Allan T. Showler

Effects of Kaolin-Based Particle Film Application on Boll Weevil (Coleoptera: Curculionidae) Injury to Cotton

Abstract This study examined a non-insecticidal tactic for suppressing boll weevil, Anthonomus grandis grandis Boheman, damage to cotton, Gossypium hirsutum L. In cage assays, kaolin, a reflective white mineral, applied to excised cotton squares or to the cotton foliage, initially resulted in lower levels of boll weevil injury to squares than nontreated squares. Boll weevil oviposition and feeding on kaolin-treated squares and squares on kaolin-treated cotton plants increased when nontreated squares and cotton plants were in short supply. A laboratory assay and field trials suggested that boll weevils distinguished between cotton plots based on color differences caused by kaolin and this appeared to influence levels of damage to squares. Random sampling in small plots indicated that oviposition damage to squares in plots treated with kaolin was reduced (P < 0.05) compared with nontreated controls, except when rain washed the kaolin off the foliage. Lint yield differences were not detected between the small plots, but the kaolin-treated small plots yielded as much as 2.36 times more cotton lint than a large but unreplicated adjacent nontreated control plot, and up to 1.39 times more than another large but unreplicated adjacent plot sprayed twice with preemptive applications of azinphosmethyl when cotton squares were first developing (pinhead stage). Potentially important avenues for future research on boll weevil injury suppression using kaolin are discussed.

Effects of drought stressed cotton, Gossypium hirsutum L., on beet armyworm, Spodoptera exigua (Hubner), oviposition, and larval feeding preferences and growth

The beet armyworm, Spodoptera exigua (Hübner), has been anecdotally reported to oviposit more on drought stressed than on nonstressed cotton plants. Using potted cotton plants in cages, this study demonstrated that beet armyworms deposited 3.3, 4.6, and 2.3 times more (P ≤ 0.05) eggs on cotton plants that were grown on 1500, 1000, and 750 ml water/wk, respectively, than on cotton plants grown in well watered (4000 ml water/wk) soil. Third instars, however, showed no preference for stressed cotton foliage over nonstressed foliage. Third instar beet armyworms raised on well watered cotton plants were 1.5, 2.3, and 2.6 times heavier than those reared on cotton grown in the 1500, 1000, and 750 ml water/wk plants (P ≤ 0.05), respectively. Physiochemical analyses showed that drought stressed leaves had significantly greater accumulations of free amino acids that are essential for insect growth and development. Soluble protein and soluble carbohydrates were also more abundant in stressed leaves compared to nonstressed leaves. Despite the apparent increase in nutritional quality in drought stressed plants, larval survival was reduced, probably because the limiting factor became water. Greater amounts of cotton leaf area were consumed from drought stressed leaves (P ≤ 0.05) than from nonstressed leaves, probably because the larvae had to metabolize greater portions of assimilated energy to supplement body water with metabolic water derived from respiration. The association of greater host plant nutritional quality to oviposition preference, and conversely, to reduced survivorship, is discussed.

Integrated Tactics for Managing the Mexican Rice Borer (Lepidoptera: Crambidae) in Sugarcane

Abstract A 2-yr field study conducted in Texas to evaluate the effect of several management strategies on the Mexican rice borer, Eoreuma loftini (Dyar), in sugarcane, Saccharum spp. hybrids, showed that irrigation reduced injury in both susceptible (LCP 85–384) and resistant (HoCP 85–845) cultivars by 2.5-fold. Cultivar LCP 85–384 was more susceptible than HoCP 85–845 based both on injury and moth production. Irrigation, host plant resistance, and insecticide applications of tebufenozide decreased injury from 70% bored internodes to <10% during both years. The use of multiple control tactics was substantially better at suppressing E. loftini in sugarcane than solely relying on insecticide applications. In addition to accumulations of proline, several free amino acids (histidine and isoleucine) essential for insect growth and development were increased in sugarcane leaves by drought stressed conditions, which exacerbated E. loftini infestations. Modifying the suitability of the crop by reducing water deficit stress makes rational irrigation input a key component in the integrated pest management of E. loftini, in addition to other tactics such as cultivar resistance and insecticide application.

Effects of Weeds on Selected Arthropod Herbivore and Natural Enemy Populations, and on Cotton Growth and Yield

Abstract Vegetative diversification with weeds can enhance natural enemy populations and suppress pest-related damage in various crops. Weedy and weed-free cotton (Gossypium hirsutum L.) plots were used to study the effects of weediness on selected herbivorous arthropod groups, including the boll weevil (Anthonomus grandis grandis Boheman), and natural enemies, boll weevil-induced injury to cotton squares, and cotton plant growth and yield in the Lower Rio Grande Valley of Texas, during 2000 and 2001. The presence of weeds was associated with greater populations of 9 of the 11 prey arthropod groups, and 9 of the 13 natural enemy arthropod groups counted in this study. These trends were mostly evident late in the season when weed biomass was greatest. Weed-free cotton harbored more cotton aphids (Aphis gossypii Glover), early in the season and silverleaf whiteflies (Bemisia argentifolii Bellows and Perring) later in the season than weedy cotton on some of the sampling dates. Diversity (Shannon’s index) within the selected arthropod groups counted in this study was significantly greater in dvac samples from the weed foliage than from weed-free cotton plants during both years, and diversity on weedy cotton plants was greater than on weed-free cotton plants during 2000. Boll weevil oviposition injury to squares was unaffected by weeds, but the higher weed-associated predator populations mainly occurred after most squares had become less vulnerable bolls. Weed competition resulted in lower lint yields of 89% and 32% in the 2 yr.

Effects of water deficit stress, shade, weed competition, and kaolin particle film on selected foliar free amino acid accumulations in cotton, Gossypium hirsutum (L.).

Leaves of cotton plants, Gossypium hirsutum L., stressed by water deficit, reduced daylight, and weed competition, or treated with a kaolin wettable powder formulation were analyzed for levels of 17 free amino acids (FAAs) using reversed-phase high-performance liquid chromatography. Water deficit stress resulted in heightened free proline levels (49.9-fold, P < 0.001) that were correlated with diffusive resistance (seconds per centimeter). Five other FAAs increased, and the amounts of total free essential (for insect growth and development) amino acids and total FAAs also increased (P ≤ 0.05). Cotton grown in 50% shade accumulated significantly more free arginine than control plants. In a small-plot weed competition assay, four FAAs increased and three FAAs decreased in association with weed competition, but because free proline levels were not altered and free arginine levels increased, other stresses aside from water deficit, possibly including shading by tall weeds, appear to have caused the changes. In a small-plot kaolin particle film assay, five FAAs were lower in cotton foliage sprayed weekly with kaolin. Because free proline was unaffected and free arginine was lower, it is possible that kaolins reflectivity heightened light reception. The responses of free proline and arginine to the treatments used in these assays demonstrate that types and degrees of some stresses to cotton can be characterized by accumulations of certain FAAs. The study also demonstrates how some FAA levels can indicate degrees of cotton stress resulting from weed competition and from kaolin particle film application. Porometry and leaf water potential measurements assisted in corroborating some findings of the study.

Effects of neem‐based insecticides on beet armyworm (Lepidoptera: Noctuidae)

Abstract Three commercial neem [Azadirachta indica A. Juss (Meliaceae)]‐based insecticides, Agroneem, Ecozin, and Neemix, and a non‐commercial neem leaf powder, were evaluated for oviposition deterrence, antifeedant effect on larvae, and toxicity to eggs and larvae of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), on cotton leaves in the laboratory. Oviposition deterrence in no‐choice, and two‐ and fivechoice assays, was observed for the neem‐based insecticide treatments when compared with a non‐treated control. Neem‐based insecticides also deterred feeding by beet armyworm larvae. Direct contact with neem‐based insecticides decreased the survival of beet armyworm eggs. Survival of beet armyworm larvae fed for 7 days on leaves treated with neembased insecticides was reduced to 27, 33, 60, and 61% for neem leaf powder, Ecozin, Agroneem, and Neemix, respectively. Possibilities for adoption of neem‐based insecticides in commercial cotton for beet armyworm control are discussed.

Role of oviposition preference in an invasive crambid impacting two graminaceous host crops.

Abstract Oviposition preference studies of the Mexican rice borer, Eoreuma loftini (Dyar), on sugarcane, Saccharum spp., and rice, Oryza sativa L., showed that drought stressed sugarcane was 1.8-fold more attractive based on egg masses/plant than well watered sugarcane. The E. loftini susceptible sugarcane cultivar LCP 85–384 was 1.6-fold more attractive than HoCP 85–845 based on numbers of eggs per egg mass. Egg masses were 9.2-fold more abundant and 2.3-fold larger on sugarcane than on rice. Rice, however, was preferred to sugarcane on a plant biomass basis. Oviposition on sugarcane occurred exclusively on dry leaf material, which increased under drought stress. Egg masses per plant increased on drought stressed sugarcane and were correlated with several foliar free amino acids essential for insect growth and development. The more resistant (based on injury) but more attractive (based on oviposition) rice cultivar XL8 had higher levels of several free amino acids than the susceptible cultivar Cocodrie. The association of host plant characteristics to oviposition preference is discussed. Projected oviposition patterns relative to sugarcane and rice production areas were estimated for Texas and Louisiana based on the availability of each host in different regions of each state. These results suggest that, where sugarcane and rice co-occur, the majority of eggs would be found on sugarcane early in the season, because of this crop’s substantially greater biomass compared with rice. Abundance later in the season would also favor sugarcane; however, the abundance on rice would be greater than expected solely based on host availability, largely because of the greater preference per gram of rice plant dry weight.

Spodoptera exigua Oviposition and Larval Feeding Preferences for Pigweed, Amaranthus hybridus, over Squaring Cotton, Gossypium hirsutum, and a Comparison of Free Amino Acids in Each Host Plant

The beet armyworm, Spodoptera exigua (Hübner), can utilize a number of different host plants for oviposition and larval development, but some host plants are preferred over others. This study, using cage choice tests and olfactometer assays, demonstrates the beet armyworms preference for pigweed, Amaranthus hybridus L., over cotton, Gossypium hirsutum L. Cage and olfactometer choice assays indicated that olfaction plays an important role in host selection by ovipositing females. First instars exhibited no feeding preference, but the more mobile third instars showed a significant feeding preference for excised pigweed leaves. The higher quantities and more diverse accumulations of free amino acids in pigweed might, in conjunction with other physiochemical and mechanical attractant and deterrent factors in the two-plant species system, play roles in the tendency of the beet armyworm to select pigweed over cotton and in providing a superior array of easily absorbed amino acids as compared to cotton.

Mexican Rice Borer (Lepidoptera: Crambidae) Oviposition Site Selection Stimuli on Sugarcane, and Potential Field Applications

ABSTRACT The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), a key pest of sugarcane (Saccharum spp.) and rice, Oryza sativa L., in Texas, has not been controlled with chemical insecticides or biological agents, but some sugarcane varieties have shown degrees of resistance. Assessment of selected sugarcane leaf characteristics indicate that preference for oviposition sites is mostly determined by the presence of a leaf fold and secondarily by the availability of dry leaf tissue, both of which are antixenotic nonchemical stimuli. We suggest that breeding sugarcane lines bearing leaves that do not fold on drying could provide substantial antixenotic resistance against the Mexican rice borer. Previously identified antixenotic chemical stimuli, i.e., low quantities or absence of important nutrients in green leaf tissue, only become apparent when resistant and susceptible sugarcane varieties are compared. Varietal differences in oviposition preference, however, were not observed on excised dry leaf tissue, indicating that expression of resistance in terms of chemical stimuli requires detection of biochemicals in nearby living leaf tissue. Excised dry sugarcane leaves retain the two dominant nonchemical oviposition preference stimuli for Mexican rice borers, and the leaves effectively trapped eggs away from intact plants when dry leaves were used as “mulch” at the bottom of greenhouse cages. Under commercial sugarcane field conditions, bundled dry leaves also collected Mexican rice borer eggs. Possible applications of dry sugarcane leaf substrate for egg scouting and for trapping eggs are discussed.

Relationships of Different Cotton Square Sizes to Boll Weevil (Coleoptera: Curculionidae) Feeding and Oviposition in Field Conditions

Feeding and oviposition preferences of the boll weevil, Anthonomus grandis grandis Boheman, for four different cotton square size classes in field conditions of the Lower Rio Grande Valley of Texas were studied during 2002 and 2003. Percentages of large (5.5-8-mm-diameter) squares used for oviposition and feeding were greater than pinhead or match-head squares. The preference for large squares as food and associated accelerated fecundity explain the substantial boll weevil population buildups that occur after large squares form. Medium-sized (3-5.5-mm-diameter) squares also were used but less than large squares. Feeding and oviposition on pinhead (1-2-mm-diameter) and match-head (2-3-mm-diameter) squares were negligible. Although planting date did not affect oviposition or feeding preferences for squares larger than pinhead and match-head sizes, the least amount of either damage to large squares was found in the earliest plantings during both years. This study indicates that pinhead and match-head squares, regardless of planting date, do not require pesticide applications to protect against boll weevil feeding and oviposition.