DOUGLAS C. ALLEN’s research while affiliated with University of Michigan and other places

A study of the population dynamics of Choristoneura pinus Freeman was carried out in Michigan from 1965 to 1968. Analysis of 29 life tables showed that survival during the egg to 2nd-instar age interval was of primary importance in determining population fluctuations. Survival of the late instars and realized fecundity were also important. Middle instar and pupal survival were weakly correlated with population change. Egg parasitism by Trichogramma minutum Riley was low. Fall and spring dispersal was probably the principal mortality factor for 1st and 2nd instars. Most mortality of 3rd and 4th instars was due to Apanteles spp. and Glypta fumiferanae (Viereck). No principal mortality agent was identified for the late larval period. Parasitism accounted for about half the pupal mortality. Variations in realized fecundity were attributed to moth dispersal, with wind and foliage conditions determining relative losses. It is suggested that weather during the larval and adult dispersal periods is the key factor in permitting budworm outbreaks, and unfavorable weather and defoliation cause outbreaks to collapse.

Parasites were reared from the eggs, early larvae, late larvae, and pupae of the jack-pine budworm, Choristoneurapinus Freeman. Host collections were made from the mid- and lower crown of 10 jack pine trees in each of 2 counties in Michigan for 2 generations of the budworm. Apparent parasitism by species, crown level, area, and stage of the host was determined. Twenty-six species of primary parasites and 4 species of hyperparasites were reared from the budworm. Nine species are new records for this host. The largest amount of parasitism occurred in the early larval stages and was attributed predominantly to 2 species, Apanteles fumiferanae Viereck and Glypta fumiferanae (Viereck). Mortality caused by them varied from 1.3 to 51.3%, and it was greatest at midcrown. Late-stage parasitism of budworm larvae was variable. Five species of tachinid flies accounted for most of this parasitism. The maximum parasitism obtained by this group was 17.9%. Itoplectis conquisitor (Say) was the most important parasite of budworm pupae; it killed as much as 24.5% of the pupae in 1 sample. The proportion of total mortality in a generation of C. pinus attributable to parasites of larvae and pupae was low and variable, ranging from 0.4 to 8.5%. Dirophanes banksianae Allen is reported to be a new synonym of Phacogenes hariolus (Cresson).

Invertebrate predators of Choristoneura pinus Freeman (Lepidoptera: Tortricidae) were studied in the laboratory and observed under field conditions in an investigation of their feeding response and behavior. Observations were made on the biology of important predators in northern anil central Michigan. The distribution, number, and kinds of spiders associated with 6 jack pine trees were investigated in Baraga County. Eight species of insects were recorded preying on various stages of C. pinus. Anatis occllata (L.), Podisus sereventris Uhler, and Camponotus novchoracensis Fitch were the most abundant of this group. Field observations suggested that populations of P. serieventris exhibited a numerical response to increases in buclworm numbers. Fifty-one species of spiders were collected from jack pine trees. Three-quarters of them were hunting spiders that belonged to the families Thomisidae, Salticidae, and Oxyopidae. One species,Metaphidippus flavipedes Peckham, accounted for 48.0% of this group. Theridion murarium Emerton, Dictyna phylax Gertsch ' Ivie, and Grammonota pictilis O. P.-Cambridge were the most common web-spinners encountered. Observations suggested that defoliation and natural stand closure are factors that limit populations of spiders in jack pine stands. No crown level or type of stand could be characterized by specific groups or species.

Jack-pine budworm larvae and pupae are more prevalent on the distal portions of branches and may be significantly but unpredictably concentrated into one crown level of the tree. A suitable sampling method for population dynamics work consists of counting the budworms and tips on the distal 36 inches of 2 branches from the middle crown and 2 branches from the lower crown from groups of 10 trees. The population intensity (budworms per 100 tips) is estimated for each crown level using regression equations. The weighted average of the two crown levels gives the population intensity for each tree. From this figure the numbers of budworms per tree and per acre are calculated.

A new species, Phaeogenes gilvilabris, and a new sub-species, P. ophthalmicus americanus, are described. Three species are redescribed and keys to both sexes of the known Nearctic species of the genus Phaeogenes sensu stricto are given.

Larvae of the jack-pine budworm, Choristoneura pinus Freeman, reared on artificial diet approached field collected specimens in size. Mortality during hibernation accounted for the largest reduction of individuals in each generation. Survival on the diet was high enough (70%) to make the technique efficient for mass-rearing purposes. Important points to consider are the careful handling of the insect in all stages, establishment of second-instar larvae in the diet, size of mating containers, and length of time spent in hibernation.

As one phase of a population dynamics study of the jack-pine budworm, Choristoneura pinus Freeman, this investigation on vertebrate predation was earned out (1) to describe the vertebrate predators of the budworm and (2) to assess the importance of vertebrate predation in the insect’s population dynamics. Twenty-eight species of birds and 1 mammal were found to attack the budworm in Michigan. Birds were more important than mammals as budworm predators. The significance of bird predation in the budworm’s population dynamics appears to depend on the population level of the insect and the response of bird predators to gradients in budworm numbers.

A new species of Dirophanes parasitic on Choristoneura pinus Free. is described in comparison with its closest relative D . spinicoxus Viereck and a species it superficially resembles, Phaeogenes cacoeciae Viereck. A key to the three species is included.