Research Results
Introduced Natural Enemies for the Biological Control of The Cotton Aphid in the San Joaquin Valley
The cotton aphid, Aphis gossypii, can attain pest status in a variety of crops in the San Joaquin Valley. Management of these populations must be done with care so as to avoid problems of insecticide resistance and/or cotton aphid population resurgence within adjacent crops or habitats. Biological control is one management tactic that could be used to manage aphid populations through space and time.
In an attempt to increase the amount of biological control on cotton aphid populations, a cooperative project among USDA-Agricultural Research Service, CDFA-Biological Control Program, UC-Cooperative Extension, and the University of Arkansas was initiated in 1996 and continues currently. The long-term goal of this project is to construct an introduced natural enemy complex that would complement the existing natural enemies. During the previous 4 years of the project, three parasites, Lysiphlebia japonica, Aphelinus near paramali, and Aphelinus gossypii, and one fungus, Neozygites fresenii, have been or are currently being evaluated.
Research at SREC
The evaluation of these natural enemies has been conducted in a variety of crops and habitats at the Shafter Research and Extension Center. Cotton is the target crop, but it is important to know if the introduced parasites and pathogen can impart significant mortality on cotton aphid populations in habitats adjacent to cotton in space and time. If so, these natural enemies may be able to assist in maintaining cotton aphid densities that rarely reach pest status in mid to late season cotton by substantially reducing the aphid population on an area-wide basis, or by moving with the aphids into cotton in a timely manner.
Studies on the overwintering ability of the parasites have been conducted in a garden plot containing plants attractive to aphids since the winter of 1997. During this time, a total of 689 L. japonica, 48,771 Aph. near paramali (ANP), and 56,750 Aph. gossypii (AG) have been released into the garden. From these releases, ANP and AG have been recovered, suggesting that these two parasites can survive the winter in the San Joaquin Valley.
To investigate the ability of the parasites to attack cotton aphid on citrus, cage studies were conducted in 1997 and 1998. During the spring when flush growth was present on the citrus, sleeve cages were placed on branches that had aphids, and parasites were added. Numerous parasites attacked the aphids within the cages. However, the only introduced parasite recovered was ANP.
The ability of ANP, AG, and the fungus (N. fresenii; NF) to attack cotton aphid on melons (cantaloupe and watermelon) was investigated in 1999, using cage studies and open field releases. From these studies, it does not appear that the parasites were able to successfully attack cotton aphid on melons. This was somewhat surprising because in a small study conducted in 1998 on pumpkins, the parasites readily attacked cotton aphid. It is possible that the morphology of the leaves of the cantaloupe and watermelon varieties used in these studies have characteristics that interfere with the parasite's searching ability. The results of the studies on NF are pending.
Field cage studies and open field releases have been conducted in cotton using combinations of ANP, AG, and NF since 1996. The results of the field cage studies with the two parasites suggest that both parasites can use cotton aphid on cotton, and when released together (in equal numbers) within a cage, reproduction by both species is greater than when either is released alone. This increase in reproduction is probably due to the host size preference of each species of parasites. Younger instars of aphids are preferred by AG, and older instars are preferred by ANP. The results of field cage studies with NF suggest that either a strain of fungus better adapted to the dry conditions of the San Joaquin Valley or a better method of introducing the fungus into cotton is needed. Studies on both of these aspects are continuing.
Concurrent with the cage studies, open field releases have been conducted with the two parasites species. Since 1996, 85,851 ANP and 25,575 AG have been released in cotton. Both parasites have been recovered from these releases.
Results
The results of the studies conducted since 1996 suggest that ANP and AG will be valuable additions to the natural enemy complex for the cotton aphid in the San Joaquin Valley. Distribution of these parasites throughout the valley is currently being planned. Efforts are also underway to obtain additional species of parasites that can be evaluated to determine their potential role in an introduced natural enemy complex. Studies designed to improve the efficacy of the fungus are also being planned.
Researchers
K. Godfrey of Biological Control Program, California Department of Food and Agriculture, Sacramento, California
L. Carter and D. Ballard of USDA, ARS, Shafter Research and Extension Center, Shafter, California
R. Yokomi of USDA, ARS, Crops Pathology and Genetics Research, Parlier, California
D. Steinkraus of Department of Entomology, University of Arkansas, Fayetteville, Arkansas
The cotton aphid, Aphis gossypii, can attain pest status in a variety of crops in the San Joaquin Valley. Management of these populations must be done with care so as to avoid problems of insecticide resistance and/or cotton aphid population resurgence within adjacent crops or habitats. Biological control is one management tactic that could be used to manage aphid populations through space and time.
In an attempt to increase the amount of biological control on cotton aphid populations, a cooperative project among USDA-Agricultural Research Service, CDFA-Biological Control Program, UC-Cooperative Extension, and the University of Arkansas was initiated in 1996 and continues currently. The long-term goal of this project is to construct an introduced natural enemy complex that would complement the existing natural enemies. During the previous 4 years of the project, three parasites, Lysiphlebia japonica, Aphelinus near paramali, and Aphelinus gossypii, and one fungus, Neozygites fresenii, have been or are currently being evaluated.
Research at SREC
The evaluation of these natural enemies has been conducted in a variety of crops and habitats at the Shafter Research and Extension Center. Cotton is the target crop, but it is important to know if the introduced parasites and pathogen can impart significant mortality on cotton aphid populations in habitats adjacent to cotton in space and time. If so, these natural enemies may be able to assist in maintaining cotton aphid densities that rarely reach pest status in mid to late season cotton by substantially reducing the aphid population on an area-wide basis, or by moving with the aphids into cotton in a timely manner.
Studies on the overwintering ability of the parasites have been conducted in a garden plot containing plants attractive to aphids since the winter of 1997. During this time, a total of 689 L. japonica, 48,771 Aph. near paramali (ANP), and 56,750 Aph. gossypii (AG) have been released into the garden. From these releases, ANP and AG have been recovered, suggesting that these two parasites can survive the winter in the San Joaquin Valley.To investigate the ability of the parasites to attack cotton aphid on citrus, cage studies were conducted in 1997 and 1998. During the spring when flush growth was present on the citrus, sleeve cages were placed on branches that had aphids, and parasites were added. Numerous parasites attacked the aphids within the cages. However, the only introduced parasite recovered was ANP.The ability of ANP, AG, and the fungus (N. fresenii; NF) to attack cotton aphid on melons (cantaloupe and watermelon) was investigated in 1999, using cage studies and open field releases. From these studies, it does not appear that the parasites were able to successfully attack cotton aphid on melons. This was somewhat surprising because in a small study conducted in 1998 on pumpkins, the parasites readily attacked cotton aphid. It is possible that the morphology of the leaves of the cantaloupe and watermelon varieties used in these studies have characteristics that interfere with the parasite's searching ability. The results of the studies on NF are pending.
Field cage studies and open field releases have been conducted in cotton using combinations of ANP, AG, and NF since 1996. The results of the field cage studies with the two parasites suggest that both parasites can use cotton aphid on cotton, and when released together (in equal numbers) within a cage, reproduction by both species is greater than when either is released alone. This increase in reproduction is probably due to the host size preference of each species of parasites. Younger instars of aphids are preferred by AG, and older instars are preferred by ANP. The results of field cage studies with NF suggest that either a strain of fungus better adapted to the dry conditions of the San Joaquin Valley or a better method of introducing the fungus into cotton is needed. Studies on both of these aspects are continuing. Concurrent with the cage studies, open field releases have been conducted with the two parasites species. Since 1996, 85,851 ANP and 25,575 AG have been released in cotton. Both parasites have been recovered from these releases.
Results
The results of the studies conducted since 1996 suggest that ANP and AG will be valuable additions to the natural enemy complex for the cotton aphid in the San Joaquin Valley. Distribution of these parasites throughout the valley is currently being planned. Efforts are also underway to obtain additional species of parasites that can be evaluated to determine their potential role in an introduced natural enemy complex. Studies designed to improve the efficacy of the fungus are also being planned.
Researchers
K. Godfrey of Biological Control Program, California Department of Food and Agriculture, Sacramento, California
L. Carter and D. Ballard of USDA, ARS, Shafter Research and Extension Center, Shafter, California
R. Yokomi of USDA, ARS, Crops Pathology and Genetics Research, Parlier, California
D. Steinkraus of Department of Entomology, University of Arkansas, Fayetteville, Arkansas