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Title: Field evaluation of two systemic neonicotinoid insecticides against pink hibiscus mealybug (Maconellicoccus hirsutus (Green))on mulberry trees

item Castle, Steven
item PRABHAKER, NILIMA - University Of California

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2011
Publication Date: 6/5/2011
Citation: Castle, S.J., Prabhaker, N. 2011. Field evaluation of two systemic neonicotinoid insecticides against pink hibiscus mealybug (Maconellicoccus hirsutus (Green))on mulberry trees. Journal of Pest Science. 84:363–371.

Interpretive Summary: Invasive species are often among the most troubling pests of agriculture because they are able to exploit new environments in the absence of key natural enemies left behind in their indigenous environment. Release from natural enemies may result in the rapid increase and expansion of an invasive pest in a new environment and thus requires immediate action to prevent its spread if discovered early enough. The pink hibiscus mealybug is an invasive pest from Asia that was discovered in the Imperial Valley of California in 1999. Surveys of the infestation indicated that it was distributed within a well-defined zone at the southern end of the valley and that management actions should be taken to contain it within this zone. The present study reports the results of treating infested trees and shrubs with either of two soil-applied insecticides, imidacloprid or thiamethoxam, that is taken up by the roots and distributed throughout the plant. Out of a total of 48 mulberry trees that were treated either once or twice over a two year period, 25 (52%0 were completely free of infestation during the entire second year of the experiment. Both insecticides were nearly equivalent in the number of trees they freed from mealybug infestation and in the pattern of reduced infestations that each insecticide produced. These results demonstrate the potential use of either insecticide to reduce and potentially eliminate whole tree infestations of pink hibiscus mealybug.

Technical Abstract: Infestations of the pink hibiscus mealybug, Maconellicoccus hirsutus (Green), in ornamental trees were already in an advanced state at the time of its discovery in the Imperial Valley of California (USA) in August 1999. Concern about the spread of M. hirsutus beyond the Imperial Valley led to the present study to evaluate the efficacies of two systemic neonicotinoid insecticides, imidacloprid and thiamethoxam, at reducing heavy infestations that occurred in various ornamental tree species, many located in high traffic areas. Initial studies conducted in 2001-02 provided encouraging results regarding the capacity of both insecticides to severely reduce, and in some cases completely eliminate infestations from individual trees. In 2003-04, a total of 50 infested mulberry trees (Morus alba L.) were divided into two groups of 20 trees each treated with either imidacloprid or thiamethoxam, and a third group of 10 trees retained as untreated controls. Branch samples collected from all 50 trees from early August through mid-October recorded a substantial reduction in M. hirsutus infestations in all trees treated with either insecticide, whereas infestations continued to rise in the untreated trees to a peak level on 26 September. Of the 40 treated trees that remained infested in mid-October 2003, in nearly all cases the infestations were represented by early instar nymphs, suggesting that egg hatch followed by dispersal to branch tips had enabled infestations to persist. However, by the end of the 2004 season, 10 of 20 imidacloprid-treated and 9 of 20 thiamethoxam-treated trees were completely free of M. hirsutus.