Curculio sayi

In Europe, Curculio elephas may occupy a similar ecological niche as Curculio sayi in North America. Curculio elephas is not as specialized as Curculio sayi in North America, as it infects chestnuts and acorns of some oak species. [9] For Curculio elephas, research has shown that the chestnut infestation rate of sparsely spiky burrs (90%) and densely spiky burrs (2%) can show great variation at the same location and year. [9] Other results suggest that chestnut weevil females avoid laying their eggs in certain chestnuts. [10] Most of the weevil infested chestnuts were found in the South and West orientation of the tree canopy. Timing of burr opening and nut drop apparently was not affected by weevil infestation of chestnuts.

Most of the weevil activity in chestnut trees was noted on warm nights between 6pm and 10pm. Light traps at 12 meter (40ft) height caught the most adult weevils. [9] Other research on pecan weevils ability to fly suggests warm temperature dependency and sex differences. At a temperature range in the mid 80'F to mid 90'F, female pecan weevils were more capable of flying high into the tree canopy. In comparison more male pecan weevils than female pecan weevils were observed crawling to the closest pecan tree trunk. [11] In plum curculio the temperature threshold between crawling versus flying behavior was 20C (68F). [12] In Kentucky, and Indiana big brown bats were described as specialist predators of night flying beetles such as weevils. [13] [14]

In plum curculio the period from soil emergence to mating is 6-17 days. [15] Curculio elephas exhibits capital breeding carrying developed eggs upon soil emergence and apparently no need to feed before egg laying. [16] If Curculio sayi exhibits similar behaviors to other weevils has not been researched yet.

Both the European and North American chestnut weevil species appear to exhibit an extended life cycle of a prolonged or repeated diapause. This results in a life cycle completion of one, two, three or four years. [17] In Curculio elephas a reported soil emergence from a single weevil larvae generation was 66% the first year, 30% the second year and 4% the third year on oaks. [18] A hypothesis is that diapause variation may be the result of seasonal environmental challenges to survival. In a dry summer with hardened soil, one quarter to three quarter of the developed adults may not be able to soil emerge and perish. Emergence challenges from hardened soil affected the larger female weevils at a higher rate than the smaller male adult weevils. [8]

External morphology

The average length of the body alone is about 1/4" (6mm). [4]

Dorsal view (about 6x magnification)

Males are approximately 10 mm in overall length with comparatively shorter rostrums (slender snouts). Females are approximately 15 mm in overall length with comparatively longer rostrums.

In the small chestnut weevil the first segment of the antenna funicule is longer than the second.

A mated female weevil uses her long snout to chew a hole in the side of the nut shell or lining. Research on a similar chestnut weevil (Curculio elephas) in Europe suggest that egg laying may occur into selected nuts and not random. Apparently, Curculio elephas is non selective about what burr to approach. It is also non selective to egg laying if a burr has one, two or three viable nuts. Research results suggests that European chestnut weevils select a specific nut quality for egg laying. Curculio elephas also does not appear to chemically mark a nut where it has deposited a egg, nor does it appear to sense in other ways if a nut already has an egg deposited. [8] If this egg laying behavior is similar in Curculio sayi has not been researched. If Curculio sayi taste tests nut meat before egg laying or how many nuts the weevils probe before an egg is layed has not been researched. Clean adult weevil chew holes are usually too small to visually identify on the nut shell. Only when an adult weevil chew hole starts a mold infection, may weevil chewing activity become visually identifiable on the nut shell surface.

The nutrient quantity in a viable chestnut can support development of several larvae (up to a dozen) at the same time.

Eggs hatch in five to seven days. When hatched, the large, white, legless grubs (larvae) feed on the tissue of the growing chestnut kernels. [4] When the larvae reach their last of four instar inside the chestnut, they chew a 1/8" hole in the chestnut shell and emerge. Most larvae emerge and fall to the ground while the chestnut is still in the tree.

Peak emergence of larvae from fallen nuts occurs at six days post harvest and drops to low emergence levels by day 16 post harvest. A few larvae may still emerge from infested chestnuts more than four weeks post harvest. [20] Refrigeration of harvested chestnuts or cold temperatures slows grub development.

Most nut-emerged larvae burrow 7-15cm below the soil line.[19] There they build a soil chamber. They pupate after several months (up to 18 months or longer) and remain in their chamber for at least one season. [19]

Scouting for soil emerging adults is somewhat effective with a dark colored pyramid trap. These traps should be set one per acre well before chestnut bloom occurs and checked twice a week.

The most effective method of identifying weevil presence within an orchard is via limb- tapping over a light colored sheet. Weevils drop when a branch is jarred. [21] Adult weevils are considered poor dispersers with average flight distance 220 m. [26]