Marvin K. Harris

Temperature and Host Plant Effects on Development, Survival, and Fecundity of Bemisia argentifolii (Homoptera: Aleyrodidae)

Abstract Development time and percent survival of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring (formerly referred to as B strain of sweetpotato whitefly), were determined at five constant temperatures ranging from 20 to 35°C on two cultivars of cotton, cantaloupe, and pepper (Capsicum sp.). Fecundity was recorded at 30°C during the first 10 d of adulthood. Developmental, survival, and fecundity rates were not significantly different between cultivars within crops of either cotton or cantaloupe, but varied between crops. Development time from egg to adult at 20–32°C ranged from 14.6 ± 0.8 (mean ± SE) to 36.0 ± 1.0 d on cantaloupe and from 16.3 ± 0.7 to 37.9 ± 2.1 d on cotton, respectively. Whiteflies did not develop at 35°C or on pepper at any temperature. Minimum developmental thresholds and degree-days requirements from egg to adult were 11.1°C and 312.5 DD on cotton and 13.2°C and 250.0 DD on cantaloupe, respectively. Immature survival was high (76.5 ± 11.5–100%) on cantaloupe, intermediate (37.3 ± 13.3–64.4 ± 10.2%) on cotton, and very low (0–8.3 ± 8.3%) on pepper from 20–32°C. Fecundity ranged from 153.3 ± 10.8–158.3 ± 9.3 eggs per female on cantaloupe, from 117.0 ± 6.0–117.5 ± 22.1 eggs per female on cotton, and from 2.1 ± 0.7–40.5 ± 5.8 eggs per female on pepper, at 30°C.

Pea aphid promotes amino acid metabolism both in Medicago truncatula and bacteriocytes to favor aphid population growth under elevated CO2

Rising atmospheric CO(2) levels can dilute the nitrogen (N) resource in plant tissue, which is disadvantageous to many herbivorous insects. Aphids appear to be an exception that warrants further study. The effects of elevated CO(2) (750 ppm vs. 390 ppm) were evaluated on N assimilation and transamination by two Medicago truncatula genotypes, a N-fixing-deficient mutant (dnf1) and its wild-type control (Jemalong), with and without pea aphid (Acyrthosiphon pisum) infestation. Elevated CO(2) increased population abundance and feeding efficiency of aphids fed on Jemalong, but reduced those on dnf1. Without aphid infestation, elevated CO(2) increased photosynthetic rate, chlorophyll content, nodule number, biomass, and pod number for Jemalong, but only increased pod number and chlorophyll content for dnf1. Furthermore, aphid infested Jemalong plants had enhanced activities of N assimilation-related enzymes (glutamine synthetase, Glutamate synthase) and transamination-related enzymes (glutamate oxalate transaminase, glutamine phenylpyruvate transaminase), which presumably increased amino acid concentration in leaves and phloem sap under elevated CO(2). In contrast, aphid infested dnf1 plants had decreased activities of N assimilation-related enzymes and transmination-related enzymes and amino acid concentrations under elevated CO(2). Furthermore, elevated CO(2) up-regulated expression of genes relevant to amino acid metabolism in bacteriocytes of aphids associated with Jemalong, but down-regulated those associated with dnf1. Our results suggest that pea aphids actively elicit host responses that promote amino acid metabolism in both the host plant and in its bacteriocytes to favor the population growth of the aphid under elevated CO(2).

Sticky Traps for Monitoring Pseudacteon Parasitoids of Solenopsis Fire Ants

Abstract A newly developed method for passively trapping adult Pseudacteon phorid flies, which parasitize workers of Solenopsis saevissima complex fire ants, is described. Adult flies responding to deployed Solenopsis invicta midden were captured when they landed on a Tanglefoot®-coated perch, which is part of the trap. This sampling method provided a uniform, repeatable, and verifiable sample that allowed continuous and simultaneous sampling among locations, which can only be accomplished with other techniques by substantially increasing the number of observers. A field test showed the superior operational efficiency and effectiveness of this method relative to other techniques. These traps have been shown effective in various phorid habitats in Texas and Florida. We expect this trap to also be effective in detecting/monitoring phorid flies in other locations.

Response of multiple generations of beet armyworm, Spodoptera exigua (Hübner), feeding on transgenic Bt cotton

Development, reproduction and food utilization of three successive generations of beet armyworm, Spodoptera exigua (Hübner), fed on transgenic and non‐transgenic Bt cotton were examined. Significantly longer larval life‐span and lower pupal weight were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non‐transgenic Bt cotton. Significantly higher survival rate and adult fecundity of S. exigua were found in three successive generations of S. exigua fed on transgenic Bt cotton compared with non‐transgenic Bt cotton. The survival rate and adult fecundity of S. exigua were occurred significant increase in the third generation compared with the first generation after feeding on transgenic Bt cotton. Significantly lower consumption, frass and relative growth rate (RGR) were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non‐transgenic Bt cotton. Cotton variety significantly affected all indices of larval consumption and utilization in three successive generations of S. exigua, except for efficiency of conversion of ingested food. However, beet armyworm generation only significantly affected RGR of S. exigua. The results of this study indicated food quality on the diet‐utilization efficiency of S. exigua was different along with beet armyworm generation. Measuring multigenerational development and food utilization of S. exigua at individual and population level in response to Bacillus thuringiensis (Bt) can provide a more meaningful evaluation of long‐term population dynamics than experiments on a single generation. It is imperative to develop an appropriate multigenerational pest management tactic to monitor the field population dynamics of non‐target pests (e.g., beet armyworm) in agricultural Bt cotton ecosystem.

Impact of insecticides on parasitoids of the leafminer, Liriomyza trifolii, in pepper in south Texas

Abstract Liriomyza leafminers (Diptera: Agromyzidae) are cosmopolitan, polyphagous pests of horticultural plants and many are resistant to insecticides. Producers in South Texas rely on insecticides as the primary management tool for leafminers, and several compounds are available. The objective of this study is to address the efficacy of these compounds for controlling Liriomyza while minimizing their effects against natural enemies. Research plots were established at Texas AgriLife research center at Weslaco, Texas in fall 2007 and spring 2008 seasons, and peppers were used as a model crop. Plots were sprayed with novaluron, abamectin, spinetoram, lambda-cyhalothrin and water as treatments according to leafminer infestation; insecticide efficacy was monitored by collecting leaves and infested foliage. Plant phenology was also monitored. Novaluron was the most effective insecticide and lambda-cyhalothrin showed resurgence in leafminer density in fall 2007 and no reduction in spring 2008. Other compounds varied in efficacy. Novaluron showed the least number of parasitoids per leafminer larva and the lowest parasitoid diversity index among treatments followed by spinetoram. Liriomyza trifolii (Burgess) was the sole leafminer species on peppers, and 19 parasitoid species were found associated with this leafminer. Application of these insecticides for management of leafminers with conservation of natural enemies is discussed.

Host Plant Effects on Alkaline Phosphatase Activity in the Whiteflies, Bemisia tabaci Biotype B and Trialeurodes vaporariorum

Abstract Bemisia tabaci (Gennadius) B-biotype and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) often coexist on greenhouse-grown vegetable crops in northern China. The recent spread of B. tabaci B-biotype has largely replaced T. vaporariorum, and B-biotype now overlaps with T. vaporariorum where common hosts occur in most invaded areas. The impact of the B-biotype on the agro eco system appears to be widespread, and involves the ability to compete with and perhaps replace other phytophages like T. vaporariorum. An emerging hypothesis is that the B-biotype is physiologically superior due at least in part to an improved ability to metabolically utilize the alkaline phosphatase pathway. To test this hypothesis, alkaline phosphatase activity was studied in the B-biotype and T. vaporariorum after feeding on a number of different hosts for a range of durations, with and without host switching. Alkaline phosphatase activity in T. vaporariorum was 1.45 to 2.53-fold higher than that of the B-biotype when fed on tomato for 4 and 24 h, or switched from tomato to cotton and cabbage for the same durations. However, alkaline phosphatase activity in the B-biotype was 1.40 to 3.35-fold higher than that of T. vaporariorum when the host switching time was ∼72 and ∼120 h on the same plant. Both short-term (4 h) and long-term (72 h) switching of plant hosts can significantly affect the alkaline phosphatase activity in the two species. After ∼120 h, feeding on tomato and cotton alkaline phosphatase activity in the B-biotype was significantly higher than that of T. vaporariorum. It was shown that alkaline phosphatase aids the species feeding on different plant species, and that the B-biotype is physiologically superior to T. vaporariorum in utilizing the enzyme compared to T. vaporariorum over longer periods of feeding.

Up-regulation of abscisic acid signaling pathway facilitates aphid xylem absorption and osmoregulation under drought stress

Highlight Aphid fecundity is curtailed in drought-stressed plants primarily via reduced water status; however, activation of ABA signaling by drought cross-talks with SA and JA signaling to reduce induced plant resistance effects on aphid fecundity.

Native Ant Responses to Solenopsis invicta Buren Reduction Using Broadcast Baits

Abstract A pilot study was conducted to investigate the impact of Solenopsis invicta management with an insect growth regulator bait (s-methoprene) on native ant species and to determine the responses of these species to S. invicta reduction. This invasive species alters the diversity and structure of different trophic levels of arthropod assemblages. Despite advances in S. invicta management using biological control agents, poison baits remain as the primary tool for effective fire ant management. However, the effect of these products on native ants is relatively unknown. Understanding these effects is critical to the development of S. invicta management strategies that include conservation of native ants. Native ants compete with S. invicta to some degree and can bolster efforts to release and establish exotic biological control agents to more effectively manage S. invicta. The study was carried out in Mumford, TX. Two treatments were used: a bait treatment that reduced S. invicta densities and a control. The treatments were randomly assigned to 1.33-ha blocks, replicated four times, and periodically inspected using complementary sampling techniques (pitfall traps, baited vials, manual collections, and nest surveys). Sixteen ant species were found among the two treatments. After S. invicta reduction, significant increases in densities of several other ant species were observed. Species within the assemblage shifted from the dominance by S. invicta to the dominance of the native pyramid ant, Dorymyrmex flavus McCook, which showed the most significant increase in bait treated blocks and was found to persist at densities significantly higher than the control for >2 yr after the last bait treatment. A temporary change in diversity was observed, indicating that use of a poison bait for S. invicta management benefited numerous resident species in the ant assemblage.

Density–Yield Relationships and Economic Injury Levels for Bemisia argentifolii (Homoptera: Aleyrodidae) in Cantaloupe in Texas

Abstract A range of infestation levels of the whitefly Bemisia argentifolii Bellows & Perring were established across experimental field plots of cantaloupe by varying insecticide treatments to evaluate the relationships between whitefly density and crop yield and quality. High levels of whitefly adults and immatures were associated with significant reductions in fruit yield, a decrease in fruit size, and an increase in the percentage of fruits with sooty mold. Yield loss rates (kg/ha/adult or nymph) decreased in a nonlinear fashion with increasing whitefly numbers. Estimated economic injury levels varied as a function of whitefly density, whitefly stage, control cost, crop cultivar, and crop season. Estimates of economic injury levels for one (

A New Pheromone Race of Acrobasis nuxvorella (Lepidoptera: Pyralidae)

31.2/ha), five (