Boll Weevil (Coleoptera: Curculionidae) Feeding and Reproduction as Functions of Cotton Square Availability

The influence of food item availability on boll weevil, Anthonomus grandis grandis Boheman, feeding and reproduction was determined by providing different numbers of cotton squares (flower buds) to individual weevils. Squares were replaced daily after a 5-d feeding and mating conditioning period. The number of lifetime punctures produced by boll weevil females and males increased with square availability. The total number of punctures caused by boll weevil females was 2.7-fold higher than that caused by males. Fecundity was significantly higher in the 10:1, 15:1, and 20:1 (squares:female) treatments than in the 1:1 treatment. The relationship between eggs laid per day and the square to female ratio significantly changed over the life of the female, with the largest differences among treatments occurring in the first 3 wk of adulthood. Survival of weevil progeny to adulthood was about two-fold higher in the 10:1, 15:1, and 20:1 treatments than in the 1:1 and 5:1 treatments. When each boll weevil female was provided 10, 15, or 20 cotton squares per day, estimates of a population growth index (percent of immatures surviving to adulthood divided by immature development time) and the exponential rate of increase (rm) were significantly higher than for those provided only one or five squares per day. Boll weevil populations maintained at a square:weevil ratio of 10:1 or above will increase \u3e60-fold each generation (Ro), a rate significantly higher than that exhibited under 5:1 or 1:1 square:female regimens. These data show that daily provision of 10 squares per female provides sufficient resources to elicit a maximal oviposition response in the laboratory. Our results also will be useful in predicting changes in boll weevil populations relative to crop phenology and starting population density

Influence of Different Cotton Fruit Sizes on Boll Weevil (Coleoptera: Curculionidae) Oviposition and Survival to Adulthood

Understanding the critical host plant factors that determine oviposition behavior and survival of boll weevil, Anthonomus grandis grandis Boheman, on cotton, Gossypium hirsutum L., is important for developing successful pest management strategies. However, published information is both conflicting and limited regarding how different cotton fruit sizes affect boll weevil oviposition choices and subsequent larval survival to adulthood. Consequently, we used a standard based on fruit size diameter to evaluate boll weevil feeding and oviposition punctures, and survival to adulthood on 10 different cotton fruit sizes: squares of diameter 1.5–2.0 (pinhead), 3.0–3.5 (matchhead), 5–6, 7–8, or 9–10 mm; candle; and bolls of diameter 10–15, 15–20, 20–30, or \u3e30 mm. Oviposition and feeding punctures were significantly affected by cotton fruit size. Females did not oviposit in pinhead squares. The fewest eggs were oviposited in boll sizes \u3e30 mm. The highest number of eggs was recorded in square sizes of 5–6 and 7–8 mm. Boll weevil survival to adulthood was highest on square sizes of 7–8 or 9–10 mm (58.6–59.7%). No survival occurred in matchhead squares or bolls \u3e30 mm. Duration of development was longest on boll sizes of 15–20 and 20–30 mm (18.2–18.8 d). The growth index (percentage immature survival divided by immature developmental time) of female boll weevils was 2.8-fold higher in 7–8- or 9–10-mm diameter squares than in 20–30-mm diameter bolls. This study will improve our capacity to develop methods to predict fruit losses and changes in boll weevil populations in the field, given a starting density of fruit suitable for oviposition, and a corresponding initial population density of weevils

Visual Responses of Adult Asian Citrus Psyllid (Hemiptera: Liviidae) to Colored Sticky Traps on Citrus Trees

The effects of five differently-colored sticky traps in capturing adult Diaphorina citri were evaluated in citrus orchards. Trap catches of D. citri were monitored fortnightly on blue, green, red, white and yellow sticky cards placed on three citrus varieties during D. citri active flight period from April to July in south Texas. Evaluation of mean trap catches of each color by repeated measures analysis of variance produced three separate groups: yellow traps caught significantly more D. citri adults than the other four traps; red and green traps caught significantly more D. citri than blue and white traps, which were not significantly different. Although the number of adult psyllid captured on all trap types significantly increased with time during the trapping period, the performance of traps did not change with time. Trap catches were also significantly influenced by the citrus species; traps placed on lemon trees captured more D. citri than those placed on sweet orange and grapefruit, suggesting that plant preference exhibited by D. citri may influence the performance of traps. The ratio of trap reflectance between the 680 to 700 nm and the 450 nm was significantly correlated with total trap catches in all host species studied. Thus, this index was a good indicator of the attractiveness of adult D. citri to colored traps. Additionally, we compared the reflectance values of young versus mature flush shoots of the three host plants used in this study as related to densities of D. citri recorded in colored traps. We discussed the importance of visual cues in the host finding behavior of adult D. citri

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

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 pest\u27s development can be very important in determining sampling protocols, timing insecticide applications, or implementing an integrated pest management control strategy targeting susceptible life stages

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

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

Detection of Incipient Pest Infestations on Glasshouse Crops Using Multispectral Imagery and a Common Vegetation Index

Research was conducted to evaluate the effectiveness of multispectral (conventional color and color infrared) imagery and a common vegetation index (simple ratio) for detecting incipient infestations of spider mites (Tetranychus spp.; Acari: Tetranychidae) and false spider mites (Brevipalpus spp.; Acari: Tenupalpidae) on selected crops under glasshouse conditions. Although damaging infestations of both mite species were associated with intense feeding injury which was readily detectable by visual inspection, subtle levels of foliar damage caused by the two mite species were difficult to detect by visual inspection and were not readily distinguishable from undamaged (healthy) foliage in conventional color (CC) or color infrared (CIR) imagery. In contrast, foliage exhibiting subtle levels of mite feeding injury was readily distinguished from healthy foliage in derivative imagery based on the Simple Ratio (SR), a vegetation index defined as the ratio of near-infrared to red reflectance (700-1100 nm and 600-700 nm, respectively) for each pixel in the imagery. CIR and SR images were shown to be considerably more effective than CC imagery in the initial detection and subsequent monitoring of a spider mite infestation on glasshouse cucumbers which increased from incipient to annihilative levels within a period of approximately six weeks. The rationale for and potential uses of CC, CIR, and derivative imagery based on SR and other vegetative indices for monitoring pest infestations on glasshouse crops are discussed

Size-Dependent Feeding and Reproduction by Boll Weevil (Coleoptera: Curculionidae)

The considerable variation in adult size of the boll weevil, Anthonomus grandis grandis Boheman, has been well documented, but the influences of adult size on reproductive rate are not known. We examined the relationship between the size of boll weevils and their feeding and oviposition. Weevils weighed to the nearest milligram were grouped into five categories based on pupal weight:≤5, 6-10, 11-15, 16-20, and\u3e20 mg. Numbers of lifetime punctures produced in flower buds (squares) of cotton, Gossypium hirsutum L., by both sexes of adults tended to increase with pupal weight. Boll weevil females with pupal weights \u3e10 mg produced progeny with significantly higher survival to adulthood and also produced a higher percentage of female progeny than those with pupal weights ≤10 mg. The population growth indices for females having pupal weights \u3e10 mg averaged 1.8-fold higher than those of females weighing≤10 mg. Survivorship of adults of both sexes also tended to increase with pupal weight. The percentage of females laying eggs on any given day averaged 2.1 times higher when their pupal weights were \u3e10 mg than when their pupal weights were ≤10 mg. Although small size negatively affected female reproductive potential, even extremely small females produced some viable offspring. However, the penalties of small adult size, in terms of longevity and reproductive potential, suggest that cultural practices that result in the production of small adults may be used to impact weevil populations

Boll Weevil (Coleoptera: Curculionidae) Feeding and Reproduction as Functions of Cotton Square Availability

The influence of food item availability on boll weevil, Anthonomus grandis grandis Boheman, feeding and reproduction was determined by providing different numbers of cotton squares (flower buds) to individual weevils. Squares were replaced daily after a 5-d feeding and mating conditioning period. The number of lifetime punctures produced by boll weevil females and males increased with square availability. The total number of punctures caused by boll weevil females was 2.7-fold higher than that caused by males. Fecundity was significantly higher in the 10:1, 15:1, and 20:1 (squares:female) treatments than in the 1:1 treatment. The relationship between eggs laid per day and the square to female ratio significantly changed over the life of the female, with the largest differences among treatments occurring in the first 3 wk of adulthood. Survival of weevil progeny to adulthood was about two-fold higher in the 10:1, 15:1, and 20:1 treatments than in the 1:1 and 5:1 treatments. When each boll weevil female was provided 10, 15, or 20 cotton squares per day, estimates of a population growth index (percent of immatures surviving to adulthood divided by immature development time) and the exponential rate of increase (rm) were significantly higher than for those provided only one or five squares per day. Boll weevil populations maintained at a square:weevil ratio of 10:1 or above will increase >60-fold each generation (Ro), a rate significantly higher than that exhibited under 5:1 or 1:1 square:female regimens. These data show that daily provision of 10 squares per female provides sufficient resources to elicit a maximal oviposition response in the laboratory. Our results also will be useful in predicting changes in boll weevil populations relative to crop phenology and starting population density.This article is from Environmental Entomology 32 (2003): 698, doi:10.1603/0046-225X-32.3.698.</p

Influence of Different Cotton Fruit Sizes on Boll Weevil (Coleoptera: Curculionidae) Oviposition and Survival to Adulthood

Understanding the critical host plant factors that determine oviposition behavior and survival of boll weevil, Anthonomus grandis grandis Boheman, on cotton, Gossypium hirsutum L., is important for developing successful pest management strategies. However, published information is both conflicting and limited regarding how different cotton fruit sizes affect boll weevil oviposition choices and subsequent larval survival to adulthood. Consequently, we used a standard based on fruit size diameter to evaluate boll weevil feeding and oviposition punctures, and survival to adulthood on 10 different cotton fruit sizes: squares of diameter 1.5–2.0 (pinhead), 3.0–3.5 (matchhead), 5–6, 7–8, or 9–10 mm; candle; and bolls of diameter 10–15, 15–20, 20–30, or >30 mm. Oviposition and feeding punctures were significantly affected by cotton fruit size. Females did not oviposit in pinhead squares. The fewest eggs were oviposited in boll sizes >30 mm. The highest number of eggs was recorded in square sizes of 5–6 and 7–8 mm. Boll weevil survival to adulthood was highest on square sizes of 7–8 or 9–10 mm (58.6–59.7%). No survival occurred in matchhead squares or bolls >30 mm. Duration of development was longest on boll sizes of 15–20 and 20–30 mm (18.2–18.8 d). The growth index (percentage immature survival divided by immature developmental time) of female boll weevils was 2.8-fold higher in 7–8- or 9–10-mm diameter squares than in 20–30-mm diameter bolls. This study will improve our capacity to develop methods to predict fruit losses and changes in boll weevil populations in the field, given a starting density of fruit suitable for oviposition, and a corresponding initial population density of weevils.This article is from Environmental Entomology 33 (2004): 443, doi:10.1603/0046-225X-33.2.443.</p