1. The effects of spider mite behavior and spray coverage on the performance of two miticides
Xavier Martini1, Natalie Kincy2, Christian Nansen 1, 2
1 Department of Entomology, Texas A&M University, Texas AgriLife Research, 2 Department of Plant and Soil Science, Texas Tech University
BACKGROUND
REPELLENCY OF MITICIDES
EFFECT OF INCOMPLETE SPRAY COVERAGE
We performed a choice test using non-excised cotton cotyledon leaves, in which treatments were separated by the mid vein.
We evaluated performance of the two miticides under varying spray coverages (1-70%). Both miticides showed decreasing survival of immatures in response to spray coverage. However, propargite did not suppress spider mites, even when applied at high spray coverage.
Foliar coverage of a pesticide applied to crops under commercial field conditions is often below 5% (Nansen et al 2011). Consequently, target pests have a choice between sprayed and un-sprayed plant tissue. If the pesticide is repellent it may result in a decrease in efficiency. We conducted a series of laboratory experiments with two non-systemic miticides (propargite and hexythiazox) to test their repellency to spider mites (Acari: Tetranychidae) and the effect of spray coverage. We used a modeling approach to quantify the overall miticide performance.
Choice tests showed that female spider mites were repelled by propargite but not by hexythiazox.
PERFORMANCE UNDER COMPLETE COVERAGE
In this experiment, cotyledon cotton plants were submersed directly into miticide solutions for 3 seconds to obtain full coverage. This resulted in effective control of spider mites with both miticides.
Fig. 4. Main output of our population dynamic model: (a) probability of exposure to pesticide when spray coverage increases at different repellency rates. (b) population dynamic of a theoretical pest with different repellency rates.
2.6%
28.6%
71.0%
Fig. 3. (a) Number of immatures for the two miticides, as a function of spray coverage. (b) Water sensitive cards showing the range of spray coverages obtained.
CONCLUSION
Pesticides are often tested assuming perfect spray coverage and that all target pest individuals acquire or contact the same amount of active ingredient. We demonstrated how a combination of repellency and low spray coverage may significantly decrease the performance of a pesticide.
We thank Texas State Support Committee and Cotton Inc. for partial financial support of this project.
MODEL
Combined effects of repellency and low spray coverage was interpreted in a population dynamic model. When spray coverage is low, and if the pesticide is repellent, the probability of pest exposure to pesticide is reduced (Fig 4a). A slight increase of repellency decreased efficiency of the pesticide to a point where it may not effectively control pest populations (Fig 4b).
Fig. 1. Immatures found on cotyledon cotton plants 1 week after infestation.
Fig 2. Number of females on each side of the cotyledon 10 minutes after introduction.
Nansen C et al. A decision-support tool to predict spray deposition of insecticides in commercial potato fields and its implications for their performance. Journal of Economic Entomology; 104: (2011)

2. INTRDUCTION FLIGHT MILL
In the context of a vector-borne pathogen system, the spread of disease depends on movement of vectors across a landscape. Indeed, vector dispersal is essential for pathogens to encounter new hosts to spread infection. The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of several bacterial pathogens including ‘Candidatus Liberibacter asiaticus’ (CLas). CLas is the causal agent of the citrus disease, huanglongbing (HLB), also known as citrus greening in the USA. The maximum flight distance of D. citri needs to be estimated in order to identify safe isolation and quarantine boundaries, as well as, to establish effective area-wide control protocols
FLIGHT MILL
Fig. 1: Schematic diagram of the flight mill apparatus. The measurement in the diagram is presented in mm