Our 2014 findings: Kudzu bugs persist in Maryland

Jessica Grant, Alan Leslie, and William Lamp

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Background: The kudzu bug life cycle needs to be assessed in Maryland, its northern limit 

Since Maryland is currently the northern limit of the kudzu bug’s known range, we monitored populations to develop an understanding of their life stages in the mid-Atlantic region.

During summer and fall of 2014 our goals were:

1.     Adopt a standard sampling method

2.     Check the persistence of bugs at previously known sites

3.     Monitor sites of known kudzu bug populations and expected sites of expansion

4.     Determine the number of generations of the bugs in Maryland

1. New standardized sampling method of vine cutting and sweep netting 

We adopted a standardized sampling method for kudzu bugs that allowed us to compare densities of eggs, nymphs, and adults across sample sites and times. For sampling we:

1. Collected 10 sections of 0.5m long kudzu vines

2. Swept through the kudzu foliage for a total of 60 seconds

The kudzu vine sections allowed us to count the small and hard to find life stages (that are often not found in other sampling methods) back in the lab. Sweeping made higher areas of the kudzu patch canopy easier to reach, where we often found more of them. Sweeping also allowed us to detect a presence over a large area quickly.

2. Kudzu bugs have persisted at previous sites but have not expanded their distribution in Maryland

During 2014, we resampled all kudzu patches that were positive for kudzu bugs in 2013.  17 of the 18 sites that had kudzu bugs in 2013 still had kudzu bugs in 2014.  The one site where kudzu bugs were not detected had a reduced amount of kudzu vines.  Thus, the county-level distribution of the kudzu bug in Maryland remains the same as 2013 (Fig. 1).

Figure 1: Map of Maryland counties with kudzu bugs in 2014 shown in red. 

3. Kudzu bug numbers were low in the summer but increased in early fall

 We used the new sampling approach to sample four sites each week through the summer, and every other week in the fall until kudzu leaves senesced.  Two of the sites had kudzu bugs in 2013, while the other two did not but we expected the bugs to colonize the sites in 2014. We only found kudzu bugs at the two sites with previous populations. All sites started the summer with low densities but grew quickly by fall. At several of the sites with abundant kudzu bugs, we could easily detect their presence when we first arrived at the site because of their distinctive smell!

Lower population numbers found in the summer may be due to a colder than average winter

 ased on sampling in 2013, the sites we visited in June and July in 2014 left an impression of reduced numbers of kudzu bugs compared to 2013. One possible reason for this trend is that the colder than average winter of 2013-14 may have increased mortality of overwintering adults (see temperature patterns in Fig. 2).  Fewer surviving adults may have delayed the population growth we expected to see by mid-summer.

Figure 2.  Temperature anomaly (the difference between the observed temperature and the long-term average) during winter months (Dec-Mar) in Maryland for each year starting in 2003/2004.  Note that the past winter has been the coldest over the past 10 years, and it was preceded by two of the warmest winters during the same period. (National Climate Data Center. 2015)

4. Two-generations of bugs per season found in Maryland

Patterns in adult abundance indicated there are two generations of kudzu bugs in Maryland. Looking at the life stages of our sampling, particularly August through October, we found:

·      August had the highest number of egg masses

·      September was dominated by nymphs

·      October showed an equal number of nymphs to adults  (Fig. 3).

Thus, since there is a second peak of adults beginning in October we can extrapolate that there are most likely two generations of kudzu bugs in Maryland (Fig. 4).  Furthermore, kudzu bugs may have a shifted emergence and population growth towards later in the season than is found in the Southeast as suggested by our findings of mixed life stages persisting into the late fall. 

Figure 3. The percentage of the three life stages (green: egg masses, yellow: nymphs, and blue: adults) of the total kudzu bugs found by all collection methods for August, September, and October. 

Figure 4. Our hypothesized phenology of the kudzu bug in Maryland based on observations in 2013 and 2014.  Research in 2015 will focus on refining the timing of life stages in June and July.

Continued research into understanding kudzu bug cold tolerance and development could aid in Maryland pest predictions

Overall, our observations during 2014 have confirmed that the kudzu bug can survive colder than average winters in Maryland, although its abundance may be reduced during spring and the first half of the summer. We plan to continue to monitor kudzu bug populations during 2015 with the goal of being able to predict the abundance, distribution, and timing of development for egg laying in the spring. Kudzu bugs have the potential to expand throughout Maryland and become a pest on soybeans. Knowing their cold tolerance and development will aid us in pest management plans.

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