Pteromalus Venustus Research Articles

Insecticidal Activity of Plant Powders against the Parasitoid, Pteromalus venustus, and Its Host, the Alfalfa Leafcutting Bee.

Developing a bee-friendly alternative to traditional insecticides used within commercial environments can contribute to reductions in pesticide exposure experienced by managed bees. We performed acute contact toxicity studies using fifteen plant powders from seven plant families against a parasitoid pest, Pteromalus venustus, and its host, the Alfalfa leafcutting bee (ALB). Ajwain, cinnamon, clove, cumin, fennel, ginger, nutmeg, oregano and turmeric applied at low contact concentrations had sufficient fumigant properties to cause equivalent or higher parasitoid mortality as that obtained with the traditional insecticide. Nutmeg adversely affected adult ALBs at both low and high contact concentrations, thus eliminating it as a candidate. Increasing the contact concentrations did not consistently increase parasitoid control but did increase adverse effects on the ALBs. In addition, the efficacious plant powders significantly reduced the sexual function and fertility of the female parasitoids, a feature not associated with the traditional insecticide. The dual nature of the mechanisms underlying the effects of the plant powders may translate into effective control of the parasitoid populations in the commercial environment. The results reported here support further evaluations of Ajwain, cinnamon, clove, cumin, fennel, ginger, oregano and turmeric as potential botanical insecticides for control of P. venustus.

Infection of the chalcid parasitoid Pteromalus venustus Walker (Hymenoptera: Pteromalidae) with the male-killing symbiont Arsenophonus nasoniae (Gamma-Proteobacteria: Enterobacteriaceae)

The male-killing symbiont Arsenophonus nasoniae is a gamma-proteobacterium that infects parasitic wasps; the male progeny of infected females exhibit increased embryonic death. In this study, we examined methods to horizontally infect Pteromalus venustus (a parasitoid infesting populations of the alfalfa leafcutting bee Megachile rotundata) with A. nasoniae. We then tested the success of these methods via semi-quantitative PCR and quantitative digital PCR, using a molecular marker specific to A. nasoniae. Controlled parasitoid mating experiments were then undertaken to determine whether infections of A. nasoniae in P. venustus induce the male-killing phenotype as has been reported for other host species; evidence of this male-killing phenotype was observed in the current study. Over the course of the eight parasitoid generations following introduction of A. nasoniae infection in P. venustus, the male component of the parasitoid sex ratio was substantially reduced in the infected population (1.05 ♂: 1.00 ♀) compared to the control population (2.46 ♂: 1.00 ♀). Establishment of stable A. nasoniae infections in P. venustus populations could lower the proportion of male progeny, thus negatively impacting the mating success of females, and reducing overall populations of the parasitoid in alfalfa leafcutting bee populations.

Bioassay for Detection of Dichlorvos Insecticide in Air in Alfalfa Leafcutting Bee (Megachile Rotundata F.) Incubators

Abstract Dichlorvos is an insecticide used in slow-release plastic strips for controlling chalcid wasp parasites, such as Pteromalus venustus Walker, in incubators used to raise alfalfa leafcutting bees (Megachile rotundata F.). Beekeepers need a practical method to detect dichlorvos in air and verify that it has dissipated to levels acceptable for worker re-entry and for the bees to emerge. We evaluated three methods for analysis of the dichlorvos concentration in air. Vapor sampling tubes using a manually operated pump or diffusion collection had insufficient sensitivity in the concentration range of interest. Air samples collected using battery powered pumps were analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS), which was accurate and sensitive, but too costly and slow for practical use. Finally, a convenient bioassay for detecting dichlorvos in air was developed using leafcutting bees and verified by comparison with the results obtained by LC/MS/MS for a series of dose levels. The bioassay is simple enough to be done by the beekeeper on-site, is inexpensive, and gives results within 1 h. The LC50 for dichlorvos vapor in air after 1 h of exposure was 273.2 μg/m3 by the probit regression method or 277.3 μg/m3 by the logit regression method.

POSTDIAPAUSE DEVELOPMENT AND ADULT EMERGENCE OF PTEROMALUS VENUSTUS WALKER (HYMENOPTERA: PTEROMALIDAE) DURING ALFALFA LEAFCUTTER BEE INCUBATION

Pteromalus venustus Walker is the most common parasitoid associated with the alfalfa leafcutter bee, Megachile rotundata (F.), in western Canada (Richards 1984). Leafcutter beekeepers in Canada and the United States use several methods to control P. venustus during incubation of leafcutter bee larvae, including light traps (Hobbs 1973; Richards 1984), dipping the cells in an insecticide (Brindley 1976; Parker 1979), and placing dichlorvos resin strips in the incubator (Hill et al. 1984). Previously we described the influence of temperature on survival and rate of development of the egg, larval, and pupal stages of non-diapausing P. venustus (Whitfield and Richards 1985). Here we report on the influence of temperature on rate of postdiapause development in P. venustus during leafcutter bee incubation and consider the value of this information for timing control measures for this parasitoid.

The Effect of Nest Replacement on the Production of Females of the Alfalfa Leaf-Cutter BeeMegachile Rotundata(F)

SummaryPartially filled hives, containing cells of Megachile rotundata (F) brood, were replaced with empty hives early in the field season in an attempt to obtain an increase in the number of female alfalfa leaf-cutter bees. The frequency of female bees decreased from the back of the tunnels to the front ends in both the original and replacement hives; male bees showed the opposite pattern. Ratios of male to female bees ranged from 1·6: 1 to 3·0: 1 despite the use of tunnels of standard length and diameter. There was no significant increase in females produced in the replacement nests suggesting that it is neither feasible nor economical to replace nests to increase numbers of female bees. However, chalcidoid parasitism (by Pteromalus venustus Walker) was significantly reduced in the replacement hives, possibly owing to the method used to remove bees from the original hives.

INFLUENCE OF TEMPERATURE ON SURVIVAL AND RATE OF DEVELOPMENT OF PTEROMALUS VENUSTUS (HYMENOPTERA: PTEROMALIDAE), A PARASITE OF THE ALFALFA LEAFCUTTER BEE (HYMENOPTERA: MEGACHILIDAE)

AbstractIncidence of parasitism by Pteromalus venustus Walker in populations of the alfalfa leafcutter bee, Megachile rotundata (F.), in western Canada from 1976 to 1983 was found to average ca. 1%. An average of 17.4 parasite adults emerged from each host cocoon and the ratio of males to females was 1:1. Temperature-dependent development and survival at 8 constant temperatures are described. The range of temperatures for greatest survival of the parasite (30–32 °C) coincided with the recommended incubation temperatures for cocoons of the leafcutter bee. Development data fitted a 4-parameter development model. Linear regression of development rate versus temperature provided estimates of base temperature and development time in degree-days for the egg, larval, pupal, and combined stages.

Use of Dichlorvos Resin Strips to Reduce Parasitism of Alfalfa Leafcutter Bee (Hymenoptera: Megachilidae) Cocoons During Incubation

Uninfested cocoons of the alfalfa leafcutter bee, Megachile rotundata (F.), bare prepupae, and cocoons infested with the chalcidoid, Pteromalus venustus Walker, were exposed to vapor from dichlorvos resin strips at rates of 0.16, 0.37, 0.71, and 0.99 strip per 28.3 m3 during 4 days of incubation. For uninfested cocoons, there was no significant reduction in leafcutter bee survival at the dichlorvos rates tested. For bare prepupae, there was a significant linear trend of reduced survival with increased dichlorvos rate. Cocoons apparently protect the bees from dichlorvos vapor. For infested cocoons, 0.71 strip per 28.3 m3 reduced the parasitism from 40 to 13% which significantly increased bee survival. Adult parasites were placed in different housing environments and exposed to the 0.71 strip per 28.3 m3 rate. When parasites were directly exposed to dichlorvos vapor, mortality occurred within 2 h. When parasites were shielded by layers of cocoons, mortality was delayed 7 to 10 h. Because 25% parasitism can occur within 4 h of P. venustus emergence, it is unlikely that dichlorvos resin strips alone will totally control parasitism in a commercial operation.

Male Courtship Behaviour, Female Receptivity Signal, and Size Differences Between the Sexes in Pteromalinae (Hym., Chalcidoidea Pteromalidae), and Comparative Notes On Other Chalcidoids

In the evolutionary history of the Pteromalidae, the position of the courting male has moved from the rear (the area where copulation will take place) to the front (the area where an exchange of stimuli between partners may occur most efficiently). The shift of position is related to a number of other developments, one of which is the antennal receptivity signal by the female. The effect of this signal is that the male stops courting, leaves the frontal position by backing up on the female, and establishes a genital contact (VAN DEN ASSEM, 1974). In the present paper I have argued that, once a frontal position for courtship has been realised, and female receptivity can be perceived by the male at the front, a further reduction of the size of the male seems advantageous. Small males are found in many groups of Chalcidoidea including the Pteromalinae. In several species of this subfamily the size differences between the sexes are considerable. In a gregarious parasite, small males take a smaller share of the host which leaves more food for their sisters whose average reproductive success seems to be proportional to their longivity (which, within limits, is proportional to body size as adult). Small-sized males are likewise advantageous in solitary parasites: a small host (e.g. a young instar) may be insufficient as a food source for a female offspring, to complete its development, but sufficient for a male. A discriminative parasite will lay unfertilised eggs on small hosts and fertilised eggs on large hosts. In this way the number of hosts available in a certain area to a parasitising parent becomes greater and hence searching for hosts more successful. (It is true that a small instar will become larger with time, if left undisturbed, but a delay of egg-laying will certainly result in losses due to the competitive activity of other parasites, conspecifics or otherwise). Additional advantages of small males are the more rapid development, which ensures a timely presence where females come to emerge a little later. Further, a smaller body size had no effect on the duration of a courtship sequence required to induce receptivity in virgin females. The reduction of male body size also has negative effects: a limitation of the number of possible inseminations, a reduction of longivity, and an increased vulnerability to competing conspecific males (who may steal a copulation) are the most obvious ones. The advantages and disadvantages of size reduction were discussed. Courtship behaviour of Pteromalus venustus was described and two other species, Pteromalus puparum and Muscidifurax uniraptor were dealt with in detail because of their peculiarities. In P. puparum the antennal movements made by the receptive female no longer seem to serve a signal function (although they are completely identical to those of other Pteromalinae). I argued that this ineffectiveness is a secondary phenomenon, due to the peculiar behaviour of the male which may be an adaptation to oppose strong competition for females. In M. uniraptor males are extremely rare, and they no longer serve a reproductive function. Virgin females lay diploid eggs which produce female offspring exclusively. Morever, males (who may arise as progeny of females who were exposed to high temperatures during oviposition) appear to have retained a normal courtship. Conspecific females, however, were never seen to respond to it, but females of a related species (M. raptorellus) did signal receptivity when courted by uniraptor males. Fertilisation did not occur because uniraptor-mated raptorellus females produced only male offspring. A few courtship repertoires of Encyrtidae were described. To all appearances the evolution of courtship behaviour of Pteromalidae, Encyrtidae, and Eulophidae exhibits parallel developments.

Studies on Trapping, Nesting, and Rearing of some Magachile Species (Hymenoptera, Megachilidae) and on their Parasites in Denmark

AbstractPopulations of three indigenous species of leaf-cutting bees, Megachile centuncularis, M. leachella, and M. willughbiella, were compared to one of the alien bee, M. pacifica. In contrast to M. leachella and M. pacifica the two other species had so unfavourable a sex ratio that it proved prohibitive to propagation, while the rate of emergence showed the indigenous bees better adapted to our natural conditions than is M. pacifica. Parasitic wasps and bees were important enemies of the bees. Melittobia acasta occurred in all species reared in the greenhouse, Monodontomerus obscurus was present in the colony of Megachile willughbiella gathered in nature, and Pteromalus venustus seriously diminished the population of M. willughbiella when this bee was moved to a new nesting site. Coelioxys mandibularis is very common in naure, but was only observed once in connection with the studies presented. Several species of fungi were associated with the indigenous bees, while the alien M. pacifica was practically free of fungi. In M. centuncularis Ascosphaera proliperda and A. major caused chalkbrood-like diseases, though the latter seems merely a facultative parasite. A hitherto undescribed species of Microascus was associated to and probably pathogenic in M. willughbiella. The mucous ascopores of the fungi stick to the fur of the bees as they pass through one cell after the other when emerging. That is one way of transfer from one generation to the next.

COMPARATIVE BEHAVIOR OF THREE CHALCIDOID (HYMENOPTERA) PARASITES OF THE ALFALFA LEAFCUTTER BEE, MEGACHILE ROTUNDATA, IN THE LABORATORY

AbstractThe following behavioral patterns of three chalcidoid parasites, Monodontomerus obscurus, Pteromalus venustus, and Melittobia chalybii, were compared in the laboratory: feeding by adults, precopulatory routines, copulating, anesthetizing the host, ovipositing, mobility of the larvae, cannibalism among larvae, overwintering, diapause, life cycle, and the ability of a host to support a parasite.

CHALCIDOID (HYMENOPTERA) PARASITES OF THE ALFALFA LEAF-CUTTER BEE, MEGACHILE ROTUNDATA, IN CANADA

AbstractMegachile rotundata (F.) is a domesticated bee used to pollinate alfalfa in southern Alberta. There it may have four species of parasites, all chalcidoids. These parasites are removable by water traps before the hives are set in the field. Three of these parasites, Monodontomerus obscurus Westw., Dibrachys maculipennis Sz., and Pteromalus venustus Wlkr,, are European in origin. The first seems not to be established in Canada; the latter two have been reared from Canadian species of Megachile and thereby may prove a source of parasitism. The fourth species, Melittobia chalybii Ashm., is a widespread, nearctic, multivoltine species and is known as a laboratory pest of hymenopterous nests; it is likely to be the major parasite in rotundata nests. A key is given for the parasitic species.

CONTROLLING INSECT ENEMIES OF THE ALFALFA LEAF-CUTTER BEE, MEGACHILE ROTUNDATA

AbstractThe debris-feeding insects Trogoderma glabrum (Hbst.), Tribolium madens Charp., Cryptolestes ferrugineus (Steph.), and Vitula edmandsae Pack, were controlled by cleaning out die nests of Megachile rotundata L. annually and screening off the debris, and by discarding the cells of M. rotundata after emergence was complete. The chalcidoid parasites Monodontomerus obscurus Westw. and Pteromalus venustus Wlkr. and the depredators Coelioxys spp., were removed by light-trapping them in the incubators in which M. rotundata was being hatched. The removal was made possible because the incubation period of each of the indigenous enemies was considerably shorter than that of their exotic host.