Sarah Mansfield

Host Egg Characteristics, Physiological Host Range, and Parasitism Following Inundative Releases of Trichogramma platneri (Hymenoptera: Trichogrammatidae) in Walnut Orchards

Abstract Under controlled conditions we exposed eggs of 17 potential host taxa representing five orders and 14 families to females of Trichogramma platneri Nagarkatti, an egg parasitoid used as an inundative biological control agent against codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae). Trichogramma platneri successfully parasitized species from five lepidopteran families (Gelechiidae, Noctuidae, Pyralidae, Sphingidae, Tortricidae) and the green lacewing, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae). Female wasps spent more time on heavier host eggs and the probability of successful parasitism was related to the structural integrity of the chorion of the host egg. We observed oviposition attempts on all other lepidopteran hosts offered and on eggs of Geocoris punctipes Say (Hemiptera: Lygaeidae) and Nezara viridula L. (Hemiptera: Pentatomidae). Dipteran and coleopteran eggs were not attacked. Sentinel eggs of the six physiologically acceptable hosts were exposed in a walnut orchard in California during inundative releases of T. platneri and all hosts were attacked equally. Parasitoids were also equally active at all heights from 1.5 to 6.5 m within the orchard canopy. Inundative releases of T. platneri may impact naturally occurring populations of green lacewings within walnut orchards, and have the potential to impact nontarget lepidopteran populations within the release area.

Direct estimation of the survival time of commercially produced adult Trichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) under field conditions

Abstract Studies were conducted to estimate survival time of commercially produced Trichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) in a walnut orchard in California. Batches of 23±7 female T. platneri were held in sleeves of dialysis tubing attached to walnut tree branches. Mean time to 50% survivorship of unfed parasitoids was 2.0±0.1 days whereas honey-fed parasitoids lived significantly longer (2.6±0.1 days) than unfed parasitoids. The presence of a leaf within a sleeve also increased mean time to 50% survivorship (2.9±0.2 days), relative to unfed parasitoids. Median survival time was inversely correlated with mean temperature for all treatments. The relationship between degree–day accumulation and survivorship was described using a Weibull function. Survival time in the field was less than expected from comparable laboratory estimates and reasons for these differences are discussed.

The effect of tibia morphology on vector competency of mushroom sciarid flies

Mushroom sciarid flies Lycoriella ingenua (Dufour) and Bradysia ocellaris (Comstock) are major pests of cultivated mushrooms, Agaricus bisporus (Lange) Imbach. The economic threshold of these pests is very low because they vector pathogens across mushroom beds, e.g. Verticillium fungicola which causes ‘dry bubble’ disease. Under controlled conditions, B. ocellaris transported more V. fungicola spores than L. ingenua from infected to sterile culture plates. Similar results were obtained when L. ingenua and B. ocellaris were collected from a growing room infected with V. fungicola then introduced onto sterile culture plates for 90 min. The external morphology of B. ocellaris and L. ingenua was examined using scanning electron microscopy. The micrographs showed clusters of V. fungicola spores attached to the inner side of a comb‐like row of bristles on the fore tibia of B. ocellaris whereas L. ingenua does not possess an equivalent structure on the fore tibia. These morphological differences are the most probable explanation for the greater competence of B. ocellaris as a vector of V. fungicola compared with L. ingenua.

Effect of compost and casing treatments of insecticides against the sciarid Bradysia ocellaris (Diptera: Sciaridae) and on the total yield of cultivated mushrooms, Agaricus bisporus

BACKGROUND Bradysia ocellaris (Comstock) is one of the major pests of cultivated mushrooms, Agaricus bisporus (Lange) Imbach. The feeding of sciarid fly larvae causes damage to the cultivation substrates, compost and casing. A comparative study of insecticidal treatments incorporated into compost and casing against B. ocellaris was conducted during 2003-2004. Treatments with an organophosphate, diazinon, a pyrazole, fipronil, and an insect growth regulator (IGR), triflumuron, were incorporated into casing. Another IGR, cyromazine, was incorporated into compost. Insecticidal incorporation into compost and casing has been associated with reductions in mushroom yield. Therefore, the effect of these insecticidal treatments on the overall yield was evaluated. RESULTS A combined treatment, incorporation of cyromazine at 10 mg kg(-1) into compost and of triflumuron at 20 mg kg(-1) into casing, provided 100% control against B. ocellaris. There was no apparent reduction in yield as a result of incorporation of the tested chemicals into either compost or casing. CONCLUSION The results obtained from this study suggest that incorporation of insecticides into both compost and casing is required to control a moderate to high pressure of insect pests. There were no significant yield reductions as a result of the incorporation of pesticides in the Australian mushroom-growing system.

Host–parasite interaction between cultivated mushroom, Agaricus bisporus hybrid strain Sylvan A15, and the mycoparasite Verticillium fungicola, a causal agent of dry bubble disease

Verticillium fungicola is one of the most economically significant pathogens of the cultivated mushroom Agaricus bisporus throughout the world. A. bisporus basidiomes are reported to be more susceptible to infection by V. Fungicola than the vegetative mycelium. V. Fungicola spores were also reported to be dependent on A. bisporus mycelium. Transmission and scanning electron microscopy were used to investigate the host-pathogen interactions at the mycelial and sporophore stages of A. bisporus. The transmission electron micrographs showed that the V. Fungicola mycelium grows very close to the A. bisporus mycelium. There were no specialised penetration structures or any evidence of direct penetration of the pathogen in the host tissue. The scanning electron micrograph of the necrotic tissue of the diseased mushroom shows clusters of phialoconidia and hyphae of the pathogen in large numbers.

A TaqMan qPCR method for detecting kdr resistance in Aphis gossypii demonstrates improved sensitivity compared to conventional PCR–RFLP

Cotton aphid, Aphis gossypii Glover, has emerged as a prominent pest in Australian cotton production, and monitoring pesticide resistance including pyrethroids in field populations is crucial for its sustainable management. We examined the distribution of kdr resistance in 35 field-collected A. gossypii populations and used TaqMan qPCR assays with pooled samples. The study demonstrated proof of concept that pooled insect qPCR methodology provided effective detection with better sensitivity than individual PCR–RFLP genotyping techniques for the kdr resistance allele. The practical outcome is that routine resistance monitoring can examine more sites while increasing the likelihood of detecting incipient resistance at those sites. More importantly, the method is adaptable to any genetically caused resistance and so not limited to A. gossypii or even insect control. It cannot be overstressed that the ability to detected resistance at very low frequencies is critical to all sustainable resistance management. Early detection of resistance provides critical time for the modification of chemical use prior to potential insecticide control failure.

Carbohydrate diet and reproductive performance of a fruit fly parasitoid, Diachasmimorpha tryoni

Abstract Augmentative releases of parasitoid wasps are often used successfully for biological control of fruit flies in programs worldwide. The development of cheaper and more effective augmentative releases of the parasitoid wasp Diachasmimorpha tryoni (Cameron) (Hymenoptera: Braconidae) may allow its use to be expanded to cover Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), a serious pest of many vegetables and most fruit production in Australia. This demands a fuller understanding of the parasitoids reproductive biology. In this study, mating status, fecundity, and size of female D. tryoni were determined under laboratory conditions. A range of pre-release diets, 10% concentrations of honey, white sugar, and golden syrup, were also assessed in the laboratory. Mature egg loads and progeny yields of mated and unmated parasitoid females were statistically similar, demonstrating that mating status was not a determinant of parasitoid performance. Female lifespan was not negatively impacted by the act of oviposition, though larger females carried more eggs than smaller individuals, indicating a need to produce large females in mass-rearing facilities to maintain this trait. White sugar gave the highest adult female lifespan, while honey and golden syrup shared similar survivorship curves, all significantly greater compared with water control females. Pre-release feeding of D. tryoni, particularly with white sugar, may enhance the impact of released parasitoids on B. tryoni. These findings are important because honey is currently the standard diet for mass-reared braconids, but white sugar is less than one-third the cost of other foods; however further work is required to assess postrelease performance of the parasitoid.

Adoption of Exotic Plants by an Endemic Australian Weevil, Orthorhinus cylindrirostris (Coleoptera: Curculionidae)

ABSTRACT The elephant weevil Orthorhinus cylindrirostris (F.) (Coleoptera: Curculionidae) is endemic to Australia and has colonized several exotic crops including citrus, blueberries, and grapevines. Wecompared the life history of this pest on two native and two exotic host plants: hickory wattle Acacia falcata Willdenow, rough-barked apple Angophora floribunda (Smith) Sweet, lemon Citrus limon (L.) Burman, and blueberry Vaccinium corymbosum (L.). Blueberry was attacked more often (22 of the 24 plants) than lemon, rough-barked apple, and hickory wattle (6–8 plants of each species attacked of the 24). Adult emergence followed a similar pattern across hosts but emergence was low overall (58 adults from 176 eggs). Only blueberry had more than one weevil emerge from a single plant. Development from oviposition to adult emergence can take up to 2 yr, particularly on blueberry. Adult life span and weight varied between individuals although no effect of host plant was detected. Similar plant chemistry is unlikely to have triggered host range expansion by this species because the exotic host plants are from different families (Rutaceae, Vitaceae, and Ericaceae) to the native host plants (Myrtaceae, Mimosaceae, and Fabaceae). O. cylindrirostris colonized citrus trees over a century ago, yet it appears to have no preference for lemon over native host plants. In contrast, O. cylindrirostris has developed a preference for blueberry, the higher quality host plant, only a few decades after colonization.

New Communities on Eucalypts Grown Outside Australia

The expansion of eucalypt forestry worldwide has been accompanied by accidental and deliberate introductions of Australian insects associated with eucalypts. Local insect species have also colonized introduced eucalypts in many regions. This situation provides a unique opportunity to observe the development of new insect communities across trophic levels. Here the history of Australian invaders and native colonizers on eucalypts outside Australia is reviewed from the perspective of herbivore guilds: leaf chewers, sap suckers, wood borers, gall formers, termites. Historical patterns of invasion are identified across these guilds. Very few species of Australian leaf chewers, wood borers or termites have become widespread but these guilds are proportionately high in native colonizers. In contrast, sap suckers have multiple invasive species globally with relatively fewer native colonizers. The gall former guild also has several invasive species but so far includes no native colonizers, perhaps due to their tendency to have highly specific host plant associations. Natural enemies of Australian invaders are also members of new eucalypt insect communities, partly through planned biological control programs, but the rate of accidental introductions at higher trophic levels is increasing steadily. At the same time, local natural enemies enter eucalypt communities either to form new associations with Australian invaders or to follow native colonizers into this new habitat. Australian sap suckers have attracted far more new associations than other guilds so far. Native leaf chewers have often been followed by their local natural enemies into eucalypt communities, particularly in Brazil. Generally there are fewer records relating to local natural enemies and their role in new eucalypt communities. The complexity of new eucalypt communities outside Australia is expected to increase in future.

Standardization of prey immunomarking: does a positive test always indicate predation?

Abstract A prey immunomarking procedure (PIP) in combination with generic anti-rabbit and anti-chicken immunoglobulin G (IgG) enzyme-linked immunosorbent assays (ELISAs) are used frequently to study arthropod predation. This study was conducted to: (1) further standardize the PIP as a tool for predator gut analysis research, (2) investigate the most effective means for administering IgG marks to prey items, and (3) assess the possibility of the PIP yielding false positive reactions as a consequence of a predator obtaining a mark by incidental contact with, or by a failed predation attempt on, a protein-marked prey item. The pest Lygus hesperus Knight (Hemiptera: Miridae) was tagged with either an external rabbit IgG mark, an internal chicken IgG mark, or a double (external rabbit IgG and internal chicken IgG) mark treatment. Then, the variously marked prey items were fed to chewing and piercing-sucking type predators and their gut contents were examined for the presence of IgG remains. Data revealed that all three marking treatments were highly effective at tagging targeted prey. However, ELISA results showed that the prey items should only be marked internally to maximize the likelihood of detecting prey remains while minimizing the risk of obtaining false positive errors. The merits and limitations of using the generic PIP for predator gut analysis research are discussed.