CONE AND SEED INSECTS OF TAMARACK, LARIX LARICINA (DU ROI) K. KOCH, AND ATTEMPTS TO CONTROL DAMAGE USING CHEMICAL INSECTICIDES

Abstract

An investigation of the insects that damage cones (megasporangiate strobili) and seeds of tamarack [Larix laricina (Du Roi) K. Koch] in New Brunswick was undertaken. During two growing seasons (1982 and 1983) cones were removed from natural and planted stands of tamarack on a weekly basis. These cones were dissected, the nature and amount of insect damage recorded, and insect habits documented. Efforts were made to rear to adults any destructive insects encountered in order to identify them and to isolate parasites. Insects destroyed from 24.6 to 88.0% of the seed produced in the stands under study. Larvae of the spruce budworm [Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)] and the cone maggot [Lasiomma viarium (Huckett) (Diptera: Anthomyiidae)] were responsible for most of the damage. Among insects that caused lesser amounts of damage were a cone midge [Resseliella sp. (Diptera: Cecidomyiidae)], a seed chalcid [Megastigmus sp. (Hymenoptera: Torymidae)], and various lepidopterous larvae. Applications of the insecticides carbofuran and dimethoate reduced the amount of insect damage. Carbofuran applied at the rate of 13.5 g active ingredient per centimetre of diameter at breast height provided the best protection. Trees treated in this manner had 37.0% of their seeds destroyed by insects as opposed to 74.2% on control trees.

OVIPOSITION, TEMPORAL DISTRIBUTION, AND POTENTIAL IMPACT OF STROBILOMYIA LARICIS MICHELSEN AND S. VIARIA (HUCKETT) (DIPTERA: ANTHOMYIIDAE) ON EASTERN LARCH, LARIX LARICINA (DU ROI) K. KOCH

“…These estimates of egg developmental time are similar to those reported previously for the S. laricislviaria complex (Amirault and Brown 1986;Chau 1993) and for other Strobilomyia spp., which range from 4 to 15 days (Tripp and Hedlin 1956;Michelsen 1988;Yao et al 1991). These estimates of egg developmental time are similar to those reported previously for the S. laricislviaria complex (Amirault and Brown 1986;Chau 1993) and for other Strobilomyia spp., which range from 4 to 15 days (Tripp and Hedlin 1956;Michelsen 1988;Yao et al 1991).…”

“…Densities of larch cone maggots vary widely, however, and depend on the size of cone crops and the presence of other cone feeders (Amirault 1984;Eavy 1987;Roques 1988). Spruce budworm, Choristoneura fumiferana (Clemens), which caused heavy damage at the same time as cone maggots in other studies (Amirault 1984;Eavy 1987), was not present at our study site and cecidomyiids were found only after larvae of S. laricis and S. viaria had completed development. Strobilomyia viaria preferred unoccupied cones over those occupied by either S. viaria or S. laricis, suggesting that the largest interspecific influence on larch cone maggots in our study may have been by S. laricis on S. viaria.…”

“…Although previous studies (Amirault 1984;Amirault and Brown 1986;Eavy 1987) indicated L. viarium damaged up to 90% of potential seed, these results were obtained before it was known that two species of cone maggots occurred on eastern larch and so the relative impact of each species also remains unknown.…”

“…Historically, damage to cones of eastern larch, Larix laricina, in North America has largely been attributed to one species of cone maggot, Hylemya (Lasiomma) viarium Huckett (Amirault 1984;Eavy 1987). In 1988, a world revision of all adult cone flies revealed that two species, Strobilomyia viaria (=Hylemya viarium) and S. laricis, occurred sympatrically on L. laricina (Michelsen 1988), and a third species, S. macalpinei Michelsen, infested seed cones of L. laricina and alpine larch, Larix lyallii (Parl.…”

Proximate and ultimate factors influencing oviposition site selection by endoparasites on conifer seed cones: two sympatric dipteran species on larch

“…Factors affecting oviposition site selection have received little attention in cone and seed insects in general (Miller & Borden, 1984;Mattson, 1986;Rappaport & Roques, 1991;Turgeon et al, 1994) and in Strobilomyia species in particular (Roques, 1988). Several authors have noted that S. laricis and S. viaria tend to lay one egg per cone (Amirault, 1984;Turgeon, 1989;Chau, 1993;McClure et al, 1996), which suggests that females probably recognize and avoid previously occupied oviposition sites when seed cones are abundant. When seed cones are limited however, Strobilomyia spp.…”