Case study:  A weekly survey of spider mites and their eggs
Methods: For two consecutive seasons, the mite populations in two commercial cotton fields in northeast Arkansas were monitored weekly for numbers of mites and their eggs.  The objective was to determine when and where mites entered the fields.  Each week, 10 randomly-selected cotton leaves were collected at distances of 3 meters and 25 meters along each side of the fields.  The number of mites and mite eggs on each leaf were counted.

Conclusions:  In 1998 mite populations in the two fields were relatively low, with populations increasing during the last week of June.  The data indicated that mites entered Jennings field from the west edge, and Nall field from the north edge.   In 1999, mite populations were higher, again increasing during the last week of June, and being abundant sooner at 3 meters than at 25 meters. Treatment of mite-infested field edges or “hot spots” during early to mid-June with an acaricide could help prevent mite infestations from developing.

Because we found mites earlier and more abundantly at 3 meters than 25 meters, we think that mites were entering the fields by crawling or being blown from close range sources (weeds) rather than being carried in by wind from distant sources.
Figures 1 - 4 show the mean numbers of spider mites and eggs found per leaf during each week of the study.  (Click on a graph to enlarge it.)
Fig. 1.
1998 Jennings fieldclick to enlarge
Fig. 2.
1998 Nall field
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Fig 3.
1999 Jennings fieldclick to enlarge
Fig. 4.
1999 Nall fieldclick to enlarge
   
Figures 5 - 8 show the relative locations of spider mites and their mean populations per leaf in the test fields for each week of the study.  (Click on a graph to enlarge it.)
Fig. 5.
1998 Jennings fieldclick to enlarge
Fig. 6.
1998 Nall field
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Fig. 7.
1999 Jennings fieldclick to enlarge
Fig. 8.
1999 Nall fieldclick to enlarge