Sustainable pepper weevil management by integration of kaolin clay and oviposition deterring pheromone

Commodities

Practices

Current management strategies are heavily dependent on using chemical insecticidal sprays to reduce the population of Anthonomus eugenii in the field. This method primarily focuses on reducing the adult population of A. eugenii with limited success due to increasing insecticide resistance and specific biological traits, such as long-lived adults and the ability to easily move. Growers must spray frequently during pepper production to achieve some amount of control as the weevil has overlapping generations, with up to 5 generations in a season. Presently, no control strategies can effectively target the immature stages of the weevil protected by the pepper fruit. In addition to the limited control of A. eugenii from chemical insecticides, growing concerns around the negative impacts of chemical insecticides on environmental and human health have generated interest in researching sustainable pest management strategies.

Oviposition-deterring pheromones (ODP) are used as a signal by females to determine if conspecific larvae are already present in the fruit. Marking pheromones have been observed in many different insect orders and can be deposited by females during oviposition events or by the larvae (Addesso et al., 2007; Rizvi et al., 2021).  Female A. eugenii oviposits a single egg into a cavity created by feeding and covers it with an oviposition plug created from frass combined with the ODP. Eventually, the pepper fruit is dropped from the plant and the larva completes its development in the fallen fruit.

The pepper weevil ODP has been characterized as a fatty acid blend and acetophenone (Addesso et al., 2021). When applied to uninfested peppers, the ODP was found to deter oviposition behaviors of female A. eugenii with ODP-treated peppers having 75% less oviposition compared to control peppers (Addesso et al., 2021). Due to the strong deterrent abilities of the pheromone, it has been suggested for potential use in open field and greenhouse settings as a new method of organic control to be integrated into pest management strategies of A. eugenii (Addesso et al., 2007; Addesso et al., 2021). Other organic methods, such as kaolin clay, have been evaluated for their ability to increase control of A. eugenii (Addesso et al., 2014). Kaolin clay is used as an organic pest management strategy in agricultural settings to decrease pest abundance through deterrence. When used in laboratory and open field settings, kaolin clay was found to reduce pepper fruit dropping, adult feeding, and infestation percentage compared to control plants (Addesso et al., 2014).

The long-term goal of this research project is to increase the integration and use of organic methods of control in new and pre-existing integrated management strategies for A. eugenii occurring in open field and greenhouse settings by using a combination of kaolin clay infused with the weevil’s ODP. The concept of using kaolin clay infused with semiochemicals in agricultural systems is not new (Johnston et al., 2022); however, it has not yet been tested in pepper production to deter oviposition behaviors of A. eugenii.   
            Currently, the integration of kaolin clay and the ODP has not been tested in open field or greenhouse settings, even though kaolin clay infused with semiochemicals has been shown to have a synergistic effect on pest repellence (Johnston et al., 2022). By increasing the use of organic methods, such as infused kaolin clay, the dependence on chemical insecticides can be reduced, which will benefit human and agroecosystem health. Semiochemical-infused kaolin clay has a short restricted-entry interval compared to chemical insecticides and can be removed from peppers during processing, leaving behind minimal residues in contrast to chemical insecticides.

1. Evaluation of oviposition deterrent pheromone blends in laboratory conditions

The oviposition deterrent pheromone (ODP) has been previously identified by Addesso et al. (2021) through gas chromatography-mass spectrometry (GC-MS) as a blend of compounds from oviposition plugs collected from fruits laid by female pepper weevil. The blend of compounds present in the oviposition plugs is a combination of acetophenone, oleic, linoleic, and linolenic acid. For this study, the ODP blend will consist of a blend of 6:3:1 (oleic, linoleic, and linolenic acid) with 10% acetophenone (Adesso et al. 2021).

The laboratory trial will be conducted at the USDA: ARS (Tallahassee, FL) facility.  Mated pepper weevil females between 1-to-2 months old post-emergence from our laboratory rearing will be used for this experiment. Jalapeno pepper plants (Pantera variety) will be used for the rearing and the experiments. Jalapenos will be grown from seed and fruits measuring 1 – 4 cm in length will be used for the experiments. 10 peppers will be placed in a cage mesh (1m x 0.5m x 0.5m). Half of the peppers will be treated with the kaolin blend, the other with water. The different kaolin blends will be sprayed onto the peppers to simulate field application and let dry for 30 minutes at room temperature. 10 females will be introduced in the cage, and 7 days later feeding hole punctures and oviposition sites will be counted under a microscope. Females will be used only once. The temperature of the room will be set at 78 F, RH 65%, and 14:10 day: night cycle. Cages will be under growth light, and the peppers will be rotated between each replicate. 

ODP-kaolin blends will be evaluated in laboratory settings with a series of two-choice tests. The following combinations will be tested:  1) 0.1% ODP + kaolin clay vs control; 2) 1% ODP + kaolin clay vs control; 3) 10% ODP + kaolin vs control; 4) kaolin clay vs control; 5) 1% ODP vs control; 6) control vs control (negative control). For all the combinations, the rate of kaolin will be at 1/8 per Lb of water. 

There will be 15 replicates for each choice-test combination. For each choice test, the difference between the control and the kaolin treatment will be evaluated with a paired t-test. Then the number of feeding hole punctures and oviposition sites between the different control plants in the different choice tests will be compared with a GLM with binomial distribution. Differences between treatments will be analyzed with a Tukey test.

2. Field evaluation of kaolin clay infused with optimized ODP to prevent eugenii infestation.

The two field trials will occur in the fall of 2025 and 2026 and will be conducted with our cooperative farmer. This farm grows bell peppers and has been impacted by pepper weevils every year in the last decade, and it is expected that the density of pepper weevils will be high enough to conduct our field experiments. Five treatments will be evaluated: 1) kaolin clay (surround) with ODP blend; 2) kaolin clay alone; 3) ODP blend alone; 4) Pesticide treatment (Thiamethoxam and oxamyl rotation) as a positive control; 5) Untreated control (water). The ODP blend will consist of a blend of 6:3:1 (oleic, linoleic, and linolenic acid) with 10% acetophenone (Adesso et al. 2021), as for the first experiment. The rate of kaolin will be at 1/8 per Lb which is half of the recommended rate for Surround. This rate is effective in repelling whiteflies (Johnston et al. 2022) and is easier to apply as it reduces the risk of clogging the sprayer’s nose and helps reduce the cost of the treatment. The rate of the ODP will be decided based on the results obtained from the laboratory experiment (experiment 1). If two concentrations give comparable results in terms of reducing oviposition and feeding, the lowest concentration will be used. We will have 8 rows to conduct our field trial. The farmer will be compensated financially for this service (see budget). Each plot will consist of 2 rows with 40 plants each, with 4 replicates per treatment. Beds, fertilization, application of fungicides, and bactericides will be the same as the growers’ program. Treatments will be applied at the first bloom weekly and repeated weekly until the first fruits start to emerge. Insecticide treatments before and after the experiment will be the same as the grower’s program.

Data will be collected weekly. A subsample of 10 peppers per plot will be collected and evaluated in the laboratory for a count of feeding puncture holes, and oviposition sites. Additionally, 10 pepper flowers or fruits will be inspected in situ, and the number of pepper weevil adults recorded. Two yellow sticky traps will be deposited in each plot to evaluate the density of weevil per plot. Yellow sticky traps will be attached to a wooden stick at the same height as pepper fruits, changed weekly, and the number of pepper weevils will be counted under a microscope in the laboratory. Finally, the total peppers dropped in each treatment will be counted. At the end of the trial, yield data that will include total weight, number of fruits, and marketable fruits, will be taken.

Number of pepper weevil adults in flower and sticky trap count will be analyzed with a GLM with a Poisson distribution, followed by a Tukey test if a difference between treatments is found. Puncture holes, yield, and oviposition sites will be analyzed with an ANOVA followed by a Tukey test as we expect these data to be normally distributed.