Trapping oestrid parasites of reindeer: the response of Cephenemyia trompeand Hypoderma tarandi tobaited traps

Abstract. At 340–360 km North of the Arctic Circle in Norway, Hypoderma tarandi (L.) and Cephenemyia trompe (Modeer) females were caught in baited traps from 10 July to 21 August. During three summers, adverse climatic conditions inhibited flight activity of these oestrids on 56–68% of the days. Flies were not caught prior to or after these dates, nor at winds above 8 m/s, temperatures below 10C, light intensities below 20,000 lux, or during periods of rain or snow. C0₂-baited insect flight traps caught significantly more H. tarandi females than non-baited traps. However, neither a white reindeer hide or reindeer interdigital pheromone glands enhanced the attraction of C0₂to H. tarandi or C. trompe. Hypoderma tarandi females also were attracted to mobile people, but not to stationary individuals. There were no significant differences in the numbers of C.trompe or H.tarandi caught in C0₂-baited traps in a birch/willow woods, on the treeless vidda (=tundra-like biome), or at woodsrvidda ecotone sites. Flies were caught in traps on days when the nearest reindeer herds were 25–100 km away. Significantly more H.tarandi and C.trompe were caught from 09.30 to 14.30 hours than from 14.30 to 19.30 hours; no flies were caught from 20.00 to 07.00 hours (Norwegian Standard Time = NST). Because CO_z-baited traps caught from hundreds to thousands of mosquitoes, blackflies and Culicoides midges, when climatic conditions inhibited oestrid activity, reindeer aggregations and movements attributed to insect attacks during warm sunny days may be largely in response to attacks by H.tarandi and C.trompe.     

Factors affecting size, longevity and fecundity in the reindeer oestrid flies Hypoderma tarandi (L.) and Cephenemyia trompe (Modeer)

1. Laboratory reared reindeer oestrid flies Hypoderma tarandi and Cephenemyia trompe (Diptera: Oestridae) were weighed to determine progressive weight loss and death weights at treatments with various temperature and humidity conditions.
2. Four individual measurements of size were taken: larval weight, wet weight of newly eclosed flies, wing length, and weight of flies after dehydration and fat extraction. In H. tarandi, males were bigger than females (except for wing length), whereas the reverse was true for C. trompe .
3. Size variation was not significantly related to conditions (temperature, humidity, duration) during the pupal stage, but individual reindeer produced flies (both species) of different mean sizes. These size differences were not correlated with larval burden (= number of larvae per individual host), but are hypothesized to be connected to unknown host quality factors.
4. Longevity of flies kept in vials and subjected to various temperature and humidity conditions revealed that C. trompe lived significantly longer than H. tarandi (range: 4–44 and 1.2–27 days, respectively) at 5–33 °C. Male H. tarandi survived longer than females; female C. trompe survived longer than males. Longevity was not significantly correlated to any of the size measures.
5. Most flies had a large portion of their fat reserves left at death.
6. In H. tarandi , mean number of eggs was 609 ± SD 73 (range 354–772, n = 119). Egg number was slightly dependent on larval size, but not on wet weight of newly eclosed flies or wing length. In C. trompe , mean number of eggs was 960 ± SD 208 (range 493–1349, n = 31).
7. The possible adaptive value of large size in oestrids is questioned. Benefits of flexibility in size in oestrids are hypothesized.     

Moxidectin as an Endectocide in Reindeer

During the winter 1991–92, 42 reindeer hinds of the Kaamanen Experimental Reindeer Herd in Finnish Lapland, naturally infected with various parasites, were allocated to 3 groups. One group was an untreated control group and the other 2 groups received either moxidectin or ivermectin at a dose of 200 µg kg−1 subcutaneously. The efficacy of treatment was followed with monthly faecal examinations for nematode eggs and counting of warbles, Hypoderma tarandi larvae, and throat bots, Cephenemyia trompe larvae, from live animals in spring. The efficacy of moxidectin against warbles (92.8%) and throat bots (70.8%) did not match that of ivermectin, which was 100% against both species. Both moxidectin and ivermectin were effective against gastrointestinal trichostrongylid egg production over the December to May trial period indicating good efficacy against adult and inhibited trichostrongylids. Only non-significant differences were seen in weight development and calf birth weights between the groups. Because of its only moderate insecticidal efficacy, moxidectin cannot be recommended as an endectocide in reindeer.     

Abiotic factors influencing embryonic development, egg hatching, and larval orientation in the reindeer warble fly, Hypoderma tarandi

Wild-caught, tethered females of the reindeer warble fly, Hypoderma tarandi (L.) (= Oedemagena tarandi (L.)), (Diptera, Oestridae) were stimulated to oviposit on hairs of a reindeer hide. Newly laid eggs incubated at constant temperatures and relative humidities hatched within 3 days to 2 weeks, depending on the experimental conditions. Over a range of 7-40 degrees C, hatching only occurred between 20 and 37 degrees C. Eggs held at 100% relative humidity had lower hatchability and longer time to hatch relative to eggs held at 77% relative humidity. The average number of degree-days for hatching was 50.35. Between 20 and 33 degrees C there was a temperature-dependent linear trend in developmental rate, and the proportion of eggs hatching was highest, and least variable, at the mid-temperature ranges. The temperature range found in the natural host micro-habitat where H. tarandi commonly affix their eggs (close to the skin at the base of a host hair) was consistent with the experimental temperature treatments that produced the highest hatching rate. Newly emerged larvae displayed positive thermotaxis, while showing no phototaxic or geotaxic behaviour. Results indicate that constraints of the host environment, coupled with temperature-dependent hatching success, may impose a selective pressure on oviposition behaviour.     

Flight Performance of <Emphasis Type="Italic">Agrilus planipennis</Emphasis> (Coleoptera: Buprestidae) on a Flight Mill and in Free Flight

Computer-monitored flight mills were used to record the flight performance of the emerald ash borer, Agrilus planipennis Fairmaire. Flight performance of fed and unfed, and mated and unmated beetles of both sexes were recorded and compared. Mated females flew further per day and longer than unmated females or males. Mated females that were allowed to feed between flight periods flew an average of 1.3 km/day for four days; 10% flew more than 7 km/day. Measurements of free-flight speed using a mirror and a high-speed camera were used to calibrate the flight mill results, permitting absolute estimates of flight performance to be made. Free-flight speeds were approximately three times the speeds recorded by the flight mills. The median corrected distance flown by mated females was >3 km with 20% flying >10 km and 1% flying >20 km. The flight performance of mated females suggests a considerable capacity for range expansion by this invasive species. The implications for quarantine and control are discussed.     

Escaping parasitism in the selfish herd: age, size and density-dependent warble fly infestation in reindeer

It has been suggested that animals may escape attack from mobile parasites by aggregating in selfish herds. A selfish herd disperses the risk of being attacked among its members and the per individual risk of parasite infection should therefore decrease with increasing animal density through the encounter–dilution effect. Moreover, in a selfish herd, dominant and agile animals should occupy the best positions and thereby receive fewer attacks compared to lower ranked animals at the periphery. We tested these predictions on reindeer ( Rangifer tarandus tarandus ) parasitized by warble flies ( Hypoderma tarandi ). Warble flies oviposit their eggs on reindeer during summer and induce strong anti-parasitic behavioural responses in the herds. In this period, reindeer are sexually segregated; females and calves form large and dense herds while males are more solitary. After hatching, the warble fly larvae migrate under the skin of their host where they encyst. In the present study encysted larvae were counted on newly slaughtered hides of male calves and 1.5 year old males from 18 different reindeer herds in Finnmark, northern Norway with large contrasts in reindeer density. In reindeer, body mass is correlated with fitness and social status and we hypothesized that individual carcass mass reflected the animal's ability to occupy the best positions within the herd. Larval abundance was higher among the 1.5 year old males than among the calves. For calves we found in accordance with the selfish herd hypothesis a negative relationship between larval abundance and animal density and between larval abundance and body mass. These relationships were absent for the 1.5 year old males. We suggest that these differences were due to different grouping behaviour where calves and females, but not males, aggregated in selfish herds where they escaped parasitism.     

Tethered flight of the potato moth, Phthorimaea operculella

ABSTRACT. The effects of sex, age and mated state on average flight speed, duration and distance were determined for potato moths, Phthorimaea operculella (Zeller) (Lepidoptera, Gelechiidae), tethered to flight mills. Moths were classified as non-fliers (NFs), good-fliers (GFs) and remaining-fliers (RFs) on the basis of their performance over the first two flights. Some moths flew for over 5 h non-stop, while others tethered overnight flew between 20 and 30 km. Speed, duration and distance flown were greater during the first flight. First flight duration and distance flown by females decreased with age, whereas no trend was evident for males. Mated males and females flew slower first flights with increasing age, whereas virgin moths showed no marked trend. The analysis of fliers and NFs revealed that GFs were heavier than both RFs and NFs, GFs were faster than RFs, the percentage of NFs increased with age especially for mated females, and the percentage of GFs decreased with age. Age and mated state are important factors influencing flight performance especially for female moths. The relevance of these results to the field situation and the possible application of tethered flight to tests of potato moth quality are discussed.     

Relative flight responses of Rhagoletis indifferens as influenced by crowding, sex, and resources

Although flight is believed to be the primary mechanism for dispersal in the Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), an orchard pest of both sweet (Prunus avium L.) and sour (Prunus cerasus L.) (Rosaceae) cherry crops, the movement of these flies between host patches is difficult to quantify in the field. A tethered flight mill system was used in the laboratory to examine the flight behaviour of sexually mature flies exposed to different levels of conspecific contact and resource availability. A complete 2 × 2 × 3 factorial design compared the relative influence of the factors ‘context’ (crowded, isolated), ‘sex’ (female, male), and ‘resources’ (low = food only; medium = food + leaf; high = food + leaf + cherries) on flight performance measures including distance flown, net trial time, and stopping patterns. Rather than using a minimum time or distance to determine trial length, flight observations were continued for each fly until a behavioural protocol based on stopping time was met. In this protocol each successful trial was composed of three consecutive flight intervals and included a minimum of three stops lasting a combined total of 5 min. Of the 160 flies tested, 86.9% flew <500 m on the flight mill. Individuals from both sexes were capable of maximum flights in the same order of magnitude, ca. 3 km on the flight mill. Distance flown was significantly influenced by ‘context’ such that crowded individuals flew >1.5-fold farther than isolated individuals. Sex influenced the frequency and duration of stops made, with females stopping more often and longer than males. Although females and males in high resource treatments had the shortest net trial times, the factor ‘resources’ did not produce any highly significant main effects, but did generate significant interaction terms with the factors ‘context’ and ‘sex’, suggesting that past experience with ‘resources’ modifies individual flight behaviour. We have shown for the first time using a tethered flight mill system that R. indifferens flight behaviour is context dependent and sensitive to adult crowding. The implications of this study for improved field experiments on dispersal are discussed.     

The causes of seasonal changes in numbers of the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)

ABSTRACT. 1. Counts of adult Scathophaga stercoraria (L.) on cow pats were made in Houghall, County Durham, in 1964 and 1965.
2. A spring peak of numbers was due to adults (overwintered mainly as pupae or larvae) maturing and going to dung to breed. Numbers then dropped, rising to one or more peaks in late June—early July. In 1964 there was then a summer drop in numbers until late September. In 1965 high numbers persisted in summer associated with cooler, wetter weather. Autumn peaks in both years persisted until severe frosts or snow.
3. Mature adults, developed from eggs laid during the spring peak, form the first generation when breeding in mid-late June. No clear generations can be identified after this, due to eggs being laid daily (females have successive gonotrophic cycles). Changes in adult numbers breeding reflects survival of eggs and newly-hatched larvae 5–6 weeks earlier, and lower survival rates of adults in mid-summer compared with spring and autumn.
4. Adult Scathophaga numbers in vegetation rose as numbers on dung dropped. Females dissected to count ovariole tunica dilatations showed that most flies in vegetation were immature, with some parous flies hunting insects to develop the next batch of eggs.
5. Females on dung were dissected and found to range from immature to seven-parous. Those gravid for the first time were grossly under-represented, possibly due to wider dispersal.
6. It is suggested that seasonal changes in this r-strategist cannot be explained simply in terms of generations nor by the occurrence of adult diapause.     

Mating behavior and thermoregulation of the reindeer warble fly,Hypoderma tarandi L. (Diptera: Oestridae)

Hypoderma (=Oedemagena) tarandi L. (Diptera: Oestridae) is characterized by a mating strategy in which both sexes meet and mate at two types of distinct topographical landmarks. In the expansive, treeless vidda (= tundra-like) biome, mating places are unique, rocky areas located along rivers and streams or in rocky areas of drying river and stream beds. In wooded valleys below the vidda, flies mated at certain topographical areas along dirt road tracks/paths. Thermoregulatory activities of males occupying perches at mating places included selection of substratum at perch site, orientation of body to sun's rays, crouching, stilting, and flights into upper cooler air. On warm sunny days males perched for just 1–2 min before flying up into cooler air to promote cooling. Laboratory and field studies revealed that flies could not metabolically cool down when held at 25–38°C. Time spent at mating places depended on temperature, duration of sunshine, and wind velocity. Males were very aggressive in pursuing allHypoderma-sized objects that passed by them or that landed near them, but they did not defend specific perch sites. Males either pursued and caught females in flight, or they hopped onto females that landed near them. During 5 years, 74 males and 14 females were seen at mating places. Dissection of six females caught at mating places revealed them to be recently eclosed flies full of fat body and with all eggs intact; two not paired with males were non-inseminated. Three experimentally paired females remainedin copulo for 10, 13, and 19.5 min.     

Age structure of overwintered face fly populations estimated by pteridine concentrations and ovarian dynamics

Pteridines in the head capsules of face flies, Musca autumnalis DeGeer, were measured spectrofluorometrically to provide estimates of age. The flies also were dissected to determine ovarian development and fat body hypertrophy. Physiological ages in terms of degree-day accumulations were estimated among late autumn, winter, and early spring face flies. The reproductive history of eight overwintered face fly populations near Ames, Iowa, U.S.A., suggested that each had behaved as a single cohort, maturing their eggs and ovipositing according to a simple heat unit model. 83.8 +/- 16.4 degree-days above a 12 degrees threshold (DD > 12 degrees) were estimated to elapse between 1 January and the date at which 50% of overwintered cohorts had oviposited. Pteridine deposits indicated that diapausing females in late autumn had acquired a mean 96 +/- 36 DD > 9.8 degrees and the males 135 +/- 39 DD > 9.8 degrees. Soon after emergence from hibernaculae, females were average physiological ages of 135 +/- 25 DD > 9.8 degrees and the males were 152 +/- 28 DD > 9.8 degrees. Mean physiological age of overwintered females was 155 +/- 37 DD > 9.8 degrees compared with 110 +/- 38 DD > 9.8 degrees among parous flies in summer. Overwintered males in spring were an average 175 +/- 41 DD > 9.8 degrees compared with 144 +/- 65 DD > 9.8 degrees among summer flies.     

Upwind flight by the cabbage root fly, Delia radicum

ABSTRACT. In fourteen releases, most female D.radicum (L.) (Diptera, Anthomyiidae) flew upwind or at an angle to it of less than 77° regardless of the presence of host-plant odour. Females ready to lay eggs flew upwind without prior stimulation by odours from either a host crop or a trap releasing up to 3 ml/day of the attractant allylisothiocyanate. Upwind flight was more pronounced in flies from a diapause than from a continuous, non-diapause culture. Males from the non-diapause culture dispersed upwind and downwind in more or less equal numbers; old males flew mainly downwind. But, like the females, most males from the diapause culture flew upwind. Long-distance, odour-modulated anemotaxis did not appear to be used to locate distant host crops by either sex. It is concluded that the distances of insect orientation to plant odours recorded to date are only of intermediate range, and that long-range orientation to the odours of a host-plant still has to be proven. It is suggested that host-plant volatiles are involved not only in the final stage of host location but also in the first, and probably most important stage of host selection whilst the insect is still in flight.     

The relationship of age and ovarian development to mating of Delia antiqua (Diptera: Anthomyiidae)

Abstract. The relationship between age and sexual receptivity for male and female onion flies, Delia antiqua (Meigen) (Diptera: Anthomyiidae), and factors affecting ovarian development were examined under various conditions. Confinement in small arenas had a significant negative effect on the rate of oogenesis over the first 10 days of adult life and, in some cases, on the percentage of females inseminated. The rate of oogenesis was not affected by male population density, but high density of females in large arenas appeared to have a priming effect. Few males in single-pair mating bioassays conducted over 24 h were sexually mature at 3–4 days post-eclosion, but > 50% mated when aged 6–7 days. Although females first mated at 3–4 days post-eclosion when confined for 24 h with sexually mature males, most females mated at 6–7 days of age when oocytes in the terminal ovariole position comprised 50% of total egg volume (stage 7 or greater on a 10-stage scale). No females aged 3 days were mated in no-choice and two-choice bioassays with sexually mature males over 24 h. Previtellogenic females (stage 3) were not inseminated, and ovarian development was only correlated weakly ( r = 0.48) with mating. Frequency of mating in mixed-sex groups of twenty flies was comparable with that in single pairs. However, more females were inseminated at 3–4 days, probably as a result of multiple matings by a few precocious males. These results do not support the hypothesis that females mate only when ovarioles are mature.     

刀豆氨酸对亚洲玉米螟生长发育的影响

以不同浓度刀豆氨酸注射和饲喂亚洲玉米螟`Ostrinia furnacalis`` 5龄幼虫,影响其以后各虫态的生长发育,有引起畸蛹和畸蛾的明显作用,发育成的雌蛾性腺发育受到抑制,卵管变短,卵细胞数减少。不同交配实验表明对发育成的雄蛾影响更为严重,能使其不育。供试幼虫48小时后取血样,表明血淋巴蛋白质区带与对照组不同,认为刀豆氨酸对亚洲玉米螟的上述作用可能与刀豆氨酸取代精氨酸参入蛋白质的结果有关。     

Lifetime ovipositional patterns of mated and virgin onion flies,Delia antiqua (Diptera: Anthomyiidae)

Over their 47.2±1.9 (mean±SEM) day lifespan, mated onion flies, Delia antiqua, oviposited more uniformly than did virgins. Mated females began ovipositing at 6.4±0.2 days old and regularly deposited 14.2±0.6 eggs/day for 3-4 weeks. Thereafter, oviposition slowed and stopped at about 1 week before death. Virgin flies began ovipositing 24.7±1.5 days into their 59.0±3.8 day lifespan, and deposited eggs at an increasing rate for 3-4 weeks, generating a mean overall ovipositional rate of 5.8±0.5 eggs/day. The later onset of virgin oviposition (ovipositional activation) and not a shorter ovipositional period largely accounted for the disparity between virgin and mated female lifespans. Mean lifetime egg production of mated females was 475±27 eggs versus 179±30 eggs for virgins. Ovipositional and post-ovipositional periods (34.4±1.8 and 7.2±1.0 days) for mated females were not significantly different from those of virgin females (30.9±3.6 and 6.7±1.2 days). Over 90% of virgin females laid eggs. The distinction between mated and virgin ovipositional patterns may be specifically attributed to differences in: (1) egg maturation, (2) age at ovipositional activation, and (3) egg-laying rate.     

Some aspects of oögenesis in the stable fly Stomoxys calcitrans (Diptera: Muscidae)

Two distinct patterns of blood ingestion in the female stable fly, Stomoxys calcitrans L. were observed, based on whether or not the female was mated. Mating is not required for oögenesis, but is necessary for oviposition. Virgin females develop eggs but, in the absence of mating, they retain eggs until death. In stable flies, oögenesis appears to be atypical among other dipterans as the penultimate follicles develop and deposit up to 50% yolk before the terminal follicles are matured. Oösorption was seen in the penultimate follicles of virgin females retaining eggs. Accessory-gland implants initiated oviposition in virgin females. However, the total number of eggs laid by such females was 50% less than the number of eggs laid by mated flies.     

The effects of temperature on development of the large narcissus fly (Merodon equestris)

Eggs, larvae, pupae and adults of the large narcissus fly (Merodon equestris) were reared at a series of constant temperatures between 9–24°C. Egg development required from 37 days at 9°C to 7 days at 21.5°C. The low-temperature threshold for development was 6.7°C. Larvae reared at 1424°C were fully-grown after 18 weeks, but it took much longer for such insects to pupate, and adult flies emerged only after about 45 weeks of development. Large narcissus flies enter diapause during the larval stage and overwinter as fully-fed larvae, forming pupae in the following spring. Post-winter pupation and pupal development took from 169 days at 10°C to 36 days at 21.5°C. Of this, pupal development required from 91 days at 10°C to 19 days at 21.5°C. The low-temperature threshold for post-winter pupation and pupal development was 7.1°C, and for pupal development alone, 7.2°C. Females maintained at or below 19°C laid few eggs, whereas some females kept at or above 21.5°C laid more than 100 eggs (mean 69 ± 36). Approximately 50% of females maintained at or above 21.5°C laid less than 10 eggs during their lifetime. The mean egg-laying time was 6 to 9 days. Although temperatures at or below 19°C inhibited mating, once a female had mated, such temperatures did not prevent oviposition.     

Activity patterns in Glossina longipennis : a field study using different sampling methods

Abstract .Studies on the daily activity of Glossina longipennis at Galana Ranch using a black odour-baited electrocuting target confirmed its crepuscular activity profile. Activity started at 05.00–05.30 hours and peaked at 06.00–06.30 hours, stopped by 09.00 hours, then started again at 17.00–17.30 hours with a peak at 18.30–19.00 hours, ceasing by 19.30 hours. Females made up 60% of the overall catch, and tended to arrive later than males. Other stationary sampling methods (trap, stationary ox) gave similar results. With the stationary methods, very few flies were caught outside the periods of peak activity (only 1.5% of the total between 09.00 and 17.00 hours); the ox was the only stationary bait to catch any flies between 10.00 and 16.00 hours. More flies were caught throughout the day at mobile baits (8.3% of the male and 2.3% of the female catch was taken between 09.00 and 17.00 hours). Mobile baits caught considerably more males than females (females were 17% of the catch). These males had on average higher fat and haematin reserves. Similar nutritional differences were not observed for females. There were fewer older females (ovarian category 3 or more) in mobile compared to stationary baits, and a lower proportion of the youngest males (wing fray category 1) at natural compared with artificial baits.     

Avoidance of occupied hosts by the Hessian fly: oviposition behaviour and consequences for larval survival

Abstract 1. Unoccupied wheat plants and wheat plants occupied by conspecific eggs or larvae were presented to ovipositing female Hessian flies in choice tests.
2. The presence of conspecific eggs on the leaf surfaces of wheat plants did not appear to have any effect on the responses of ovipositing Hessian fly females.
3. The presence of conspecific larvae at the base and nodes of wheat plants for 1, 6, or 11 days had significant effects on Hessian fly oviposition. Eggs oviposited on plants were inversely proportional to larval densities and days of larval occupation.
4. Feeding by Hessian fly larvae is associated with several changes in wheat plants. One of these changes, the growth arrestment of the plant, was measured by recording the heights of plants used in oviposition tests. Plant heights were inversely proportional to both larval densities and days of occupation. Plant heights were directly proportional to eggs oviposited on plants.
5. The consequences of adult female avoidance of plants occupied by conspecific larvae were investigated by allowing females to oviposit on unoccupied plants and 1-day, 6-day, and 11-day larval occupied plants, then scoring at the end of the first larval instar the survival of the offspring that resulted from this oviposition.
6. Survival during the first larval instar was 88% for the offspring of females that oviposited on unoccupied plants, decreasing to 82, 31, and 4% on the 1-day, 6-day, and 11-day occupied plant treatments. On these four plant treatments, a positive correlation was found between larval performance (i.e. survival) and the preferences of ovipositing females.
7. On the four plant treatments, relationships between first-instar larval density and first-instar larval survival varied significantly. On unoccupied plants, survival was inversely proportional to density. On plants oviposited on at 6 days of larval occupation, survival was directly proportional to density.     

Impact of a novel species of Nosema on the southwestern corn borer (Lepidoptera: Crambidae)

A study was undertaken to elucidate the impact of an undescribed Nosema sp. on the southwestern corn borer (SWCB; Diatraea grandiosella Dyar). The Nosema sp. (isolate 506) included in the study was isolated from an overwintering SWCB larva in Mississippi. It was highly infectious per os, with a median infective dose of 2.0 x 10(3) spores per larva. Even at the highest dosage tested (10(7) spores per larva), minimal mortality (< or = 3%) was observed in infected larvae, pupae, and adults reared in the laboratory on an artificial diet. However, infected pupae (0- and 7-d-old) were smaller, and the time to adult eclosion from pupation was slightly increased. Furthermore, the number of eggs produced by infected SWCB female moths substantially decreased (32%), and this effect was most pronounced on day 2, when the greatest number of eggs were oviposited by infected and noninfected moths. For eggs produced by infected females mated with infected males, hatch was slightly decreased by 16 and 15% for eggs laid on days 2 and 3, respectively. In addition, egg hatch was reduced in eggs oviposited by noninfected females mated with infected males on day 3. A low prevalence of infection (< 6%) was observed in the F1 generation originating from infected females mating with noninfected males, from noninfected females mating with infected males, and from infected females mating with infected males. Nosema 506 spores were observed in the proximity of reproductive tissues of infected female and male moths. Spores also were detected on the chorion surface and within eggs laid by infected females. Furthermore, 1-11% of larvae hatching from surface-sterilized eggs were infected by Nosema 506 indicating a transovarial mechanism of transmission.