Bernie C Dominiak

A review of 16 years of quality control parameters at a mass-rearing facility producing Queensland fruit fly, Bactrocera tryoni

From 1996 to 2012, the mass‐rearing facility at Camden (NSW, Australia) has been producing Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). During this time, the facility has regularly recorded fly quality parameters, creating a unique data set that provides an invaluable opportunity to evaluate the interrelationships among standard quality control (QC) parameters and test for redundant QC variables. Here, we conducted an exploratory data analysis to reveal relationships among the QC parameters. We found that pupal weight, adult lifespan, and longevity under nutritional stress (i.e., survival duration without food or water) had distinct monthly trends, suggesting that these QC parameters are sensitive to seasonal conditions. Furthermore, emergence percentage, flight ability, and adult lifespan were adversely affected by the dyeing/handling/irradiation process associated with sterile insect releases. Using a multivariate approach and controlling for monthly and yearly patterns, we showed that pupal weight and egg hatch are consistently negatively related and that percentage male and emergence rates are consistently negatively related. These results suggest that these correlation pairs measure similar quality information and hence one QC variable from each pair could be dropped. Flight ability was not strongly correlated with any of the QC variables, suggesting that this QC variable remains a useful QC metric. Finally, the longevity under nutritional stress QC appears to be fairly insensitive to QCs and we suggest that it should be replaced by the standard mortality under stress test.

Field performance of Lynfield and McPhail traps for monitoring male and female sterile Bactrocera tryoni (Froggatt) and wild Dacus newmani (Perkins)

BACKGROUNDnMcPhail traps, baited with protein food lure, are used worldwide for surveillance of many species of fruit flies. Queensland fruit fly (Qfly) Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) is a native Australian fruit fly and normally monitored using Lynfield traps baited with cuelure. On some occasions, McPhail traps with wet food lures are deployed to detect female flies or to find the incursion epicentre. This paper reviews field results on the merits of Lynfield and McPhail traps for detection of male and female Qfly.nnnRESULTSnFollowing release of equal numbers of sterile males and females, Lynfield traps baited with cuelure captured more Qfly males than protein autolysate or orange concentrate in McPhail traps. Significantly more male than female Qfly were captured in McPhail traps baited with protein autolysate or orange. There was no significant difference between orange concentrate lure and protein autolysate lure in attracting either males or females. Another Australian native fruit fly, Dacus newmani (Perkins), was attracted to cuelure in Lynfield traps but not to either lure in McPhail traps.nnnCONCLUSIONSnThe data obtained run counter to the reputation of McPhail traps baited with protein autolysate or orange concentrate as a specialist lure/trap combination for female Qfly.

Effect of conditions in sealed plastic bags on eclosion of mass-reared Queensland fruit fly, Bactrocera tryoni

The sterile insect technique has been used for more than 50u2003years to control a range of insects around the world. Sterile insect technique is rapidly becoming a major component of many area‐wide fruit fly management programmes. Irradiation of immature life stages induces sterility in adults, which are then distributed over large areas to mate with wild flies, resulting in no viable offspring. However, irradiation in normal air results in declining adult quality. To optimize the quality of sterile adult flies, several techniques are available to lower the levels of oxygen in fruit fly tissues prior to irradiation. The simplest method is to seal pupae in plastic bags and allow the oxygen consumption of pupae to minimize oxygen in both the air and pupal tissue. Some fruit fly species have rapid decreases in eclosion as a result of low oxygen atmospheres. We tested the tolerance of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), to low oxygen for the first time. In the first two experiments, unirradiated B. tryoni pupae were tested for different periods in sealed plastic bags at 17, 21, and 26u2003°C. Optimum eclosion occurred at 21u2003°C with the lowest eclosion at 26u2003°C. In general, mean full eclosion declined at ca. 0.1% eclosion per hour sealed in plastic bags during the first 96u2003h for all temperatures. In the third and fourth experiments at 17u2003°C, there was a decline in average eclosion for irradiated and unirradiated pupae of about 13.4% after they were sealed in plastic bags for 192u2003h. In general, B. tryoni eclosion declined at 0.1% per hour inside sealed plastic bags for periods up to 192u2003h at 17u2003°C. Queensland fruit flies can tolerate long periods of conditions found inside sealed plastic bags and current practices for sterile B. tryoni release programmes will result in minimum decrease in eclosion. The possible evolution of tolerance of these conditions is discussed.

Optimising irradiation dose in mass‐produced Queensland fruit fly, Bactrocera tryoni, for sterile insect release: the incorporation of residual effects on F1 progeny

The sterile insect technique (SIT) is a potential tool for the management and eradication of incursions of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Mass‐produced B. tryoni are irradiated during the pupal stage to induce reproductive sterility. As increasing irradiation dosage results in declining fly quality, determining the lowest possible dosage that induces sufficient reproductive sterility is of particular interest. However, in calculating reproductive sterility, previous research has not considered carryover irradiation effects to F1 progeny. To test for these effects, B. tryoni pupae were exposed to one of five target dose ranges: 0, 20–25, 40–45, 60–65, or 70–75 Gy. Upon adult eclosure, fly quality was assessed using standard quality control (QC) measures: adult eclosure rates, flight ability, sex ratio, and longevity under nutritional stress. No effect of irradiation dose on any of the QC measures was found. Residual fertility was assessed by measuring larval eclosure failure for all doses. For the 0–45 Gy doses, mortality was measured during development of F1 progeny and larval eclosure rates were measured in F2 progeny. For irradiated females, irradiation dose significantly affected egg production, as well as increasing mortality during pupation of F1 progeny. For irradiated males, irradiation dose strongly affected larval eclosure of F1 progeny and, similar to females, mortality increased during pupation with higher doses. Our results suggest that residual effects of irradiation dose decreases F1 progeny viability and current estimates of residual fertility for B. tryoni underestimate the actual residual fertility. We conclude by synthesising our results with the previous findings and we propose that the target irradiation dose for B. tryoni may be lowered to 55–60 Gy.

Screening mitochondrial DNA sequence variation as an alternative method for tracking established and outbreak populations of Queensland fruit fly at the species southern range limit

Abstract Understanding the relationship between incursions of insect pests and established populations is critical to implementing effective control. Studies of genetic variation can provide powerful tools to examine potential invasion pathways and longevity of individual pest outbreaks. The major fruit fly pest in eastern Australia, Queensland fruit fly Bactrocera tryoni (Froggatt), has been subject to significant long‐term quarantine and population reduction control measures in the major horticulture production areas of southeastern Australia, at the species southern range limit. Previous studies have employed microsatellite markers to estimate gene flow between populations across this region. In this study, we used an independent genetic marker, mitochondrial DNA (mtDNA) sequences, to screen genetic variation in established and adjacent outbreak populations in southeastern Australia. During the study period, favorable environmental conditions resulted in multiple outbreaks, which appeared genetically distinctive and relatively geographically localized, implying minimal dispersal between simultaneous outbreaks. Populations in established regions were found to occur over much larger areas. Screening mtDNA (female) lineages proved to be an effective alternative genetic tool to assist in understanding fruit fly population dynamics and provide another possible molecular method that could now be employed for better understanding of the ecology and evolution of this and other pest species.