Brief Description: Green Stink Bugs are large, green, triangular insects with a large scutellum. Their name comes from the fact that they produce a disagreeable odor (I have never smelled this odor so I can't confirm that it is disagreeable).
Pest Status: The pest status depends on the species.
Three species can be found in the United States:
1. Nezara viridula (Southern Green Stink Bug) is a pest on many crops including soybeans
2. Podisus maculiventris (Spined Soldier Bug) is a beneficial insect which primarily feeds on caterpillars
3. Acrosternum hilare (Green Stink Bug) can be either a pest or a beneficial insect; as a pest it will suck sap from the stems, leaves, and reproductive parts of soybeans and other crops
Development & Life Cycle: Green Stink Bugs have paurometabolis (gradual-metamorphosis) development. This form of development is characterized by the life stages living in similar environments and eating similar foods; the nymphs (young) resemble the adults except that they have no wings, later nymphal stages have wing pads, coloration is different, the nymphs molt into larger and more developed stages until they reach adulthood, and they have no external genitalia. Adults and nymphs have sucking-piercing mouth parts.
Sampling & Damage: Green Stink Bugs are typically found in field borders before fruit is set and then they move into the field as pods and fruit are available. In soybeans, the adults and nymphs pierce the pods and feed on the seeds. This feeding results in small and shriveled seeds which reduce the market value of the crop.
NOTE: this damage is chewing damage likely from a caterpillar NOT a stink bug! I did see several caterpillars and adult grasshoppers which also cause chewing damage but are usually at the leaf edge not in the middle of the leaf.
Below is the map of the farm and the locations where I sampled (each sample is 10 sweeps of the net- so you take a step, sweep, step, sweep, continue for 10 net sweeps) for pentamids.
I tried to use a stratified-random sampling plan. However, I didn't realize the extent of the soybeans until I was in the back of the research plot and discovered that there were more soybeans on the sides of the wheat plots. I, also, chose not to sample in front of the research plots since I didn't want to disturb the research going on there & we parked there so we likely disturbed the area moving around. In the future, I want to get a generalized map BEFORE sampling so I can get a better handle on what type of method to use.
Below is the chart for my samples, numbers found, mean (average found in sample), variance (variation of samples), and standard deviation (also known as standard error, square root of variance).
The mean, variance, and standard error are used to determine the correct sample size to determine stink bug densities.
2.77 samples at the 90% confidence interval
1.36 samples at the 95% confidence interval
Please note that this is a very small number of samples but the mean and variance is going to be "pushed" by the number of zeros in the samples. For the adults this may not matter as much since I either found one or no adults. However, the number of nymphs found ranged from 0-5 so the zeros could definitely be skewing the data. My sampling plan could have missed some "hot spots" since I didn't sample four areas (including the research plot which we were asked NOT to sample) of the field.
We were, also, asked to time our sampling which I neglected to do. However, it took about 1.5 hours to do all the sampling and take all the photos. It may have been easier to do a present/absent count and given what I found it may have been just as precise.
I, also, observed multiple beneficial insects in every sample except numbers 2 and 14. The beneficial insects found: Adult & Nymph Lady Bug, Lacewing Nymph & Adult, Adult Spiders (several kinds), Adult Opiliones (Daddy-Long Legs - I won't get technical here but they are different from spiders {subject for another blog?}), and an Adult Nabid (Damsel Bug). I observed a Dragonfly flying around the field; I'm going to assume that was a female looking for food since males tend to be protecting territories at this time of year. In addition, in sample seven I found a cute, tree frog which is another form of biological control. Unfortunately, I didn't have a container with me otherwise he/she would have gotten to come home with me to live with the cats, tarantulas, & small jungle.
Experience Rating: I have previously sampled for insects in soybeans & this was different than I expected but it was a different field location. The number of pentamids found was similar to the previous sampling but there were far more beneficial insects. In addition, there were not many other damaging insects such as grasshoppers, caterpillars, and bean leaf beetles which were in abundance in the previously sampled field. However, the other field was sampled last year so it is possible that the results from this field are similar to what can be found in that field this year.
I would say that this was a positive experience especially since this is the FIRST time I have caught a frog (NOTE to self- MUST carry a container for living specimens)!
Interesting/Educational Links:
http://ipm.ncsu.edu/ag271/soybeans/stink_bugs.html (stink bug fact sheet)
http://en.wikipedia.org/wiki/Green_stink_bug (stink bug fact sheet with color photos)
http://www.entomology.ksu.edu/DesktopDefault.aspx?tabindex=361&tabid=567 (management options for Kansas)
References Used:
Pedigo, l. P., Rice, M. E. 2006. Entomology and Pest management, 5th Edition, Pearson/ Prentice Hall, Upper Saddle River, New Jersey.
I loved the frog
ReplyDeleteOriginal comments from diigo:
ReplyDeleteI've never heard the term "Pentamid" used for these critters before. Stink bugs belong to the Pentatomidae family, which is why I'm more familiar with the term "pentatomid".
Unfortunately, I have smelled these things before. I'm not quite sure I'd classify it as "disagreeable", but it's certainly a distinguishable one.
If you're talking about pest species, you should also include redbanded stink bug and the brown marmorated stink bug. In North America, there are 221 described species that cover 61 genera, but only a few have economic importance.
[life cycle image] This is a helpful description of their life cycle.
Had the damage been in the middle of the leaf, what could have caused the damage? Where was most of the damage located? Early in the season, you can often tell how recent the infestation was based on the location of the feeding. For example, if most of the damage is only in the new growth, then the infestation was recent. If there's no damage in the new growth but a ton in the old growth, this might tell you that the infestation was old. In late season or during non-vegetative growth stages, it's more difficult to distinguish such patterns.
Using the numbers from the above table I get 576 samples at the 90% CI ( or =((2*1.68)/(0.1*1.4))^2) and 2304 samples at the 95% CI (or =((2*1.68)/(0.05*1.4))^2). Rarely would a 90 to 95% CI require only 1 to 3 samples. You might want to check your math.
Again, great use of photos.