Catalpa worms/ tree care.
The catalpa sphinx overwinters as a pupa in the soil under or near trees infested the previous season. In spring, pupae work their way to the soil surface and moths begin to emerge shortly after host trees have leafed out. Time of moth emergence varies considerably by locality within the range and even from year to year in the same locality, depending on temperature and general weather conditions. Spring moth activity can be expected in most years from about mid April into early May. Moths mate and females lay eggs in masses on the undersurface of leaves. Masses may contain 100-1000 eggs (1). Eggs usually hatch in five to seven days (1); in normal years, hatch has usually occured and first-brood larvae are present by mid-May. Newly hatched caterpillars feed as a group skeletonizing areas of leaf, (Photo 9). Later, larvae separate and feed singly, consuming whole leaves except for stubs of midribs and large veins. Duration of the caterpillar stage varies but generally is about three weeks. Full-grown caterpillars enter the soil and pupate. New adults of summer generations emerge in about two weeks, but pupae of the last brood of the season overwinter in the soil and moths do not emerge until the following spring. The total length of the lifecycle is about six weeks. Three or four generations may occur in a single season, and caterpillars may be present into fall. Time of moth emergence and duration of developmental stages vary, consequently, generations often overlap and different life stages and caterpillars of different sizes may be present at the same time.
Infestations of the catalpa sphinx occur sporadically; they come and go and often seem to be highly localized. Certain trees appear to be preferred and are attacked regularly while others of the same catalpa species seem to escape attack; the reason for this is unknown. Caterpillars may be abundant for one, two, or three years, then scarce for several. Natural enemies such as parasites and predators, take a heavy toll of eggs and larvae, and are largely responsible for maintaining populations at low levels. One of the most common and important parasites is a small wasp that attacks the larva. The female wasp deposits eggs through the skin of the caterpillar. Wasp larvae feed and develop inside, then emerge to the outside and spin conspicuous white, silken cocooons on the caterpillar skin, (Photo 10). Parasitized catalpa worms do not survive to adulthood.
When caterpillars are numerous, infested trees may be completely defoliated. Defoliated catalpas produce new leaves readily and trees usually refoliate promptly. However, with multiple generations occurring, new foliage maybe consumed by subsequent broods. Most trees survive but some dieback may occur. Severe defoliation over several consecutive years can cause death of trees. Multiple defoliations of nursery stock, (Photo 11), may adversely affect survival of young trees when transplanted.
The catalpa tree, with its broad, dense crown and showy flowers, is prized by many as a shade or ornamental tree. Catalpa worms can essentially destroy this ornamental value. In this circumstance, the catalpa sphinx is a destructive, unwanted pest. However, there is another viewpoint. As indicated previously, catalpa worms are prized for fish bait. To many fishermen their presence is welcomed, even encouraged. Catalpa foliage is the only food of the catalpaworm, and it is likely that many catalpa trees are planted and maintained as much or more for production of fish bait as for any other purpose. Whether the catalpa sphinx is destructive or beneficial is a matter of point of view.
