Edovum Puttleri Research Articles

Foreign exploration for natural enemies of the Colorado potato beetle in Central and South America

Abstract To expand the area searched for natural enemies of the Colorado potato beetle, Leptinotarsa decemlineata (Say) we collected throughout Honduras, Guatemala, and El Salvador and also made collecting trips to Colombia, Bolivia, and Ecuador. In South America the only Leptinotarsa beetles encountered were L. undecimlineata (Say) collected in Colombia, where few natural enemies were found. In Central America, L. undecimlineata Stal was again the only Leptinotarsa collected, and this species was found commonly on several wild Solanum species. Among natural enemies collected from L. undecimlineata were several species of tachinid parasitoids (Myiopharus spp.), the egg parasitoid Edovum puttleri Grissell, and several hyperparasitic species (Exoristobia sp., Perilampus sp., and Conura n. sp.). Only one pathogen, the microsporidium Endoreticulatus fidelis (Hostounsky and Weiser) was found. Predators included a number of generalists, primarily of the egg, and early larval stages. The ectoparasitic mite, Chrysomelobia spp., was also observed under the elytra of infested beetles. Although many of the natural enemies had been discovered previously, options for importation biological control of L. decemlineata could be improved by a better understanding of the taxonomy of existing groups, determination of the specificity of the beetle’s hyperparasitoids and predators, and further study of the impact of ectoparasitic mites and natural enemies attacking the pupal stage. Finally, the spatial and temporal occurrence of Leptinotarsa on their host plants suggest meta-population effects that could serve as selective forces influencing the densities and diversity of beetle natural enemies.

Artificial diets for rearing the Colorado potato beetle, <italic>Leptinotarsa decemlineata</italic>

Colorado potato beetles have been reared successfully through 12 generations on artificial diets containing either 2.5% potato leaf powder or 2.5% lettuce leaf powder/0.75% potato leaf powder. For all but one of the treatment groups, the mean duration of each of the four larval stages was between 0.8 and 1.5 days longer than the durations exhibited by control beetles that had been fed on potato leaves. Maximum weights of prepupae, newly emerged adults and day 5 - 9 adults were approximately 78, 80 and 82%, respectively, of the weights for comparable stages of control beetles. Mean percent mortality for 1 st instars was two to six times higher for artificial diet-fed CPBs than for leaf-fed beetles. However, since pupal mortality was four times higher for control beetles than for beetles reared on artificial diet, mean percent total mortality (newly hatched through the 9 day old adult) was equivalent for leaf-fed beetles and for later generations of potato and Lettuce+Potato diet-fed CPBs. Hemolymph ecdysteroid levels and fluctuations in mature 4 th instar larvae and prepupae were similar in controls and experimental groups. Number of hatchlings produced per adult pair per day (fertility) was approximately eight times greater in control beetles than in later generations of artificial diet-fed beetles, primarily because fewer egg masses were laid per day, percent hatch was lower and cannibalism of eggs was higher in these latter groups. Interestingly, the mean percent hatch, although only 68% of the control value, was 1.5 times greater for beetles reared on diet containing lettuce-leaf powder, and a small percentage of potato leaf powder, than on diet containing only potato leaf powder. Percent hatch was equal for beetles fed on diet containing only lettuce-leaf powder and those fed on potato leaves. Finally, it is noteworthy that the quality of eggs, as judged by the ability of the wasp parasitoid, Edovum puttleri , to parasitize and develop in the eggs, was similar for eggs produced by control beetles and for those produced by beetles fed on potato and Lettuce+Potato diets. The diets and rearing system described here will be useful for providing beetles on a year-round basis for experiments designed to evaluate the effects of potential insect control agents, to investigate the mechanism(s) by which insects become resistant to control agents and for other applied and fundamental studies related to the control of this serious pest. The use of lettuce leaf powder in place of most of the potato leaf powder is especially advantageous because of the much reduced cost and greater availability of lettuce as compared to potato leaves.

Artificial diets for rearing the Colorado potato beetle, Leptinotarsa decemlineata

Colorado potato beetles have been reared successfully through 12 generations on artificial diets containing either 2.5% potato leaf powder or 2.5% lettuce leaf powder/0.75% potato leaf powder. For all but one of the treatment groups, the mean duration of each of the four larval stages was between 0.8 and 1.5 days longer than the durations exhibited by control beetles that had been fed on potato leaves. Maximum weights of prepupae, newly emerged adults and day 5-9 adults were approximately 78, 80 and 82%, respectively, of the weights for comparable stages of control beetles. Mean percent mortality for 1(st) instars was two to six times higher for artificial diet-fed CPBs than for leaf-fed beetles. However, since pupal mortality was four times higher for control beetles than for beetles reared on artificial diet, mean percent total mortality (newly hatched through the 9 day old adult) was equivalent for leaf-fed beetles and for later generations of potato and Lettuce+Potato diet-fed CPBs. Hemolymph ecdysteroid levels and fluctuations in mature 4th instar larvae and prepupae were similar in controls and experimental groups. Number of hatchlings produced per adult pair per day (fertility) was approximately eight times greater in control beetles than in later generations of artificial diet-fed beetles, primarily because fewer egg masses were laid per day, percent hatch was lower and cannibalism of eggs was higher in these latter groups. Interestingly, the mean percent hatch, although only 68% of the control value, was 1.5 times greater for beetles reared on diet containing lettuce-leaf powder, and a small percentage of potato leaf powder, than on diet containing only potato leaf powder. Percent hatch was equal for beetles fed on diet containing only lettuce-leaf powder and those fed on potato leaves. Finally, it is noteworthy that the quality of eggs, as judged by the ability of the wasp parasitoid, Edovum puttleri, to parasitize and develop in the eggs, was similar for eggs produced by control beetles and for those produced by beetles fed on potato and Lettuce+Potato diets. The diets and rearing system described here will be useful for providing beetles on a year-round basis for experiments designed to evaluate the effects of potential insect control agents, to investigate the mechanism(s) by which insects become resistant to control agents and for other applied and fundamental studies related to the control of this serious pest. The use of lettuce leaf powder in place of most of the potato leaf powder is especially advantageous because of the much reduced cost and greater availability of lettuce as compared to potato leaves.

In vitro rearing of Edovum puttleri, an egg parasitoid of the Colorado potato beetle, from egg to pupal stage in artificial diets devoid of insect sources: Effects of dietary amino acid and carbohydrate levels

Previous studies have demonstrated that Edovum puttleri, an egg parasitoid of the Colorado potato beetle, can be reared through the pupal stage in an artificial diet containing either hemolymph from Manduca sexta or CPB embryonic cell line-conditioned medium. In order to improve the diet and reduce production costs, i.e., eliminate the insect-derived components, the effects of 13 amino acids and 20 carbohydrates on the growth and development of the parasitoid were determined. In the presence of any one of five of the amino acids (arginine, glutamine, lysine, threonine and valine) at a concentration of 1%, or eight of the carbohydrates (cellobiose, fructose, gentiobiose, glucose, lactose, melinbiose, sorbitol and threhalose), also at a concentration of 1%, more than 75% of the larvae molted to the second instar. At higher concentrations (2 and 3%), all five of the amino acids and most of the eight sugars promoted third instar formation. Prepupal formation was also observed. In the presence of threonine (at 2 and 3%) or glutamine (at 3%), between 22 and 29% of the parasitoids formed prepupae. Of the six sugars (at 3%) that promoted prepupal formation, lactose and sorbitol which promoted 18 and 20% prepupation, respectively, were the most effective. In the presence of all 13 amino acids (each at 3%) or all 20 carbohydrates (each at 3%), 36 and 39%, respectively, of the parasitoids formed prepupae. At lower concentrations, reduced percentages of prepupal formation were observed. Since the amino acids, glutamine and threonine, and the sugars, fructose, gentiobiose, glucose, lactose, sorbitol and trehalose, when added individually to the diet (at a concentration of 3%) were most effective in promoting prepupal formation, the effect of one of these two amino acids in combination with each of the six sugars was tested. Glutamine in combination with lactose or sorbitol was able to promote pupation (≤6.3%), and threonine in combination with any one of five of the sugars (lactose and sorbitol were most effective) supported pupal formation (≤6.7%). Our study demonstrated that E. puttleri can be successfully reared from the egg through the pupal stage in an artificial diet devoid of insect materials.

Irradiation of Colorado potato beetle eggs—effect on parasitism by the wasp Edovum puttleri

Summary In order to extend the period of time during which Colorado potato beetle (CPB) eggs are suitable hosts for the parasitic wasp Edovum puttleri, CPB eggs were subjected to various doses of gamma radiation between 2.5 x 104 and 5.0 x 106 rads prior to storage. For given storage times there were specific doses of radiation that resulted in notably, but not significantly, higher percent absolute emergence (number of adult wasps that emerged/total number of CPB eggs exposed to E. puttleri). After 7 days of storage, absolute emergence was highest after exposure to 2.5 x 104, 4.4 x 105 and 1.2 x 106 rads; and after 14 days of storage it was highest after exposure to 4.4 x 105 and 1.2 x 106 rads. For these doses of radiation and storage times, percent absolute emergence was equal to 40 ± 8%, a value that overlaps the range reported for CPB eggs that have not been irradiated. With increased storage time, absolute emergence dropped below 25%. While storage of irradiated eggs had a negative effect on percent parasitization, it did not affect the percentage of wasps that emerged (percent emergence = number of adult wasps that emerged/number of CPB eggs that were parasitized) from parasitized eggs. Percent emergence from non-irradiated eggs has been reported to average 78%, while in these studies, percent emergence from irradiated eggs typically was greater than 90%. Irradiation and storage of CPB eggs had little effect on the weights of adult wasps, and these wasps appeared to be active and in good condition. However, for unfed adult wasps, longevity decreased with increasing doses and storage times. Gamma irradiation of CPB eggs can be used to kill developing CPB embryos and to prevent deterioration of the host eggs. Our results show that irradiation can increase the period of time (from 72h to 14 days) in which CPB eggs are suitable hosts for rearing E. puttleri.

Ecdysteroid and free amino acid content of eggs of the Colorado potato beetle, Leptinotarsa decemlineata.

In order to identify components of the Colorado potato beetle (CPB) egg that may be required by Edovum puttleri, a parasitic wasp that parasitizes the CPB egg, to complete development, ecdysteroid and free amino acid content of CPB eggs were analyzed by reversed phase high pressure liquid chromatography followed by radioimmunoassay to identify ecdysteroids. Ecdysteroid titers were relatively low (<300 pg/egg) through day 2 post-oviposition and then increased sharply, reaching concentrations >2,500 pg/egg on day 3 post-oviposition. Ecdysone (E), 20-hydroxyecdysone (20E), and polar conjugates of E were prominent ecdysteroids present in eggs sampled on days 0 and 1 post-ecdysis, and E, 20E, three peaks containing more polar ecdysteroids (metabolic inactivation products), and polar conjugates of E were present in eggs sampled on day 2. Thus, at a time when parasitization of CPB eggs by E. puttleri is relatively high (0-48 h), physiologically-active ecdysteroids (20E and perhaps E are physiologically active) are present at concentrations between 50 and 200 pg/egg. Ecdysone and 20E reached their highest levels in day-3 eggs, indicating that ecdysteroid may direct physiological processes associated with the completion of CPB embryonic development. In day-4 eggs, the concentration of E and 20E fall dramatically and polar metabolites of E and/or 20E are now responsible for the high ecdysteroid content of the eggs. Interestingly, conjugates of E decrease to relatively low levels in day-3 eggs and are absent in day-4 eggs. Therefore, it is likely that the increase in E in day-3 eggs is due, in part, to the breakdown of polar conjugates of E. Nine amino acids were present in significant quantities in eggs sampled at various times between 0 and 48 h post-oviposition. These include histidine, glutamine, proline, asparagine, serine, glutamic acid, threonine, lysine, and tyrosine. The first three amino acids were present at concentrations that were approximately 2 to 6 times greater than the concentrations of the last six amino acids. Amounts of most of the free amino acids varied with the age of the eggs from which the extract was prepared, but in general, there was no correlation between the levels at times of maximum parasitization (0 and 30 h) and the levels at the less favored times of parasitization (16 and 48 h). This information should facilitate the development of diets for both parasites and predators of pest species of beetles. Arch. Insect Biochem. Physiol. 44:172-182, 2000. Published 2000 Wiley-Liss, Inc.

Life History Characteristics of Three Populations of Edovum puttleri Grissell (Hymenoptera: Eulophidae) at Three Temperatures

Abstract The exotic egg parasitoid Edovum puttleri Grissell has shown promise for biological control of the Colorado potato beetle, Leptinotarsa decemlineata (Say). However, because the activity of currently available populations is decreased at low temperatures, the use of biotypes of E. puttleri adapted to low temperatures may provide more effective control. To determine if there are populations of E. puttleri adapted to low temperatures, the life history characteristics of three populations collected in Honduras were compared at three temperatures (15, 24, and 30°C) over three generations. In general, life history characteristics differed between the first generation and subsequent generations. Among temperatures, parasitoids reared at 24°C were more reproductively active, lived longer, and survived better than those reared at other temperatures. At the lowest temperature, there was a significant difference in the frequency of total egg production, with females from the “River” collection site producing more eggs than females from the other two sites. Coincidentally, the River area is located at the highest elevation and experiences a cooler climate. Comparison of E. puttleri collected in Honduras, Colombia, and Mexico showed differences in life history characteristics. The implications for this study for selection of biotypes of E. puttleri are discussed.

Evaluating Edovum puttleri Grissell and Podisus maculiventris (Say) for Augmentative Biological Control of Colorado Potato Beetle in Tomatoes

Multiple releases of Edovum puttleri Grissell (Hymenoptera: Eulophidae) and Podisus maculiventris (Say) (Heteroptera: Pentatomidae) resulted in increased parasitism and predation rates of eggs of Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), in small plots of staked tomatoes grown in plastic or hairy vetch mulch. No consistent effect of the mulch on CPB infestations was found over the years of the study. No parasitism by E. puttleri occurred in 1995, while parasitism ranged from 0 to 30.6% per sample date in 1997. P. maculiventris nymphs were found at higher densities in release plots and readily attacked CPB egg masses. Despite the ability of both beneficials to search the structurally complex plant and find the pest, the cost of maintaining release rates that were high enough to achieve significant control of the pest would be prohibitive on a larger scale.

Effects of selected physical and chemical treatments of Colorado potato beetle eggs on host acceptance and development of the parasitic wasp, Edovum puttleri

Effects of various physical and chemical treatments of Colorado potato beetle [Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)] eggs on parasitization and development of the egg parasitoid Edovum puttleri (Hymenoptera: Eulophidae) were investigated. UV irradiation did not affect host acceptance but reduced host suitability for UV exposure times greater than or equal to 90 min. Susceptibility of host eggs to UV irradiation varied with host age; eggs were most vulnerable to damage from irradiation at 12, 18, and 24 h post-oviposition. The rate of parasitization also was influenced by host age. Percent parasitization was greatest in freshly laid eggs and 24-30 h old eggs. Seventy-seven percent of host eggs frozen at -20 degrees C (5 min) were parasitized by E. puttleri, but extended exposure of eggs to -20 degrees C reduced both acceptance and suitability. Host eggs that had been washed with hexane (removal of kairomone and sticky layer) also were parasitized. After 5 min of washing, application of kairomone significantly increased the rate of parasitism (from 74.7% to 88.2%), but with longer periods of washing, kairomone application had no significant effect on percent parasitism. Thus, the sticky material(s) coating the egg did not appear to be essential for parasitization to occur. Our results provide effective methods and times for treating Colorado potato beetle eggs to maximize parasitization and development of E. puttleri.

Responses of two parasitoid wasps to nectar odors as a function of experience

AbstractAdult parasitoid wasps can learn to recognize specific resource‐based cues, making them adept at locating essential resources within their native habitats. However, relatively little is known about their ability to recognize the odors emitted by flowers and extra‐floral nectar glands. A novel test arena mimicking the distribution of nectaries within an umbelliferous inflorescence was developed to measure and compare the responses of two eulophid wasps, Edovum puttleri and Pediobius foveolatus, to nectar‐based odors. Although both parasitoid species were able to associate nectar location with the odors emitted by both real nectaries (dill flowers and snap bean stipules) and artificial nectars (1 M sucrose solution scented with banana or lemon food flavoring), the responses of inexperienced wasps to nectary odors differed. While inexperienced E. puttleri displayed little attraction to the odor of either dill flowers or snap bean stipules, inexperienced P. foveolatus displayed a strong attraction to odors of both types of nectaries. However, once it had experienced foraging on either dill or snap bean nectar, E. puttleri responded to those nectary odors as strongly as did P. foveolatus. The responsiveness of both wasp species to the odor of artificial nectar greatly increased after they foraged on sugar solution scented with either banana or lemon odor. That parasitoid wasp species can differ in their ability to recognize food‐based cues is of fundamental and applied importance.

In vitro rearing of Edovum puttleri, an egg parasitoid of the Colorado potato beetle, on artificial diets: Effects of insect cell line‐conditioned medium

In vitro rearing of Edovum puttleri, an egg parasitoid of the Colorado potato beetle, on artificial diets: Effects of insect cell line‐conditioned medium

In vitro rearing of Edovum puttleri, an egg parasitoid of the Colorado potato beetle – development from egg through the pupal stage

A variety of semi-defined artificial diets were developed and tested for their ability to support the in vitro development of Edovum puttleri. In the most effective diet, 2.6% of E. puttleri pupated. This diet contained high levels of hen egg yolk combined with Manduca sexta larval hemolymph, or with a mixture of M. sexta egg homogenate and larval hemolymph. Egg homogenate alone (without the addition of hemolymph) was not capable of supporting the parasitoid's development. Thus, hemolymph appears to contain unidentified factor(s) important for inducing pupation of the wasp. Addition of M. sexta pupal fat body tissue extract (in place of hemolymph) also promoted pupation of E. puttleri. Gypsy moth (Lymantria dispar) larval hemolymph could not replace M. sexta larval hemolymph. Fractionation irreversibly reduced the growth-promoting effects of M. sexta larval hemolymph. However, the most effective fraction contained components whose molecular weights were ≥1000 kd. In diets that were devoid of insect materials, the best results were achieved when hen egg yolk, FreAmine, yeast extract, lactalbumin, trehalose, fetal bovine serum and bovine milk were included. This is the first report of an artificial diet for in vitro rearing an eulophid parasitoid from the egg through the pupal stage.

Alightment of Edovum puttleri Grissell (Hymenoptera: Eulophidae) in Response to Colors Mimicking Three Hosts of the Colorado Potato Beetle (Coleoptera: Chrysomelidae)

The effect of leaf color on alighting behavior of Edovum puttleri Grissell was examined in a laboratory sticky-board test. Paint models mimicking the leaf top colors of eggplant, potato, and tomato and a model mimicking average underside leaf color were tested in paired comparisons. The underside leaf color mimic was the most preferred; no significant differences in landing rates occurred among any of the three leaf top color mimics. The underside leaf color mimic also was tested against two gray shades sharing the same intensity of reflectance; no significant differences were detected. The parasitoid, therefore, preferentially alighted based on the intensity and not the hue of the models. For all assays, a significant departure from randomness was found because a higher percentage of females alighted on the paint models than that which was in the colony. This suggests that parasitoids were alighting in a search for host eggs.

Foraging success of parasitoid wasps on flowers: interplay of insect morphology, floral architecture and searching behavior

AbstractIntercropping with flowering herbaceous plants increases parasitoid survivorship, fecundity and retention and pest suppression in agroecosystems. Few studies, however, have examined the compatibility of parasitoid morphology and foraging ability with floral architecture. This study shows that floral architecture influences the selection of floral host resources used to provide nutrients to parasitoids in cropping systems. Parasitoid foraging performance was evaluated using real and artificial flowers which varied in degree of nectar accessibility for two eulophid parasitoids, Edovum puttleri Grissell and Pediobius foveolatus Crawford. Comparisons were made of searching performance on artificial flowers with nectars that were either scented (made from 1:1 honey‐water solution) or scentless (made from 1 m sucrose solution) and differences in head widths were compared with corolla apertures. Our results showed a disparity in the ability of E. puttleri and P. foveolatus to gain access to nectar from particular types of floral architectures. E. puttleri fed efficiently only from flowers with exposed nectaries while P. foveolatus foraged efficiently from flowers having either exposed nectaries or nectaries partially obstructed by petals and stamens. Neither wasp species could forage on flowers with cup‐ or tube‐shaped corollas because their heads are wider than the floral apertures. E. puttleri's foraging performance decreased as nectar inaccessibility increased in the artificial flowers, while P. foveolatus' foraging performance was uniform among the different artificial flowers. This indicates that E. puttleri has less propensity to search small openings for nectar than does P. foveolatus. The foraging success of both E. puttleri and P. foveolatus on artificial flowers was lower when 1 M sucrose solution was used as an artificial nectar rather than honey‐water solution, indicating that the wasps were stimulated and attracted by the nectar odor. Our systematic evaluation of floral architecture with respect to parasitoid foraging ability has enabled us to predict which types of flowers would serve as suitable floral host plants for parasitoids in the field. That is, only flowers with nectaries that are completely exposed would function as suitable floral host plants for E. puttleri, while P. foveolatus could forage on flowers with either exposed or partially exposed nectaries. Examples of potentially suitable floral hosts suggested from our study include dill (Anethum graveolens L.) and fennel (Foeniculum vulgare L.) for both E. puttleri and P. foveolatus and coriander (Coriandrum sativa L.) for P. foveolatus.

Comparison of Conventional and Biological Control Intensive Pest Management Programs on Eggplant in New Jersey

Adoption of biological control and Integrated Pest Management programs by growers depends on adequate control of pests while remaining cost effective. Some New Jersey eggplant growers follow a biological control intensive pest management (BCIPM) program, utilizing the egg parasitoid Edovum puttleri Grissell for the control of Colorado potato beetle. This study evaluates the profitability of the BCIPM program based on comparisons of planting and insecticide application costs, and yield information from conventional and BCIPM growers during the 1993 and 1994 growing seasons. On average, BCIPM growers utilized less insecticide and made fewer applications than conventional growers to control Colorado potato beetles. Differences for the control of aphids, eggplant flea beetles, and two-spotted spider mites were less evident. Each year, BCIPM growers harvested increased levels of higher quality fruit when compared with conventional growers, while incurring similar production costs. These differences resulted in higher per hectare crop values, increased monetary returns, and a more environmentally friendly production system for BCIPM growers.

Impact of Selected Insecticides Used in Eggplant Production on Edovum puttleri Grissell (Hymenoptera: Eulophidae)

The impact of insecticides currently used in commercial eggplant fields to control the Colorado potato beetle, Leptinotarsa decemlineata (Say), on the egg parasitoid Edovum puttleri Grissell was evaluated. Mortality from contact exposure to leaf residues and ingestion of contaminated honey, and parasitoid emergence from treated egg masses were compared for the following insecticides: esfenvalerate alone and in combination with piperonyl butoxide (PBO), oxamyl, PBO, and rotenone alone and in combination with PBO. Studies were conducted using concentrations of 1.0X, 0.75X, 0.5X, and 0.25X of the maximum labeled rate. Mortality was high and significantly different from controls for all chemicals and rates in both the leaf residue tests and feeding studies. Emergence of E. puttleri from treated egg masses also was significantly impacted by all materials and rates with the exception of PBO. The data suggest that the use of these materials in a pest management program that utilizes E. puttleri may reduce the survival of adults and emergence from eggs, thereby slowing parasitoid establishment.

Oviposition behavior of Edovum puttleri, reared on two hosts, Leptinotarsa decemlineata and L. texana

AbstractFemale Edovum puttleri Grissell [Hymenoptera: Eulophidae], reared from eggs of Leptinotarsa decemlineata (Say) or Leptinotarsa texana Schaeffer [Coleoptera: Chrysomelidae], were videotaped as they attacked egg masses of L. decemlineata containing 20 host eggs. We identified 15 components of ovipositional behavior. Parasitoids reared on L. texana attacked and oviposited in significantly more host eggs than did females reared on L. decemlineata. Ethometric analyses of behavioral transitions and a clustering analysis of 34 behavioral parameters showed that females reared on L. texana attacked the host egg mass in a different manner than those reared from L. decemlineata. It was concluded that differences were associated with the host species upon which they were reared. Contrary to previous reports, mortality of unparasitized hosts was caused by an ovipositor probe of short duration, which was not related to host‐feeding.

Parasitization by Edovum puttleri (Hymenoptera: Eulophidae) in relation to host density in the field

Abstract. The relationship between parasitization by Edovum puttleri Grissell and density of eggs of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), was studied on two spatial scales (eggs mass and 6 m2 cage). For both scales, rates of parasitism were generally inversely related to host density for periods ranging from 2 to 8 days after parasitoid release. Thereafter, parasitism became independent of host density. The initial inverse‐density relationship and subsequent shift to density independence may result from several factors: (1) ambient temperatures, (2) the parasitoid's limited egg production, (3) differential times of exposure of egg masses to parasitoids, and/or (4) the parasitoid's patterns of host feeding and oviposition. Although overall levels of parasitism were relatively low, total mortality of L.decemlineata eggs (including nonviable and cannibalized eggs, and those killed by parasitoid feeding) in parasitized egg masses was consistently high (˜70–90%).

Persistence of Edovum puttleri (Hymenoptera: Eulophidae) on Potato Plants and Parasitism of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae): Effects of Resource Availability and Weather

The persistence and distribution of Edovum puttleri Grissell, an egg parasitoid of Colorado potato beetle, Leptinotarsa decemlineata (Say), on potato ( Solanum tuberosum L.) plants with different host resources were quantified. E. puttleri were released into 1.5-m3 field cages enclosing pairs of potato plants with different combinations of host eggs, aphids producing honeydew, or without these resources. Observations every 2 h throughout the day revealed that the parasitoids spent more time during peak foraging periods on plants with aphids or host eggs, or both. However, the percentage of parasitism and mortality of beetle egg masses was not significantly higher on plants with aphids. The relationship between parasitism and mortality of beetle eggs by E. puttleri and weather conditions were analyzed.

Host Influences on the Bionomics of Edovum puttleri (Hymenoptera: Eulophidae): Effects on Size and Reproduction

Edovum puttleri parasitoids reared from eggs of Leptinotarsa texana Schaeffer were larger than parasitoids produced from eggs of L. decemlineata (Say), the Colorado potato beetle. Female parasitoids reared from eggs of L. texana had more mature oocytes in their ovaries than those reared from eggs of L. decemlineata when dissected 1–7 d after their last exposure to hosts. L. texana -reared females, isolated from host eggs for 2 d to permit ovigenesis, produced significantly more offspring when they attacked a host egg mass than similarly treated L. decemlineata -reared females. Despite this, lifetime fecundity, sex ratio, longevity, preoviposition period, and the duration of the egg-laying period were not significantly affected by host species when females were constantly exposed to hosts throughout their lifetimes. For parasitoids from both host species, 2 d was sufficient time for females to redevelop a full clutch of eggs after oviposition, and females maintained a full clutch of eggs for at least 5 d after their last exposure to host eggs.