Genetically-modified (GM) crops presently are central components of pest management strategies fo... more Genetically-modified (GM) crops presently are central components of pest management strategies for several important crops worldwide. GM crops include insect-resistant varieties (expressing transgenes from the bacterium Bacillus thuringiensis, or from plant species other than the GM crop, though only the former varieties are commercially available), and herbicide-tolerant varieties (which tolerate post-emergent applications of particular herbicides). This chapter examines potential and known impacts of GM crops on egg parasitoids. Egg parasitoids can be affected by insect-active toxins or proteins produced by insect-resistant GM crops, or by herbicides applied to herbicide-tolerant crops. A review of the literature showed that very little research has addressed the impacts of GM crops on egg parasitoids, compared to the research on larval parasitoids or predatory insects. The amount and focus of research involving egg parasitoids, though, may be subject to existing factual prejudices: (i) the presence of toxins from insect-resistant varieties in herbivore eggs used as hosts by egg parasitoids is improbable, and (ii) the target of herbicide-tolerant varieties is weeds, by way of herbicide applications. However, egg parasitoids can be affected by GM crops through infrequently explored, direct or indirect pathways, such as exposure to GM crop toxins in honeydew or nectars, or pauperization of host populations in insect-resistant crops or of flowering plant communities in herbicide-tolerant crops. These pathways of GM crop effects on egg parasitoids are likely the most important, but have not been adequately addressed. A fuller understanding of any effects of GM crops on egg parasitoids is particularly significant in the context of analyses pointing to the importance of movement of natural enemy populations among crops and between seasons within a landscape, for pest management and biological control at regional scales.
Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters wer... more Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters were collected in northwestern Mexico in relation to biological control of glassy-winged sharpshooter, Homalodisca vitripennis (Germar) in California. These included an unidentified (likely new) species of Gonatocerus Nees (Mymaridae), an egg parasitoid reared from Proconiini eggs in Sonora state, Mexico. The other species, also reared from Proconiini eggs in Sonora and Sinaloa, included Gonatocerus atriclavus Girault, Gonatocerus morrilli (Howard), and Gonatocerus novifasciatus Girault, and the trichogrammatids Burksiella sp(p)., Paracentrobia sp., Pseudoligosita sp., Ufens ceratus Owen, and U. principalis Owen. Colonies of Gonatocerus atriclavus, Gonatocerus novifasciatus and Pseudoligosita sp. were successfully established in the quarantine laboratory of the Department of Entomology, University of California, Riverside (UCR), on eggs of the glassywinged sharpshooter.
Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters (Ci... more Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters (Cicadellidae: Cicadellinae) were collected in northwestern Mexico in relation to neoclassical biological control efforts against glassywinged sharpshooter, Homalodisca vitripennis (Germar), in California. Gonatocerus chula Triapitsyn and Bernal sp. n., which belongs to the ater species group of Gonatocerus Nees (Mymaridae), is described. Specimens of G. chula sp. n. were reared from eggs of the smoke-tree sharpshooter, Homalodisca liturata Ball, on jojoba [Simmondsia chinensis (Link) C. K. Schneider] leaves collected in central Sonora state, Mexico. Also given are new data on other egg parasitoids of Homalodisca spp. and Oncometopia spp. in Sinaloa and Sonora states, Mexico, including Gonatocerus atriclavus Girault, G. morrilli (Howard), and G. novifasciatus Girault, and the Trichogrammatidae Burksiella sp(p)., Ittys sp., Pseudoligosita sp., Ufens ceratus Owen, and U. principalis Owen. For the first time, a species of Ittys is recorded from eggs of Proconiini, and U. principalis from Mexico. Colonies of G. atriclavus, G. novifasciatus and Pseudoligosita sp. were successfully established in a quarantine laboratory at University of California, Riverside, on eggs of the glassy-winged sharpshooter. These three parasitoid species had never been reared under laboratory conditions. In addition, seven species of Proconiini were collected in central and northwestern Mexico: Cyrtodisca major (Signoret), Homalodisca insolita Walker), H. liturata Ball, Oncometopia sp. cf. clarior (Walker), O. sp. cf. trilobata Melichar, O. (Similitopia) sp., and Phera centrolineata (Signoret). Oncometopia sp. cf. clarior, O. sp. cf. trilobata, and O. (Similitopia) sp. appeared to be undescribed species.
Parallorhogas pyralophagus (Marsh) is the principal parasitoid of the Mexican rice borer [Eoreuma... more Parallorhogas pyralophagus (Marsh) is the principal parasitoid of the Mexican rice borer [Eoreuma loftini (Dyar)], the primary pest of sugarcane in south Texas. Insect resistant transgenic sugarcane producing Galanthus nivalis agglutinin (GNA) was developed to improve control of E. loftini. The present laboratory study addressed whether over two consecutive generations transgenic sugarcane delivered via artiÞcial diet has adverse host-mediated effects on P. pyralophagus life history parameters. The results of this study showed that a number of life history parameters were affected by transgenic sugarcane, whereas others were not affected, and that effects varied between generations. In the Þrst generation, adult longevity was increased by Ϸ2 d, and cocoon to adult and egg to adult developmental times were prolonged by Ϸ1 d in parasitoids exposed to transgenic sugarcane, whereas effects were not evident on adult size; egg load; egg to cocoon developmental time; rates of gain of longevity and egg load with adult size; and egg, larval, and pupal mortality. However, in the second generation, adult longevity was reduced by Ϸ3 d, adult size by Ϸ5%, egg load by Ϸ24%, and rate of gain of longevity with adult size by Ϸ21%, whereas effects were not evident on the rate of gain of egg load with adult size. It was concluded that although GNA transgenic sugarcane, ingested via E. loftini tissues, was not acutely toxic to P. pyralophagus, the sublethal effects on life history parameters measured in this study must be considered in a broader context to determine their possible ecological signiÞcance.
We assessed in the laboratory the attraction of the parasitoid Cotesia marginiventris (Cresson) t... more We assessed in the laboratory the attraction of the parasitoid Cotesia marginiventris (Cresson) toward odors emitted by conventional maize (Zea mays L. ssp. mays) and Bt (Bacillus thuringiensis) maize seedlings following actual or simulated injury by Spodoptera frugiperda (Smith), the parasitoid’s host, and emitted by the host’s frass, produced following consumption of conventional or Bt maize seedlings. Females of C. marginiventris exhibited similarly strong responses to conventional and Bt maize seedlings injured by the host or with simulated injury, and these were stronger than responses to clean air. In contrast, the responses of C. marginiventris females were consistently weaker toward host frass derived from Bt maize tissue compared to frass derived from conventional maize tissue. We hypothesized that the weakened response was due to a detrimental effect of Bt endotoxins, present in the Bt maize tissue, on the bacterial community present in the host’s gut and frass, including bacteria that produce odors attractive to C. marginiventris. As an initial test of our hypothesis, we compared between the responses of C. marginiventris females to host frass produced following consumption of Bt maize and frass produced from conventional maize which had been treated with an antibiotic (tetracycline) to eliminate host gut bacteria. Our results showed that C. marginiventris females responded similarly weakly to host frass derived from conventional maize tissue treated with antibiotic and to frass derived from Bt maize tissue, treated or untreated with antibiotic, while they responded strongly to frass derived from conventional maize untreated with antibiotic, so provided initial, partial support for our hypothesis. We discussed the weakened response of C. marginiventris females to host frass derived from Bt maize in the context of plausible impacts of transgenic crop cultivars on parasitoid foraging and populations, and the implications for biological control of non-target, polyphagous pests, such as S. frugiperda.
Parallorhogas pyralophagus (Marsh) is the principal parasitoid of Mexican rice borer, Eoreuma lof... more Parallorhogas pyralophagus (Marsh) is the principal parasitoid of Mexican rice borer, Eoreuma loftini (Dyar), the primary pest of sugarcane in south Texas. Insect resistant transgenic sugarcane producing Galanthus nivalis agglutinin (GNA) was developed to improve control of E. loftini. The present laboratory study addressed whether transgenic sugarcane adversely affects parasitism of E. loftini by P. pyralophagus. Females of P. pyralophagus preferentially probed, drilled, and parasitized E. loftini larvae fed artiÞcial diet based on conventional sugarcane versus larvae fed diet based on transgenic sugarcane. Activity levels of E. loftini were reduced when fed diet based on transgenic sugarcane, but no differences were evident in frass volatile proÞles. Overall, the results suggested a positive association between larval activity level and likelihood of parasitism, which may render E. loftini larvae feeding on transgenic sugarcane less susceptible to parasitism by P. pyralophagus. However, it was concluded that this may not signiÞcantly affect control of E. loftini because (1) while E. loftini larvae that are most susceptible to transgenic sugarcane may be less prone to parasitism by P. pyralophagus, they are less likely to cause severe crop damage and reproduce successfully; and (2) those E. loftini larvae least susceptible to transgenic sugarcane, and therefore more active and damaging to plants, may be more prone to parasitism by P. pyralophagus.
The influences of artificial and natural rearing substrates on mating success were investigated f... more The influences of artificial and natural rearing substrates on mating success were investigated for the parasitoid wasp Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a candidate for augmentative biological control of various lepidopteran pests. Five rearing substrates were tested: plastic, glass, chiffon fabric, and leaves of two host plants, bean [Vigna unguiculata (L.) (Fabaceae)] and maize [Zea mays L. (Poaceae)]. Mating success was highest on chiffon, lowest on plastic and glass, and intermediate on maize and bean. The transmission characteristics of one component (buzz 1) of the courtship vibrations produced by male wing fanning were investigated using laser vibrometry. The duration of buzz 1 was longer on maize, bean, and chiffon than on plastic and glass. The fundamental frequency of buzz 1 (~300 Hz) was lowest on bean and highest on glass, and intermediate among other substrates. The relative amplitude of buzz 1 was higher on chiffon than on plastic, glass, or bean, and intermediate on maize. The relative importance of airborne sound and substrate vibration as courtship signals was also investigated with experiments that manipulated the production of courtship vibrations and the mating substrates. The amplitude of courtship vibrations on chiffon was significantly higher for winged males than for dealated males. The mating success of males was impacted by both the presence of wings and the mating substrate. These findings suggest that mating success and transmission of courtship vibrations are influenced by the rearing substrate, and that courtship vibrations are critical to mating success in C. marginiventris. Future efforts to mass rear this parasitoid and other insects should consider the potential influences of rearing substrates on mating.
Female and male mate choice in relation to adult size were examined for the solitary and gregario... more Female and male mate choice in relation to adult size were examined for the solitary and gregarious parasitoids, Cotesia marginiventris (Cresson) and Cotesia flavipes Cameron, respectively. In addition, male precopulatory behaviors were observed for evidence of male competition or a large-male advantage in mate acquisition. Male parasitoids are not known to offer female mates direct benefits, but females that mate high quality males may obtain indirect benefits, such as offspring that are more successful in obtaining mates. Female choice experiments for C. marginiventris found that large males approached females first more frequently than small males, and that females mated large males significantly more often than small males. Male choice experiments for C. marginiventris did not demonstrate a male preference for female size. In contrast, female choice experiments with C. flavipes found that females mated equally with large or small males, while male choice experiments showed that males attempted copulation and mated more frequently with smaller females. Male competition was not observed in the gregarious species C. flavipes, but competition in this gregarious parasitoid could be moderated by dispersal.
The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential ... more The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential candidates for augmentative biological control of Anastrepha (Schiner) species (Diptera: Tephritidae), were compared between recently colonized individuals and those continuously reared 70–148 generations. During courtship, males of these parasitoid species fan their wings and produce a series of low amplitude pulses. The first series of 15 or more continuous courtship pulses was used to measure the pulse duration, frequency, and interpulse interval (IPI) from the beginning, middle, and end of the pulse series. Each parameter was compared between young and old colonies, and among species. Several differences in courtship acoustics were detected in colonies that had been continuously reared. The pulse duration at the end of the pulse series was longer in old colonies for Doryctobracon crawfordi (Viereck) (Hymenoptera: Braconidae), but shorter for old colonies of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). The IPI of the middle pulse was shorter in old colonies of Opius hirtus (Fischer) (Hymenoptera: Braconidae), and was also shorter at the last pulse for old colonies of both Utetes anastrephae (Viereck) (Hymenoptera: Braconidae) and D. longicaudata. The duration of the middle pulse distinguished the three native species, and separated the two introduced species from each other. We discuss our findings in light of their biological and applied implications, particularly those dealing with quality control of mass-reared parasitoids.
We assessed the influences of ambient temperature, rainfall, shade cover and elevation on seasona... more We assessed the influences of ambient temperature, rainfall, shade cover and elevation on seasonal abundance of coffee leafminer Leucoptera coffeella (Guérin-Ménèville) and its natural enemies in coffee farms in the Soconusco region of Chiapas, Mexico. Mined coffee leaves were most abundant during the rainy season (i.e. historical average rainfall >200 mm/mo, AprileNovember) compared to the dry season (<100 mm/mo, DecembereMarch), and at low (<600 m asl) relative to high (>900 m asl) elevations. The abundance of mined leaves increased with rainfall, and decreased with maximum daily temperatures. Coffee leafminer survivorship was highest during the dry season (>40%), when predation was lowest (<10%). Predation was the main source of coffee leafminer mortality, and was greatest during the rainy season (>25%) when coffee leafminer incidence was highest (>30% mined leaves per plant). None of the weather variables that were evaluated (viz. maximum and minimum temperatures, and rainfall) significantly impacted parasitism ratios. Shade cover moderated on-farm temperatures, by reducing maximum daily temperatures and any potential, direct impacts of rainfall on coffee leafminer, by providing partial shelter from rainfall, but did not significantly affect coffee leafminer incidence. In 48 h laboratory trials, coffee leafminer oviposition was highest at 28 C (w15 eggs/female), minimal at 25 C (w3 eggs) and nil at 20 C, and higher during night-time hours (>8 eggs/female/day) compared to daytime hours (<1 egg). Historical average temperatures were higher at low elevation (yearly average ca. 25 C; range ¼ 18.0e32.0 C) than at high elevation (ca. 21 C; 13.5e28.5 C), and we predicted that physical environmental conditions (i.e. night-time hours with temperatures > 20 C) were permissive of coffee leafminer oviposition during twice as many hours each year at low elevation (4060 h) compared to high elevation (2081 h). Overall, our results suggested that evident differences in the abundance of coffee leafminer between elevations may be due in considerable part to differences in ambient temperatures, particularly night-time temperatures, rather than rainfall, shade cover, or elevation per se.
Coffee leafminer, Leucoptera coffeella, is a pest in many New World coffee growing areas. Previou... more Coffee leafminer, Leucoptera coffeella, is a pest in many New World coffee growing areas. Previous studies suggested that its population dynamics were strongly affected by natural enemies, particularly of larvae, and physical environmental conditions. Our study documented through field surveys and life table analyses (i) the natural enemy complex associated with coffee leafminer and (ii) the impacts of natural enemies on the population dynamics of coffee leafminer, on coffee (Coffea arabica) at two elevations and two rainfall levels in the Soconusco region of Chiapas, Mexico. Twenty-two larval parasitoid species (including 14 morphospecies) were collected. Egg and pupal parasitoids were not recovered. Life table analyses showed that parasitism contributed 610% of real mortality, and parasitism rates were 8-10-fold higher at the low (<550 m) versus high (>950 m) elevation; parasitism rates were similar under low (<100 mm) and high (>400 mm) rainfall. Seventeen predator species (including five morphospecies) were collected, of which most were ants (Formicidae, 14 species) that contributed >58% of real mortality. Life table analyses showed that predation rates were higher at high versus low elevation and under high versus low rainfall. Independently of elevation and rainfall, egg predation (likely by ants) was the most important source of indispensable mortality (range = 0.13-0.30), except at low elevation and high rainfall where pupal predation (=0.14) was similarly important. Also, predation was the main source of coffee leafminer larval and pupal mortality during a 13-month period in a low elevation coffee farm and was highest during the rainy season (>400 mm rainfall/month), when coffee leafminer prevalence was highest. Overall, predation of eggs and pupae (the latter particularly at low elevation), mostly by ants, were the most important sources of coffee leafminer mortality. Because ants were the main source of coffee leafminer egg and pupal mortality, their importance and potential role in coffee pest management strategies were discussed.
Genetically-modified (GM) crops presently are central components of pest management strategies fo... more Genetically-modified (GM) crops presently are central components of pest management strategies for several important crops worldwide. GM crops include insect-resistant varieties (expressing transgenes from the bacterium Bacillus thuringiensis, or from plant species other than the GM crop, though only the former varieties are commercially available), and herbicide-tolerant varieties (which tolerate post-emergent applications of particular herbicides). This chapter examines potential and known impacts of GM crops on egg parasitoids. Egg parasitoids can be affected by insect-active toxins or proteins produced by insect-resistant GM crops, or by herbicides applied to herbicide-tolerant crops. A review of the literature showed that very little research has addressed the impacts of GM crops on egg parasitoids, compared to the research on larval parasitoids or predatory insects. The amount and focus of research involving egg parasitoids, though, may be subject to existing factual prejudices: (i) the presence of toxins from insect-resistant varieties in herbivore eggs used as hosts by egg parasitoids is improbable, and (ii) the target of herbicide-tolerant varieties is weeds, by way of herbicide applications. However, egg parasitoids can be affected by GM crops through infrequently explored, direct or indirect pathways, such as exposure to GM crop toxins in honeydew or nectars, or pauperization of host populations in insect-resistant crops or of flowering plant communities in herbicide-tolerant crops. These pathways of GM crop effects on egg parasitoids are likely the most important, but have not been adequately addressed. A fuller understanding of any effects of GM crops on egg parasitoids is particularly significant in the context of analyses pointing to the importance of movement of natural enemy populations among crops and between seasons within a landscape, for pest management and biological control at regional scales.
Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters wer... more Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters were collected in northwestern Mexico in relation to biological control of glassy-winged sharpshooter, Homalodisca vitripennis (Germar) in California. These included an unidentified (likely new) species of Gonatocerus Nees (Mymaridae), an egg parasitoid reared from Proconiini eggs in Sonora state, Mexico. The other species, also reared from Proconiini eggs in Sonora and Sinaloa, included Gonatocerus atriclavus Girault, Gonatocerus morrilli (Howard), and Gonatocerus novifasciatus Girault, and the trichogrammatids Burksiella sp(p)., Paracentrobia sp., Pseudoligosita sp., Ufens ceratus Owen, and U. principalis Owen. Colonies of Gonatocerus atriclavus, Gonatocerus novifasciatus and Pseudoligosita sp. were successfully established in the quarantine laboratory of the Department of Entomology, University of California, Riverside (UCR), on eggs of the glassywinged sharpshooter.
Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters (Ci... more Nine species of Mymaridae and Trichogrammatidae parasitic on eggs of Proconiini sharpshooters (Cicadellidae: Cicadellinae) were collected in northwestern Mexico in relation to neoclassical biological control efforts against glassywinged sharpshooter, Homalodisca vitripennis (Germar), in California. Gonatocerus chula Triapitsyn and Bernal sp. n., which belongs to the ater species group of Gonatocerus Nees (Mymaridae), is described. Specimens of G. chula sp. n. were reared from eggs of the smoke-tree sharpshooter, Homalodisca liturata Ball, on jojoba [Simmondsia chinensis (Link) C. K. Schneider] leaves collected in central Sonora state, Mexico. Also given are new data on other egg parasitoids of Homalodisca spp. and Oncometopia spp. in Sinaloa and Sonora states, Mexico, including Gonatocerus atriclavus Girault, G. morrilli (Howard), and G. novifasciatus Girault, and the Trichogrammatidae Burksiella sp(p)., Ittys sp., Pseudoligosita sp., Ufens ceratus Owen, and U. principalis Owen. For the first time, a species of Ittys is recorded from eggs of Proconiini, and U. principalis from Mexico. Colonies of G. atriclavus, G. novifasciatus and Pseudoligosita sp. were successfully established in a quarantine laboratory at University of California, Riverside, on eggs of the glassy-winged sharpshooter. These three parasitoid species had never been reared under laboratory conditions. In addition, seven species of Proconiini were collected in central and northwestern Mexico: Cyrtodisca major (Signoret), Homalodisca insolita Walker), H. liturata Ball, Oncometopia sp. cf. clarior (Walker), O. sp. cf. trilobata Melichar, O. (Similitopia) sp., and Phera centrolineata (Signoret). Oncometopia sp. cf. clarior, O. sp. cf. trilobata, and O. (Similitopia) sp. appeared to be undescribed species.
Parallorhogas pyralophagus (Marsh) is the principal parasitoid of the Mexican rice borer [Eoreuma... more Parallorhogas pyralophagus (Marsh) is the principal parasitoid of the Mexican rice borer [Eoreuma loftini (Dyar)], the primary pest of sugarcane in south Texas. Insect resistant transgenic sugarcane producing Galanthus nivalis agglutinin (GNA) was developed to improve control of E. loftini. The present laboratory study addressed whether over two consecutive generations transgenic sugarcane delivered via artiÞcial diet has adverse host-mediated effects on P. pyralophagus life history parameters. The results of this study showed that a number of life history parameters were affected by transgenic sugarcane, whereas others were not affected, and that effects varied between generations. In the Þrst generation, adult longevity was increased by Ϸ2 d, and cocoon to adult and egg to adult developmental times were prolonged by Ϸ1 d in parasitoids exposed to transgenic sugarcane, whereas effects were not evident on adult size; egg load; egg to cocoon developmental time; rates of gain of longevity and egg load with adult size; and egg, larval, and pupal mortality. However, in the second generation, adult longevity was reduced by Ϸ3 d, adult size by Ϸ5%, egg load by Ϸ24%, and rate of gain of longevity with adult size by Ϸ21%, whereas effects were not evident on the rate of gain of egg load with adult size. It was concluded that although GNA transgenic sugarcane, ingested via E. loftini tissues, was not acutely toxic to P. pyralophagus, the sublethal effects on life history parameters measured in this study must be considered in a broader context to determine their possible ecological signiÞcance.
We assessed in the laboratory the attraction of the parasitoid Cotesia marginiventris (Cresson) t... more We assessed in the laboratory the attraction of the parasitoid Cotesia marginiventris (Cresson) toward odors emitted by conventional maize (Zea mays L. ssp. mays) and Bt (Bacillus thuringiensis) maize seedlings following actual or simulated injury by Spodoptera frugiperda (Smith), the parasitoid’s host, and emitted by the host’s frass, produced following consumption of conventional or Bt maize seedlings. Females of C. marginiventris exhibited similarly strong responses to conventional and Bt maize seedlings injured by the host or with simulated injury, and these were stronger than responses to clean air. In contrast, the responses of C. marginiventris females were consistently weaker toward host frass derived from Bt maize tissue compared to frass derived from conventional maize tissue. We hypothesized that the weakened response was due to a detrimental effect of Bt endotoxins, present in the Bt maize tissue, on the bacterial community present in the host’s gut and frass, including bacteria that produce odors attractive to C. marginiventris. As an initial test of our hypothesis, we compared between the responses of C. marginiventris females to host frass produced following consumption of Bt maize and frass produced from conventional maize which had been treated with an antibiotic (tetracycline) to eliminate host gut bacteria. Our results showed that C. marginiventris females responded similarly weakly to host frass derived from conventional maize tissue treated with antibiotic and to frass derived from Bt maize tissue, treated or untreated with antibiotic, while they responded strongly to frass derived from conventional maize untreated with antibiotic, so provided initial, partial support for our hypothesis. We discussed the weakened response of C. marginiventris females to host frass derived from Bt maize in the context of plausible impacts of transgenic crop cultivars on parasitoid foraging and populations, and the implications for biological control of non-target, polyphagous pests, such as S. frugiperda.
Parallorhogas pyralophagus (Marsh) is the principal parasitoid of Mexican rice borer, Eoreuma lof... more Parallorhogas pyralophagus (Marsh) is the principal parasitoid of Mexican rice borer, Eoreuma loftini (Dyar), the primary pest of sugarcane in south Texas. Insect resistant transgenic sugarcane producing Galanthus nivalis agglutinin (GNA) was developed to improve control of E. loftini. The present laboratory study addressed whether transgenic sugarcane adversely affects parasitism of E. loftini by P. pyralophagus. Females of P. pyralophagus preferentially probed, drilled, and parasitized E. loftini larvae fed artiÞcial diet based on conventional sugarcane versus larvae fed diet based on transgenic sugarcane. Activity levels of E. loftini were reduced when fed diet based on transgenic sugarcane, but no differences were evident in frass volatile proÞles. Overall, the results suggested a positive association between larval activity level and likelihood of parasitism, which may render E. loftini larvae feeding on transgenic sugarcane less susceptible to parasitism by P. pyralophagus. However, it was concluded that this may not signiÞcantly affect control of E. loftini because (1) while E. loftini larvae that are most susceptible to transgenic sugarcane may be less prone to parasitism by P. pyralophagus, they are less likely to cause severe crop damage and reproduce successfully; and (2) those E. loftini larvae least susceptible to transgenic sugarcane, and therefore more active and damaging to plants, may be more prone to parasitism by P. pyralophagus.
The influences of artificial and natural rearing substrates on mating success were investigated f... more The influences of artificial and natural rearing substrates on mating success were investigated for the parasitoid wasp Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a candidate for augmentative biological control of various lepidopteran pests. Five rearing substrates were tested: plastic, glass, chiffon fabric, and leaves of two host plants, bean [Vigna unguiculata (L.) (Fabaceae)] and maize [Zea mays L. (Poaceae)]. Mating success was highest on chiffon, lowest on plastic and glass, and intermediate on maize and bean. The transmission characteristics of one component (buzz 1) of the courtship vibrations produced by male wing fanning were investigated using laser vibrometry. The duration of buzz 1 was longer on maize, bean, and chiffon than on plastic and glass. The fundamental frequency of buzz 1 (~300 Hz) was lowest on bean and highest on glass, and intermediate among other substrates. The relative amplitude of buzz 1 was higher on chiffon than on plastic, glass, or bean, and intermediate on maize. The relative importance of airborne sound and substrate vibration as courtship signals was also investigated with experiments that manipulated the production of courtship vibrations and the mating substrates. The amplitude of courtship vibrations on chiffon was significantly higher for winged males than for dealated males. The mating success of males was impacted by both the presence of wings and the mating substrate. These findings suggest that mating success and transmission of courtship vibrations are influenced by the rearing substrate, and that courtship vibrations are critical to mating success in C. marginiventris. Future efforts to mass rear this parasitoid and other insects should consider the potential influences of rearing substrates on mating.
Female and male mate choice in relation to adult size were examined for the solitary and gregario... more Female and male mate choice in relation to adult size were examined for the solitary and gregarious parasitoids, Cotesia marginiventris (Cresson) and Cotesia flavipes Cameron, respectively. In addition, male precopulatory behaviors were observed for evidence of male competition or a large-male advantage in mate acquisition. Male parasitoids are not known to offer female mates direct benefits, but females that mate high quality males may obtain indirect benefits, such as offspring that are more successful in obtaining mates. Female choice experiments for C. marginiventris found that large males approached females first more frequently than small males, and that females mated large males significantly more often than small males. Male choice experiments for C. marginiventris did not demonstrate a male preference for female size. In contrast, female choice experiments with C. flavipes found that females mated equally with large or small males, while male choice experiments showed that males attempted copulation and mated more frequently with smaller females. Male competition was not observed in the gregarious species C. flavipes, but competition in this gregarious parasitoid could be moderated by dispersal.
The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential ... more The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential candidates for augmentative biological control of Anastrepha (Schiner) species (Diptera: Tephritidae), were compared between recently colonized individuals and those continuously reared 70–148 generations. During courtship, males of these parasitoid species fan their wings and produce a series of low amplitude pulses. The first series of 15 or more continuous courtship pulses was used to measure the pulse duration, frequency, and interpulse interval (IPI) from the beginning, middle, and end of the pulse series. Each parameter was compared between young and old colonies, and among species. Several differences in courtship acoustics were detected in colonies that had been continuously reared. The pulse duration at the end of the pulse series was longer in old colonies for Doryctobracon crawfordi (Viereck) (Hymenoptera: Braconidae), but shorter for old colonies of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). The IPI of the middle pulse was shorter in old colonies of Opius hirtus (Fischer) (Hymenoptera: Braconidae), and was also shorter at the last pulse for old colonies of both Utetes anastrephae (Viereck) (Hymenoptera: Braconidae) and D. longicaudata. The duration of the middle pulse distinguished the three native species, and separated the two introduced species from each other. We discuss our findings in light of their biological and applied implications, particularly those dealing with quality control of mass-reared parasitoids.
We assessed the influences of ambient temperature, rainfall, shade cover and elevation on seasona... more We assessed the influences of ambient temperature, rainfall, shade cover and elevation on seasonal abundance of coffee leafminer Leucoptera coffeella (Guérin-Ménèville) and its natural enemies in coffee farms in the Soconusco region of Chiapas, Mexico. Mined coffee leaves were most abundant during the rainy season (i.e. historical average rainfall >200 mm/mo, AprileNovember) compared to the dry season (<100 mm/mo, DecembereMarch), and at low (<600 m asl) relative to high (>900 m asl) elevations. The abundance of mined leaves increased with rainfall, and decreased with maximum daily temperatures. Coffee leafminer survivorship was highest during the dry season (>40%), when predation was lowest (<10%). Predation was the main source of coffee leafminer mortality, and was greatest during the rainy season (>25%) when coffee leafminer incidence was highest (>30% mined leaves per plant). None of the weather variables that were evaluated (viz. maximum and minimum temperatures, and rainfall) significantly impacted parasitism ratios. Shade cover moderated on-farm temperatures, by reducing maximum daily temperatures and any potential, direct impacts of rainfall on coffee leafminer, by providing partial shelter from rainfall, but did not significantly affect coffee leafminer incidence. In 48 h laboratory trials, coffee leafminer oviposition was highest at 28 C (w15 eggs/female), minimal at 25 C (w3 eggs) and nil at 20 C, and higher during night-time hours (>8 eggs/female/day) compared to daytime hours (<1 egg). Historical average temperatures were higher at low elevation (yearly average ca. 25 C; range ¼ 18.0e32.0 C) than at high elevation (ca. 21 C; 13.5e28.5 C), and we predicted that physical environmental conditions (i.e. night-time hours with temperatures > 20 C) were permissive of coffee leafminer oviposition during twice as many hours each year at low elevation (4060 h) compared to high elevation (2081 h). Overall, our results suggested that evident differences in the abundance of coffee leafminer between elevations may be due in considerable part to differences in ambient temperatures, particularly night-time temperatures, rather than rainfall, shade cover, or elevation per se.
Coffee leafminer, Leucoptera coffeella, is a pest in many New World coffee growing areas. Previou... more Coffee leafminer, Leucoptera coffeella, is a pest in many New World coffee growing areas. Previous studies suggested that its population dynamics were strongly affected by natural enemies, particularly of larvae, and physical environmental conditions. Our study documented through field surveys and life table analyses (i) the natural enemy complex associated with coffee leafminer and (ii) the impacts of natural enemies on the population dynamics of coffee leafminer, on coffee (Coffea arabica) at two elevations and two rainfall levels in the Soconusco region of Chiapas, Mexico. Twenty-two larval parasitoid species (including 14 morphospecies) were collected. Egg and pupal parasitoids were not recovered. Life table analyses showed that parasitism contributed 610% of real mortality, and parasitism rates were 8-10-fold higher at the low (<550 m) versus high (>950 m) elevation; parasitism rates were similar under low (<100 mm) and high (>400 mm) rainfall. Seventeen predator species (including five morphospecies) were collected, of which most were ants (Formicidae, 14 species) that contributed >58% of real mortality. Life table analyses showed that predation rates were higher at high versus low elevation and under high versus low rainfall. Independently of elevation and rainfall, egg predation (likely by ants) was the most important source of indispensable mortality (range = 0.13-0.30), except at low elevation and high rainfall where pupal predation (=0.14) was similarly important. Also, predation was the main source of coffee leafminer larval and pupal mortality during a 13-month period in a low elevation coffee farm and was highest during the rainy season (>400 mm rainfall/month), when coffee leafminer prevalence was highest. Overall, predation of eggs and pupae (the latter particularly at low elevation), mostly by ants, were the most important sources of coffee leafminer mortality. Because ants were the main source of coffee leafminer egg and pupal mortality, their importance and potential role in coffee pest management strategies were discussed.
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Papers by Julio Bernal