Farmer Management Practices of Stink Bug (Bathycoelia Distincta) and Its Occurrence in Selected Macadamia Growing Areas in Kenya

Abstract

Macadamia F. Muell. (Proteaceae) a nut bearing medium sized tree is steadily gaining global popularity because of its high nutritional value nut being used as a supreme dessert. Hence there is expansion in acreage to provide the raw material needed. Intensification comes with challenges and one of these are pests such as the Stink bug (Bathycoelia distincta Distincta) an important pest of macadamia. Stinkbug feeding action results in kernel damage that contributes 55-70% nut losses. The study was undertaken to contribute to the management of pests and diseases limiting macadamia production to improve nut quality from Kenya. The objectives of the study were i) to determine the farmer knowledge and management practices of macadamia stinkbug in selected macadamia growing Counties; and ii) to assess the damage levels of nuts by stink bug and occurrence of the egg parasitoid in macadamia orchards in Murang’a County. Farmer knowledge on stinkbug and its management was collated and assessed using a structured questionnaire administered to 384 randomly selected macadamia farmers in Kiambu, Embu, Nyeri, Meru and Murang’a counties. The study utilized probability sampling technique entailing cluster sampling and simple random sampling procedure from which sub counties were selected as clusters and simple random sampling within the sub counties for the respondents. The sample size was calculated using the Krejcie & Morgan (1970) table and the farmer respondents drawn from a sampling frame (a list of macadamia growers) from each of the selected counties. Half of the respondents were male and the rest female. Slightly above 50% of the respondents were 50 years old and above while only 8% were youth. Greater than 50% of respondents had basic level of education. 80% were aware of the pests that affect macadamia and macadamia nut. Three quarters reported that stinkbug was the most difficult to manage causing losses in terms of yield and quality of the nuts. Other pests of importance after stinkbug were nut borer, mealybugs and thrips. Significantly (p< 0.05) over 80% respondents in UM1 and UM3 used various strategies to manage stinkbugs and they used cultural approach to manage stinkbug. That is weeding, pruning and burning of trash under the trees. Very few (negligible) farmers used pesticides to manage the stinkbug and other pests infesting macadamia. None reported using indigenous knowledge or biological control methods but over 84% of respondents across gender were willing to adopt biocontrol agents for management of macadamia stinkbug. Experiments were conducted in three agro-ecological zones; (UM1), (UM2) and (UM3) to measure the damage levels and losses. Bi-weekly monitoring for presence of the pest, pest eggs and nuts damaged by the pest was done. Thirty trees were randomly selected per zone for the study. Another experiment was undertaken to collect and rear an egg parasitoid (Trissolcus basalis) within the macadamia orchards. Trissolcus basalis was reared in 85-ml glass tubes (30 mm diameter × 150 mm length) and incubated at (25 ± 1°C, 80 ± 5% RH, 15L: 9D photoperiod) in the laboratory on Nezara egg masses. The populations of stinkbug significantly (P<0.05) differed across zones with lower altitude zones UM2 and UM3 recording higher populations of stinkbugs compared to UM1. No differences were observed in pest incidence and egg masses collected between UM2 and UM3.Trissolcus basalis parasitization was detected in orchards. The egg parasitoid were reared in the laboratory on Nezara eggs which varied in sizes from 44 to 131 (n = 143). Parasitoid discovery efficiency, was not influenced by the size of the egg masses (F > 2.34, df = 2, P > 0.05) indicating the ability to detect and locate the egg masses. However, with the increasing egg numbers per egg mass, there was a significant decline in parasitism efficiency (F = 3.23, df = 2, P < 0.05) with 40-70 eggs having 96% parasitism while 100 eggs and above had only 30% parasitism. This relationship was described by the regression equation: y = 99.88 - 0.34x, with an R2 value of 0.42 (P < 0.05) describing an inverse relationship between parasitism efficiency and size of egg mass exposed. Trissolcus basalis females showed a high (90%) efficiency in parasitizing Nezara eggs and the females of the parasitoid parasitized 59.7% of exposed egg masses. A strong parasitic affinity between T. basalis and N. viridula eggs was demonstrated. The presence of T. basalis avails a potential biological tool for controlling Bathycoelia distincta and there is significant potential for laboratory rearing of T. basalis