Jamil Hossain Biswas

Symbiotic bacteria play crucial roles in growth, development, behaviour, immunity, and metabolism of insects. Most of the research until now has explored the role of gut bacteria in insect model systems. The extent to which gut bacteria affect mating behaviour and reproduction of insect pest species still needs, however, to be fully comprehended. In this study, we aimed to investigate the effects of gut bacteria manipulation on mating behaviour and fecundity of a major beehive pest, the small hive beetle Aethina tumida (Murray). We manipulated gut bacteria of both sexes and determined the effects on mating behaviour and reproductive output. Our results provided evidence that manipulation of the gut bacteria influences reproduction in both sexes, negatively affecting mating latency, mating number, mating duration and offspring number (larvae). These results highlight the role of gut bacteria on the reproduction of insect pests, which might help in designing new pest control methods.

The Queensland fruit fly (Q‐fly), Bactrocera tryoni (Froggatt), is a major horticultural pest in Australia. Sterile insect technique (SIT) is increasingly used in area‐wide integrated management of Q‐fly, as well as for eradication of outbreaks in Q‐fly‐free regions. Quality control (QC) procedures are important to monitor and maintain high standards of mass‐reared insects for SIT. Effective use of QC procedures, and the setting of meaningful standards, requires a clear understanding of the short‐term factors that can cause changes in key parameters, such as failures in production systems, and also of the longer‐term effects of domestication on the performance of mass‐reared colonies. Artificial rearing conditions impose substantial selection pressures that can lead to changes in performance, and hence changes in the expected baseline values in QC assays. We investigated the effects of domestication on QC parameters of old and young Q‐fly colonies originating from three distant geographical locations in Australia: Sydney (Generation >100 and 7), Brisbane (Generation 59 and 14) and Cairns (Generation 29 and 9). Standard QC parameters including development time, pupal recovery, pupal weight, adult emergence, sex ratio, flight ability, fecundity, egg hatchability and longevity were assessed. Regardless of their origin, older Q‐fly colonies had lower egg hatchability, shorter developmental time, higher fecundity, higher survival under stress and greater longevity. We emphasize the importance of understanding the effects of continued domestication on QC measures when setting standards for assessment of fruit fly strains used in SIT programmes, particularly when using strains that are regularly replaced or infused with wild stock.

In Sterile Insect Technique (SIT) programs, the released sterile insects must attain sexual maturity at an early adult age so that a large proportion survive to mature and contribute to reducing reproduction of pest populations. Previous field studies based on release of adult Queensland fruit fly, Bactrocera tryoni (Froggatt) (‘Q‐fly’), at 2 days of age found a significant increase in the recapture of mature male Q‐flies when they were provided methoprene or raspberry ketone (RK) before release. SIT for Q‐flies has subsequently adopted release at 5 days of age; there is now a contextual need to re‐assess the merit of methoprene and RK supplements. We assessed field abundance and dispersal of mature sterile male Q‐flies that had been held for 5 days on pre‐release standard diets of sugar and yeast hydrolysate (3:1) (control) with and without methoprene or RK supplements. Overall, the proportion of control‐ and RK‐treated flies recaptured was higher than the proportion of methoprene‐treated flies recaptured. We found no evidence that either methoprene or RK supplements yielded improvements over the control diet alone concerning abundance and dispersal of the male Q‐flies. Laboratory studies indicate that while the doses of methoprene (control + methoprene at 0.05% or 0.5%) and RK (control + RK at 1.25% or 5%) used in field releases at 2 days of age did not affect male longevity when sustenance was provided, these doses resulted in reduced longevity when no sustenance was provided. Furthermore, all doses of methoprene and RK used in field releases at 5 days of age reduced male longevity regardless of sustenance. At 5 days of age, the flies are already in an advanced state of maturity when released and in this context, it appears that additional pre‐release treatments of methoprene and RK provide no further improvement and may even be detrimental when nutrition is scarce.

The sterile insect technique (SIT) is a sustainable pest management tool based on the release of millions of sterile insects that suppress reproduction in targeted populations. Success of SIT depends on survival, maturation, dispersal, and mating of released sterile insects. Laboratory and field cage studies have demonstrated that dietary supplements of methoprene and raspberry ketone (RK) promote sexual maturation of adult Queensland fruit fly, Bactrocera tryoni (Froggatt), and may hence shorten the delay between release and maturity in the field. We investigated the effects of methoprene and RK dietary supplements on field abundance of sexually mature sterile Q-flies relative to untreated flies fed only sugar and yeast hydrolysate before release at 2 d of age. Compared with untreated flies, more methoprene- and RK-treated flies were recaptured in cuelure traps to which only sexually mature males are attracted. At distances of 100 and 200 m from the release point, recapture rates were higher for methoprene- and RK-treated flies than for untreated flies, but at 300 m recapture rates were low and were similar for treated and untreated flies. Rainfall, relative humidity, wind speed, and wind direction did not affect recapture rates, but temperature was positively correlated with recapture rates for all treatments. There was a strong correlation between the number of sterile and wild flies caught in traps, indicating co-location in the field. Dietary supplements of methoprene and RK can substantially increase abundance of sexually mature sterile male Q-flies in the field following release as 2-d-old immature adults.

Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), presents a major threat to Australian fruit production and trade. The sterile insect technique (SIT) is increasingly employed to manage Q-fly. Quality of sterile males released in SIT programs, and hence program efficacy, can be affected by pre- and post-production processes, such as mass rearing, packing, irradiation, transportation, and release. Given long distances from rear-out facilities to release sites, adult flies are usually chilled to reduce metabolism and stress during transportation. To guide SIT procedures, it is important to understand the impact of such practices on performance of sterile Q-fly. The present study assesses the effect of chilling temperature and exposure period on quality parameters of sterile Q-fly. We considered the effects of two temperature regimes (4 and 6°C) and six exposure periods (0, 1, 2, 4, 6, and 12 h) on chill-coma recovery time, flight ability, survival under nutritional stress, and longevity of both males and females. Flies chilled at 4°C took longer to recover than that those chilled at 6°C. Flight ability, survival under nutritional stress, and longevity all decreased as chilling period increased but did not differ between the two tested temperatures. We recommend that periods of chilling during transportation from rear-out facilities to release sites be minimized in order to retain quality of sterile Q-fly and that increased release rates be considered when longer chilling periods are required.

The sterile insect technique (SIT) and male annihilation technique (MAT) are important tools for the control of Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), a major insect pest of horticultural crops in Australia. In MAT, mature Q-fly males are attracted to a toxic bait using Cuelure, a synthetic analog of raspberry ketone (RK). Substantial improvements in control could be achieved by simultaneous use of SIT and MAT, but this requires suppression of the Cuelure response in released sterile flies. Recent studies report that prerelease feeding with RK during the first 48 h after emergence can reduce the response of mature Q-fly males to Cuelure, but the mechanism underpinning this is unknown. Here, to test whether reduced sensory sensitivity to Cuelure is involved, we evaluated the effects of RK supplements, adult diet (yeast-supplemented diet throughout adult stage vs yeast-supplemented diet only for 48 h), and age on electroantennogram (EAG) and electropalpogram (EPG) responses of Q-flies to Cuelure stimuli. EAG responses did not vary with RK supplements, sex, or age of Q-flies fed yeast-supplemented diet throughout the adult stage, but the responses of Q-flies fed other diet regime decreased with age. EPG responses of both sexes of Q-flies were affected by RK supplements, age, and their interaction, but without patterns that might indicate reduced maxillary palp response of RK supplemented flies to Cuelure. Our findings do not support the hypothesis that reduced Cuelure response of male Q-flies fed RK supplements is explained by reduced electrophysiological response in antennae or maxillary palps.