Jawwad A. Qureshi

Cry1F Resistance in Fall Armyworm Spodoptera frugiperda: Single Gene versus Pyramided Bt Maize

Evolution of insect resistance to transgenic crops containing Bacillus thuringiensis (Bt) genes is a serious threat to the sustainability of this technology. However, field resistance related to the reduced efficacy of Bt maize has not been documented in any lepidopteran pest in the mainland U.S. after 18 years of intensive Bt maize planting. Here we report compelling evidence of field resistance in the fall armyworm, Spodoptera frugiperda (J.E. Smith), to Cry1F maize (TC 3507) in the southeastern region of the U.S. An F2 screen showed a surprisingly high (0.293) Cry1F resistance allele frequency in a population collected in 2011 from non-Bt maize in south Florida. Field populations from non-Bt maize in 2012–2013 exhibited 18.8-fold to >85.4-fold resistance to purified Cry1F protein and those collected from unexpectedly damaged Bt maize plants at several locations in Florida and North Carolina had >85.4-fold resistance. In addition, reduced efficacy and control failure of Cry1F maize against natural populations of S. frugiperda were documented in field trials using Cry1F-based and pyramided Bt maize products in south Florida. The Cry1F-resistant S. frugiperda also showed a low level of cross-resistance to Cry1A.105 and related maize products, but not to Cry2Ab2 or Vip3A. The occurrence of Cry1F resistance in the U.S. mainland populations of S. frugiperda likely represents migration of insects from Puerto Rico, indicating the great challenges faced in achieving effective resistance management for long-distance migratory pests like S. frugiperda.

Incidence of invasive Diaphorina citri (Hemiptera: Psyllidae) and its introduced parasitoid Tamarixia radiata (Hymenoptera: Eulophidae) in Florida citrus.

ABSTRACT Diaphorina citri Kuwayama (Hemiptera: Psyllidae), vectors the bacterium Candidatus Liberibacter asiaticus, one of the causal organisms of the devastating citrus disease “huanglongbing” or citrus greening. In the United States, D. citri was first discovered in Florida, in 1998. Tamarixia radiata Waterston (Hymenoptera: Eulophidae) was imported from Asia and released in Florida in 1999–2001 to improve biological control of D. citri before citrus greening was detected in Florida in 2005. Florida citrus groves were surveyed during 2006 – 2007 for D. citri and T. radiata. Results showed that D. citri was established in all 28 citrus groves surveyed across 16 counties. Adult populations averaged 3.52, 1.27, and 1.66 individuals per “tap” sample at locations in the central, southwest, and eastern coastal regions, respectively. A tap sample consisted of 22- by 28-cm white paper sheet (on a clipboard) held under branches selected at random that were tapped three times. Averages of 67, 44, and 45% citrus shoots infested with psyllid eggs or nymphs were obtained in the central, southwest, and eastern coastal regions, respectively. T. radiata was recovered from fourth- and fifth-instar psyllid nymphs at 26 of the 28 locations. However, apparent parasitism rates were variable and averaged <20% during spring and summer over all locations. Incidence of parasitism increased during fall at some locations, averaging 39% in September and 56% in November in the central and southwest regions, respectively. Further efforts are warranted to enhance the biological control of D. citri and thereby reduce psyllid populations and spread of citrus greening disease.

CITRUS FLUSHING PATTERNS, DIAPHORINA CITRI (HEMIPTERA: PSYLLIDAE) POPULATIONS AND PARASITISM BY TAMARIXIA RADIATA (HYMENOPTERA: EULOPHIDAE) IN PUERTO RICO

Abstract Discovery of citrus greening disease or Huanglongbing in Brazil and Florida has elevated the vector psyllid, Diaphorina citri (Hemiptera: Psyllidae), to key pest status in both regions. Detected in Puerto Rico within 3 years of first detection in Florida, the psyllid appeared to be relatively scarce in the Island’s limited citrus and alternate rutaceous host, orange jasmine, Murraya paniculata. Monthly surveys were conducted at 4 locations during 2004 through 2005 to evaluate citrus flushing patterns, psyllid densities, and prevalence of parasitism by Tamarixia radiata. Although low levels of D. citri are known to be established in the high, cool areas of Adjuntas, a total lack of psyllids at the particular study location was attributed to scarcity of flush except for a short period in Feb. Greatest and most prolonged production of new flush, highest psyllid numbers, and greatest incidence of parasitism occurred at Isabela, the most coastal location and the only one with irrigated citrus. Favorable climate and irrigation resulted in prolonged availability of new foliage needed to maintain populations of psyllids and consequently its parasitoid. There, apparent parasitism of late instars was estimated to average 70% and approached 100% on 3 different occasions. Tamarixia radiata also was found parasitizing psyllid nymphs in orange jasmine at the rate of 48% and 77% at Río Piedras and San Juan, respectively, approaching 100% on 5 occasions during spring and summer. The corresponding decline in infestation during peak flush in spring and later in the year could indicate that T. radiata made important contributions to the regulation of D. citri populations at these locations. Better understanding of factors favoring high parasitism rates in Puerto Rico could lead to more effective biological control of D. citri in other citrus producing areas.

Insecticidal Suppression of Asian Citrus Psyllid Diaphorina citri (Hemiptera: Liviidae) Vector of Huanglongbing Pathogens

Diaphorina citri vectors pathogens that cause ‘huanglongbing’ or citrus greening disease which poses a serious threat to citrus production worldwide. Vector suppression is critical to reduce disease spread. Efficacy is a main concern when choosing an insecticide. Insecticidal treatments of 49 products or 44 active ingredients (a.i) labeled or experimental were field tested between 2005–2013 as foliar sprays (250 treatments, 39 a.i) or soil applications (47 treatments, 9 a.i) to control D. citri in citrus. A combined effect of nymphal and adult suppression in response to sprays of 23 insecticides representing 9 modes of action (MoA) groups and 3 unknown MoA provided more than 90% reduction of adult D. citri over 24–68 days. Observable effects on nymphs were generally of shorter duration due to rapid maturation of flush. However, reduction of 76–100% nymphs or adults over 99–296 days was seen on young trees receiving drenches of the neonicotinoids imidacloprid, thiamethoxam or clothianidin (MoA 4A) and a novel anthranilic diamide, cyantraniliprole (MoA 28). Effective products identified for foliar sprays to control D. citri provide sufficient MoA groups for rotation to delay evolution of insecticide resistance by D. citri and other pests. However, cyantraniliprole is now the only available alternative for rotation with neonicotinoids in soil application to young trees. Sprays of up to eight of the most effective insecticides could be rotated over a year without repetition of any MoA and little or no recourse to neonicotinoids or cyantraniliprole, so important for protection of young trees. Other considerations effecting decisions of what and when to spray include prevalence of huanglongbing, pest pressure, pre-harvest intervals, overall budget, equipment availability, and conservation of beneficial arthropods. Examples of spray programs utilizing broad-spectrum and relatively selective insecticides are provided to improve vector management and may vary depending on individual or regional assessment of all factors.

Adult dispersal of Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) and its implications for resistance management in Bt-maize

Abstract:  Dispersal of European corn borer, Ostrinia nubilalis Hübner was examined by release and recapture of the dye marked adults and by capture of the feral adults in and around the large 50 ha center pivot irrigated fields of Bacillus thuringiensis (Bt) maize. Pheromone and black light traps were used to catch the adults. In 1999, 15 094 marked males and 7993 marked females were released, and in 2001, 13 942 marked males and 9977 marked females were released. In 1999, maximum mean recapture beyond the release point was 1.95 and 1.67% for males and females, but in 2001, the recapture rate was 9.97 and 4.37% for males and females. Few males (3.8%) and females (2.07%) were recaptured in neighbourhood maize fields. An exponential decay function explained recapture of marked adults across the dispersal distance. More than 90% of marked adults were recaptured within 300 m of the release point. Large numbers of feral adults were captured throughout the study fields. Feral adult dispersal could be fitted to a linear model. Virgin females (20% marked and 8% feral) were captured throughout the study fields. The recapture of marked insects suggests that the dispersal was limited. However, capture of feral adults throughout Bt‐maize fields indicate that the actual dispersal may be more extensive than indicated by recapture of marked adults. Potential refuge sources for the feral adults were 587–1387 m from the edge of the study fields. It is not clear if the dispersal recorded in this study is extensive enough to support the current resistance management strategy for corn borers. There appears to be some dispersal of corn borers from the non‐transgenic ‘refuge’ fields into the transgenic fields that allows some genetic mixing of the two populations.

Comparison of Laboratory Colonies and Field Populations of Tamarixia radiata, an Ectoparasitoid of the Asian Citrus Psyllid, Using Internal Transcribed Spacer and Cytochrome Oxidase Subunit I DNA Sequences

ABSTRACT The genetic diversity of Tamarixia radiata Waterston (Hymenoptera: Eulophidae) laboratory colonies derived from collections in China, northern Vietnam, Pakistan, and a mixed colony from Taiwan and southern Vietnam was evaluated using the internal transcribed spacer (ITS) region 1, ITS-2, and the 5′ end of the cytochrome oxidase subunit I gene. The strains share the same ITS sequence, consistent with the morphological hypothesis that the collections represent a single species. The COI marker was variable and could distinguish the northern Vietnam and Pakistan colonies from each other and from the other colonies. Comparison of COI sequences from field-collected populations of Puerto Rico, Guadeloupe, and Texas indicates that Florida is not a likely source of the introduction into Puerto Rico but is a likely source of the introduction into Texas.

Monitoring for Insecticide Resistance in Asian Citrus Psyllid (Hemiptera: Psyllidae) Populations in Florida.

Abstract The development of insecticide resistance in Asian citrus psyllid, Diaphorina citri Kuwayama, populations is a serious threat to the citrus industry. As a contribution to a resistance management strategy, we developed a glass vial technique to monitor field populations of Asian citrus psyllid for insecticide resistance. Diagnostic concentrations needed to separate susceptible genotypes from resistant individuals were determined for cypermethrin (0.5 µg per vial), malathion (1.0 µg per vial), diazinon (1.0 µg per vial), carbaryl (1.0 µg per vial), carbofuran (0.1 µg per vial), methomyl (1.0 µg per vial), propoxur (1.0 µg per vial), endosulfan (1.0 µg per vial), imidacloprid (0.5 µg per vial), acetamiprid (5.0 µg per vial), chlorfenapyr (2.5 µg per vial), and fenpyroximate (2.5 µg per vial). In 2014, resistance to two carbamate insecticides (carbaryl and carbofuran), one organophosphate (malathion), one pyrethroid (cypermethrin), and one pyrazole (fenpyroximate) was detected in field populations of Asian citrus psyllid in Immokalee, FL. There was no resistance detected to diazinon, methomyl, propoxur, endosulfan, imidacloprid, and chlorfenapyr. The levels of insecticide resistance were variable and unstable, suggesting that resistance could be successfully managed. The results validate the use of the glass vial bioassay to monitor for resistance in Asian citrus psyllid populations and provide the basis for the development of a resistance management strategy designed to extend the efficacy of all classes of insecticides used for control of the Asian citrus psyllid.

Predatory Mite, Amblyseius swirskii (Acari: Phytoseiidae), for Biological Control of Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Psyllidae)

ABSTRACT The Asian Citrus Psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is a serious pest of citrus in many citrus-producing regions. It vectors the bacterium ‘Candidatus Liberibacter asiaticus’ thought to be the causal agent of the devastating “Huanglongbing” (HLB) or citrus greening disease. Both pest and the disease are well established in Florida. Several insect predators, particularly lady beetles and the parasitoid Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae), are known to cause significant mortality to ACP immatures. However, there are no reports on the effectiveness of predatory mites against ACP We evaluated the suitability of D. citri eggs and nymphs as prey for the predatory mite Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) in laboratory arenas, and its potential to reduce psyllid populations in the glasshouse on caged Murraya paniculata (L.) Jack plants. Mortality of D. citri eggs on M. paniculata shoots exposed to A. swirskii in plastic arenas was 4 times greater after 6 d compared to unexposed control plants. Mites were also observed sucking out body fluids of first instar nymphs. In the glasshouse, total number of D. citri adults collected over 8 wk from infested plants in ventilated cylinders with A. swirskii present averaged 80% less than the control without mites. These findings showed a significant negative impact of A. swirskii on D. citri under controlled conditions. Further research needs to focus on rates and frequency of release, impact of A. swirskii on D. citri populations in citrus and other hosts under field conditions, and interactions of A. swirskii and D. citri with native predatory mites.

Comparative Biology of Three Cereal Aphids on Tam 107 Wheat

Abstract Greenbug, Schizaphis graminum (Rodani); bird cherry-oat aphid, Rhopalosiphum padi L.; and Russian wheat aphid, Diuraphis noxia (Mordvilko), developed and reproduced successfully on TAM 107 wheat (Triticum aestivum L.) from 21.0 to 22.6°C when transferred to individual plants as single first instars. Both D. noxia “foundresses” and second-generation nymphs developed slower than those of S. graminum and R. padi. In all three species, nymphs developed faster in small colonies of siblings than did their foundress mother developing in solitude. However, when nymphs developed in solitude, only those of S. graminum developed faster than their mothers on the same plants, suggesting maternal induction of plant suitability. Isolated nymphs of D. noxia did not differ in developmental rate from their mothers on maternal plants, and those of R. padi developed more slowly, suggesting that effects of group feeding were responsible for the faster development of second-generation nymphs observed within growing colonies of these species. D. noxia cumulative foundress fecundity and daily reproductive rate were lower than those of S. graminum and R. padi. The estimated intrinsic rates of increase were S. graminum > R. padi > D. noxia. The preferred feeding location of S. graminum foundresses was the primary leaf, whereas for R. padi, it was the stem, and for D. noxia, it was the upper leaves, primarily the terminal leaf. Foundresses of R. padi were observed to change position on the plant from day to day more often than did those of S. graminum or D. noxia. R. padi colonies initiated from 10 first instars accumulated more biomass over a 10-d period than did those of S. graminum or D. noxia.

Behavioral Response of Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) to Volatiles Emanating from Diaphorina citri Kuwayama (Hemiptera: Psyllidae) and Citrus

Tamarixia radiata Waterston (Hymenoptera: Eulophidae) is an effective idiobiont ectoparasitoid of the psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae), vector of the huanglongbing (HLB). We examined the olfactory responses of T. radiata to volatiles emanating from D. citri or plant volatiles using a custom designed T-maze olfactometer and open arena bioassays. We also examined the behavioral response of male and female T. radiata to conspecifics of the opposite sex to determine whether olfactory signals mediate mate location. T. radiata adults exhibited a sexually dimorphic response to volatiles emanating from D. citri and citrus. Female T. radiata responded positively to the odors emanating from D. citri nymphs in both olfactometer and open arena bioassays. However, female wasps showed no response to odors emanating from D. citri adults, D. citri honey dew secretions, intact citrus or orange jasmine leaves. Odors emanating from D. citri damaged citrus were not attractive to T. radiata females but stimulated attraction of wasps to D. citri on damaged plants. T. radiata females were not attracted to D. citri immatures when they were presented as visual cues. Male T. radiata did not show attraction to D. citri nymphs or other putative odors that were attractive to female T. radiata. In olfactometer bioassays, more male T. radiata responded to the odor of female conspecifics than blank controls in the absence of associated citrus host plant volatiles. Odors emanating from female T. radiata were not attractive to male T. radiata. Male or female T. radiata were not attracted to the odors emanating from same sex conspecifics. Both male and female T. radiata adults showed positive phototactic behavior. Collectively, our results provide behavioral evidence that: 1) female T. radiata use volatiles emanating from D. citri nymphs to locate its host and: 2) female T. radiata release a volatile pheromone that attracts male conspecifics.