J. Scott Armstrong

Temperature‐dependent development and reproduction of the boll weevil (Coleoptera: Curculionidae)

Abstract Effects of temperature on development, survival, and fecundity of boll weevil, Anthonomus grandis grandis Boheman, were assessed at 10, 11, 12, 15,20,25,30,35,45, and 46 °C; 65% relative humidity; and a photoperiod of 13:11 (L: D) h. The mortality of boll weevil immature stages was 100% at 12°C and decreased to 36.4% as the temperature increased to 25°C. When the temperature increased from 30 °C to 45 °C, the mortality of weevils also increased from 50.1% to 100%. From 15°C to 35°C, the bollweevilpreimaginal development rate was linearly related to temperature. The average development time of total boll weevil immature lifestages decreased 3.6‐fold and the preovipositional period decreased 3.3‐fold when the temperature was increased from 15°C to 30°C. The lower threshold for development was estimated at 10.9, 6.6, 7.0, and 9.0 °C for eggs, larval, pupal, and total immature stages, respectively, with total thermal time requirement to complete immature stages of 281.8 DD (degree day) (15°C) and 247.8 DD (35 °C). At 1LC and 46°C, weevil females did not oviposit. Longevity of adult females decreased 4.6‐fold with increasing temperatures from 15°C to 35°C. Fecundity increased with increasing temperatures up to 30°C and significantly decreased thereafter. These findings will be useful in creating a temperature‐based degree‐day model for predicting the occurrence of key life stages in the field. An accurate predictor of a pests development can be very important in determining sampling protocols, timing insecticide applications, or implementing an integrated pest management control strategy targeting susceptible life stages.

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.

EFFICACY OF SINGLE AND DUAL GENE COTTON GOSSYPIUM HIRSUTUM EVENTS ON NEONATE AND THIRD INSTAR FALL ARMYWORM, SPODOPTERA FRUGIPERDA DEVELOPMENT BASED ON TISSUE AND MERIDIC DIET ASSAYS1

ABSTRACT We evaluated mortality and developmental parameters of fall armyworms, Spodoptera frugiperda (J. E. Smith), to the single Bacillus thuringiensis (Bt) cotton trait, Bollgard® and dual Bt cotton traits (Bollgard II® and WideStrike™) by using a cotton leaf-tissue assay and by incorporating lyophilized cotton tissue into a meridic diet. Bioassays were conducted for both neonate and 3rd instars. Leaf tissue bioassays indicated that Bollgard II® and WideStrike™ are highly effective against fall armyworm neonates by causing mortality and by retarding development parameters such as larval weight, pupal duration, and time to adulthood. Bollgard® was not significantly different from non-transgenic cotton in terms of mortality or feeding, with the exception of the non—Bt (PhytoGen 425RF), which had an inherent form of resistance that is not associated with a transgenic event. Third instars evaluated with lyophilized diet bioassays were not as affected by the Bt traits to the same degree as neonates; however, larval weights were lower, and developmental parameters such as time to pupation and time to adulthood were longer. The duration of pupal development was significantly longer for 3rd instars that survived the highest dose of 5,000 µg of WideStrike™ cotton tissue. Sublethal doses for Bollgard II® and WideStrike™ were generally observed at 500 to 5,000 µg of lyophilized cotton tissue per mg of meridic diet, depending upon the variable (time to pupation, pupal duration, time to adult emergence) measured.

Actual and Simulated Injury of Creontiades signatus (Heteroptera: Miridae) Feeding on Cotton Bolls

The actual feeding injury of Creontiades signatus Distant (Heteroptera: Miridae) was compared with a simulated technique during 2005, 2006 and 2008 by injecting varying dilutions of pectinase into cotton bolls at different boll sizes (ages) and into 2 or 4 locules to determine if such a technique could be used to reduce the time and labor involved with conducting economic injury level studies in the field. The most accurate simulation occurred in 2008 by injecting 1 μL of 10% pectinase into all 4 locules of a cotton boll. This improved the relationships of injury score to seed cotton, seed, and lint weights. The youngest boll age class of ≥ 2 cm diam. (2 d of age) was not significantly more damaged than the medium age ≥ 2.5 cm (8 d of age) bolls, and both sustained significantly more injury than the large boll classification of ≥ 3 cm (12 d of age). However, small bolls were at least 3 times more likely to abscise than medium-sized bolls, and large bolls did not abscise regardless of treatment. Some damage was observed for large bolls from the injected and actual feeding compared with the controls, but the lint and seed weights were not significantly different for any of the treatments including the controls. Our study characterizes the feeding injury caused by C. signatus and describes a simulated technique that may be used to further economic injury studies.

Plant growth stage-specific injury and economic injury level for verde plant bug, Creontiades signatus (Hemiptera: Miridae), on cotton: effect of bloom period of infestation.

ABSTRACT Verde plant bugs, Creontiades signatus Distant (Hemiptera: Miridae), were released onto caged cotton, Gossypium hirsutum L., for a 1-wk period to characterize the effects of insect density and bloom period of infestation on cotton injury and yield in 2011 and 2012, Corpus Christi, TX. When plants were infested during early bloom (10–11 nodes above first white flower), a linear decline in fruit retention and boll load and a linear increase in boll injury were detected as verde plant bug infestation levels increased from an average of 0.5 to 4 bugs per plant. Lint and seed yield per plant showed a corresponding decline. Fruit retention, boll load, and yield were not affected on plants infested 1 wk later at peak bloom (8–9 nodes above first white flower), even though boll injury increased as infestation levels increased. Second-year testing verified boll injury but not yield loss, when infestations occurred at peak bloom. Incidence of cotton boll rot, known to be associated with verde plant bug feeding, was low to modest (<1% [2012] to 12% [2011] of bolls with disease symptoms), and drought stress persisted throughout the study. Caging effect was minimal: a 10% fruit retention decline was associated with caging, and the effect was not detectable in the other measurements. Overall, reduced fruit retention and boll load caused by verde plant bug were important contributors to yield decline, damage potential was greatest during the early bloom period of infestation, and a simple linear response best described the yield response—insect density relationship at early bloom. Confirmation that cotton after peak bloom was less prone to verde plant bug injury and an early bloom-specific economic injury level were key findings that can improve integrated pest management decision-making for dryland cotton, at least under low-rainfall growing conditions.

Sampling Strategies for Square and Boll-Feeding Plant Bugs (Hemiptera: Miridae) Occurring on Cotton

ABSTRACT Sampling methods for square and boll-feeding plant bugs (Hemiptera: Miridae) occurring on cotton, Gossypium hirsutum L., were compared with the intent to assess if one approach was viable for two species occurring from early-season squaring to late bloom in 25 fields located along the coastal cotton growing region of south Texas. Cotton fleaphopper, Pseudatomoscelis seriatus (Reuter), damages squares early-season and dominated collections using five sampling methods (≈99% of insects collected). A major species composition shift occurred beginning at peak bloom in coastal fields, when verde plant bug, Creontiades signatus Distant, represented 55–65% of collections. Significantly more cotton fleahoppers were captured by experienced samplers with the beat bucket and sweep net than with the other methods (30–100% more). There were more than twice as many verde plant bugs captured by experienced and inexperienced samplers with the beat bucket and sweep net than captured with the KISS and visual methods. Using a beat bucket or sweep net reduced sampling time compared with the visual method for the experienced samplers. For both species, comparing regressions of beat bucket-based counts to counts from the traditional visual method across nine cultivar and water regime combinations resulted in only one combination differing from the rest, suggesting broad applicability and ability to translate established visual-based economic thresholds to beat bucket-based thresholds. In a first look at sample size considerations, 40 plants (four 10-plant samples) per field site was no more variable than variation associated with larger sample sizes. Overall, the beat bucket is much more effective in sampling for cotton fleahopper and verde plant bug than the traditional visual method, it is more suited to cotton fleahopper sampling early-season when plants are small, it transitions well to sample for verde plant bug during bloom, and it performs well under a variety of soil moisture conditions and cultivar selections.

Verde plant bug (Hemiptera: Miridae) feeding injury to cotton bolls characterized by boll age, size, and damage ratings.

ABSTRACT The verde plant bug, Creontiades signatus (Distant), has been present in south Texas for several years but has more recently been documented as an economic threat to cultivated cotton, Gossypium hirsutum L. Our studies over 2 yr (2009 and 2010) and two locations (Weslaco and Corpus Christi, TX) investigated feeding-injury of the verde plant bug to a range of cotton boll age classes defined by boll diameter and accumulated degree-days (anthesis to the time of infesting) for first-position cotton bolls infested with the plant bugs. The most detrimental damage to younger cotton bolls from verde plant bug feeding was boll abscission. Cotton bolls <04 accumulating daily degree-days (ACDD), or a boll diameter of 1.3 cm were subject to 60–70% higher boll abscission when compared with the noninfested controls. Significantly higher boll abscission occurred from verde plant bug injured bolls compared with the controls up to 162 ACDD or a mean boll diameter 2.0 cm. Cotton seed weights were significantly reduced up to 179 ACDD or a boll diameter of 2.0 cm at Weslaco in 2009, and up to 317 ACDD or boll diameter 2.6 cm for Weslaco in 2010 when compared with the noninfested controls. Lint weight per cotton boll for infested and noninfested bolls was significantly reduced up to 262 ACDD or boll diameter 2.5 for Corpus Christi in 2010 and up to 288 ACCD or boll diameter 2.6 cm for Weslaco, TX, in 2010. Damage ratings (dependant variable) regressed against infested and noninfested seed-cotton weights showed that in every instance, the infested cotton bolls had a strong and significant relationship with damage ratings for all age classes of bolls. Damage ratings for the infested cotton bolls that did not abscise by harvest showed visual signs of verde plant bug feeding injury and the subsequent development of boll rot; however, these two forms of injury causing lint and seed mass loss are hard to differentiate from open or boll-locked cotton bolls. Based on the results of both lint and seed loss over 2 yr and four studies cotton bolls should be protected up to ≈300 ACDD or a boll diameter of 2.5 cm. This equilibrates to bolls that are 12–14 d of age dependent upon daily maximum and minimum temperatures.

Nonlinear Degree-Day Models for Postdiapause Development of the Sunflower Stem Weevil (Coleoptera: Curculionidae)

ABSTRACT The sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), has caused yield losses across much of the western Great Plains, Little is known about the field biology of this pest. Simple prediction models, such as degree-day models, are an integral tool for development of C. adspersus management strategies. Using data collected in Colorado, Kansas, and Nebraska, we sought for predictable variation between C. adspersus pupation, adult eclosion, and emergence and accumulated degree-days Celsius (DD) by using a temperature threshold of 5°C. Accurate phenological models can be used to time scouting efforts and pesticide applications. The relationship between phenological data and accumulated DD fit nonlinear, Gaussian distributions better than uniform distributions. Phenological models were developed to describe these distributions for pupation, adult presence within the stalk and adult emergence, The pupation model predicts 50% pupation at 197 DD and 90% at 307 DD. Model results predict that 50% of adult eclosion within the stalks will have transpired at 396 DD and 90% at 529 DD. A model-averaged result from two data sets predicts 5% adult emergence from stalks at 262 DD, 50% emergence at 540 DD, 75% emergence at 657 DD, and 90% at 777 DD. Scouting for adults thus can be initiated at 262 DD. Current chemical controls target adults to prevent oviposition. Thus, applications therefore should not be made before this point.

Circadian rhythms of feeding, oviposition, and emergence of the boll weevil (Coleoptera: Curculionidae)

Abstract Circadian rhythm of feeding, oviposition, and emergence of boll weevil adults were determined at five different photophases (24, 14, 12, 10, and 0 hours) and a constant 27°C temperature, 65% RH in the laboratory. Squares from Petri dishes, where they were exposed to boll weevil females, were removed and examined for feeding and oviposition punctures every 4 hours during daylight (0700–1900 h) and every 12 h at night (1900–0700 h) over eight consecutive days. Cohorts of randomly selected egg‐punctured squares were sampled from ovipositing females at 0700, 1100, 1500, and 1900 during 24 hours and under different photophase treatments, and maintained in Petri dishes at 27 ± 1°C, 65% RH. Dishes were observed twice daily (1900 and 0700 h) for adults emerging at day or night. Circadian rhythm of oviposition was not affected by the length of the photophase. The boll weevil has round‐the‐clock circadian rhythm of oviposition, with a daytime preference. We observed that 82.4%‐86.0% of the boll weevil eggs were deposited between 0700 and 1900 h, and 14.0%‐17.6% between 1900 and 0700 h during a 24‐h period. Feeding of boll weevil females in photoperiods 24: 0 h (complete light) and 0: 24 h (complete darkness) did not significantly change between 0700–1900 h versus 1900–0700 h, while the daily cycle of light and darkness in other photoperiods significantly increased the feeding punctures from 0700–1900 compared with 1900–0700 h. The circadian rhythm of emergence depended significantly on the time of oviposition and the length of the photophase. Investigation of boll weevil circadian rhythm provides a better understanding of boll weevil ecology and reveals potential weak links for improving control technologies targeting their reproductive strategies.

Single and Multiple In-Season Measurements as Indicators of At-Harvest Cotton Boll Damage Caused by Verde Plant Bug (Hemiptera: Miridae)

ABSTRACT The ability to monitor verde plant bug, Creontiades signatus Distant (Hemiptera: Miridae), and the progression of cotton, Gossypium hirsutum L., boll responses to feeding and associated cotton boll rot provided opportunity to assess if single in-season measurements had value in evaluating at-harvest damage to bolls and if multiple in-season measurements enhanced their combined use. One in-season verde plant bug density measurement, three in-season plant injury measurements, and two at-harvest damage measurements were taken in 15 cotton fields in South Texas, 2010. Linear regression selected two measurements as potentially useful indicators of at-harvest damage: verde plant bug density (adjusted r 2 = 0.68; P = 0.0004) and internal boll injury of the carpel wall (adjusted r 2 = 0.72; P = 0.004). Considering use of multiple measurements, a stepwise multiple regression of the four in-season measurements selected a univariate model (verde plant bug density) using a 0.15 selection criterion (adjusted r 2 = 0.74; P = 0.0002) and a bivariate model (verde plant bug density-internal boll injury) using a 0.25 selection criterion (adjusted r 2 = 0.76; P = 0.0007) as indicators of at-harvest damage. In a validation using cultivar and water regime treatments experiencing low verde plant bug pressure in 2011 and 2012, the bivariate model performed better than models using verde plant bug density or internal boll injury separately. Overall, verde plant bug damaging cotton bolls exemplified the benefits of using multiple in-season measurements in pest monitoring programs, under the challenging situation when at-harvest damage results from a sequence of plant responses initiated by in-season insect feeding.