Mamoudou Sétamou

Feeding and Life History of Spodoptera exigua (Lepidoptera: Noctuidae) on Different Host Plants

Abstract Consumption rates, development times, and life table parameters of the beet armyworm, Spodoptera exigua (Hübner), were determined on five host plants: cabbage, Brassica oleracea capitata L; cotton, Gossypium hirsutum L.; bell pepper, Capsicum annuum L.; pigweed, Amaranthus retroflexus L.; and sunflower, Helianthus annuus L. Mean total leaf weight consumed by larvae was highest in cabbage (2.7 g) and lowest in pigweed (1.6 g). The feeding index (pupal weight divided by total weight of leaf tissue consumed) was highest on pigweed, followed by cotton, pepper, sunflower, and cabbage. On all host plants, significant relationships were found between amount of leaf tissue consumed and resulting pupal weight. Likewise, significant relationships were found between pupal weight and subsequent adult fecundity on all host plants. The highest percentage of female progeny was recorded in S. exigua reared on pigweed (62.2%) and the lowest for larvae reared on cabbage (43.6%). Duration of the larval stage was shortest on pigweed (12.4 d) and longest on pepper (18.0 d). Larval survival was highest on pigweed (94.4%) and lowest on cabbage (67.1%). Three key statistics were used to assess performance of S. exigua on the different host plants: 1) feeding index, 2) intrinsic rate of increase, r; and 3) growth index (percentage immature survival divided by immature development time). Using these measures, S. exigua performance was best on pigweed, worst on cabbage, and intermediate on cotton, pepper, and sunflower. We discuss the implications of these findings for control of S. exigua.

Dispersion Patterns and Sampling Plans for Diaphorina citri (Hemiptera: Psyllidae) in Citrus

Abstract The abundance and spatial dispersion of Diaphorina citri Kuwayama (Hemiptera: Psyllidae) were studied in 34 grapefruit (Citrus paradisi Macfad.) and six sweet orange [Citrus sinensis (L.) Osbeck] orchards from March to August 2006 when the pest is more abundant in southern Texas. Although flush shoot infestation levels did not vary with host plant species, densities of D. citri eggs, nymphs, and adults were significantly higher on sweet orange than on grapefruit. D. citri immatures also were found in significantly higher numbers in the southeastern quadrant of trees than other parts of the canopy. The spatial distribution of D. citri nymphs and adults was analyzed using Iowa’s patchiness regression and Taylor’s power law. Taylor’s power law fitted the data better than Iowa’s model. Based on both regression models, the field dispersion patterns of D. citri nymphs and adults were aggregated among flush shoots in individual trees as indicated by the regression slopes that were significantly >1. For the average density of each life stage obtained during our surveys, the minimum number of flush shoots per tree needed to estimate D. citri densities varied from eight for eggs to four flush shoots for adults. Projections indicated that a sampling plan consisting of 10 trees and eight flush shoots per tree would provide density estimates of the three developmental stages of D. citri acceptable enough for population studies and management decisions. A presence–absence sampling plan with a fixed precision level was developed and can be used to provide a quick estimation of D. citri populations in citrus orchards.

Olfactory and Visual Stimuli Affecting Host Plant Detection in Homalodisca coagulata (Hemiptera: Cicadellidae)

Abstract The relative effects of visual and olfactory stimuli on host plant detection in immature and adult Homalodisca coagulata Say (Homoptera: Cicadellidae) were studied using a novel olfactometer and factorial experimental designs. Colored, gray, and white cards were used as visual targets. Each card was attached to a glass thistle tube from which host-plant odor (from Vigna unguiculata L.) or blank, humidified air was dispensed. Visual + odor stimuli combinations were presented in no-choice tests. Nymphs were released onto a perch stick downwind from the target. Nymph response to color + odor treatments was measured by the duration of orientation behavior, residence time on the perch, and percentage of individuals that jumped to the target. The assay was modified so that adults crawled from the perch onto the target. Adult response was measured by the duration of individual behaviors (e.g., foraging) and by their position and residence time on the target. Both main effects and interactive effects of the stimuli were observed. Nymphs showed a decrease in orientation and residence times in the colored target + host odor treatments and increased jumping response in the gray + host odor treatment. When adults were exposed to host odor, the duration of foraging behavior increased, whereas crawling and phototactic behaviors decreased. Although nymphs and adults responded to visual stimuli + blank air treatments, host odor enhanced their responses. The primary effect of host odor on host detection behavior may be to enhance H. coagulata responsiveness to visual cues.

Climate Change or Urbanization? Impacts on a Traditional Coffee Production System in East Africa over the Last 80 Years

Global environmental changes (GEC) such as climate change (CC) and climate variability have serious impacts in the tropics, particularly in Africa. These are compounded by changes in land use/land cover, which in turn are driven mainly by economic and population growth, and urbanization. These factors create a feedback loop, which affects ecosystems and particularly ecosystem services, for example plant-insect interactions, and by consequence agricultural productivity. We studied effects of GEC at a local level, using a traditional coffee production area in greater Nairobi, Kenya. We chose coffee, the most valuable agricultural commodity worldwide, as it generates income for 100 million people, mainly in the developing world. Using the coffee berry borer, the most serious biotic threat to global coffee production, we show how environmental changes and different production systems (shaded and sun-grown coffee) can affect the crop. We combined detailed entomological assessments with historic climate records (from 1929–2011), and spatial and demographic data, to assess GECs impact on coffee at a local scale. Additionally, we tested the utility of an adaptation strategy that is simple and easy to implement. Our results show that while interactions between CC and migration/urbanization, with its resultant landscape modifications, create a feedback loop whereby agroecosystems such as coffee are adversely affected, bio-diverse shaded coffee proved far more resilient and productive than coffee grown in monoculture, and was significantly less harmed by its insect pest. Thus, a relatively simple strategy such as shading coffee can tremendously improve resilience of agro-ecosystems, providing small-scale farmers in Africa with an easily implemented tool to safeguard their livelihoods in a changing climate.

Two Separate Introductions of Asian Citrus Psyllid Populations Found in the American Continents

ABSTRACT A phylogeographic analysis inferred from the partial mitochondrial cytochrome oxidase subunit I gene (433 bp) was performed with 22 populations of Diaphorina citri Kuwayama collected in the Americas and one in the Pacific. Eight populations from four countries in South America, 14 from four countries in North America, and one from Hawaii were analyzed. Twenty-three haplotypes (hp) were identified and they fell into two groups: hp1–8 were identified in South America (group 1) and hp9–23 were identified in North America and Hawaii (group 2). Hp1 and nine were present in the highest frequencies within each population and within their group, 81 and 85% for group 1 and group 2, respectively. A diagnostic nucleotide at position 48 was identified that allowed for the discrimination of the two groups; in addition, no haplotypes were shared between the two groups. An analysis of molecular variance uncovered significant genetic structure (&phgr;CT = 0.733; P < 0.001) between the two groups of the Americas. Two haplotype networks (ParsimonySplits and Statistical Parsimony) discriminated the two groups and both networks identified hp1 and nine as the predicted ancestral or founding haplotypes within their respective group. The data suggest that two separate introductions or founding events of D. citri occurred in the Americas, one in South America and one in North America. Furthermore, North America and Hawaii appear to share a similar source of invasion. These data may be important to the development of biological control programs against D. citri in the Americas.

Beet Armyworm (Lepidoptera: Noctuidae) Host Plant Preferences for Oviposition

Abstract Beet armyworm, Spodoptera exigua (Hübner), oviposition preferences were determined on five host plants: cabbage (Brassica oleracea capitata L.), cotton (Gossypium hirsutum L.), bell pepper (Capsicum annuum L.), pigweed (Amaranthus retroflexus L.), and sunflower (Helianthus annuus L.) in no-choice, two-choice, and five-choice tests. Tests were conducted in the laboratory, greenhouse, and field cages. Oviposition preferences were compared on the basis of two measurements, the proportion of eggs laid on the plants to total that were deposited, and the oviposition preference index defined as [(number of eggs laid on the plant) - (number of eggs laid on the cage)] × 100/total number of eggs laid. The proportion of eggs laid on the plants to total that were deposited was highest for pigweed and lowest for cabbage in all tests. Beet armyworm females were significantly deterred from laying eggs on cabbage and sunflower, while pigweed and cotton elicited a positive oviposition preference. Pepper tended to be neutral or slightly unattractive. Apparent interactions among plant species in choice tests produced measurable shifts in oviposition preference. Most notably, female response to pepper was enhanced in the presence of cotton or pigweed. Egg masses laid on the plants contained significantly higher numbers of eggs than those laid on the surface of the cage, except in the case of cabbage leaves. Knowledge of hierarchies of host plant oviposition preference by beet armyworm females will be useful in understanding the population dynamics of this important agricultural pest, and for developing effective monitoring and management strategies.

Molecular Evidence Suggests That Populations of the Asian Citrus Psyllid Parasitoid Tamarixia radiata (Hymenoptera: Eulophidae) from Texas, Florida, and Mexico Represent a Single Species

ABSTRACT We genetically characterized Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) populations from Texas, Florida, and Mexico and the sister taxon Tamarixia triozae (Burks) by two molecular methods. T. radiata is an ectoparasitoid of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), nymphs. The populations were submitted to intersimple sequence repeat-polymerase chain reaction DNA fingerprinting with two primers. No fixed banding pattern differences were uncovered among the populations of T. radiata with either primer, whereas different patterns were observed in T. triozae, suggesting that there is no genetic differentiation among the populations. Support for these results was obtained by sequence analyses of the internal transcribed spacer region one and the mitochondrial cytochrome oxidase subunit one (COI) gene. In both genes, the intrapopulational variation range (percentage divergence, %D) fell within the interpopulational variation range. The %D at the COI gene between T. radiata and T. triozae was 9.0–10.3%. However, haplotype structure was uncovered among the populations. No haplotypes were shared between Florida and Texas/Mexico, whereas sharing was observed between Texas and Mexico. Two population-specific nucleotides were identified that allowed the discrimination of the Florida and Texas/ Mexico individuals. A neighbor-joining and a parsimonious tree clustered the populations into two distinct clades. The Florida population clustered into one clade, whereas the Texas/Mexico populations clustered into another clade. The COI phylogeographic analysis suggests that the population of T. radiata in Texas did not come from Florida. The data also suggest that the population in Texas came from Mexico, or vice versa, because the Mexico population showed less haplotype diversity.

Living on the Edges: Spatial Niche Occupation of Asian Citrus Psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), in Citrus Groves

The spatial niche occupation of the Asian citrus psyllid, Diaphorina citri Kuwayama, 1908, was evaluated to determine its field colonization and food resource exploitation strategies in citrus groves. Mature grapefruit and sweet orange groves were surveyed as part of an area-wide program in 2009–2010 to determine D. citri population densities and between-tree distribution. In both cultivars, significantly more psyllids were found on perimeter trees throughout the study period suggesting a strong edge effect in D. citri distribution in the groves. D. citri densities and infestation levels gradually declined from the edge to the center of grove. Higher numbers of D. citri were recorded on trees located on the east and south sides of the groves than those on the west and north sides. Citrus groves located at the outer edge of the study with at least one side non-surrounded to other citrus groves harbored significantly more D. citri than groves located within the block cluster and entirely surrounded by other groves. In detailed field studies during 2012, infestation of D. citri started from border trees in the grove where possibly one generation is completed before inner trees become infested. In addition, psyllid densities decreased significantly with increasing distance from the grove edge. Using the selection index, D citri exhibited a strong niche occupation preference for border trees.

Survival of boll weevil (Coleoptera: Curculionidae) adults after feeding on pollens from various sources

The survival of overwintering boll weevil, Anthonomus grandis grandis (Boheman), adults on non‐cotton hosts in the Lower Rio Grande Valley (LRGV) of Texas was examined from 2001 to 2006. The success of the Boll Weevil Eradication Program, which was re‐introduced into the LRGV in 2005, depends on controlling overwintering boll weevil populations. Laboratory studies were conducted using boll weevil adults that were captured in pheromone traps from September through March. The number of adults captured per trap declined significantly in the field from fall to the beginning of spring (3.5‐7.0‐fold). The proportion of trapped males and females did not differ significantly. The mean weight of boll weevil adults captured in September was 13.3 mg, while those of captured adults from November to February were significantly lower and ranged from 6.7 to 7.8 mg. Our results show that boll weevil adults can feed on different plant pollens. The highest longevity occurred when adults were fed almond pollen or mixed pollens (72.6 days and 69.2 days, respectively) and the lowest when they fed on citrus pollen or a non‐food source (9.7 days or 7.4 days, respectively). The highest adult survival occurred on almond and mixed pollens [88.0%‐97. 6% after 1st feeding period (10 days), 78.0%‐90.8% after 3rd feeding period (10 days), 55. 0%‐83.6% after 5th feeding period (10 days), and 15.2%‐32.4% after 10th feeding period (10 days)]. The lowest adult survival occurred on citrus pollen [52.0%‐56.0% after 1st feeding period (10 days), 13.3% after 3rd and 5th feeding periods (10 days), and 0 after 6th feeding period (10 days)]. Pollen feeding is not a behavior restricted to adult boll weevils of a specific sex or physiological state. Understanding how boll weevil adults survive in the absence of cotton is important to ensure ultimate success of eradicating this pest in the subtropics.

Oviposition patterns of Creontiades signatus (Hemiptera: Miridae) on okra-leaf and normal-leaf cotton.

ABSTRACT We investigated the oviposition behavior of Creontiades signatus Distant (Hemiptera: Miridae), a relatively new plant bug pest of south Texas cotton, Gossypium hirsutum L, on okra-leaf and normal-leaf genotypes that differed significantly in their leaf morphology and trichome densities. In a no-choice study, the site preference and numbers of eggs oviposited by C. signatus were identical for the okra-leaf and normal-leaf. In a free-choice test, C. signatus showed a significant preference for the normal-leaf by ovipositing 3 times the number of eggs than on okra-leaf, but the site locations and percentages of egg distributions were similar for the two cotton types. The leaf petiole was the most preferred site for oviposition, followed by the main stem, and fruiting structures (squares and small bolls). The majority of eggs were oviposited in the leaf petioles associated with the mid-portion (nodes 4–8) of the plant. Trichome densities on the leaf petioles, main stem, and leaf veins were similar for node 3, but they were significantly higher on these structures for nodes 5 and 8 for the okra-leaf compared with the normal-leaf. The strong selection of oviposition sites in the normal-leaf cotton in this study may be due to some factor other than trichome density. This information should increase the knowledge for scouting for the presence of eggs and young nymphs and serve as a starting point for the selection of nonpreferred cotton varieties for oviposition by this mirid.