Mortality of the cotton boll weevil in drip and sprinkler irrigated cotton crops

The cotton boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a key cotton crop pest in Brazil. Adverse climatic factors, such as high temperatures and low soil moisture, dehydrate oviposited cotton squares (bud flowers) on the ground and cause high mortality of its offspring within these plant structures. The objective of this research was to evaluate the mortality of the cotton boll weevil in drip and sprinkler irrigated cotton crops. The experimental design was in randomized blocks with two treatments: drip (T1) and sprinkler (T2, control) irrigated cotton crops with sixteen replications. Each parcel had one emergence cage, installed between two cotton rows per irrigation system, with 37 cotton squares with opened oviposition punctures and yellowish bracts, to capture adult cotton boll weevils. The average number of boll weevils that emerged from the cotton squares and the causes of mortality at different development stages were determined per treatment. Third-generation life tables of the boll weevil were prepared using the natural mortality data in drip and sprinkler irrigation treatments and plus actual, apparent and indispensable mortality rates and the lethality of each mortality cause. We conclude that the application of water directly to the root zone of the plants in a targeted manner, using the drip irrigation system, can cause high mortality of the cotton boll weevil immature stages inside cotton squares fallen on the ground. This is because the cotton squares fallen on the drier and hotter soil between the rows of drip-irrigated cotton dehydrates causing the boll weevils to die. This is important because it can reduce its population density of the pest and, consequently, the number of applications of chemical insecticides for its control. Thus, contributing to increase the viability of cotton production, mainly in areas of the Brazilian semiarid region where the cotton is cultivated in organic system.

The Identification of Boll Weevil, Anthonomus grandis grandis (Coleoptera: Curculionidae), Genes Involved in Pheromone Production and Pheromone Biosynthesis

Eradication programs for the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), rely almost exclusively on pheromone traps to indicate the need for insecticide applications. However, the effectiveness of traps in detecting weevil populations is reduced during certain times of the year, particularly when cotton is actively fruiting. Consequently, this could result in fields becoming heavily infested with weevils. It is widely speculated that the lack of weevil captures in traps during this period is largely due to the overwhelming amount of pheromone released by weevils in the field, which outcompete the pheromone released from traps. Thus, this work sought to identify genes involved in pheromone production so that new control methods that target these genes can be explored. We conducted an RNA-seq experiment that revealed 2479 differentially expressed genes between pheromone-producing and non-pheromone-producing boll weevils. Of those genes, 1234 were up-regulated, and 1515 were down-regulated, and most had gene annotations associated with pheromone production, development, or immunity. This work advances our understanding of boll weevil pheromone production and brings us one step closer to developing gene-level control strategies for this cotton pest.

Multiple Factors Mediate Insecticide Toxicity To A Key Predator For Cotton Insect Pest Management

Mortality of agricultural pests caused by arthropod predators is a valuable ecosystem service for crop production. The earwig, Euborellia annulipes (Lucas), attacks different pest species in various crop ecosystems, including larvae and pupae of the boll weevil, Anthonomus grandis grandis (Boh.). Despite such biological control, cotton pest management remains heavily dependent on synthetic insecticides. In this study, multiple factors were assessed to measure the selectivity of insecticides used against sap-sucking and chewing cotton pests for two E. annulipes populations. Nymphs and adults of E. annulipes were exposed to the insecticides in two ways: ingestion of contaminated prey, and contact with dried residues on either inert surfaces or treated plants bearing prey. Pymetrozine, chlorantraniliprole, and spinetoram had little effect on the predator regardless the tested earwig population, life stage, or the route of exposure. Cyantraniliprole affected the predator in some life stages and through some types of contact. Pyriproxyfen was harmless to adult earwigs, but prevented normal development of nymphs to adults. Chlorfenapyr, indoxacarb, lambda-cyhalothrin, chlorpyrifos, dimethoate, and malathion were harmful to the predator regardless earwig life stage or method of exposure. The negative impact was diminished when exposure occurred on plants with predator allowed to shelter in the soil. The results indicate that insecticide selectivity outcome is a multi-factor driven by the insecticide, predator life stage and the redator’s behavior. Therefore, testing different predator life stages via several routes of exposure, without denying the insect the opportunity to engage in its normal behaviors can provide better estimates of insecticide selectivity.

Susceptibility of Boll Weevil (Coleoptera: Curculionidae) to Ethiprole, Differential Toxicity Against Selected Natural Enemies, and Diagnostic Concentrations for Resistance Monitoring

Synthetic insecticide application is one tactic for reducing boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), infestations during the cotton, Gossypium hirsutum L., reproductive stage. We assessed the susceptibility of the boll weevil and its natural enemies to ethiprole (mode of action 2B), a phenylpyrazole insecticide, and diagnostic concentrations of ethiprole indicative of boll weevil susceptibility. Differences in the lethal concentrations of ethiprole were calculated with susceptibility ratios based on LC50 ranging from 2.89- to 10.34-fold relative to a natural susceptible population. The lowest and the highest recommended field rates of ethiprole, 100 and 200 g a.i./ha, produced residues that caused 83.3% and 93.7% mortality of weevils caged with cotton leaves from field-treated plants for 8 d. We found that ethiprole was less toxic than fipronil to the boll weevil parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae) and to the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), while fipronil was highly toxic to both. Adult earwigs, Euborellia annulipes Lucas (Dermaptera: Anisolabididae), were relatively tolerant to ethiprole and fipronil at the highest field rates. Pooled LC50-and LC95-concentrations of ethiprole calculated from studied populations were used as diagnostic for boll weevil mortality, and the outcome fitted to the expected mortality for boll weevil populations from different locations serving for further control failure assessment. Ethiprole appears to be suitable for boll weevil control with low impact on natural enemy communities.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Dry bolls and their association with Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae) survival through cotton fallow periods

The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), can remain inside dry and deformed reproductive structures of cotton, Gossypium hirsutum Linnaeus (Malvaceae), known as dry bolls, during the cotton fallow to infest the next cotton crop. In this study, the influence of cotton cultivars and sowing densities on the formation of dry bolls was evaluated. In addition, dry bolls were dissected and internal structures that were related to boll weevil development were estimated. Finally, the presence and survival of boll weevils inside dry bolls were evaluated. The results indicate that the number of dry bolls, empty pupal cells, and emergence holes was influenced by cultivar and not by sowing density. Almost one-quarter (22.53%) of adult boll weevils examined was found alive inside the dry bolls after 10 weeks, which is slightly longer than the duration of cotton fallow in Brazil’s main cotton-producing regions. Therefore, remaining inside the dry bolls is an important survival strategy for boll weevils during the cotton fallow period, and cotton cultivars with a greater propensity for the formation of dry bolls might favour survival of the pest during this period.

Thespesia populnea (portia tree).

A small to medium-sized evergreen tree, with a rather dense crown and spreading branches (Troup et al., 1975) which reaches about 18 m in height. It has showy, bell-shaped yellow flowers, long-petioled, heart-shaped leaves, and a tough, fibrous bark. It is indigenous to tropical Asia, but has been widely planted throughout tropical regions, including Africa, and coastal woodlands in the Caribbean and elsewhere in the Neotropics. The seed floats in sea water, and can remain viable in sea water for more than a year, making natural distribution by sea currents possible (Nakanishi, 1989). It prefers well-drained sandy, gravelly and rocky soils derived from coral limestone and volcanic parent materials, and it is salt-tolerant (Desale et al., 1989). It is often found close to, but not growing in, mangrove forests which are occasionally inundated, or on saline sands behind mangrove forests (Siddiqi et al., 1995; Sosef et al., 1998; Morton, 1976). In India growth is reported to be rapid, and it flowers and fruits throughout the year (Sosef et al., 1998). In the Caribbean, flowering occurs primarily from April to January (Parrotta, 1994). T. populnea can be easily raised from seed and from cuttings, usually branch or shoot cuttings up to 2 m in length and 10 cm in diameter, although smaller cuttings are generally preferred (Parrotta, 1994). In India it is often planted to consolidate bunds and ridges in aqua-silvicultural systems for prawn production, or along the coast as protection against erosion (Latiff and Faridah Hanum, 1997; Harikrishnan, 1993). It produces a fine-grained, durable wood (density 400 to 770 kg/cubic metre at 15% moisture content), with a red-brown to dark brown heartwood and a sharply differentiated white sapwood. The wood is valued for furniture, flooring, musical instruments, mouldings, utensils and vehicle bodies. The wood is durable under water, and is therefore used for boat-building. The bark is also utilized for caulking and rope. The wood and a yellow gum from the fruits and flowers yield a dye, and core-wood has medicinal uses. It is a sacred tree in many parts of the Pacific, often planted near temples, and is also grown as an ornamental and roadside tree. Planting T. populnea is outlawed, or strongly discouraged, in some cotton-growing areas, as it is an alternative host of several damaging cotton pests, including the cotton weevil (Anthonomus grandis grandis), the red cotton bug (Dysdercus cingulatus), the Indian dusky cotton bug (Oxycarenus laetus), and Pyroderces simplex (Parrotta, 1994).