Are Spiders a Chemical Free Way to Eliminate Pests in Your Garden?
So what is your opinion?
Should we agriculture focus more on diversity rather than eradication?
Arachnids are an extremely diverse group. There are over 30,000 species of spiders and they make up only a fraction of all arachnids (Riechert, 1984). They are predators that invoke fear in humans. The very site of a small spider is enough to make some grown men whimper. We watch them build their webs with little thought to their place in the food web. This hub will give insight into how arachnids can be used as a bio-control in pest management for agricultural practices. To do this I will be referring to two studies that attempt to quantify the usefulness of arachnid species in bio-control.
Study Involving Control of Strawberry Mites
Strawberries are susceptible to two phytophageus mites known as Phytonemus pallidus (strawberry mite) and Tetranychus urticae (two-spotted spider mite). When infected with these mites, the strawberry plants experience a decrease in crop yield (Alford 1972). In 1997 a group of scientists studying in the United Kingdom sought out to determine if Neoseiulus spp. showed potential to be used to control the above mentioned mites. One of the preliminary experiments in the study included infesting thirty separate strawberry plants located in a greenhouse. The temperature monitored in the green house was comparable to the temperature experienced in early summer in the United Kingdom where this study took place. The plants were then separated at random into three separate groups. There were four female Neoseiulus californicus (predatory mites) per plant used on group one. Two Female Neoseiulus californicus per plant were used on group two. Group three was not exposed. There was indication that the Neoseiulus californicus had effectively controlled Tetranychus urticae when the predator: prey ratio was from 1: 8 to 1: 11. Multiple other experiments took place from 1997 to 1999 using the two species mentioned above. Some of them used whole strawberry plants and some of them used only leaves. Many of the experiments showed a 71% to 81% reduction in the numbers of mites and their offspring (Easterbrook 2001).
Arachnids and Soybeans
Another study was done with soybeans in the Butler County, Ohio, United States. In these studies, twelve plots of crop land measuring 60m by 70m, planted east to west, with 90 rows of soybeans were considered. Each of the twelve plots also had a 15m mowed grass edge. Though pesticides were used on the land previously, none were being used during this study. Over the course of three years 10 plots were investigated; four in 1990, three in 1991, and three in 1992. Each plot had crates placed on them. These were to provide protection to spiders during the growing season. They augmented the spider population by encouraging the spiders to flourish on these plots of land. After three years of study they were able to prove that the average mass of the dried insect carcasses found in crates placed at the different plots was positively correlated with the average mass of spiders inhabiting the crates. They were also able to prove that there was statistically less leaf damage when spider populations were augmented (Carter 1995).
The Importance of Diversity In Agricultural Ecosystems
There are a few themes in the literature that appear often. They all relate back to diversity. The predator environment has to be plentiful in not only individuals but in species. Practices must take place to ensure great predator diversity in the agroecosystem (Riechert, 1984). This may be the opposite of what the land owner was doing previously. Many commercial agricultural systems used heavy pesticides and herbicides which will affect diversity in a negative way on the land being studied (Landis 2000). Many arachnids are also specialized feeders. If you push for one arachnid species to be present on the land over another, there won’t be a consistency in your pest management program. The desired effect will not be achieved. Every experiment examined included multiple species in their study. For success when using this technique, diversity is crucial.
The Importance of Biodiversity in Modern Agriculture
Can Arachnids be used for pest management in agroecosystems? The two studies mentioned along with many others investigated show that they can be affective in pest management. A new question comes to mind: can arachnids be used as pest management in large scale agricultural operations? The world’s population has now reached over seven billion by United States Census Bureau estimates. It is common knowledge pesticides used in agriculture have the potential to pollute soil and water. Can we modify our agricultural better management practices to include spiders? Books have been written on the topic. They outline how to start making agricultural ecosystems more dynamic, yet it is not a widely adopted practice in the United States.
Alford, D. V. (1972). The effect of Tarsonemus fragariae Zimmermann (Acarina: Tarsonemidae) on strawberry yields. Annals of applied biology, 70(1), 13-18.
Carter, P. E., & Rypstra, A. L. (1995). Top-down effects in soybean agroecosystems: spider density affects herbivore damage. Oikos, 433-439.
Landis, D. A., Wratten, S. D., & Gurr, G. M. (2000). Habitat management to conserve natural enemies of arthropod pests in agriculture. Annual review of entomology, 45(1), 175-201.
Easterbrook, M. A., Fitzgerald, J. D., & Solomon, M. G. (2001). Biological control of strawberry tarsonemid mite Phytonemus pallidus and two-spotted spider mite Tetranychus urticae on strawberry in the UK using species of Neoseiulus (Amblyseius)(Acari:Phytoseiidae). Experimental & applied acarology, 25(1), 25-36.
Riechert, S. E., & Lockley, T. (1984). Spiders as biological control agents. Annual Review of Entomology, 29(1), 299-320.
United States Census Bureau. (n.d.). U.s. and world population clock. Retrieved from https://www.census.gov/popclock/