Occurrence and impact of pasture mealybug (Balanococcus poae) and root aphid (Aploneura lentisci) on ryegrass (Lolium spp.) with and without infection by Neotyphodium fungal endophytes

Abstract

Pasture mealybug (Balanococcuspoae) was found infesting two field trials evaluating the performance of selected strains of the endophyte Neotyphodium lolii in ryegrass (Lolium spp.) in Canterbury, New Zealand. Deterioration of endo‐phyte‐free plots relative to endophyte‐infected plots had been observed. In Trial A, pasture mealybug were sampled in plots of the perennial ryegrass cultivar ‘Grasslands Nui’, without endophyte (nil), or infected with the wild‐type endophyte, or the selected strains, AR1 and AR37. In Trial B, mealybug numbers on six ryegrass cultivars infected with AR1 or wild‐type were compared with those on the same cultivars without endophyte. In sampling these trials, the presence of a root aphid, Aploneura lentisci, was also noted. Populations of mealybug in both trials were similar on all endophyte‐infected treatments and significantly lower than populations on nil treatments. Neither AR1 nor wild‐type appeared to reduce root aphid numbers, while AR37 may have had some effect. The amount of dead grass was significantly greater in nil than in endophyte‐infected plots in Trial A, and yield of ryegrass was correlated with numbers of mealybug and root aphid present. Pasture productivity in nil treatments had recovered by spring, in the year of the outbreak. The presence of endophyte, strain of endophyte and cultivar were all significant factors affecting both total dry matter and green yield in Trial B. Pasture mealybug accounted for 55% of the variation in a decline in growth rate that occurred in this trial over the summer‐autumn periods between 2000 and 2001, particularly in the nil treatments. Two years after the outbreak there was 25% less ryegrass and persistently lower pasture yields in nil plots. We conclude that pasture mealybug are capable of inflicting severe damage to endophyte‐free ryegrass in Canterbury, particularly during dry summer‐autumn periods.

Keywords:

• endophyte
• plant resistance
• Neotyphodium lolii
• perennial ryegrass
• Balanococcus poae
• Aploneura lentisci
• drought
• pasture production

Notes

Author for correspondence.