1995 Annual Report for AW95-205
Effectiveness of Beauveria Bassiana as a Microbial Control Agent for Coleopteran and Homopteran Pests of Irrigated Alfalfa
Summary
This project is intended to evaluate the efficacy of the fungal biological control agent Beauvaria bassiana against insect pests of alfalfa as well as negative effects on some of the biological control agents that occur in this crop. Field studies have been conducted to assess the potential for alfalfa weevil control under commercial conditions, to measure the impact on biological control agents, and to determine the distribution of conidia in the crop canopy. Laboratory studies of pathogenic effects of this fungus on lady beetles have also been implemented. This reports covers progress towards determining the optimum temperature range for efficacy of Beauvaria bassiana against the major insect pests of alfalfa in Colorado, alfalfa weevil and pea aphid.
The efficacy of an insecticidal formulation of B. bassiana was tested against adult and immature alfalfa weevil, Hypera postica, and pea aphid, Acyrthosiphon pisum, under four temperature regimes. Larval alfalfa weevil feeding behavior, weight, and survival were affected negatively by B. bassiana at 20?C, as was adult alfalfa weevil mortality at 25?C. The fungal pathogen had no measurable negative effects on alfalfa weevil at 10?C and 15?C and did not affect pea aphid at any of the temperatures used in this study.
Objectives/Performance Targets
1.Compare the efficacy of inundative applications of B. bassiana to conventional chemical applications and untreated controls for alfalfa weevil control.
2.Compare the efficacy of inundative applications of B. bassiana to conventional chemical applications and untreated controls for pea aphid control.
3.Evaluate the impact of inundative applications of B. bassiana on selected non-target insect species found in alfalfa.
4.Evaluate B. bassiana conidial distribution in the alfalfa canopy and on the soil surface to assess its potential to impact non-target insects.
Accomplishments/Milestones
Objective 1.Compare the efficacy of inundative applications of B. bassiana to conventional chemical applications and untreated controls for alfalfa weevil control.
Results of a preliminary field trial indicated that the B. bassiana formulation tested did not have the expected activity against pea aphid, but had some unexpected activity against alfalfa weevil. Further tests of B. bassiana against alfalfa weevil under greenhouse conditions continued to show control potential, but temperature seemed to influence the outcome. (Previous work)
The results provided in the following table indicate that B. bassiana mortality in alfalfa weevil is greater at higher temperatures and that larvae are more susceptible to this pathogen than are adults. (Current work)
Temperature (?C)
Treated with B. bassiana Untreated Control p > F-value
% Adult Alfalfa Weevil Mortality
10 25 42 0.865
15 33 17 0.657
20 33 25 0.817
25 58 8 0.022
% Immature Alfalfa Weevil Mortality
10 10 27 0.457
15 73 40 0.898
20 100 47 0.001
25 97 80 0.441
Larval weight and percent defoliation by larvae were also reduced at 20?C.
Objective 2.Compare the efficacy of inundative applications of B. bassiana to conventional chemical applications and untreated controls for pea aphid control.
Further field testing against pea aphid failed to demonstrate the potential of B. bassiana to control this species. (Previous work)
The lack of activity was not related to temperature. We tested B. bassiana against pea aphid held at 10, 15, 20 and 25?C. The results in the following table support our conclusion that B. bassiana is not a viable alternative for pea aphid management in Colorado alfalfa. (Current work)
Temperature (?C)
Treated with B. bassiana Untreated Control p > F-value
% Adult Pea Aphid Mortality
10 40 51 0.224
15 95 100 0.490
20 74 98 0.152
25 100 100 ---
% Immature Pea Aphid Mortality
10 12 19 0.179
15 92 98 0.097
20 42 30 0.937
25 97 96 ---
Objective 3.Evaluate the impact of inundative applications of B. bassiana on selected non-target insect species found in alfalfa.
Beneficial insects were sampled, using sweep net and pitfall trap techniques, from alfalfa plots treated for alfalfa weevil and pea aphid. Few effects of B. bassiana treatment on biological control agent species were noted. Follow up studies, however, involving direct applications of B. bassiana to selected biological control agents demonstrated the potential for nontarget effects from the use of this microbial insecticide. (Previous work)
Objective 4.Evaluate B. bassiana conidial distribution in the alfalfa canopy and on the soil surface to assess its potential to impact non-target insects.
Conidial distribution was determined for the B. bassiana field applications. There was a small (approximately 20%) decline in colony forming units from the upper and middle portions of the canopy to the lower portion. (Previous work)
Impacts and Contributions/Outcomes
Findings have been presented previously at one large industry meeting and at the national Entomological Society of America meetings. The observations in this progress report have not been presented publically, but will be included in a scientific article summarizing all project results. Cooperative Extension recommendations for Colorado, western Nebraska and Wyoming also may be modified in light of our findings.
Based on our preliminary analyses, the best course for alfalfa hay producers is to maintain their current insect pest management practices. Insecticidal products based on B. bassiana do not appear to be a viable nonchemical alternative for management of alfalfa weevil and pea aphid. Although this remains a major insecticide use in the region, we still lack effective nonchemical alternatives.
Two grower cooperators provided land and crop. Results were presented to approximately 350 agricultural industry representatives, of whom roughly 10% were full time farmers.