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The glassy-winged sharpshooter, Homalodisca vitripennis(Germar) (Hemiptera: Cicadellidae), is an important vector of bacterial Xyllela diseases throughout the southern and southwestern portions of the United States. Strong insect control measures, such that population densities of the insect vector are significantly reduced, are often necessary to limit the spread of Xylella fastidiosa. Glassy-winged sharpshooter populations within the Central Valley of California have developed a high resistance to imidacloprid (resistance ratio greater than 3,200) and tolerance to pyrethroids (ratio of less than 10) due to frequent applications of these materials. The purpose of this study was to determine the potential effects of insecticide resistance upon a variety of sharpshooter life history parameters associated with reproductive fitness. Our results indicate that individuals from susceptible populations of glassy-winged sharpshooters exhibited significantly higher fecundity and longer adult lifespans than those from the resistant populations. Additionally, resistant individuals were on average slightly larger than susceptible individuals. These results provide a strong indication that resistance to neonicotinoids imposes a reproductive fitness cost in an insecticide-free environment.

The Gram-negative bacterium Xylella fastidiosa causes disease in a number of important crops and plants within natural ecosystems. Most notable among these diseases are Pierce’s disease of grapevine, Citrus Variegated Chlorosis, Almond Leaf Scorch, Oleander Leaf Scorch and Olive Quick Decline Syndrome. In response to substantial economic losses, extensive research efforts have been underway over the past several decades in North and South America. Recently, X. fastidiosa has been detected in several countries of Europe and Asia, likely appearing as a result of global trading of plant material. Once established in a new region, X. fastidiosa spread is dependent on the obligate transmission by xylem-sap feeding insects. Sharpshooter leafhoppers (Hemiptera: Cicadellidae: Cicadellinae) are the best-studied group of vectors of this bacterium; however the list of known vector species is expanding. As X. fastidiosa moves into new regions, the combination of an introduced pathogen with existing or introduced vectors carries the potential of increasing economically important disease problems in the local context. By reviewing ecological and biological information of known X. fastidiosa vectors and the epidemiology of local X. fastidiosa outbreaks, this paper aims at increasing our understanding of vector– X. fastidiosa interactions.

Abstract: The California gnatcatcher is a threatened species essentially restricted to coastal sage scrub habitat in southern California. Its distribution and population dynamics have been studied intensely, but little is known about its diet. We identified arthropod fragments in 33 fecal samples of the California gnatcatcher to gain insight into its foraging ecology and diet. Fecal samples were collected from adult males, adult females, fledglings, and nestlings. Leaf- and planthoppers (Homoptera) and spiders (Araneae) predominated numerically in samples. Spider prey was most diverse, with eight families represented. True bugs (Hemiptera) and wasps, bees, and ants (Hymenoptera) were only minor components of the gnatcatcher diet. Gnatcatcher adults selected prey to feed their young that was larger than expected given the distribution of arthropod size available in their environment, and chicks were provisioned with larger prey items and significantly more grasshoppers and crickets (Orthoptera) and spiders than adults consumed themselves. Both adults and young consumed more sessile than active prey. Further studies are needed to determine whether arthropods sampled in coastal sage scrub that are common in fecal samples are good indicators of California gnatcatcher habitat.

Bioassays were conducted under greenhouse conditions to determine the effect of imidacloprid on adult and nymphal stages of the silverleaf whitefly, Bemisia argentifoliiBellows and Perring, and parasitism by Encarsia formosa(Gahan). A flowable formulation (24Oglitre-1) of imidacloprid at six rates (0.09, 0.04 and 0.02 g a.i. litre-1pot volume for experiments 1 and 2; 0.009, 0.004, and 0.002 g a.i. litre-1pot volume for experiment 3) was evaluated. After a 48 h exposure to treated plants, high mortality of adult whitefly (>94) was observed. Adults exposed to poinsettias treated 150 days earlier also had significantly greater mortality (>79) than the adults on control plants. When exposed to treated plants for only 6 h, >65 of adults were killed. All three rates of imidacloprid caused >97 mortality of immature whiteflies by day 19. When treated plants were continually exposed to adult whiteflies, immature mortality was 100 for the three higher rates of imidacloprid up to and including 88 days after treatment. During the same time, emerging adults were reduced significantly. Immatures reinfested on plants treated 161 days earlier, incurred 80 mortality at the higher rate 0.09 g a.i. litre-1pot volume and 38 mortality at 0.02 g a.i. litre-1pot volume. At lower treatment rates, results varied. At 0.009 g a.i. litre-1of pot volume, mean percentage whitefly mortality (65) 25 days after treatment was significantly higher than the controls; however, whitefly mortality at 0.004 and 0.002 g a.i. litre-1pot volume was not significantly different from controls or plants treated with the higher rate. Parasitoids could develop to the adult stage on whiteflies infesting imidacloprid treated plants. Parasitism occurred at low levels (< 10), doe to high levels of whitefly mortality on treated plants. No phytotoxicity was observed for any treatment throughout the length of the trials that lasted through flowering.

Population parameters of the melon aphid, Aphis gossypiiGlover, were compared for insects grown on six cultivars of chrysanthemum, Dendranthema grandifloraTzvelev (‘Fontana’, ‘Iridon’, ‘Pink Lady’, ‘Splendor’, ‘White Diamond’, and ‘White View Time’) fertilized with 3 different levels of nitrogen (80, 160 and 240 mg N/l) and 2 levels of irrigation (high 300 ml and low 210 ml every other day). Fecundity, longevity, and survivorship of aphids were significantly affected by the cultivar treatment, but were not affected by irrigation or fertilizer treatments or by any combination of interactions among cultivar, fertilizer and irrigation. Significantly fewer aphids survived on the cultivar ‘Pink Lady’ (populations reduced by 20.8%) than any other cultivar examined. Intrinsic rates of increase (rm), finite rates of increase (R0), and population doubling times (DT) for aphids were different among fertilizer levels and cultivars, but were not different among irrigation levels. There were no significant fertilizer by irrigation interaction effects upon rm, R0, or DT. The highest rate of fertilizer applied (240 mg N/liter) adversely affected the intrinsic rate of increase of melon aphids; however, aphid intrinsic rate of increase was weakly correlated with foliar soluble protein levels (r= 0.989, P = 0.0954). Foliar soluble protein levels were not associated with fertilization treatment. Melon aphids perform consistently better on the cultivars ‘White Diamond’, ‘Fontana’, and ‘Splendor’, relative to those aphids growing on ‘Iridon’, ‘Pink Lady’, or ‘White View Time’. In general, melon aphids performed best on ‘White Diamond’ and poorest on ‘Pink Lady’.

Acutaspis albopicta (Cockerell) is an exotic scale detected on imported ‘Hass’ avocados arriving in California from Mexico. An effort was made to understand how well this species might be biologically controlled by the parasitoid, Aphytis melinus DeBach. In no-choice trials, single life stages of A. albopicta and Aonidiella aurantii (Maskell) were exposed to one Ap. melinus female. Ap. melinus attacked and developed to adult on all A. albopicta life stages tested, which included early, middle, and late male and female second instars, and early, middle, and late female third instars. However, the proportion of scales attacked was relatively low (≤20%), as were the number of eggs laid on each scale stage. In six of seven comparisons of scale cover surface area between A. albopicta and Ao. aurantii that were similarly aged, Ao. aurantii was significantly larger. With intraspecific choice trials, females of Ap. melinus strongly preferred to parasitize the oldest and largest female scales in both single- and mixed-sex offerings. Younger, smaller scales were preferred for host feeding. Five comparisons of preference between A. albopicta and Ao. aurantii showed that Ap. melinus preferred 28- and 36-d-old Ao. aurantii females over similarly aged A. albopicta. However, Ap. melinus preferred 23-d-old males of A. albopicta. In three of five comparisons, Ao. aurantii was the preferred species to host feed on. More F1 females of Ap. melinus were recovered from both intraspecific choice trials compared with any stage in no-choice trials. Implications of incorporating Ap. melinus into biological control programs are discussed.

Operational parameters of traps baited with the pheromones of three mealybug species were optimized in nurseries producing ornamental plants. All pheromone doses (1-320 μg) attracted Pseudococcus longispinus (Targioni Tozzetti) and Pseudococcus viburni (Signoret) males, with the lowest dose (1 μg) attracting the fewest males for both species. Doses of 3.2-100 μg were as attractive to male P. longispinus as the highest dose (320 μg); doses from 10 to 320 μg were equally attractive for P. viburni males. Lures containing 25-μg doses of either pheromone had effective field lifetimes of at least 12 wk. Experiments were performed to test the efficacy of combining multiple pheromones to attract several species of mealybugs simultaneously. Lures loaded with a mixture of the pheromones of P. longispinus, P. viburni, and Planococcus citri (Risso) were as attractive to P. viburni and P. citri as lures with their individual pheromones. Response of P. longispinus to the blend was decreased by 38% compared with its pheromone as a single component. A subsequent trial with two-component blends showed that the pheromone of P. citri was responsible for this modest decrease in P. longispinus response. This should not affect the overall efficacy of using these lures for monitoring the presence of all three mealybug species simultaneously. Pheromone traps were used to detect infestations of P. longispinus throughout the season and to track population cycles. When pheromone-baited traps for P. longispinus were compared with manual sampling, trap counts of male mealybugs were significantly correlated with mealybugs counted on plants in the vicinity of the traps.

Although larvae and adults of the herbivorous beetle Trirhabda geminata Horn (Coleoptera: Chrysomelidae) are primarily considered to be specialists on Encelia farinosa (Compositae: Asteraceae), some reports exist of these beetles feeding on related Encelia species. Within the genus Encelia, many species are thought to have evolved relatively recently. In addition, some Encelia species have very similar secondary chemistries and overlapping geographic distributions. In the laboratory, individual T. geminata were reared on E. farinosa or the sympatrically occurring species E. actoni or E. californica. Survival, growth, and development were analyzed for larvae feeding on each host plant species. Overall, herbivore performance was better on E. farinosa, with significantly greater survival, faster development, and greater mass gain. Beetle development on E. californica was intermediate, with some measure, indicating better performance than on E. actoni and other measure, indicating no difference between these potential hosts. Importantly, although performance was decreased on E. actoni and E. californica, some individuals were able to develop successfully, suggesting that populations of T. geminata may be able to adapt to use these host plants.

A mark–release–recapture technique was developed and tested for use in tracking the field movements of adult glassy-winged sharpshooters, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), in various agricultural and urban plantings. Greenhouse experiments in which adult H. coagulata were marked with one of five colored fluorescent dusts (Aurora Pink-A11, Horizon Blue-A19, Blaze Orange-A15N, Saturn Yellow-A17, and Corona Magenta-A21) and released into cages with citrus seedlings showed that their mortality rates during a 30-d period were statistically similar to that of the undusted controls. Adults marked with a sixth dust color (Signal Green-A18N) suffered higher rates of mortality than did the undusted controls and thus were eliminated from further consideration. Adult H. coagulata marked with one of the five accepted colors of fluorescent dust were able to fly beyond 100 m in a field devoid of vegetation within minutes of their release, and the marking did not affect overall flight behavior significantly compared with that of the undusted controls. However, at wind speeds above 5 m/s, percentage recapture was significantly reduced, which indicates that both dusted and undusted adults were unable to orient their flight. In total, 41,124 marked and unmarked adults were released in the three field experiments in southern California (Riverside and Kern counties) during 2000 and 2001 to evaluate flight dispersal and estimate densities of H. coagulata. The mark–release–recapture and feral data obtained during the June, July, and August 2001 studies, when coupled with the Lincoln index, yielded estimates of adult H. coagulata of 1.2 and 2.2 million per ha, respectively, at a San Joaquin Valley (Kern Co.) and a southern California (Riverside Co.) citrus grove. The use of colored dusts to mark H. coagulata proved to be reliable, cost-effective, and time-efficient for mark–release–recapture studies with this insect within a citrus grove, but they are less likely to be useful for studies of adult H. coagulata movements among plantings.

Homalodisca coagulata (Say) is a recent introduction to California. It is known to spread a strain of the bacterium Xylella fastidiosa Wells, Raju, Hung, Weisberg, Mandelco-Paul & Brenner that induces oleander leaf scorch disease in oleander, Nerium oleander L. Oleander leaf scorch is lethal to oleander and threatens to decimate one of the most important landscape shrubs in California. Towards developing a management strategy for H. coagulata-spread oleander leaf scorch, we documented the affects of selected insecticides on H. coagulata mortality, feeding behavior, and disease transmission in a greenhouse study. Oleanders treated with fenpropathrin, fenpropathrin + acephate, and imidacloprid caused significant mortality to caged H. coagulata within 4 h of exposure. Within 24 h, these pesticides caused nearly 100% mortality 3 wk after treatment. In other experiments, acetamiprid and fenpropathrin treatments reduced time spent feeding and total time on plants. H. coagulata on fenpropathrin-, acetamiprid-, and imidacloprid-treated oleander died in less than 13 min on average. Oleander leaf scorch transmission by H. coagulata was blocked by applications of foliar-applied acetamiprid, and soil-applied imidacloprid and thiamethoxam.

Homalodisca coagulata (Say) is a recent introduction to California. It is known to spread a strain of the bacterium Xylella fastidiosa Wells, Raju, Hung, Weisberg, Mandelco-Paul & Brenner that induces oleander leaf scorch disease in oleander, Nerium oleander L. Oleander leaf scorch is lethal to oleander and threatens to decimate one of the most important landscape shrubs in California. Towards developing a management strategy for H. coagulata-spread oleander leaf scorch, we documented the affects of selected insecticides on H. coagulata mortality, feeding behavior, and disease transmission in a greenhouse study. Oleanders treated with fenpropathrin, fenpropathrin + acephate, and imidacloprid caused significant mortality to caged H. coagulata within 4 h of exposure. Within 24 h, these pesticides caused nearly 100% mortality 3 wk after treatment. In other experiments, acetamiprid and fenpropathrin treatments reduced time spent feeding and total time on plants. H. coagulata on fenpropathrin-, acetamiprid-, and imidacloprid-treated oleander died in less than 13 min on average. Oleander leaf scorch transmission by H. coagulata was blocked by applications of foliar-applied acetamiprid, and soil-applied imidacloprid and thiamethoxam.

Microhabitats of postdiapause larvae of Euphydryas editha quino (Behr) were found to differ from random habitat points in percentage cover, grass, shade, shrub, and host plant (Plantago erecta E. Morris). Abundant host plant and little shade or overstory cover characterized larval microhabitat. Larvae found in shrub versus more open habitats occupied similar microhabitats but were significantly smaller, presumably because of delayed diapause break. Larval use of coastal sage scrub, when shrubs have been removed by disturbance (grading of dirt roads), suggests that some degree of intermediate disturbance resulting in removal of shrub canopy and increased insolation may benefit populations of this endangered insect.

The major pest of the cut-flower crop, Geraldton wax, Chamelaucium uncina-tum Schauer, is a gall-forming wasp, Oncastichus goughi Headrick & Lasalle. Little information is available concerning the activity and distribution of this pest in California. The objectives of this study, then, were to determine if sticky cards would trap adult gall wasps in the field and to determine the seasonal and varietal distribution of these wasps in southern California Geraldton wax fields. Field trials determined that either yellow or green insect sticky cards may be used to trap populations of adult gall wasps. Trap data indicated that populations of adult gall wasps peaked during fall (October-November) and varied throughout the remainder of the year. Furthermore, among the varieties examined, the cultivar 'Lady Stephanie' was least susceptible to adult gall wasps, whereas the cultivar White' was most susceptible.

A California native grassland was sampled to describe recovery of grasshopper communities after prescribed spring burning. Grasshopper density and grasshopper biomass were significantly reduced by spring burning both the year of the burn (1993) and the subsequent year (1994). Grasshopper density and grasshopper biomass appeared to stabilize 2 yr after a burn (1995). Immediately after burning, grasshopper diversity was higher because of a reduction in the dominance of the migratory grasshopper, Melanoplus sanguinipes (F.), and a relative increase in the number of Oedipodinae species, which prefer sparsely vegetated areas. Time since burning had no effect on grasshopper diversity 1 or 2 yr after burning. Burning significantly reduced the cover of exotic grasses and increased the cover of bare ground 1 yr after a burn. Grasshopper density was positively related to forb cover 1 yr after burning. Prescribed spring burning reduces grasshopper density and grasshopper biomass and likely increases grasshopper diversity.

The seasonal distribution of Trirhabda geminata Horn, the dominant herbivore of brittle brush, Encelia farinosa Gray, was monitored in California coastal sage scrub. Larval emergence coincided with the 1st precipitation of the growing season and the development of young host-plant foliage. Larvae were present from December through April; 3 instars were detected. Pupation occurs in the upper 5 cm of the soil immediately underneath host plants. Adults were present from early March through mid-June. The number of adults exhibiting mating behaviors (mate selection, copulation, mate guarding) was at a maximum in April. Larval T. geminata are parasitized by the tachinid fly Chaetonodexodes vanderwulpi (Town-send) with parasitism rates ranging from 3.4 to 34.9% for the 2 yr of study. The presence of a summer quiescence period and the apparent lack of a diapause period is discussed for this species.

Eggs of Trirhabda geminata (Horn) were subjected to several constant temperatures (15, 22, 25, and 30°C) and moisture (wet or dry for varying lengths of time) regimens. Upon wetting, eggs changed color (from brown to yellow-orange) and swelled from 1.07 by 0.64 to 1.14 by 0.72 mm (length by width). Warmer temperatures shortened embryonic development time for eggs held wet. Eggs that were continuously held dry did not develop. A chilling requirement or diapause was not required for successful hatch. Optimal temperature for egg survival (98%) was 25°C. Some eggs hatched at all temperature regimens as long as they were in contact with a moisture source. The longer the period that eggs were held dry, however, the greater the decrease in survivorship. Approximately 10% of eggs held dry for extended periods (322 d) are still able to hatch when moistened. Our results indicate that moisture is required for egg development and is likely used as a proximal stimulus by T. geminata for the availability of its host plant.

Crop contents of the lesser migratory grasshopper, Melanoplus sanguinipes F., were identified from specimens collected in a California native grassland, an increasingly rare habitat. Samples were taken of late immature stages (early summer 1994 and 1995) and adults (late summer 1994 and 1995) from areas burned in 1992 and 1993. Overall, forbs were the most common vegetation type found in grasshopper diets for late summer 1994 and 1995, and early summer 1995. For all sample dates, native grasses were significantly more abundant in grasshopper diets than exotic grasses. Percentage of cover of forbs (an index of food availability) was lower than cover of both native and exotic grasses in the field; however, forbs were the most abundant vegetation type in grasshopper diets for 3 of 4 samples, indicating a feeding preference for forbs. Time since rangeland burning (1992 versus 1993) had a significant effect on grasshopper diets in both early and late summer 1994, but not in 1995. The proportion of forbs found in grasshopper crops from recently burned areas (1993) in the late summer 1994 sampling period was higher than in areas burned earlier (1992); the burning treatment had the opposite effect on the proportion of native grasses in grasshopper diets. No effects of time since burning treatment were found in 1995. These data support the hypothesis that grasshopper herbivory has a stronger impact on native grasses than exotic grasses in California native grasslands; however, this impact is diluted, because forbs are preferred over both native grasses and exotic grasses. Furthermore, fire alters grasshopper diets 1 yr after a fire, and this effect is undetectable two years after a fire.