Micaela Buteler

Novel use of nanostructured alumina as an insecticide

BACKGROUND The worldwide need to produce an inexpensive and abundant food supply for a growing population is a great challenge that is further complicated by concerns about risks to environmental stability and human health triggered by the use of pesticides. The result is the ongoing development of alternative pest control strategies, and new, lower-risk insecticidal molecules. Among the recent technological advances in agricultural science, nanotechnology shows considerable promise, although its development for use in crop protection is in its initial stages. RESULTS This study reports for the first time the insecticidal effect of nanostructured alumina. Two species were used as model organisms, Sitophilus oryzae L. and Rhyzopertha dominica (F.), which are major insect pests in stored food supplies throughout the world. Both species experienced significant mortality after 3 days of continuous exposure to treated wheat. Nine days after treatment, the median lethal doses (LD(50)) observed ranged from 127 to 235 mg kg(-1). CONCLUSION Comparison of these results with recommended rates for commercial insecticidal dusts suggests that inorganic nanostructured alumina may provide a cheap and reliable alternative for control of insect pests. This study expands the frontiers for nanoparticle-based technologies in pest management. Further research is needed to identify its mode of action and its non-target toxicity, and to determine the potential of other nanostructured materials as pest control options for insects.

Cultivar preferences of ovipositing wheat stem sawflies as influenced by the amount of volatile attractant

ABSTRACT The wheat stem sawfly, Cephus cinctus Norton, causes severe losses in wheat grown in the northern Great Plains. Much of the affected area is planted in monoculture with wheat, Triticum aestivum L., grown in large fields alternating yearly between crop and no-till fallow. The crop and fallow fields are adjacent. This cropping landscape creates pronounced edge effects of sawfly infestations and may be amenable to trap cropping using existing agricultural practices. The behavioral preference for two wheat varieties was assessed in the context of developing trap crops for this insect. In field nurseries, stem lodging assessments indicated that the cultivar ‘Conan’ was infrequently damaged, whereas ‘Reeder’ was often heavily damaged. In laboratory choice and no-choice tests, ‘Reeder’ was significantly preferred by ovipositing wheat stem sawfly females. These two cultivars did not differ significantly in height or developmental stage, factors known to impact sawfly preference. Although Conan received fewer eggs than Reeder in no-choice tests, oviposition was further reduced in choice tests, indicating that females clearly preferred Reeder. In field trials where the overall dimensions of the spatial structure in choice tests was varied, females always selected Reeder over Conan in alternating block, row, and interseeded planting scenarios. Reeder releases greater amounts of the attractive compound, (Z)-3-hexenyl acetate than Conan but is similar to Conan for three other known, behaviorally active volatile compounds. The results are discussed in terms of cultivar selection for large scale trap crop experiments for the wheat stem sawfly.

Behavioural responses of wheat stem sawflies to wheat volatiles

1 Adult wheat stem sawflies Cephus cinctus, pests of cultivated cereals that also infests wild grasses, migrate into wheat fields where they oviposit in elongating, succulent stems.

Oviposition Behavior of the Wheat Stem Sawfly When Encountering Plants Infested With Cryptic Conspecifics

ABSTRACT Insect herbivores typically oviposit on the most suitable hosts, but choices can be modulated by detection of potential competition among conspecifics, especially when eggs are deposited cryptically. Larvae of the wheat stem sawfly, Cephus cinctus Norton, developing within an already infested stem, experience elevated risk when only one will survive because of cannibalism. To increase our understanding of host selection when the choices made by females can lead to severe intraspecific competition, females were presented with either uninfested wheat plants or with plants previously exposed to other females in laboratory choice tests. The oviposition behavior of this insect was described by recording the behavioral sequences that lead to and follow the insertion of the ovipositor in both previously infested and uninfested stems. No significant differences were found in frequencies of specific behaviors or behavioral transitions associated with oviposition. In choice tests, there was no difference in the numbers of eggs laid in infested and uninfested plants. Taller plants received more eggs, irrespective of infestation. Females neither preferred nor avoided previously infested hosts. Other characteristics of the host, such as stem height, may be more important in determining suitability for oviposition. These findings support the use of management tactics relying on the manipulation of oviposition behavior, such as trap cropping. Given that there is no evidence for response to previously infested hosts, the infested plants in a trap crop would remain as suitable as they were when uninfested, which could also lead to an increase in mortality caused by intraspecific competition.

Wheat stem sawfly‐infested plants benefit from parasitism of the herbivorous larvae

1 Parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck and their herbivorous host the wheat stem sawfly Cephus cinctus Norton, a pest of wheat Triticum aestivum, were investigated for yield in T. aestivum grown in the field.

Development of nanoalumina dust as insecticide against Sitophilus oryzae and Rhyzopertha dominica

This study aims to characterize and improve the insecticidal activity of nanostructured alumina dusts. To accomplish these goals, multiple solution based synthesis routes utilizing standard aluminum salt precursors were utilized to synthesize three unique types of alumina dust. These were compared with regards to morphology, particle size and surface area using electron microscopy and dynamic light scattering particle size analysis. Insect toxicity of the various dusts was assessed using two insect species that are pests of stored grain, Sitophilus oryzae and Rhyzopertha dominica. The dust synthesized using a modified glycine-nitrate combustion process consistently yielded greater mortality rates, and all dust types were more effective on S. oryzae than on R. dominica, although the difference varied across dust types. The data show that insecticidal activity is dependent on particle size, particle morphology and surface area but also indicated that minimizing particle size and maximizing surface area are not the sole dominant factors influencing efficacy. This study does however suggest that pesticide dusts can be engineered through modified synthesis to better target different insect species.

A Multiple Decrement Life Table Reveals That Host Plant Resistance and Parasitism Are Major Causes of Mortality for the Wheat Stem Sawfly

ABSTRACT This study investigated the dynamics of parasitism, host plant resistance, pathogens, and predation on the demography of wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), developing in susceptible (hollow stem) and resistant (solid stem) wheat hosts. This study is also the first to investigate the prevalence and impact of cannibalism on wheat stem sawfly mortality. Wheat stem sawflies were sampled in two commercial wheat fields over 4 yr from the egg stage through adult emergence, and multiple decrement life tables were constructed and analyzed. Cannibalism, host plant resistance, or unknown factors were the most prevalent factors causing egg mortality. Summer mortality of prediapause larvae ranged from 28 to 84%, mainly due to parasitism by Bracon cephi (Gaban) and Bracon lissogaster Muesebeck, cannibalism, and host plant resistance. Winter mortality ranged from 6 to 54% of the overwintering larvae, mainly due to unknown factors or pathogens. Cannibalism is a major cause of irreplaceable mortality because it is absolute, with only a single survivor in every multiple infested stem. Subsequent to obligate cannibalism, mortality of feeding larvae due to host plant resistance was lower in hollow stem wheat than in solid stem wheat. Mortality from host plant resistance was largely irreplaceable. Irreplaceable mortality due to parasitoids was greater in hollow stem wheat than in solid stem wheat. Host plant resistance due to stem solidness and parasitism in hollow stems cause substantial mortality in populations of actively feeding larvae responsible for all crop losses. Therefore, enhancing these mortality factors is vital to effective integrated pest management of wheat stem sawfly.

Parasitism and the demography of wheat stem sawfly larvae, Cephus cinctus

Previous research has suggested that insect herbivores in protected environments have higher mortalities from biotic factors such as parasitism compared to herbivores in less protected situations, although overall mortalities in protected environments are often lower. However, this has not been examined using life table approaches. In this study, we used demographic methods to characterize the mortality dynamics of parasitism for pre-diapause wheat stem sawfly larvae, Cephus cintus Norton (Hymenoptera: Cephidae), a stem-mining wheat pest. Larvae were intensively sampled from commercial wheat fields at two locations in Montana, USA from 2005 through 2008. The feeding larvae present in the summer succumbed to only two mortality categories: parasitism and unknown factors. In Conrad, a location with relatively high densities of the parasitoids, mortality by parasitism was largely irreplaceable. In contrast, in Amsterdam, where parasitism did not occur to any appreciable degree, overall mortality remained relatively low.

Host selection by the wheat stem sawfly in winter wheat and the role of semiochemicals mediating oviposition preference

The wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), causes significant damage in cereal crops in the northern Great Plains of North America. This study assessed oviposition preference in winter wheat, Triticum aestivum L. (Poaceae), and investigated how it is affected by the emission of semiochemicals, with the overall goal of enhancing trap crop efficacy. We studied five winter wheat cultivars that could be recommended as trap crops for WSS and compared them with regards to agronomic characteristics influencing oviposition behavior and their emission of behaviorally active volatiles. Subsequently, we evaluated oviposition preference on three selected cultivars, ‘Norstar’, ‘Neeley’, and ‘Rampart’, using choice tests at two plant growth stages. Most eggs were found in Norstar at both stages tested when females were exposed to the three cultivars simultaneously making it the preferred choice for a trap crop. Norstar also emitted more behaviorally active volatiles, primarily (E)‐ and (Z)‐β‐ocimene. The results for the effect of main stem height or diameter on oviposition was inconsistent between infested vs. uninfested stems within cultivars, although there was a correlation between infestation and height for younger plants. These results show that these agronomic characteristics, typically viewed as explanatory, did not clearly explain oviposition preference and suggest a role of β‐ocimene in determining suitability for oviposition among these cultivars. This study supports previous findings suggesting oviposition preference in winter wheat involves several cues, including stem height and volatile attractants that may be important in determining suitability.

A Review on the Mode of Action and Current Use of Petroleum Distilled Spray Oils

Petroleum based mineral oils have been used for insect pest control for over a century (Agnello, 2002). However, their use is as current today as it was before the advent of chemical insecticides, given that they are compatible with modern sustainable management practices. These products pose a number of advantages over conventional pesticides and they have very low mammalian toxicity, low residual activity, they have never been associated with development of insect resistance, and are less disruptive to natural enemies than broad spectrum insecticides (Beattie and Smith, 1993). Continuous studies on the efficacy and chemistry of petroleum based oils over the last sixty years, led to identification of the main factors related to their insecticidal activity as well as their phytotoxicity and allowed for the development of more refined and effective spray oils (Agnello, 2002). The efficacy of isoparaffinic petroleum distilled spray oils (PDSOs) typically increases as the molecular weight of their constituent oil molecules increases, but so does the risk of PDSO induced phytotoxicity (Riehl, 1969), which has been one of the main hindrances to the use of these products. Modern PDOs are highly refined, linear molecules with a range between 21 and 24 carbons, to combine good insecticidal efficacy with low phytoxicity. The use of UV additives (e.g. sunscreens) to reduce the detrimental effect of the ultraviolet light on the breakdown of oil molecules has reduced the potential of some PDSOs to damage plants (Hodgkinson, 1999; Hodgkinson et al., 2002). Thus, once limited to early season or dormant sprays to avoid oil injury to green plant tissue, newer narrow-range PDSOs are being reconsidered and assessed for incorporation into integrated pest management programs. PDSOs have been found to be effective against numerous orchard pests including scales and mites (Beattie et al., 1995; Beattie, 1990; Beattie and Smith, 1993), whiteflies (Larew and Locke, 1990; Liang and Liu, 2002), aphids (Najar-Rodriguez et al., 2007), psylla (Zwick and Westigard, 1978; Weissling et al., 1997), and fruit-feeding Lepidoptera (Davidson et al., 1991; Al Dabel et al., 2008). In apple orchards, the interest in PDSOs as part of integrated pest management programs has increased in the past years, particularly for the control of secondary pests (Fernandez et al., 2005). This is in part due to better PDSOs formulations, but it also arises from a decline in the use of broad spectrum insecticides due to stricter regulations and to the widespread use of mating disruption (Fernandez et al., 2005). Recent studies have also