Greg Baker

Local Dispersal of the Diamondback Moth (Plutella xylostella (L.)) (Lepidoptera: Plutellidae)

Abstract Local dispersal of the diamondback moth (Plutella xylostella [L.]) was studied using the mark-recapture technique in commercial cauliflower and broccoli crops in the northern Adelaide plains. Moths were marked with fluorescent powder and released at one or more points within the experimental fields. Recaptures of the marked moths were made with pheromone traps and yellow sticky buckets, the latter being used to study the dispersal of both males and females. Four indices of dispersal ranges were estimated from the recapture data, the average dispersal distance and the distances from the release point within which 95, 99, and 99.9% of the released moths were expected to remain. Separate estimates were obtained for recapture data of males from the pheromone traps, recapture data of males from the yellow sticky buckets, and recapture data of females from the yellow sticky buckets. Overall, the estimated average dispersal distance ranged 14 to 35 m and the 95, 99, and 99.9% distances ranged 40 to 106 m, 63 to 177 m, and 113 to 300 m, respectively. Longer dispersal distances were obtained from the pheromone traps than from the yellow sticky buckets. Data from the yellow sticky buckets revealed similar dispersal ranges of the males and the females. The positions of recapture centers of the two sexes were also largely similar. While the distance ranges of recaptures increased gradually during the experiments, the recapture centers stayed within close vicinity of the release points. Temperature and wind did not appear to influence the dispersal ranges or directions. Implications of the results in the management of diamondback moth are discussed.

The use of dyes to mark populations of beneficial insects in the field

Dyes and dusts have been used to mark insects internally and externally for decades, the majority of examples coming from laboratory-reared pest species used in mark-release-recapture studies. Using dyes or dusts to mark populations of pests and beneficial insects simultaneously in the field has received less attention. We evaluated a water-soluble fluorescent dye and a resin-based fluorescent pigment sprayed on crops to mark beneficial and pest insects, and monitored the dispersal of marked insects. Our results show that resin-based dyes provide an effective mark on several species of insects among several orders. The resin-based dye is also relatively inexpensive, non-toxic, UV-stable and water resistant, unlike a water-soluble dye. Using the resin-based dye in a broccoli production system, we were able to monitor simultaneously the movement of field populations of the parasitoids, Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae), and Apanteles ippeus (Nixon) (Hymenoptera: Braconidae) and the adult stage of the host, diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). Resin-based dye applied on a crop is an effective way to mark and monitor the dispersal of populations of beneficial and pest insects in relation to agricultural practices, integrated pest management and conservation biological control.

Thermal Tolerance Limits of Diamondback Moth in Ramping and Plunging Assays

Thermal sensitivity is a crucial determinant of insect abundance and distribution. The way it is measured can have a critical influence on the conclusions made. Diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae) is an important insect pest of cruciferous crops around the world and the thermal responses of polyphagous species are critical to understand the influences of a rapidly changing climate on their distribution and abundance. Experiments were carried out to the lethal temperature limits (ULT0 and LLT0: temperatures where there is no survival) as well as Upper and Lower Lethal Temperature (ULT25 and LLT25) (temperature where 25% DBM survived) of lab-reared adult DBM population to extreme temperatures attained by either two-way ramping (ramping temperatures from baseline to LT25 and ramping back again) or sudden plunging method. In this study the ULT0 for DBM was recorded as 42.6°C and LLT0 was recorded as −16.5°C. DBM had an ULT25 of 41.8°C and LLT25 of −15.2°C. The duration of exposure to extreme temperatures had significant impacts on survival of DBM, with extreme temperatures and/or longer durations contributing to higher lethality. Comparing the two-way ramping temperature treatment to that of direct plunging temperature treatment, our study clearly demonstrated that DBM was more tolerant to temperature in the two-way ramping assay than that of the plunging assay for cold temperatures, but at warmer temperatures survival exhibited no differences between ramping and plunging. These results suggest that DBM will not be put under physiological stress from a rapidly changing climate, rather access to host plants in marginal habitats has enabled them to expand their distribution. Two-way temperature ramping enhances survival of DBM at cold temperatures, and this needs to be examined across a range of taxa and life stages to determine if enhanced survival is widespread incorporating a ramping recovery method.

Ecology of diamondback moth in Australian canola: landscape perspectives and the implications for management

The ecology of diamondback moth (DBM), Plutella xylsotella L. (Lepidoptera: Plutellidae), and records of its frequent, but sporadic, population outbreaks in the canola agroecosystems of southern and western Australia are reviewed. The migratory capacity of DBM, possible maintenance of pest populations on brassicaceous weeds and forage crops, resistance to commonly used pyrethroid insecticides, a lack of effective natural enemies (due to disruption by insecticides and difficulties associated with colonising the vast areas of canola crops) and suitable climatic conditions during critical phases of the crop cycle are all likely to contribute to the observed pest outbreaks. A greater understanding of the ecology of DBM in the canola landscape is fundamental to improving its management in the crop but relevant long-term DBM abundance data are currently lacking. Five critical research issues are identified: (i) improved understanding of the factors which determine regional movement patterns of diamondback in canola-growing areas; (ii) the development and implementation of flexible insecticide resistance management strategies; (iii) better understanding of canola crop colonisation by natural enemies of DBM and their population dynamics under current and alternative insecticide application strategies; (iv) greater appreciation of the interactions between DBM and its crop and weedy host plants; and (v) the development of validated simulation models to aid in the forecasting of possible DBM outbreaks. Each issue represents a significant challenge but all must be addressed if the development of a sustainable integrated strategy for the management of DBM in Australian canola is to become a reality.

Behavioral Avoidance - Will Physiological Insecticide Resistance Level of Insect Strains Affect Their Oviposition and Movement Responses?

Agricultural organisms, such as insect herbivores, provide unique opportunities for studies of adaptive evolutionary processes, including effects of insecticides on movement and oviposition behavior. In this study, Brassica leaves were treated with one of two non-systemic insecticides and exposed to two individual strains (referred to as single or double resistance) of diamondback moth (Plutella xylostella) (DBM) exhibiting physiological resistance. Behavioral responses by these two strains were compared as part of characterizing the relative effect of levels of physiological resistance on the likelihood of insects showing signs of behavioral avoidance. For each DBM strain, we used choice bioassays to quantify two possible types of behavioral avoidance: 1) females ovipositing predominantly on leaf surfaces without insecticides, and 2) larvae avoiding insecticide-treated leaf surfaces. In three-choice bioassays (leaves with no pesticide, 50% coverage with pesticide, or 100% coverage with pesticide), females from the single resistance DBM strain laid significantly more eggs on water treated leaves compared to leaves with 100% insecticide coverage (both gamma-cyhalothrin and spinetoram). Females from the double resistance DBM strain also laid significantly more eggs on water treated leaves compared to leaves with 100% gamma-cyhalothrin, while moths did not adjust their oviposition behavior in response to spinetoram. Larvae from the single resistance DBM strain showed a significant increase in mobility in response to both insecticides and avoided insecticide-treated portions of leaves when given a choice. On the other hand, DBM larvae from the double resistance strain showed a significant decrease in mobility in response to insecticides, and they did not avoid insecticide-treated portions of leaves when given a choice. Our results suggest that pest populations with physiological resistance may show behavioral avoidance, as resistant females avoided oviposition on leaves without gamma-cyhalothrin. Thus, physiological resistance and behavioral avoidance do not appear to be controlled by the same selection pressures, and the mechanisms responsible for behavioral avoidance may vary among life stages. Our analysis also suggested that a population with lesser physiological resistance to insecticides may be under a stronger selection pressure and therefore be more likely to develop avoidance behaviors than a population with higher levels of physiological resistance.

Determining the drift potential of Venturi nozzles compared with standard nozzles across three insecticide spray solutions in a wind tunnel

BACKGROUNDnPrevious research has sought to adopt the use of drift-reducing technologies (DRTs) for use in field trials to control diamondback moth (DBM) Plutella xylostella (L.) (Lepidoptera: Plutellidae) in canola (Brassica napus L.). Previous studies observed no difference in canopy penetration from fine to coarse sprays, but the coverage was higher for fine sprays. DBM has a strong propensity to avoid sprayed plant material, putting further pressure on selecting technologies that maximise coverage, but often this is at the expense of a greater drift potential. This study aims to examine the addition of a DRT oil that is labelled for control of DBM as well and its effect on the drift potential of the spray solution. The objectives of the study are to quantify the droplet size spectrum and spray drift potential of each nozzle type to select technologies that reduce spray drift, to examine the effect of the insecticide tank mix at both (50 and 100 L ha(-1) ) application rates on droplet size and spray drift potential across tested nozzle type and to compare the droplet size results of each nozzle by tank mix against the drift potential of each nozzle.nnnRESULTSnThe nozzle type affected the drift potential the most, but the spray solution also affected drift potential. The fine spray quality (TCP) resulted in the greatest drift potential (7.2%), whereas the coarse spray quality (AIXR) resulted in the lowest (1.3%), across all spray solutions. The spray solutions mixed at the 100 L ha(-1) application volume rate resulted in a higher drift potential than the same products mixed at the 50 L ha(-1) mix rate. The addition of the paraffinic DRT oil was significant in reducing the drift potential of Bacillus thuringiensis var. kurstkai (Bt)-only treatments across all tested nozzle types. The reduction in drift potential from the fine spray quality to the coarse spray quality was up to 85%.nnnCONCLUSIONnThe addition of a DRT oil is an effective way to reduce the spray solution drift potential across all nozzle types and tank mixes evaluated in this study. The greatest reduction in drift potential can be achieved by changing nozzle type, which can reduce the losses of the spray to the surrounding environment. Venturi nozzles greatly reduce the drift potential compared with standard nozzles by as much as 85% across all three insecticide spray solutions. Results suggest that a significant reduction in drift potential can be achieved by changing the nozzle type, and can be achieved without a loss in control of DBM.

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.

Is the Combination of Insecticide and Mating Disruption Synergistic or Additive in Lightbrown Apple Moth, Epiphyas postvittana?

Pest suppression from combinations of tactics is fundamental to pest management and eradication. Interactions may occur among tactical combinations and affect suppression. The best case is synergistic, where suppression from a combination is greater than the sum of effects from single tactics (AB >> A+B). We explored how mating disruption and insecticide interacted at field scale, additively or synergistically. Use of a pheromone delivery formulation (SPLAT™) as either a mating disruption treatment (i.e. a two-component pheromone alone) or as a lure and kill treatment (i.e. the two-component pheromone plus a permethrin insecticide) was compared for efficacy against the lightbrown apple moth Epiphyas postvittana. Next, four point-source densities of the SPLAT™ formulations were compared for communication disruption. Finally, the mating disruption and lure and kill treatments were applied with a broadcast insecticide. Population assessment used virgin female traps and synthetic pheromone in replicated 9-ha vineyard plots compared with untreated controls and insecticide-treated plots, to investigate interactions. Lure and kill and mating disruption provided equivalent suppression; no additional benefit accrued from including permethrin with the pheromone suggesting lack of contact. The highest point-source density tested (625/ha) was most effective. The insect growth regulator methoxyfenoxide applied by broadcast application lowered pest prevalence by 70% for the first ten weeks compared to pre-trial. Pheromone addition suppressed the pest further by an estimated 92.5%, for overall suppression of 97.7% from the treatment combination of insecticide plus mating disruption. This was close to that expected for an additive model of interactivity between insecticide and mating disruption (AB = A+B) estimated from plots with single tactics as 98% suppression in a combination. The results indicate the need to examine other tactical combinations to achieve the potential cost-efficiencies of synergistic interactions.

New species of gall midge (Diptera: Cecidomyiidae) damaging flower buds of ornamental Alstroemeria plants

Alstroemeria (Liliales: Alstroemeriaceae) is a plant genus native to South America with many interspecific hybrids cultivated as ornamentals worldwide. Several yellow larvae of an undescribed gall midge (Diptera: Cecidomyiidae) were found feeding inside flower buds of Alstroemeria plants grown in production greenhouses in South Australia in 2013; Queensland, Australia, in 2015 and the Netherlands in 2016. Infested buds became malformed, did not produce flowers and turned necrotic later. In Queensland and the Netherlands, the necrotised buds became additionally infected by a saprophytic fungus Cladosporium sp. With up to 80% of flower buds infested, the new gall midge decreased the value of plants aimed for the cut flower market and reduced seed of reproduction plants. The new species, named Contarinia jongi Kolesik sp. nov., is described, and a segment of its Cytochrome Oxidase unit I mitochondrial gene is sequenced. This is the first gall midge known to feed on a host plant from the family Alstroemeriaceae. Previously, Alstroemeria cut flowers imported from Australia and New Zealand to Japan were found to contain viable larvae of the new species, demonstrating that the new species can spread with the flower trade. It is possible that Contarinia jongi is native to South America, the homeland of its host plant.

A plant volatile-based attractant formulation is not attractive to Diadegma semiclausum (Hymenoptera: Ichneumonidae)

A synthetic plant volatile‐based attractant has been commercialised for integrated pest management (IPM) of Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) in Australian cotton, corn and beans. This attract‐and‐kill formulation is being tested in Australia in canola as an IPM tool to minimise the amount of insecticide used for the control of diamondback moth (DBM) Plutella xylostella (Linnaeus). DBM is a destructive insect pest of cruciferous crops with a cosmopolitan distribution and has developed resistance to almost every synthetic insecticide applied in the field. However, in brassica crops, naturally occurring parasitoids are often important components of IPM. Therefore, it is essential to investigate how parasitoids deal with plant volatiles released from this formulation and whether this formulation is safe for non‐target insects especially parasitoids. Wind tunnel experiments were conducted to assess the effect of the formulation on larval parasitoid Diadegma semiclausum (Hellén), which is an effective biological control agent of DBM. Our results showed that the formulation was significantly less attractive than either water or untreated leaves. Unfed female D. semiclausum were highly attracted to the honey food source, while after feeding, there was no significant preference among treatments with the exception of significantly less visits to leaves treated with the formulation. Furthermore, the presence of the formulation appears to have reduced the attractiveness of leaves, which were infested with DBM larvae. Our result shows that 2 days after application, female wasps visited leaves treated with the formulation significantly less than untreated healthy leaves, even if DBM larvae were present on the leaves treated with the formulation. We conclude that the formulation is not attractive to D. semiclausum female wasps. The wasps avoidance of leaves treated with the attractant, even if those leaves were infested with DBM larvae, suggests that the formulation can act as a repellent to the female wasps.