Date of Award

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Entomology

Advisor

Reay-Jones, Francis PF

Committee Member

Greene , Jeremy K

Committee Member

Toews , Michael D

Committee Member

Adler , Peter H

Abstract

A three-year study (2009-2011) was conducted to examine the spatial and temporal dynamics of stink bugs in three commercial farmscapes in South Carolina and Georgia. Crops included wheat, Triticum aestivum (L.), corn, Zea mays (L.), soybean, Glycine max (L.), cotton, Gossypium hirsutum (L.), and peanuts, Arachis hypogaea (L.). Farmscapes were sampled weekly using whole-plant examinations for corn, with all other crops sampled using sweep nets. The predominant pest species of phytophagous stink bugs were the brown stink bug, Euschistus servus (Say), the green stink bug, Chinavia hilaris (Say), and the southern green stink bug, Nezara viridula (L.). Chi-square tests indicated a departure from a normal distribution in 77% of analyses of the variance to mean ratio, with 37% of slopes of Taylor's power law and 30% of coefficient β of Iwao's patchiness regression significantly greater than one, indicating aggregated distributions. SADIE indices indicated aggregated patterns of stink bugs in 18% of year-end totals and 42% of weekly counts, with 80% of adults and nymphs positively associated using the SADIE association tool. Peak stink bug densities were linked to crop phenology, following the fruiting pattern of crops in the farmscape. Stink bugs exhibited higher densities in crops adjacent to soybean in Barnwell and Lee Counties, SC, compared with crops adjacent to corn or fallow areas.
Efficacy of applications of insecticide limited to the borders of fields to mitigate injury by stink bugs in cotton was evaluated from 2007 to 2011 in South Carolina and Georgia. Stink bug densities and boll injury were greater around the exterior compared with the interior portions of fields based on ANOVA models and interpolation maps of SADIE aggregation indices. Border and whole-field applications had no significant effect (P > 0.05) on average numbers of stink bugs, but boll injury was significantly lower (P < 0.05) in both border and whole-field insecticide treatments compared with untreated controls. No significant difference (P > 0.05) was found between injury levels in fields receiving border or whole-field treatments. Fields receiving no insecticide treatments exceeded economic thresholds 55% of the time. Fields receiving whole-field and border applications of insecticide exceeded thresholds 41% and 30% of the time, respectively. Treated area was 4.4-fold smaller in fields receiving border applications than in fields receiving whole-field applications, indicating substantial savings in insecticide. Results suggested that border treatments of insecticides provided protection from stink bug injury similar to whole-field insecticide treatments, but with considerable savings in application costs.
Studies of stink bugs in the field could be improved if movement could be monitored in real time. Harmonic radar tagging was investigated as a method for monitoring the movement of N. viridula. Because adhesive toxicity and tag weight limit the use of this technology, initial efforts focused on selection of the optimal adhesive and design of harmonic radar tags to reduce influence on movement of stink bugs. A design consisting of a 6-cm long 0.10-mm thick silver-plated copper monopole on the anode terminal of a three-contact Schottky barrier diode attached with a rubberized cyanoacrylate (Gorilla super glue) provided a compromise between unimpaired movement and tracking range, adding an additional 8% to the weight of the stink bug while not significantly (P > 0.05) reducing walking or flying mobility in the laboratory. Recovery of tagged stink bugs in cotton and fallow fields ranged from 10-75% after 24 hours, while marked stink bugs were recovered at rates of 0-35% using sweep-net or drop-cloth sampling. The distance dispersed in the field was not influenced (P > 0.05) by crop, tagged status, or gender of the insect. Future research should examine improvements to the harmonic radar transceiver and the wire antenna to decrease encumbrance.
Laboratory studies were conducted to determine host preference of the tachinid parasitoid fly Trichopoda pennipes (F.) for E. servus and N. viridula. In choice and no-choice tests, 8-fold fewer eggs were laid on E. servus, compared with N. viridula. Twenty-four T. pennipes emerged from 100 N. viridula, whereas only two larvae emerged from 100 laboratory-parasitized E. servus. Post-mortem dissections of egg-bearing stink bugs without larval emergence revealed 20 T. pennipes larvae inside N. viridula but only one inside E. servus. These results confirmed that T. pennipes prefers N. viridula as a host and is likely an infrequent parasitoid of E. servus.
While gathering T. pennipes for the selection trials, Cylindromyia euchenor (Walker), previously found in E. servus, was collected. Unlike most tachinids, which deposit eggs on or near the hosts, members of the genus Cylindromyia have an ovipositor formed from an abdominal sternite, which, assisted by serrated curved claspers, implants eggs directly into hosts. No research has been done on the behavior or host preferences of C. euchenor. My observations were limited to three females over approximately two weeks. Female parasitoids directly injected eggs into E. servus exclusively, ignoring N. viridula. The sequence of oviposition was recorded and described, demonstrating the ovipositional behavior for the first time and indicating a host preference for E. servus.

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Entomology Commons

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