E. R. Oatman

BIOLOGY OF TRICHOGRAMMA BREVICAPILLUM

The biology of Trichogramma brevicapillum Pinto & Platner (Hymenoptera, Trichogrammatidae) reared on eggs of Trichoplusia ni (Hübner) (Lepidoptera), and the influence of some abiotic and biotic conditions on the parasitization strategy of the adults were studied. Egg, larva, prepupa, and pupa are described. Development of these stages lasted ca. 1,3, 1, and 5 days, respectively, at 25°. Reproduction is biparental, arrhenotokous. The preoviposition period lasts ca. 3 hr, and oviposition activity was maximal in the 3rd and 4th hr of the photophase and was minimal in the scotophase. The suitability of T. ni eggs as a host was maximal in the blastula stage of the embryo, decreased sharply in the early stages of differentiation, and increased rapidly in the later stages of embryological differentiation. A single ♀ reared from a host egg was larger and more fecund than 2 2 from eggs yielding 2 or 3 parasites. Oviposition by individual ♀♀ was restrained when the host egg density was limited, thus preventing superparasitization. The number of progeny per host egg and the ♂ proportion of the sex ratio were inversely related to the host egg density over a range of limited host densities.

Effect of a nuclear polyhedrosis virus on the relationship between Trichoplusia ni (Lepidoptera: Noctuidae) and the parasite, Hyposoter exiguae (hymenoptera: Ichneumonidae)

Abstract The effect of a nuclear polyhedrosis virus on the relationship between Trichoplusia ni and the parasite, Hyposoter exiguae , was investigated to determine if the virus could invade and multiply in the tissues of the parasites, if parasites which emerged from virus-infected T. ni larvae had normal emergence, fecundity, and longevity, and if the parasite could serve as a vector for the virus. Light microscopy revealed particles which appeared to be polyhedra within the lumen of the midgut of parasite larvae from virus-infected hosts. Transmission electron microscopy confirmed the presence of polyhedra and free virions within the midgut of the larvae. Polyhedra or free virions were never found within any parasite tissues. Parasite larvae within hosts exposed to virus before parasitization perished when their hosts died of virus infection. Parasite larvae in hosts exposed to virus after parasitization completed their development before their hosts died of virus infection. The proportion of parasites which survived increased as the time between host parasitization and host virus exposure increased. Parasite larvae which developed in hosts exposed to the virus soon after parasitization spent significantly less time in their hosts than did parasites which developed in noninfected hosts. There was no significant difference in time spent in the pupal stage, percent adult emergence, adult longevity with and without food and water, and fecundity of parasites which developed in virus-infected hosts and those which developed in noninfected hosts. Female parasites laid as many eggs in virus-infected hosts as they did in noninfected hosts. Sixty percent of the female parasites which oviposited in virus-infected hosts vectored infective doses of virus to an average of 6% of the healthy hosts subsequently exposed to them. None of the healthy host larvae exposed to male parasites which had been exposed to virus-infected host larvae became infected with the virus. Forty percent of the female parasites which developed in virus-infected hosts transmitted infective doses of the virus to an average of 65% of the healthy host larvae exposed to them. Ninety percent of the male parasites which developed in virus-infected hosts transferred infective doses of the virus to an average of 21% of the healthy host larvae exposed to them.

Comparative life table, behavior and competition studies of Trichogramma brevicapillum and T. pretiosum

Life‐table studies of Trichogramma brevicapillum Pinto & Platner and Trichogramma pretiosum Riley were conducted at various fluctuating temperatures (means ± 5°), from 15 to 35°. The intrinsic rate of natural increase (r) was higher for T. brevicapillum than that for T. pretiosum at 30 and 35°, and was higher for T. pretiosum between 15 and 25°, due to differences between the 2 spp. in development, longevity, fecundity, sex ratio, and number of progeny per host egg. T. brevicapillum had a higher fecundity than T. pretiosum, but its development was slower (ca. 10%), and was retarded facultatively at temperatures of 20° and below, probably due to diapause. Ovipositional behavior of T. brevicapillum and T. pretiosum was similar, but differed in the duration of the different ovipostional activities. Superparasitization occurred by both species when the host egg supply was limited and exposed to more than 1 female simultaneously. T. pretiosum laid more eggs per host egg than T. brevicapillum at various parasite densities. When eggs were exposed to both species simultaneously, oviposition was intermediate between the number of eggs laid by each species separately. From such eggs, 24 and 76% of the emerged progeny was T. brevicapillum and T. pretiosum, respectively, and these percentages were independent of parasite density. The results may explain the distribution of T. brevicapillum and T. pretiosum in California, and may assess their fitness for mass‐release and establishment attempts.

Precise sex allocation, local mate competition, and sex ratio shifts in the parasitoid wasp Trichogramma pretiosum

Abstract We determined the sex, order, and clutch size of eggs laid by the parasitoid wasp, Trichogramma pretiosum Riley, in the eggs of one of its natural hosts, Trichoplusia ni (Hübner). The parasitoid allocated sex non-randomly to hosts in the laboratory with a variance significantly less than that of a binomial (random) distribution, our null model. More clutches of two or more eggs contained a single male egg as the second or third egg laid than would be expected by chance and none contained two or more male eggs. T. pretiosum also increased the sex ratio (% male) of its offspring with increasing foundress numbers by increasing the frequency of male offspring as the second egg in a two-egg clutch allocated to unparasitized hosts and as the single egg allocated to previously parasitized hosts. These results indicate that T. pretiosum allocates the sex of its offspring precisely. Precise sex allocation is favored under local mate competition because it reduces variation in the number of sons per patch thus maximizing the number of inseminated daughters emigrating from the patch. Similar combinations of female and male offspring emerged from T. ni eggs parasitized by T. pretiosum in the field, again with a sex ratio variance less than that expected for a binomial distribution. These results strongly suggest that this parasitoid species manifests local mate competition.

Differential susceptibility of parasitized and nonparasitized larvae of Trichoplusia ni to a nuclear polyhedrosis virus.

Abstract Nonparasitized second-instar larvae of Trichoplusia ni were twice as susceptible (at the LD 50 level) to the singly enveloped T. ni nuclear polyhedrosis virus as those parasitized by Hyposoter exiguae (Hymenoptera: Ichneumonidae). The LD 50 values for nonparasitized and parasitized larvae were 1.58 × 10 3 and 3.16 × 10 3 polyhedra/ml of diet, respectively. The LD 95 value for parasitized larvae was approximateely 5 times higher than that for nonparasitized larvae. The slopes ( b values) were 1.2 for parasitized larvae and 1.7 for nonparasitized larvae. The LT 50 values for parasitized larvae also were significantly longer than those for nonparasitized larvae. No significant difference was found between the food consumption of parasitized and nonparasitized T. ni larvae.

Natural control ofLiriomyza sativae [Dip.: Agromyzidae] in pole tomatoes in southern California

Liriomyza sativaeBlanchard and its associated parasites were monitored during the growing season on untreated fresh market tomatoes in southern California in 1978.Chrysonotomyia (Achrysocharella) punctiventris (Crawford) andChrysocharis parksiCrawford were the predominant larval and larval-pupal parasites, respectively, parasitizing the leafminer. A significant linear relationship was found between the percentage parasitization of viableL. sativae larvae byC. parksi and the number ofL. sativae viable pupae per sampling unit.RésuméLiriomyza sativaeBlanchard et ses parasites ont été dénombrés pendant une saison dans une culture maraîchère non traitée de tomates en Californie méridionale en 1978.Chrysonotomyia (Achrysocharella) punctiventris (Crawford) etChrysocharis parksiCrawford représentaient respectivement les parasites larvaires et larvo-nymphaux dominants de la mineuse des feuilles. Une relation linéaire significative a été obtenue entre le taux de parasitisme de larves viables deL. sativae parC. parksi et le nombre de pupes viables deL. sativae par unité d’échantillonnage.

Dispersion analyses and resource utilization of aphid parasitoids in a non-depletable environment

Dispersions and resource utilization of primary and secondary parasitoids developing in non-depletable primary host populations were determined for an aphid-parasitoid community occurring on strawberries. Analyses of dispersions based onGreens coefficient andLloyds Patchiness Index indicated parasitized aphids were highly aggregated initially, became less aggregated as density increased, and remained aggregated following collapse of the aphid populations. The “index of aggregation” values calculated usingTaylors Power Law concurred with results from the other indices, and the similarity of the regression coefficients from both seasons suggests that the index of aggregation may be characteristic for communities as well as species. Analysis withIwaos regression of mean crowding on the mean generated similar results when population data were stratified temporally, and also indicated that the individual was the basic unit of the population. In a non-depletable environment, oviposition of individuals exhibiting an aggregated dispersion pattern within clumps of hosts provides primary parasitoids with a suitable trade-off between energy utilization or genetic potential, and losses associated with hyperparasitism.

A Blacklight Trap Effective for Single Tree Sampling

Blacklight traps were used successfully for surveying fruit insect pest populations in Wisconsin orchards from 1956 through 1962 (Oatman 1964). The traps were of an omnidirectional design with a 15-w blacklight fluorescent lamp mounted vertically in the center of a single baffle. When suspended in an orchard, the light attracted insects from all directions for considerable distances. As a result, voluminous numbers of insects foreign to fruit trees were caught, especially on still, warm nights. Separating known pest species from even 1 nights catch was a laborious, time-consuming task.

Chemical Control of the Eye-Spotted Bud Moth on Sour Cherry in Wisconsin

Chemical control studies of the eye-spotted bud moth, Spilonota ocellana (Denis & Schiffermuuller), on sour cherry in Wisconsin from 1960 through 1961 showed that delayed dormant and post-harvest sprays of Sevin® (1-naphthyl N -methylcarbamate), parathion, malathion, Guthion® ( O,O -dimethyl S-(4-oxo-1,2,3-benzotriazin-3-(4 H )-ylmethyl) phosphorodithioate), diazinon, and phosphamidon gave good control of spring and summer larvae. Dormant sprays of dinitro materials did not give economic control of high populations. Timing and dosage were important factors in preventing larval feeding injury with the former being the more critical. A spray at the green-tip stage (when terminal leaf buds showed between ⅛- and ¼-inch green tip) was most effective for preventing fruit bud and pistil injury. A delay of 1 week meant the loss of 15 to 34% of the pistils, and 24 to 56% when delayed 2 weeks. Pistil destruction was kept below 1% by the most effective insecticides compared with 50 and 85% in the check blocks. Post-harvest sprays applied the latter part of August effectively reduced the over-wintering larval population to a level where a pre-blossom spray the following year would not be necessary. Higher dosage rates of Sevin were required to give control comparable to that obtained by lower dosages of the organophosphate materials.