Date of Award


Degree Type


Degree Name

Master of Science (MS)



First Advisor

Clifford S. Sadof

Committee Chair

Clifford S. Sadof

Committee Member 1

Ricky E. Foster

Committee Member 2

Doug Richmond


Spider mite outbreaks can occur in urban forests after insecticides are applied to control early season pests. We used thornless honeylocust (Gleditsia triacanthos var. inermis) and honeylocust spider mite (Platytetranychus multidigituli) as a model to investigate this phenomenon by applying both topical and systemic insecticides to treat early season pests of honeylocust. Impacts of these applications on populations of P. multidigituli and its associated predatory mites were assessed. Early season applications of bifenthrin caused outbreaks of honeylocust spider mite and drastically reduced phytoseiids but not the stigmaeid mite, Zetzellia mali. In contrast later season applications suppressed populations of P. multidigituli. Pyriproxyfen, an insect growth regulator, did not affect predatory mite populations, nor did they stimulate outbreaks of spider mites. Soil applications of imidacloprid and dinotefuran were not regularly associated with spider mite outbreaks. Due to irregular irrigation and inconsistent performance against calico scale, it is difficult to determine whether the absence of outbreaks after neonicotinoid applications was due to lack of product uptake or compound activity. Historically extreme drought and high temperatures of 2012 in Indiana drastically reduced populations of phytoseiid mites but not the stigmaeid mite, Z. mali. Overall, Z .mali, did not seem to impact P. multidigituli densities as much as the phytoseiid mites. Densities of Z. mali typically followed the abundance of their spider mite prey. We conclude that outbreaks of P. multidigituli could be attributed to conditions that reduced the abundance of phytoseiid mites of honeylocust trees.