio of parasitoids obtained from irradiated and non-irradiated hosts (50.0 ± 1.6 and 47.0 ± 1.4% female, respectively). The successful use of A. suspensa larval hosts can greatly ease the process of rearing, transporting, and releasing fruit fly parasitoids while eliminating the need to separate flies from parasitoids. Further improvements in the laboratory rearing process of D. areolatus, including irradiating late A. suspensa larvae at a lower dosage and irradiating A. suspensa as egg or early instars, are discussed.

The Thermal Environment of Immature Caribbean Fruit Flies, Anastrepha suspensa (Diptera: Tephritidae)

Abstract Because many plants regulate their internal temperatures, there is no a priori reason to believe air temperature accurately reflects the temperatures faced by tephritid larvae inhabiting fruit interiors. Larvae also move across and burrow into soil to pupate, and immature flies at this point are also likely to encounter temperatures that might be less than or exceed air temperature. Using thermocouples and a computerized data logger we measured a range of temperatures in the 4 major hosts of Anastrepha suspensa (Loew), the Caribbean fruit fly: Surinam cherry, Eugenia uniflora L., Cattley guava, Psidium cattleianum Sabine, guava, Psidium guajava L., and loquat, Eriobotrya japonica (Thunb.), and in grapefruit, Citrus paradisi Macf., an economically important secondary host. Generally, temperatures were higher in the southwestern portions of tree canopies relative to those in the northeastern interiors. Fruit on the ground was warmer than in the tree, but there was no significant pattern of maximum fruit core temperatures being warmer than subcutaneous pulp. Soil temperatures were also higher than fruit-in-tree temperatures, and decreased and displayed less variance with increasing depth. Fruit in trees seldom reached temperatures ±0.05 of air temperatures, but fruit on the ground could be more than 0.25 the adjacent air temperature. There were positive relationships between the ratio of mean and minimum fruit temperature/adjacent air temperature and fruit diameter. Information on the temperatures confronted by immature fruit flies can be used to model population dynamics, and to design temperature sensitive strains through conditional gene expression for mass-rearing and release.