Eight plant essential oils and five vegetable oils were evaluated under laboratory conditions for their repellency and oviposition deterrence effects against female Queensland fruit fly Bactrocera tryoni, using artificial substrates and apple fruits. The results showed that vegetable oils were more effective than essential oils in deterring oviposition. The oil with most potential was that of safflower Carthamus tinctorius. This vegetable oil, at a concentration of 10 mL/L, significantly reduced oviposition in apples by 56.4% in a 24 h choice test, but none of the tested essential and vegetable oils had a significant effect on oviposition in apples in a no‐choice test. Based on the number of fruit flies landing on treated apples, vegetable oils were not repellents but deterred oviposition. The likely mechanism is that safflower and other vegetable oils created a slippery surface, and females were unable to make punctures in the fruit for egg deposition. Essential oils, especially lemon‐scented tea tree Leptospermum petersonii, peppermint Mentha piperita and honey myrtle Melaleuca teretifolia, repelled female B. tryoni, but their persistence on apple fruits was very low, only for a few hours.
Spiders are among the most abundant predators recorded in grain crops in Australia. They are voracious predators, and combined with their high abundance, may play an important role in the reduction of pest populations. The significance of spider assemblages as biological control agents of key pests such as Helicoverpa spp. in Australian agroecosystems is largely unknown. A thorough inventory was made of the spider fauna inhabiting unsprayed soybean fields at Gatton, south-east Queensland. Onehundred-and-two morphospecies from 28 families were collected using vacuum sampling and pitfall traps across two summer seasons . No-choice feeding tests in the laboratory, using eggs and larvae of Helicoverpa armigera (Hübner) as prey, were used to ascertain the predatory potential of each spider group. The field-collected spider assemblage ate on average 2.4 ( ± 0.7 standard error) to 5.0 ( ± 0.8) eggs per 24 h per spider (10-25% of those available), depending on level of starvation. Clubionidae were the only spiders to readily consume eggs in the laboratory (mean of 18.4 ± 1.5 eggs per starved spider and 8.2 ± 3.9 per non-starved spider after 24 h). Starved spiders consumed 9.4 ( ± 0.1) first-instar larvae per 24 h per spider (90% of those available). This information was combined with field observations and literature from Australian and overseas studies to assess the potential of spider groups as predators of Helicoverpa spp. Lycosidae, Clubionidae, Oxyopidae, Salticidae and Thomisidae have the capacity to contribute to control of Helicoverpa spp.
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