Physiological Entomology (2010) 35, 148–153 DOI: 10.1111/j.1365-3032.2010.00726.x
Activity patterns of Queensland fruit flies (Bactrocera
tryoni) are affected by both mass-rearing and
sterilization
C H R I S T O P H E R W . W E L D O N, J O H N P R E N T E R and P H I L L I P
W . T A Y L O R
Department of Brain, Behaviour and Evolution, Macquarie University, Sydney, Australia
Abstract. Mass-reared sterile tephritid flies released in sterile insect technique (SIT)
programmes exhibit behaviour, physiology and longevity that often differ from their
wild counterparts. In the present study, video recordings of flies in laboratory cages are
used to determine whether the sequential processes of mass-rearing and sterilization
(using gamma radiation) that are integral to SIT affect general activity patterns of male
and female Queensland fruit flies Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)
(‘Q-flies’). Compared with wild flies, mass-reared flies exhibit a marked reduction
in overall activity, and further reduction is found after sterilization. In terms of the
frequency of activities, both fertile and sterile mass-reared Q-flies fly less often and
exhibit more bouts of inactivity and grooming than wild Q-flies. In addition, in terms of
the duration of activities, fertile and sterile mass-reared Q-flies spend less time flying
and more time walking, grooming and being inactive than wild Q-flies. Although
fertile and sterile mass-reared flies are similar in other regards, sterile mass-reared
flies spend more time being inactive than fertile mass-reared flies. These findings raise
new questions about how changes in behaviour and activity levels may influence the
performance of mass-reared sterile Q-flies in the field, as well as the physiological and
metabolic processes that are involved. The frequency and duration of inactivity could
provide a simple but powerful and biologically relevant test for quality in mass-rearing
and SIT programs.
Key words. Behaviour, gamma-irradiation, inactivity, locomotor activity, quality
control, sterile insect technique (SIT), Tephritidae.
Introduction
The sterile insect technique (SIT) is an important method
for environmentally benign suppression and eradication of
some of the world’s most destructive agricultural, horticultural
and medical insect pests; a recent review of SIT history
is provided by Klassen & Curtis (2005). Sterile insect
technique programmes rely on the ability of sterile mass-
reared males to mate with wild females, inducing reproductive
sterility in their mates and thereby reducing population
levels in the next generation (Knipling, 1959). Because SIT
Correspondence: Christopher W. Weldon, Department of Brain,
Behaviour and Evolution, W19F, Macquarie University, North
Ryde, NSW 2109, Australia. Tel.: +61 2 9850 1311; e-mail:
cwweldon@gmail.com
requires vast numbers of sterile insects, it is necessary to
mass-rear insects under factory conditions that bear little
resemblance to their natural environment (Calkins & Parker,
2005). In modern SIT programmes, mass-reared insects are
then sterilized reproductively with radiation, typically from
radioisotopes (Bakri et al., 2005). Once released, males need
to locate adequate food sources, mature sexually, survive,
locate conspecifics and mate successfully with wild females.
However, both mass-rearing and sterilization are found to alter
insect behaviour, with a consequent reduction in sterile male
sexual performance (Cayol, 2000; Calkins & Parker, 2005).
Determining the extent of such changes, as well as whether
and how they impinge on performance, is important for the
development and maintenance of effective SIT.
The Queensland fruit fly Bactrocera tryoni (Froggatt)
(Diptera: Tephritidae) (referred to here as the ‘Q-fly’) is the
© 2010 The Authors
148 Journal compilation © 2010 The Royal Entomological Society

Activity patterns of B. tryoni 149
most widespread, destructive and costly horticultural pest in
Australia (Plant Health Australia, 2008). Q-flies that have been
mass-reared and sterilized as pupae with gamma radiation
are used routinely in SIT programmes to combat outbreaks.
Many generations under mass-rearing have been shown to
modify both mating behaviour (Weldon, 2005; Pe´rez-Staples
et al., 2009) and reproductive physiology (Meats et al., 2004;
Meats & Kelly, 2008) of Q-flies. Sterilization of Q-flies with
gamma radiation causes reduced longevity when flies are under
additional stress from crowding and deprivation of food and
water (Collins et al., 2008, 2009) or when maintained on
diets containing water and carbohydrate but no protein (Perez-
Staples et al., 2007). Sterilization also induces changes in the
calling and courtship songs of male Q-flies, increasing the
interval between pulses of sound for both song types (Mankin
et al., 2008).
Although the above studies provide insights into how mass-
rearing and sterilization affect the longevity and performance
of Q-flies in specific reproductive contexts, there has been
no prior investigation of how these processes affect general
activity patterns and levels in this species. Such information
would provide useful insights into potential deficiencies and
might also form the basis for new methods for the routine
assessment of how mass-rearing and sterilization influence
Q-fly quality. Quantification of unperturbed animal activity is
often used to explore underlying genetic, neural, conditional
and motivational processes (Martin et al., 1999; Gatti et al.,
2000; Klarsfeld et al., 2003; Martin, 2003; Ritzmann &
Bu¨schges, 2007). Furthermore, locomotor activity is often
central to decision-making processes and directly related to
reproductive success and survival (Martin, 2003). Accordingly,
in the present study, the general activity patterns of flying,
walking, grooming and inactivity of male and female Q-flies
is video recorded and assessed to determine the effects of mass-
rearing and sterilization.
Materials and methods
Source and treatment of flies
Wild flies used in the present study were the offspring of
adults reared from infested fruit (loquat, Eriobotrya japonica)
collected from trees in the Sydney Basin, New South Wales,
Australia. Wild adult flies reared from these fruit were housed
in a mesh cage (45 × 45 × 45 cm) kept outside in a covered
and shaded location and were provided with fresh plant
cuttings on which to perch, and sources of water and food
(sucrose and yeast hydrolysate enzymatic; MP Biomedicals,
Aurora, Ohio). After flies had matured sexually, they were
provided with organic tomatoes into which females could
oviposit. Tomatoes are one of the many preferred Q-fly
host plants (Hancock et al., 2000). Tomatoes were removed
after 1 week and placed on wire mesh suspended above a
20-mm deep bed of vermiculite (Grade 1, Ausperl, Orica
Australia Pty Ltd, Australia) in plastic trays. The vermiculite
was sieved gently at weekly intervals to remove pupae.
Pupae were allowed to emerge into a 5-L, ventilated, plastic
cage (24 × 15 × 15 cm) in the laboratory. On the day of
emergence, wild flies were separated by sex into separate
5-L cages (70 flies per cage). Flies were provided with ad
libitum access to water and food (sucrose and yeast hydrolysate
enzymatic).
Fertile mass-reared Q-flies were obtained as pupae from a
mass-rearing facility at Elizabeth Macarthur Agricultural Insti-
tute (New South Wales Industry and Investment, Australia).
Adults emerging from irradiated pupae produced by this facil-
ity (approximately 5 million per week) are released routinely in
SIT programmes to control Q-fly outbreaks (Dominiak et al.,
2008). The mass-reared colony was housed in two or three
adult cages with approximately 200 000 adults in each cage
(Jessup, 1999), and had been maintained in the facility for
over 20 generations at the time of the present study. Sterile flies
were produced by exposing hypoxic pupae to gamma radiation
(70–75 Gy) from a cobalt-60 Gammacell source at Macquarie
University (Collins et al., 2008, 2009). Fricke dosimeters con-
firmed that all irradiation treatments fell within the target range.
Pupae were allowed to emerge into 5-L cages and were sorted
by sex into separate cages, with ad libitum access to water and
food as outlined above.
All experiments were carried out under an LD 14:10 h
photocycle and cages were maintained at 24–26 ◦C and
60–70% relative humidity. The lights were on full intensity
for 12 h and flies also experienced simulated dawn and dusk
as the lights stepped on and off in four stages over the course
of 1 h.
Activity assay
Five days after they emerged from pupae, three Q-flies
of a single type and sex (a ‘group’) were placed in 2-
L plastic containers (height 19.5 cm, diameter 12 cm) from
which a rectangular panel (5 × 10 cm) had been removed
and replaced with flyscreen for ventilation. Only sexually
immature adults (5 days after adult emergence) were chosen
for testing. For each replicate, the activities of seven groups
of males or females of each type (n = 42) were video
recorded. Activities of each group of Q-flies were recorded
for 10 min in MPEG-4 format using a Canon XL1 digital
video camera (Canon, Japan) connected through a USB TV
tuner (Evolution TV™, Model ETV02, Miglia Technology
Limited, U.K.) to the hard drive of an Apple MacBook laptop
computer (Apple Inc., Cupertino, California). Recordings were
taken through the side of the cylindrical cage to ensure that
all flies were visible at all times. Lighting was supplied by
overhead fluorescent tubes, augmented with two 60-W full
spectrum bulbs positioned above the 2-L cage. The time of
day at which each recording started was noted for subsequent
assessment of whether activity patterns changed through the
day. Three replicates were completed, resulting in a total of
126 recordings. Recordings were observed later in real time to
score the frequency and duration of flights, walking, grooming
and periods of inactivity (during the recorded 10-min period) of
a randomly chosen single fly within the group. The behaviour
of focal individuals was easy to monitor without the need
© 2010 The Authors
Journal compilation © 2010 The Royal Entomological Society, Physiological Entomology, 35, 148–153