Maryam Yazdani

Host stage preference of Dolichogenidea tasmanica (Cameron, 1912) (Hymenoptera: Braconidae), a parasitoid of Epiphyas postvittana (Walker, 1863) (Lepidoptera: Tortricidae)

Epiphyas postvittana (Walker, 1863), or light brown apple moth (LBAM), is a highly polyphagous native Australian species and a major insect pest in Australian vineyards. Dolichogenidea tasmanica (Cameron, 1912) is the most abundant parasitoid of the larval stages of LBAM. The prime objective of our study was to determine the parasitism success of D. tasmanica on different larval stages of E. postvittana. Additionally, we aimed to find out if larval head capsule width could be used to determine the instar number by examining the variability in head capsule size of each instar of LBAM and the effect of rearing temperature on larval head capsule size. To determine which of the first three larval stages of LBAM parasitised is most effectively by D. tasmanica, choice and no‐choice tests were conducted in a wind tunnel. Head capsule widths varied with rearing temperature, especially in the final fifth or sixth instar. We showed that the ranges of head capsule widths overlaps between successive instars three through six, which makes it impossible to distinguish these instars of LBAM using head capsule size alone. We showed that first, second and third instars of LBAM are parasitised by D. tasmanica. No‐choice and choice tests revealed that there are significant differences in parasitism among the three susceptible instars, with the highest percentage of parasitism found in second instars in no‐choice and choice tests (65.1% and 65.8%, respectively) compared with first instars (61.1% and 45.1%) and third instars (27.3% and 37.5%). Wasps developed faster in third instars, but the wasp females size was not significantly different among the instars attacked. These data confirm that D. tasmanica is capable of parasitising early larval instars, which is important for minimising damage through biological control.

Predation of Clitostethus arcuatus (Col.: Coccinellidae) on Trialeurodes vaporariorum (Hem.: Aleyrodidae)

Abstract Greenhouse whitefly, Trialeurodes vaporariorum, is a serious pest of glasshouse crops. It shows resistance to different insecticides and growers are interested in finding other useful control methods. This research was carried out to study the predation potential and biology of Clitostethus arcuatus (Rossi) as one of the most important predators of this pest. Adult C. arcuatus were reared on tobacco leaves bearing colonies of greenhouse whitefly eggs under controlled conditions (25±2°C, 65±5% RH and 16 h L:8 h D). Results showed that the average developmental time of the egg, first through fourth instar larva and pupa were 2.82±0.12, 4.47±0.14, 4.54±0.1, 6.3±0.2, 7±0.22 and 3.8±0.13 days, respectively; and longevity of female and male were 66.4±2.6 and 54.9±2.5 days, respectively. The average feeding rates of female, male and larvae (first through fourth) were 61.4±0.7, 27.6±0.9 eggs/day and 12±1.03, 30.3±2.4, 41.3±2, 68.04±2 eggs/day, respectively. The larvae consumed an average of 992.2±36 eggs during the total larval developmental period with a daily mean of 45.8±0.5. A significant difference was shown between the feeding rate of fourth instar larval stages and between sexes. Females, males and one pair of C. arcuatus (♀,♂) consumed an average of 17.2±0.4, 10.6±0.8, 23.1±0.5 nymph/day; 28.5±0.9, 20.3±0.6, 47.2±0.6 pupa/day and 8±0.3, 6.5±0.54, 13.6±0.4 adult/day, respectively. The feeding rate was significantly different among whitefly life stages. Females laid an average of 3±0.23 eggs/day.

Host discrimination by the solitary endoparasitoid Dolichogenidea tasmanica (Hymenopotera: Braconidae)

Successful parasitism of a host partly depends on a females assessment of its quality, including whether the host has already been parasitised or not. We conducted experiments to elucidate host discrimination by Dolichogenidea tasmanica (Hymenoptera: Braconidae). It is the most commonly collected parasitoid of light brown apple moth, Epiphyas postvittana (Lepidoptera: Tortricidae). To assess the rate of superparasitism avoidance by D. tasmanica, female wasps were given choices between (1) unparasitised hosts versus freshly self-parasitised hosts, (2) unparasitised hosts versus hosts at 24 h post-self-parasitisation and (3) freshly self-parasitised hosts versus hosts freshly parasitised by a conspecific female. Results confirm that host discrimination occurs in D. tasmanica. Females avoid laying eggs in hosts that have been parasitised by themselves or conspecifics, even though the frequency of first encounter with either an unparasitised or a parasitised host was the same for all choices. Thus, it appears that females are not able to discriminate the host parasitisation status prior to contacting a host, but host acceptance is not random. Host discrimination is time-dependent, with greater avoidance of superparasitism after 24 h. The ability of female D. tasmanica to distinguish healthy from parasitised hosts suggests that it could be an effective biological control agent in regulation of host populations. It should also ensure production efficiency in parasitoid mass-rearing.

Biological Traits and Life Table Parameters A and B Biotype of Bemisia tabaci (Genn.) on Cotton and Rapeseed

The aim of this work was to construct life table of Bemisia tabaci (Gen.) A and B (silverleaf whitefly B. argentifolii Bellows and Perring) biotype (Hem.: Aleyrodidae) on two host plants; cotton, (Gossypium hirsutum L.) and rapeseed, (Brassica napus L.). Experiments were conducted in a growth chamber under 24 ± 2oC, 55±3% RH and 16:8 (L:D) h photoperiod on caged plants of cotton G. hirsutum L. (Varamin 76 variety) and rapeseed B. napus L. (global variety. The intrinsic rate of natural increase (rm), net reproductive rate (R0) and mean generation time (T) for B. tabaci A biotype was 0.1010 females per female per day, 18.4075 females per female and 30.079 day (d) on cotton; 0.1286, 30.6760 and 26.77 d on rapeseed; and for B biotype (B. argentifolii) those above respective parameters averaged 0.1033, 27.8426 and 32.74 d on cotton and 0.1750, 40.75 and 21.27 d on rapeseed. The total survival of A and B biotype from the egg to adult on cotton was 22.08 and 22.25, respectively. The results showed significant differences between the two biotype reared on either host plant for gross reproductive rate (GRR), net reproductive rate (R0 or NRR), intrinsic rates of increase (rm), finite rate of increase (λ), doubling time (DT) and mean generation times (Tc). To obtain a better understanding of the biology of these biotypes, Stable age distribution (Cx) and some other aspects of life history related to their hosts were also studied. Based upon the results, both biotypes showed a greater reproduction capacity on rapeseed than on cotton. Thus, rapeseed was more suitable host than cotton for two biotypes and this was an important factor in host plant selection for optimizing the control strategies of these major pests.

First detection of Russian wheat aphid Diuraphis noxia Kurdjumov (Hemiptera: Aphididae) in Australia: a major threat to cereal production

Invasive pest species pose a major threat to agricultural production around the world. Until recently, the Russian wheat aphid, Diuraphis noxia Kurdjumov, a major pest of wheat and barley crops worldwide, was considered a high‐priority exotic pest threat to the Australian grains industry. Here, we document the initial detection and establishment of D. noxia in Australia in 2016. These are the first records for this genus from South Australia, Victoria and New South Wales. Morphological and molecular information is presented for confirmed diagnosis of the species based on voucher specimens. Known distribution data are provided, along with a list of Poaceae hosts on which D. noxia has been recorded, and a brief description of the typical damage symptoms caused by these aphids. The potential impact of this aphid on Australian cereal production is discussed, and we identify research areas required to underpin future management of this new threat to the Australian cereal industry.

Searching behaviour of Dolichogenidea tasmanica in response to susceptible instars of Epiphyas postvittana

Abstract. Dolichogenidea tasmanica (Hymenoptera: Braconidae) is the most commonly reared parasitoid from larval light brown apple moth (LBAM), Epiphyas postvittana (Lepidoptera: Tortricidae), feeding on grapevines in Australia. In order to evaluate the efficiency of searching behaviour of D. tasmanica, a laboratory study was undertaken to determine how this wasp responds to the susceptible stages of larval LBAM. Observations of searching behaviour were made in a wind tunnel, which allowed the wasp to express its full range of behaviour. The behaviour of D. tasmanica and susceptibility of LBAM to parasitism varies significantly among instars. The wasp most readily parasitises newly hatched larvae, but can parasitise the first three of the six instars. The first instars cause less damage and also produce less faeces and silk than later instars, so they are associated with less volatile cues that may be detected by the parasitoid. Flight initiation to an infested leaf was lower in the presence of first instars compared with second and third instars. The flight duration was shortest when females were exposed to plants infested by third instars. An analysis of the sequence and timing of searching behaviour indicated that females respond differently to each of the instars of LBAM.