Two entomological studies: 1, The potential of Methyl jasmonate applications as a pest management method on cruciferous crops. 2, Contributions to the biology of Disholcaspis quercusmamma (Walsh) (Hymenoptera: Cynipidae)
Date
2011
Authors
McEwen, Crystal Lee, author
Cranshaw, Whitney, advisor
Kondratieff, B.C. (Boris C.), committee member
Stonaker, Frank H., 1958-, committee member
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Abstract
Methyl jasmonate (MeJA) is known for the many physiological roles in plants, including induced resistance to herbivores. Treating plants with exogenous applications of MeJA has been shown to have various effects on the behavior of herbivores. This study sought out to quantify the effects of MeJA applications on field grown cruciferous crops in both pest response and crop response. The suitability of MeJA as a pest management tool depends on the tradeoff of costs and benefits of jasmonate-induced resistance. MeJA applications were shown to reduce flea beetle (Phyllotreta spp.) feeding in a greenhouse setting. Feeding was reduced as early as the same day of treatment and feeding was further reduced over a period of 4 days. When applied in a field setting MeJA was effective at reducing the numbers of flea beetles, at least briefly, on broccoli, Chinese cabbage, Brussels sprouts, and rutabaga. MeJA applications can affect lepidopterous pests by changing oviposition preferences or by affecting development. Brussels sprouts showed a reduction in Pieris rapae (Linnaeus) and Trichoplusia ni (Hübner) eggs found on MeJA treated foliage. Conversely multiple applications of MeJA on cabbage resulted in an increase in P. rapae eggs found on foliage. Trials where larvae were reared on field grown MeJA treated food showed that P. rapae larvae developed in the same amount of time as those larvae that were reared on untreated food and that they weighed approximately the same. In that same trial, T. ni showed that male pupal periods were longer and pupae of both sexes weighed more when they were reared on MeJA treated food. MeJA applications reduced plant size in broccoli, Chinese cabbage, and Brussels sprouts. Yield was also reduced in Chinese cabbage and rutabaga. During 2009 and 2010 MeJA applications were found to have no effect on yield in broccoli. MeJA treated broccoli showed a delay in maturity during both seasons. Protein levels on MeJA treated plants were only affected in rutabaga where there was a decrease in the protein levels in the roots of plants that were treated with both MeJA and insecticides. Studies were done to clarify the biology of the cynipid gall wasp Disholcaspis quercusmamma (Walsh). This wasp was previously known only from its asexually reproducing females that develop inside conspicuous twig galls and the sexually reproducing generation has remained unidentified. Spring bud galls were identified and sexual generation adults were reared from these galls. A morphological description was developed for the sexual generation wasps and their galls. The identity of the sexual generation of D. quercusmamma was confirmed by rearing trials ad DNA analysis. The sexual generation galls were found on both of the hosts that support the asexual generation; Quercus macrocarpa Michx. and Quercus bicolor Willd. While some trees were noted to be resistant to the formation of the asexual generation gall, those same trees were found to contain the sexual generation twig galls. The sexual generation galls develop in buds and become visible in the spring after bud break. The sexual generation wasps emerge in the spring and oviposit in newly developing twigs. Parasitoids reared from the sexual generation galls that are shared with the asexual generation are Torymus denticulatus (Breland) (Torymidae) and Sycophila dubia (Walsh) (Eurytomidae). Parasitoids that appear to be unique to the sexual generation are the pteromalid species Lyrcus nr. nigroaeneus (Ashmead), and the unidentified males of Pteromalus sp. and Mesopolobus sp. New records for the parasitoids associated with the asexual generation in northern Colorado include Eurytoma querciglobuli (Fitch), T. denticulatus, and Baryscapus racemariae (Ashmead).
Description
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Subject
crucifers
Disholcaspis
Methyl jasmonate