On Wednesday October 9th, a Brussels sprout plant sample was submitted to our Entomology laboratory for insect identification.
At the naked eye, we observed some webbing and specks on the leaf (See Fig. 1).
Fig. 1. Leaf of Brussels sprout showing some webbing and 'specks'. Affected areas are highlighted with the yellow circles.
Under magnification, we were able to see eggs, nymphs and adults of the two spotted spider mite (TSSM), Tetranychus urticae (See Fig. 2). Adults of these specimens have the two black spots on the lateral sides of the anterior end of the podosoma, the area located below their mouth parts.
Fig. 2. Eggs, nymphs and adults of two spotted spider mites on the leaf of Brussels sprout.
TSSM is one of the most polyphagous mites, having several host plants around the world. Females disperse by putting silk strands right after mating and before producing eggs. Dispersing females climb to the top of the plant and specimens are carried out by the wind. This phenomenon called ballooning, aids mites to float through the air and disperse longer distances to reach favorable host plants.
It is highly advised that Brussels sprout growers and PCAs walking this crop, pay close attention to leaves within the canopy to potentially identify the presence of TSSW in this crop.
If you believe you may have TSSM in your Brussels sprouts, please send us a plant sample at 1432 Abbott St. in Salinas for confirming identification (free service), or call us at 831-759-7359 to obtain additional information on this pest.
Since last week, I have been receiving samples with “red” aphids to get the identification. It turned out that this time, most of these ‘reddish' aphids were identified as the lettuce aphid, Nasonovia ribis-nigri (Fig. 1). To me, they look more red-orange; however, their distinct black marks on the abdomen and short cauda (finger-like, short appendage at the end of the abdomen) are some key ID features. These features help to differentiate the lettuce aphid from the other “red” aphid, the potato aphid Macrosiphum euphorbiae (Fig. 2). Yes, we do have two different species of red aphids!
More samples for aphid ID are still coming into the UC Cooperative Extension office. The pattern is still similar to last week. There are mostly lettuce aphids on the submitted samples. I was also able to notice that some samples have mixed populations between the lettuce and the potato aphids, where all the specimens were red.
We have several trial locations where we are scouting for aphids. So far, fields in Soledad have the largest number of aphids documented, as both alates (with wings, collected from yellow sticky cards) and wingless (collected from lettuce samples). If you need further information about the other scouting locations, or would like to double check your aphid ID, please contact or send samples to Alejandro Del-Pozo (firstname.lastname@example.org, 831-759-7359).
I have been receiving phone calls about the presence of “red aphids” in organic romaine lettuce that is resistant to the lettuce aphid, Nasonovia ribis-nigri (Hemiptera: Aphididae, Fig. 1). The lettuce aphid is considered a difficult pest to manage. This aphid can be green as well as red, and will be usually found in large colonies inside the heart of the lettuce head. Being inside the lettuce head protects these aphids from predators and parasitoids; and their presence is considered a contaminant when heads are harvested.
However, none of the samples that were submitted to the UC Cooperative Extension diagnostic laboratory were identified as the lettuce aphid. What are those “red aphids”?
First of all, aphids could have different color morphs within the same species. Therefore, relying only on color to identify aphids is not the ideal character to tell apart these pest species.
Submitted “red” aphid samples were identified as either: 1) the potato aphid, Macrosiphum euphorbiae, and 2) the foxglove aphid, Aulacorthum solani. Potato aphid has both the green and the red color morphs (Fig. 2). On the other hand, the foxglove aphid is usually green (Fig. 3); but infections of a naturally occurring Entomophthora fungus will make the specimens look like reddish. This sort of red coloration is due to the sporulation of the fungus from the dead aphid stuck on the leaves (Fig. 4).
If you are managing organic lettuce with resistance to the lettuce aphid and you find red aphids, it is important to consider other features beside color. Additional information on how to identify aphid species infesting lettuce can be found at http://ipm.ucanr.edu/PMG/selectnewpest.lettuce.html. If you would like to have a second opinion on your identification, you can always call and/or send your sample to the UC Cooperative Extension office in Salinas.