Essigella californica, the Monterey pine aphid
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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.
From Forest Health News No. 107, May 2001.
In October, 2000, a programme was begun to monitor populations of the Monterey pine aphid ( Essigella californica) in Pinus radiata forests in the Bay of Plenty region (FHNews 105: 2). A complementary monitoring programme in stands in Hawkes Bay has also been initiated by Tim Herman (Crop and Food Research). The aphid first appeared in Bay of Plenty study sites in mid February, and since then moderate population levels have been maintained through to early May. At this stage it appears that higher aphid population numbers are found in older stands (more than 10 years) in lower elevation forests (below 300 m above sea level). The aphid has not yet been found in stands more than 600 m above sea level in Kaingaroa Forest, although it has been recorded at this altitude in previous years.
Aphids also appear to be more numerous in yellowing trees exhibiting signs of mineral deficiency or pathogen attack. A high soluble nitrogen content in such trees may attract the aphids, and this possibility makes it difficult to determine the extent to which Essigella is influencing tree condition. Results indicate that the aphid appears to be behaving similarly in both Hawkes Bay and Kaingaroa. Overall, the aphid populations are currently at a relatively low to moderate level, but with a rapid generation time this insect has the potential to reach damaging levels very rapidly under the right conditions. For this reason it is important that we continue to keep a close watch on this aphid around the country.
The suggestion in a previous article (FHNews 105: 2) that competition by another aphid, Eulachnus brevipilosus, may keep population numbers of in check does not appear to hold true, since E. brevipilosus has not yet been collected during the monitoring programme this year. The full-grown aphids shown in the accompanying figures are approximately 2 mm long, and have a lime-green body with red-brown eyes. The muscle attachment pattern on the abdomen (black dots in the upper figure) is a key identification character.
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